>EPA
United States
Environmental Protection
Agency
Offices of Research and
Development and
Air and Radiation
Washington, DC 20460
Air and Energy Engineering
Research Laboratory
Research Triangle Park,
NC 27711
Research and Development
EPA/600/8-88/087 July 1988
Radon-Resistant
Residential
New Construction
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EPA/600/8-88/087
July 1988
Radon-Resistant Residential New
Construction
by
Michael C. Osborne
'jironmental Protection Agency
Library (o?L-16)
St-eet, Room 1670
60604
Air and Energy Engineering Research Laboratory
Office of Environmental Engineering and Technology Demonstration
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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Disclaimer
The U.S. Environmental Protection Agency (EPA) strives to provide accurate, complete,
and useful information. However, neither EPA nor any person contributing to the
preparation of this document makes any warranty, expressed or implied, with respect to
the usefulness or effectiveness of any information, method, or process disclosed in this
material. Nor does EPA assume any liability for the use of, or for damages arising from
the use of, any information, methods, or process disclosed in this document.
Mention of firms, trade names, or commercial products in this document does not
constitute endorsement or recommendation for use.
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Foreword
This document is intended for use by residential housing contractors, new house buyers,
State and Federal regulatory officials, residential code writers, and other persons as an
aid in the design and application of radon-resistant construction in new houses.
This document is the first edition of EPA's technical guidance for constructing radon-
resistant houses. This edition incorporates information obtained under EPA research and
development contracts and from interviews with residential housing contractors, including
some who do not build for radon-resistance and others who do. Additionally, some
information was obtained from States that are currently considering regulatory approaches
to resolving the radon problem for new houses being built within their jurisdiction. It is
anticipated that future editions will be prepared as additional experience is gained. New
information is continually becoming available through development and demonstration
work funded by EPA and others, and through the practical application of radon-resistant
construction methods by residential housing contractors.
A brief description of construction techniques used to minimize radon entry in new
structures and facilitate its removal after construction is available in the booklet, "Radon
Reduction in New Construction, An Interim Guide" (EPA-87b). Copies of that booklet
can be obtained from the State agencies and the EPA Regional Offices listed in the back
of this document. Copies of this report and the booklet can also be obtained from the
EPA's Center for Environmental Research Information, Distribution, 26 W. Martin Luther
King Drive, Cincinnati, OH 45268.
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Contents
Page
Foreword iii
Figures vii
Tables viii
Acknowledgments ix
Glossary x
Metric Equivalents xv
1. Introduction 1
1.1 Purpose 1
1.2 Builder Reaction 1
1.3 Regulatory Influences 1
1.4 Trade Association Influences 3
1.5 National Variability of Standard Construction Practice 3
2. Identification of Radon-Prone Sites 5
2.1 Radon in the Soil 5
2.2 Poor Correlations Between Indoor and Soil Radon Concentrations .... 5
2.3 Variations in Spatial and Temporal Soil Air Concentrations 6
2.4 Radon Observed in Nearby Houses 8
2.5 Radon in Water 8
2.6 Radon in Building Materials 9
3. Radon Entry and Barriers 11
3.1 Foundation Walls 11
3.1.1 Construction Materials 11
3.1.2 Masonry Walls with Termite Caps, Solid Blocks, and Filled
Block Tops 15
3.1.3 Masonry Walls with Weep Holes 16
3.1.4 Drainage Boards for Water and Radon Control 16
3.1.5 Dampproofing/Waterproofing to Achieve a Radon Barrier 17
3.2 Slabs 19
3.2.1 Prevention from Cracking 19
3.2.2 French Drains and Floor/Wall Cracks 21
3.2.3 Cracks and Penetrations 21
3.2.4 Sub-Slab Barriers 22
3.2.5 Rules of Thumb for Slab and Sub-Slab Barriers 23
3.3 Crawl Spaces 23
4. Avoiding Depressurization and Between-floor Pressure Differences 25
4.1 The Stack Effect 25
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4.2 Wind 25
4.3 Air Moving Devices 26
4.4 Combustion Appliances 26
5. Designing for Post-Construction Active or Passive Sub-Slab Ventilation . . 29
5.1 Sub-slab Suction System Components 29
5.2 Drainage Considerations 30
5.3 A Crawl Space Post-Construction Alternative 30
6. Current Practice in Radon-resistant Construction 33
6.1 Radon-resistant Construction Practice in Sweden 33
6.2 New York State Energy Research and Development Authority
(NYSERDA) Project Plans 34
6.3 National Association of Homebuilders' New Jersey Project Plans 35
6.4 Ryan Homes Project Plan 40
6.5 Garnet Homes Project Plan 48
6.6 New Construction House Evaluation Program (NEWHEP) 50
7. Cost of Radon-resistant Construction 53
7.1 Example Costs 53
7.2 Hidden Costs 54
8. References 55
Appendix A - Examples of Standard Construction Practice and Current
Adaptations to Radon for a Sampling of U.S. Homebuilders 57
VI
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Figures
Page
1. Estimated Share of Basement, Crawl Space, and Slab Foundations
by State 4
2. Percentage Share of New Single-Family Housing by Foundation Type . . 4
3. Major Radon Entry Routes in Basement Houses 12
4. Major Radon Entry Routes in Slab-on-grade Houses 13
5. Major Radon Entry Routes in Crawl-space Houses 14
6. Incomplete Sub-Slab Sump Suction Design for New Houses 31
7. Complete Sub-Polyethylene Suction Design for Crawl Space 32
8. Radon Prevention Details - Vented Footing Drains Technique No.1 .... 36
9. Radon Prevention Details - Vented Footing Drains Technique No. 2 .... 37
10. Radon Prevention Details - Roof Venting Technique No. 1 38
11. Radon Prevention Details - Roof Venting Technique No. 2 39
12. Baseline Radon Reduction Techniques-Poured Concrete Wall 41
13. Baseline Radon Reduction Techniques-Block Wall 42
14. Baseline Radon Reduction Techniques-Floor/Wall Joint Sealing
Options 43
15. Baseline Radon Reduction Techniques-Slab-on-grade Options .... 44
16. Baseline Radon Reduction Techniques-Crawl Space Option 45
17. Baseline Radon Reduction Techniques-Slab-below-grade Option . . 46
VII
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Tables
Page
1. Highest Indoor Radon Concentrations Measured in Florida Survey
Houses and Corresponding Soil Radon Concentrations Near
the Houses 5
2. Swedish Soil Risk Classification Scheme and Building Restrictions 6
3. Indoor Radon and Soil Radon Measurements in Colorado and Michigan . . 7
4. Results Using Vented Crawl Space Technique 15
5. Corresponding Indoor and Sub-slab Radon Measurements in Maryland
Houses Built to Be Radon Resistant 49
6. Cost Attributed to Radon Abatement 53
7. Radon-safe Construction Costs in Sweden 54
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Acknowledgments
This manual compiles and documents the experience of many individuals who have
worked in residential construction and radon mitigation. Many of these individuals are
recognized in the list of references (Section 8). It is the innovative work of these many
persons that has made this document possible.
Drafts of this document have been reviewed by a large number of individuals in
Government and in the private and academic sectors. Comments from these reviewers
have helped to significantly improve the completeness, accuracy, and clarity of the
document. Within EPA, reviews were provided by AEERL's radon reduction staff, the
Office of Radiation Programs, and the Regional Offices. The author wishes to thank the
following EPA personnel in particular for the substantive information, comments, and
guidance that they provided: A.B. Craig, D.B. Henschel, M. Samfield, W.G. Tucker, and
K.A. Witter of AEERL; H.M. Mardis and D.M. Murane of the Office of Radiation Programs;
L.G. Koehler of Region 2, W.E. Belanger of Region 3, and L. Jensen of Region 5. Of the
reviewers outside EPA, we are particularly indebted to the following for their substantive
input: T. Brennan and S. Galbraith of Camroden Associates, W.P. Brodhead of Buffalo
Homes, D. Saum of Infiltec, R.A. Furman of the University of Florida, M.G. McGuinness
of the New Jersey Home Builders Association, and M.R. Malec of the New Jersey
Department of Community Affairs.
Editing, typing, and graphics support were coordinated by C.B. Brickley of Radian
Corporation, Research Triangle Park, NC.
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Glossary
Air exchange rate - The rate at which the house air is replaced with outdoor air.
Commonly expressed in terms of air changes per hour (ach).
Airflow bypass - Any opening through the floors between stories of a house (or through
the ceiling between the living area and the attic) that facilitates the upward movement
of house air under the influence of the stack effect. By facilitating the upward
movement, airflow bypasses also facilitate exfiltration at the upper levels, which in turn
will increase infiltration of outdoor air and soil gas.
Backer rod - A rope of compressible plastic foam. Backer rod can be force-fit into
wide cracks and similar openings, to serve as a support for caulking material.
Band joist - Also called header joist, header plate, or rim joist. A board (typically same
size as floor joists) that rests (on its small dimension) on top of the sill plate around the
perimeter of the house.
Barrier coating(s) - A layer of material that obstructs or prevents passage of something
through a surface that is to be protected. More specifically, paint, grout, caulk, or
various sealing compounds, perhaps used with polyurethane membranes to prevent
soil-gas-borne radon from moving through walls, cracks, or joints in a house.
Basement - A type of house construction where the bottom livable level has a slab (or
earthen floor) which averages 3 ft or more below grade level on one or more sides of
the house.
Blower door - A device consisting of an instrumented fan which can be mounted in an
existing doorway of a house. By determining the air flows through this fan required to
achieve different degrees of house pressurization or depressurization, the blower door
permits determination of the tightness of the house shell, and an estimation of the
natural filtration rate.
Cold air return - The registers and ducting which withdraw house air from various parts
of the house and direct it to a central forced-air furnace or heat pump. The return
ducting is at low pressure relative to the house because the central furnace fan draws
air out of the house through this ducting.
Contractor - A building trades professional who works for profit to correct radon
problems, a remediation expert. At present, training programs are underway to provide
working professionals with the knowledge and experience necessary to control radon
exposure problems. Some State radiological health offices have lists of qualified
professionals.
Convective movement - As used here, the bulk flow of radon-containing soil gas into
the house as the result of pressure differences between the house and the soil.
Distinguished from diffusive movement.
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Crawl space - An area beneath the living space in some houses, where the floor of the
lowest living area is elevated above grade level. This space (which generally provides
only enough head room for a person to crawl), is not living space, but often contains
utilities. Distinguished from slab-on-grade or basement construction.
Cubic feet per minute (cfm) - A measure of the volume of a fluid flowing within a fixed
period of time.
Dampproof - To make a surface resistant to water entry by blocking diffusive
movement of water through pores. Dampproofed surfaces are not expected to keep out
water that is under pressure.
Depressurization - In houses, a condition that exists when the air pressure inside the
house is slightly lower than the air pressure outside or the soil gas pressure. The lower
levels of houses are essentially always depressurized during cold weather, due to the
buoyant force of the warm indoor air (creating the natural thermal stack effect). Houses
can also be depressurized by winds and by appliances which exhaust indoor air.
Diffusive movement - The random movement of individual atoms or molecules, such
as radon atoms, in the absence of (or independent of) bulk (convective) gas flow.
Atoms of radon can diffuse through tiny openings, or even through unbroken concrete
slabs. Distinguished from convective movement.
Duct work - Any enclosed channel that directs the movement of air or other gas.
Effective leakage area - A parameter determined from blower door testing, giving a
measure of the tightness of the house shell. Conceptually, this leakage area reflects the
square inches of open area through the house shell, through which air can infiltrate or
exfiltrate.
Entry routes - Pathways by which soil gas can flow into a house. Openings through the
flooring and walls where the house contacts the soil.
Equilibrium ratio - As used here, the total concentration of radon progeny present
divided by the concentration that would exist if the progeny were in radioactive
equilibrium with the radon gas concentration that is present. At equilibrium (i.e., at an
equilibrium ratio of 1.0), 1 WL of progeny are present when the radon concentration is
100 pCi/L. The ratio is never 1.0 in a house; that is, the progeny never reach
equilibrium in a house environment due to ventilation and plate-out. A commonly
assumed equilibrium ratio is 0.5 (i.e., the progeny are halfway toward equilibrium), in
which case 1 WL corresponds to 200 pCi/L. In practice, equilibrium ratios of 0.3 to 0.7
are commonly observed.
Exfiltration - The movement of indoor air out of the house. The reverse of infiltration.
Exhaust fan - A fan oriented so that it blows indoor air out of the house. Exhaust fans
cause outdoor air (and soil gas) to infiltrate at other locations in the house, to
compensate for the exhausted air.
Footing(s) - A concrete or stone base that supports a foundation wall and that is used
to distribute the weight of the house over the soil or subgrade underlying the house.
Forced-air furnace (or heat pump) - A central furnace or heat pump that functions
by recirculating the house air through a heat exchanger in the furnace. A forced-air
furnace is distinguished from a central hot-water space heating system, or electric
resistance heating.
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French drain (also called channel drain or floating slab) - A water drainage
technique installed in basements of some houses during initial construction. If present,
typically consists of a 1- or 2-in. gap between the basement block wall and the
concrete floor slab around the entire perimeter inside the basement.
Gamma radiation - Electromagnetic radiation released from the nucleus of some
radionuclides during radioactive decay.
Grade (above or below) - The term by which the level of ground surrounding a house
is known. In construction, typically refers to the surface of the ground. Things can be
located at grade, below grade, or above grade relative to the surface of the ground.
Hollow-block wall, Block wall - A wall constructed using hollow rectangular masonry
blocks. The blocks might be fabricated using a concrete base (concrete block), or using
ash remaining after combustion of solid fuels (cinder block). Walls constructed using
hollow blocks form an interconnected network with their interior hollow cavities.
House air - Synonymous with indoor air. The air that occupies the space within a
house.
Indoor air - Synonymous with house air. That air that occupies the space within a
house or other building.
Infiltration - The movement of outdoor air or soil gas into a house. The infiltration which
occurs when all doors and windows are closed is referred to in this document as the
natural closed-house infiltration rate. The reverse of exfiltration.
Joist - Any of the parallel horizontal beams set from wall to wall to support the boards of
a floor or ceiling.
Load-bearing - A term referring to walls or other structures in a house that contribute
to supporting the weight of the house.
Makeup air - In this application, outdoor air supplied into the house to compensate for
house air that is exhausted by combustion appliances or other devices such as exhaust
fans. Provision of makeup air can reduce the house depressurization that might
otherwise result from the use of these appliances.
Neutral plane - A roughly horizontal plane through a house defining the level at which
the pressure indoors equals the pressure outdoors. During cold weather, when the
thermal stack effect is occurring, indoor pressures below the neutral plane will be lower
than outdoors, so that outdoor air and soil gas will infiltrate. Above the neutral plane,
indoor pressures will be higher than outdoors, so that house air will exfiltrate.
Parge - To coat exterior masonry foundation walls with a layer of cementitious material.
Used to waterproof the foundation.
Performance code - A general code that describes the end product or goal to be
achieved but does not prescribe specific methods, techniques, or materials to use in
achieving the goal.
Permeability (sub-slab) - A measure of the ease with which soil gas and air can flow
underneath a concrete slab. High permeability facilitates gas movement under the slab,
and hence generally facilitates sub-slab suction.
XII
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Permeameter - A radon and permeability measurement device that allows radon to be
measured in soil at various depths.
Picocurie (pCi) - A unit of measurement of radioactivity. A curie is the amount of any
radionuclide that undergoes exactly 3.7 x 1010 radioactive disintegrations per second. A
picocurie is one trillionth (1CH2) of a curie, or 0.037 disintegrations per second.
Picocurie per liter (pCi/L) - A common unit of measurement of the concentration of
radioactivity in a gas. A picocurie per liter corresponds to 0.037 radioactive
disintegrations per second in every liter of air.
Radon - The only naturally occurring radioactive element that is a gas. Technically, the
term "radon" can refer to any of a number of radioactive isotopes having atomic
number 86. In this document, the term is used to refer specifically to the isotope
radon-222, the primary isotope present in houses. Radon-222 is directly created by
the decay of radium-226, and has a half-life of 3.82 days. Chemical symbol Rn-
222.
Radon extraction well - A deep mechanically ventilated hole dug in the soil in the
vicinity of a house with elevated radon.
Radon progeny - The four radioactive elements that immediately follow radon-222 in
the decay chain. These elements are polonium-218, lead-214, bismuth-214, and
polonium-214. These elements have such short half-lives that they exist only in the
presence of radon. The progeny are unltrafine solids which tend to adhere to other
solids, including dust particles in the air and solid surfaces in a room. They adhere to
lung tissue when inhaled and bombard the tissue with alpha particles, thus creating the
health risk associated with radon. Also referred to as radon daughters and radon decay
products.
Rebar (also called rerod) - Steel bars or rods used to reinforce concrete.
R value - A measure of the insulating capability of a wall or surface coating.
Sill plate - A horizontal board (typically 2 x 4 in. or 2 x 6 in.) that rests on top of a block
or poured concrete foundation wall and extends around the entire perimeter of the
house. The ends of the floor joists which support the floor above the foundation wall
rest on the sill plate.
Slab - A layer of concrete, typically about 4 in. thick, which commonly serves as the
floor of any part of a house whenever the floor is in direct contact with the underlying
soil.
Slab below grade - A type of house construction where the bottom floor is a slab which
averages between 1 and 3 ft below grade level on one or more sides.
Slab on grade - A type of house construction where the bottom floor of a house is a
slab which is no more than about 1 ft below grade level on any side of the house.
Soil gas - Gas which is always present underground, in the small spaces between
particles of the soil or in crevices in rock. Major constituents of soil gas include
nitrogen, water vapor, carbon dioxide, and (near the surface) oxygen. Since radium-
226 is essentially always present in the soil or rock, trace levels of radon-222 will exist
in the soil gas.
XIII
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Specification code - A detailed descriptive code setting forth methods, techniques,
materials, etc., for the construction of a structure.
Stack effect - The upward movement of house air when the weather is cold, caused by
the buoyant force of the warm house air. House air leaks out at the upper levels of the
house, so that outdoor air (and soil gas) must leak in at the lower levels to compensate.
The continuous exfiltration upstairs and infiltration downstairs maintain the stack effect
air movement, so named because it is similar in principle to hot combustion gases
rising up a fireplace or furnace flue stack.
Stub-up pipe - A 4-in. PVC pipe run vertically from the sub-slab aggregate, through
the concrete slab, and terminating a few inches above the slab surface.
Sump - A pit through a basement floor slab, designed to collect water and thus avoid
water problems in the basement. Water is often directed into the sump by drain tiles
around the inside or outside of the footings.
Sump pump - A pump to move collected water out of the sump pit, to an above-grade
discharge remote from the house.
Thermal bypass - As used here, the same thing as an airflow bypass.
Tight house - A house with a low air exchange rate. If 0.5 to 0.9 air changes per hour
(ach) is typical of modern housing, a tight house would be one with an exchange rate
well below 0.5 ach.
Top voids, Block voids, Voids - Air space(s) within masonry walls made of concrete
block or cinder block. Top void specifically refers to the air space in the top course of
such walls; that is, the course of block to which the sill plate is attached and on which
the walls of the house rest.
Veneer, Brick veneer - A single layer or tier of masonry or similar material securely
attached to a wall for the purposes of providing ornamentation, protection, or insulation,
but not bonded or attached to intentionally exert common action under load.
Ventilation rate - The rate at which outdoor air enters the house, displacing house air.
The ventilation rate depends on the tightness of the house shell, weather conditions,
and the operation of appliances (such as fans) influencing air movement. Commonly
expressed in terms of air changes per hour, or cubic feet per minute.
Warm air supply - The ducting and registers which direct heated house air from the
forced-air furnace, to the various parts of the house. The supply ducting is at elevated
pressure relative to the house because the central furnace fan is blowing air through
this ducting.
Waterproof - To make a surface resist penetration of water under a hydrostatic head.
Working level (WL) - A unit of measure of the exposure rate to radon and radon
progeny defined as the quantity of short-lived progeny that will result in 1.3 x 105 MeV
of potential alpha energy per liter of air. Exposures are measured in working level
months (WLM); e.g., an exposure to 1 WL for 1 working month (170 hours) is 1 WLM.
These units were developed originally to measure cumulative workplace exposure of
underground uranium miners to radon and continue to be used today as a
measurement of human exposure to radon and radon progeny.
XIV
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Metric Equivalents
Although it is EPA's policy to use metric units in its documents, nonmetric units are used
in this report for the reader's convenience. Readers more accustomed to the metric
system may use the following factors to convert to that system.
Nonmetric Times
cubic foot (ft3) 28.3
cubic foot per minute 0.47
(cfm, or ft3/min)
degree Fahrenheit (°F) 5/9 (°F-
32)
foot (ft) 30.5
gallon (gal.) 3.79
inch (in.) 2.54
inch of water column 248
(in. WC)
picocurie per liter 37
(pCi/L)
pound (Ib) 454
quart (qt) 0.946
square foot (ft2) 0.093
yard (yd) 0.914
Yields metric
liters (L)
liters per second (Usec)
degrees centigrade (°C)
centimeters (cm)
liters (L)
centimeters (cm)
Pascal (Pa)
Becquerels per cubic meter
(Bq/m3)
gram (g)
liter (L)
square meter (m2)
meter (m)
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Sect/on 1
Introduction
1.1 Purpose
Growing publicity about the dangers of radon, a
radioactive gas found in varying amounts in all
houses, has underscored the need for dependable
radon-resistant residential construction techniques.
In recent years, the U.S. Environmental Protection
Agency (EPA) has developed and demonstrated a
variety of methods that have been used to reduce
radon levels in existing houses. Many of these
methods should be easier and less expensive to
apply during construction than after the house is built.
Refer to Radon Reduction Techniques for Detached
Houses (EPA88) for details on modifying existing
houses. EPA has also published Radon Reduction in
New Construction, An Interim Guide (EPA87b), which
was based on experience gained in mitigating radon
problems in existing houses.
The purpose of this manual is to provide builders and
potential new house buyers with a broader selection
and explanation of techniques that are expected to be
effective in reducing the potential for elevated radon
levels in the house. In addition, legislators, regulators,
and residential code writers may choose to evaluate
these radon-resistant construction technologies for
potential application to or modification of existing
regulations or codes applicable to residential
construction.
Adequate supporting data on the effectiveness of the
radon-resistant construction techniques mentioned
in Sections 3 and 4 have NOT yet been fully
demonstrated in new houses; therefore, readers of
this report should consider the techniques identified in
Sections 3 and 4 as only developmental and NOT as
proven technology for preventing radon problems in
new houses. The soil ventilation techniques described
in Section 5 have good potential for application in
new construction based on extensive testing in
existing houses and are, therefore, more strongly
recommended.
1.2 Builder Reaction
Already, many builders in widely scattered sections of
the country recognize the word "radon" and have
some idea of what it is. Few, however, have made
any effort to deal with radon as a problem.
Fortunately, some homebuilders in identified problem
areas are, on their own initiative, educating
themselves about the mechanisms of radon entry.
Traditional construction details developed for such
purposes as moisture control, energy conservation,
and structural integrity are being evaluated and
modified to take radon control into account in new
house construction. Some builders are keeping
abreast of research developments and are
intentionally modifying construction practices, while
others are waiting for regulatory guidance and
attempting to limit liability with standard disclaimers.
In another commercial sector, vendors and suppliers
of materials used in foundation construction are
generally interested in radon problems and the market
opportunities that radon concerns may offer. New
radon-related products are constantly entering the
residential marketplace — some developed
specifically for radon control, others transferred from
the commercial and industrial sector. Manufacturers'
interests range from concern over radon-related
publicity to actively researching and promoting the
radon-resistant applications of their products.
Numerous factors and conditions influence which
materials and construction details are used by
building contractors. There is a constant tension
between the construction practices recommended or
required by regulatory agencies and the economic
realities of the marketplace. Within the limits of
acceptable practice (as enforced by building
inspectors), other factors come into play, such as: 1)
capabilities of the homebuilders' workers, 2) details
most likely to appeal to the homebuyer, and 3)
exposures to liability of the homebuilder involved in
adopting a new process or material--or
conversely--in delaying a response to a new issue
such as radon.
1.3 Regulatory Influences
Factors that influence residential construction practice
in the United States include: building codes,
environmental regulations, zoning ordinances, new
house warranty performance standards, generally
accepted standards and technical recommendations
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emanating from trade associations, and the standard
practices and cost competition typical among builders
within a given geographic area.
State-level government has the constitutional power
to regulate residential construction practice unless the
state chooses to delegate that power to local
jurisdictions. Many states have adopted residential
building codes. In some cases, these codes are
presented to municipalities as preemptive; in others,
the codes express minimum standards open to only
those local amendments that increase their
restrictiveness. At the other end of the spectrum,
some states adopt building codes which appear to
serve as mere suggestions, while others have no
state-level involvement in residential building
construction.
Local government has traditionally been responsible
for the administration and enforcement of zoning
ordinances. These ordinances may dictate, among
other things, drainage requirements and construction
practices which may be applicable to specific
geographic subareas of the community or to the
municipality as a whole. Even in states with
preemptive, mandatory building codes, municipalities
may be allowed to exercise some local autonomy by
designating "radon-prone" regions, comparable to
flood zones or other environmentally sensitive areas.
Three member organizations offer general model
building codes to state and local governing bodies.
These organizations-the Building Officials and
Code Administrators International (BOCA), the
International Conference of Building Officials (ICBO),
and the Southern Building Code Congress
International (SBCCI) each prepare their own model
codes covering all types of building occupancies
(BOCA86, ICBO85, SBCCI85). Use of these codes is
roughly distributed as follows: BOCA's National
Building Code (NBC)--- northern and eastern
United States; ICBO's Uniform Building Code
(UBC)--- western United States; SBCCI's
Standard Building Code (SBC)-southern United
States. The NBC, UBC, and the SBC are
performance codes by which the right of the building
official to approve alternative techniques and
materials "equal" to the code requirement is implicit.
These model building codes are amended annually,
with new editions issued every 3 years. The
amendment process includes a review of proposed
changes submitted by individuals, manufacturers,
trade associations, and/or special committees of the
code organization.
The Council of American Building Officials (CABO),
an umbrella group representing all three of the above
code organizations, distributes the One and Two
Family Dwelling Code (CABO86a). Responsibility for
the CABO One and Two Family Dwelling Code is
circulated among the member organizations at 3-
year intervals. It is currently BOCA's turn. The CABO
One and Two Family Dwelling Code applies only to
residential construction. It is a specification code
rather than a performance code and is not in
complete agreement with provisions of the more
general building codes.
The apparent application of codes can be misleading.
In New Jersey, for example, the statewide building
codes regarding structural, fire, and sanitary safety
matters are "mandatory and preemptive"; they cannot
be locally amended. This might lead one to expect a
great deal of consistency in residential construction
practice. However, the state adopted both BOCA's
National Building Code and the CABO One and Two
Family Dwelling Code, as amended by the New
Jersey Uniform Construction Code, as references.
Individuals (i.e., builders, architects, and others) are
free to select which code they will follow for any given
house, so long as they do not switch from one to the
other within the same building. Seven other states
have also adopted both CABO and another model
code.
In addition to the general codes mentioned above,
various regional and national codes have been
developed which focus on special topics or building
trades-for example, CABO's Model Energy Code
(CABO86b). Some model energy codes contain
discussion of infiltration or combustion air supplies for
fireplaces and heating appliances. The Northwest
Energy Code (BPA87), developed under the
sponsorship of Bonneville Power Administration,
contains a section on radon mitigation in its appendix.
The body of the Northwest Energy Code is concerned
with electrically heated buildings; the radon appendix
is intended "to establish minimum criteria for the
design and installation of radon reduction systems"
and imposes testing and mitigation requirements on
all new houses that do not have 3-1/2 in. concrete
slabs over a base of 4 in. of coarse gravel.
Local governments are able to manage construction
practice within their boundaries by developing and
enforcing local ordinances. In many states, local
governments have the power to adopt local building
regulations or to amend state regulations. States may
impose a review process or require that amendments
be more stringent than the state code. Local
ordinances can restrict construction or dictate specific
construction practice within environmentally sensitive
areas and floodplains.
Currently the states of Florida and New Jersey are
each developing guidelines for radon-resistant
construction to be applied to residential construction
within certain yet-to-be-determined radon-prone
areas of their respective states. The draft guidelines
for Florida emphasize specific barrier techniques
(Section 3) to prevent radon entry. The initial draft
guidelines for New Jersey are less restrictive,
-------
permitting French drains (Section 3.2.2) while
anticipating the ultimate need for sub-slab suction
systems (Section 5.1). It is anticipated that both
Florida and New Jersey will revise their proposed
guidelines and will make them voluntary for a time
while additional studies are conducted to verify the
effectiveness of the proposed radon-resistant
construction methods.
1.4 Trade Association Influences
Trade associations often provide written and over-
the-phone advice on the proper use of building
materials and systems. These associations evaluate
new products and provide recommendations to model
code organizations on incorporating their use as
acceptable practice. These trade organizations are
sometimes referenced in building codes as the
issuing organizations for generally accepted
standards.
Two reports issued by the National Concrete Masonry
Association (NCMA85, NCMA87) are specifically
concerned with radon; similar reports discussing
proper mortar joints, waterproofing, and control of air
leakage are also relevant to radon-resistant new
construction. The Portland Cement Association
(PCA80) has produced reports on concrete
basements, joints in below-grade walls, and earth-
integrated construction that are indirectly relevant to
preventing radon entry. The American Concrete
Institute offers guides for concrete floor and slab
construction (ACI87) and residential cast-in-place
concrete construction (ACI85).
The National Association of Homebuilders (NAHB) is
a resource organization for member contractors and
for regulatory agencies developing guidelines and
standards. The NAHB Research Foundation keeps
abreast of current information in the field of radon and
is involved in testing radon-resistant construction
techniques in New Jersey in cooperation with EPA
and the New Jersey Department of Community Affairs
(NAHB87).
1.5 National Variability of Standard
Construction Practice
Current interest in radon-resistant construction is
generally focussed on large-scale projects, whereas
a considerable amount of residential construction
activity is dispersed among small contractors.
Differences in residential construction details and
practices currently being used in various regions of
the country may have resulted from on-the-job
training as much as from formal regulations or written
guidelines.
Regional construction practice and locally available
materials have an important influence on residential
construction. Florida, for example, constructs few
houses with basements due to its high water table.
Gravel or crushed stone is not economically available
in most areas of Florida for use as a sub-slab
aggregate; therefore, sand is used instead. Both of
these construction features affect radon entry into
typical Florida houses and limit mitigation options. In
Texas, it is reported that expansive soils make
aggregate beneath the slab undesirable because of
potential water problems.
Unique radon-resistant construction options are
necessary for each substructure type. Figure 1 is a
map of the United States showing the frequencies of
basement, crawl space, and slab-on-grade
construction of one- and two-family dwellings. The
data were originally gathered by the NAHB; the map
is reprinted from the Building Foundation Design
Handbook (ORNL88). Figure 2, also from the
Handbook, shows historic trends in substructure
construction nationwide.
The dynamics of radon movement mean that careful
installation of building elements is as important as the
use of proper materials. In order to achieve radon-
resistant construction, individual contractors and
building inspectors wilt need to understand the theory
behind the various radon-resistant contruction
techniques.
-------
_CL
96.0
2.0
2.0
TN
28.5
44.0
27.B
WV
53.5
32.5
14.0
NJ
52.0
41.0
7.0
-BL
30.5
41.0
28.5
MO
92.0
2.5
5.5
60 °F Steady State Ground
Temperature Isotherm
Percent Basement
Percent Crawl Space
Percent Slab-On-Grade
Figure 1. Estimated Share of Basement, Crawl Space, and Slab
Foundations by State (Built Between 1979 and 1983)
(Source: Building Foundation Design Handbook.Oak Ridge National Laboratory)
50
40
30
20
10
/Basement
* Slab-On-Grade
Crawl Space
DC
00
1963
1968
1973
1978
1983
Figure 2. Percentage Share of New Single-Family Housing by Foundation Type
(Source: Building Foundation Design Handbook, Oak Ridge National Laboratory)
-------
Section 2
Identification of Radon-Prone Sites
2.1 Radon in the Soil
Although radon in water and radon emissions from
building materials do account for a minor share of the
radon problems found in the United States, the
overwhelming majority of residential radon problems
occur from radon emanating from the soil. The radon
gas found in soils is a product of the decay of
radium-226, a radioactive chemical element that is
ubiquitous in nature and present in trace levels in
most soils and in many types of rock. Uranium
decays through a chain of radioactive elements,
releasing radioactive particles and electromagnetic
radiation in the process. Each element in the chain is
a solid except radon-222 (radon), which is a gas.
The amount of radon gas that enters the house is a
function of how much radon gas or radon parent
compounds are found in the soil beneath the house,
the permeability of the soil, the presence of faults and
fissures in underlying and nearby rock, openings
between the house and soil, and the driving forces
that move soil gas (containing radon) along these
pathways into the house. To have a radon problem
requires radium nearby, a pathway for the gas to
move through the soil or rock, a driving force, and
openings in the foundation.
In the siting of new residential construction, builders
would like to be able to predict the potential for radon
problems associated with each building site.
Unfortunately, at present there are no reliable
methods for correlating the results of radon soil tests
at a building site with subsequent indoor radon levels
in a house built on that site. Houses vary significantly
in their ability to resist radon entry. This is true even
among houses where controlling radon entry was not
considered during construction.
2.2 Poor Correlations Between Indoor
and Soil Radon Concentrations
The Florida Statewide Radiation Study performed by
Geomet (Na87) illustrates the variability of radon-
resistant construction and the resulting problem of
trying to correlate soil radon levels with indoor radon
levels. The study reports over 3,000 paired soil radon
and indoor radon samples. A total of 77 soil radon
readings were greater than 1,000 pCi/L, and the two
highest soil radon values were 6587.0 and 6367.2
pCi/L. Interestingly, the corresponding indoor radon
levels measured were 6.8 and 0.2 pCi/L, respectively.
In addition, almost half of the houses with soil radon
levels in excess of 1,000 pCi/L had indoor radon
levels of less than 4 pCi/L.
Thomas Pugh from Florida A&M University evaluated
the Florida data reported by Geomet and listed the
houses in order of highest measured indoor radon
levels. His analysis is shown in Table 1 (Pu88 and
Na87).
Table 1. Highest Indoor Radon Concentrations
Measured in Florida Survey: Houses and
Corresponding Soil Radon Concentrations
Near the Houses
Indoor Radon Concentration Soil Radon Concentration
(pCi/L) (pCi/L)
32.4
29.5
28.0
25.3
25.3
25.0
24.1
22.9
22.9
1591.1
1846.9
786.9
555.9
200.1
353.9
439.7
3561.3
2144.5
It is clear from Table 1 that soil radon measurements
which varied over an order of magnitude produced
significantly less than a factor of 2 difference in the
indoor radon levels. Predictions of radon potential
based on soil radon measurements would be highly
suspect based on these data.
In Sweden, soils have been classified as having a
high, normal, or low radon risk based on soil radon
concentration. The soil radon values and permeability
characteristics used to established the soil
classifications and the corresponding construction
requirements are given in Table 2 (Sw82). Other
factors besides soil radon that are considered before
classification in Sweden are permeability, ground
humidity, and soil thickness.
Using only the suggested soil radon concentrations
included in the Swedish soil classification scheme, no
-------
Table 2. Swedish Soil Risk Classification Scheme and Building Restrictions
Soil Radon
Concentration
(pCi/L)
< 270
270-1350
>1350
Permeability
of Soil
very low permeability
(e.g., clay and silt)
average permeability
high permeable
(e.g., gravel and coarse sand)
Risk
Classification
Low
Normal
High
Building
Restrictions
Use conventional
construction
Use radon-
protective
construction
Use radon-safe
construction
building restrictions would be required for many of the
houses surveyed in Florida with radon measurements
greater than or equal to 4 pCi/L. Fifteen of the houses
in the Florida study with measurements greater than
or equal to 4 pCi/L had soil radon concentrations less
than or equal to 200 pCi/L. This corresponds to
13.5% of the houses with soil gas <270 pCi/L being
above the EPA action level of 4 pCi/L. Nineteen of
the 48 houses (39.6%) that had radon in the soil over
1,350 pCi/L had radon levels in the house less than 4
pCi/L This means that almost 40% of the houses that
would have been required to be built "radon-safe"
under the Swedish guidelines were already below 4
pCi/L using standard construction practices.
The Florida survey was an ideal opportunity to
compare soil radon and corresponding indoor radon
levels in slab-on-grade construction. This was
possible in Florida since 95% of the houses
constructed are of this substructure type. By looking
exclusively at slab-on-grade houses, additional
variables,including depth below grade of basements
and height and ventilation of crawl spaces, are
eliminated. These variables, which are inherent in
these common construction techniques used
throughout much of the rest of country, would only
exaggerate the difficulty in correlating indoor air radon
and soil radon levels.
The major drawback in using the Florida study to
support the insufficient correlation between indoor
and soil measurements was that indoor
measurements were obtained from 3-day closed-
house charcoal measurements and soil radon was
obtained from 1-month alpha track measurements
(buried 1 ft beneath the soil surface). Comparisons of
charcoal and alpha track data are generally not
recommended since they are quite different
measurement techniques and represent radon levels
over different time periods. However, the study was
subjected to numerous quality control checks
including deployment of alpha tracks in 10% of the
houses to obtain a check on indoor air measurements
made by charcoal canisters. In spite of the
measurement drawbacks, the study indicates that soil
radon measurements taken alone are not a
dependable predictor of potential indoor radon
concentration.
In the Office of Radiation Program's New House
Evaluation Program (NEWHEP), two builders in the
Denver area, two in Colorado Springs, and one in
Southfield, Michigan, installed various radon-
resistant features in their houses during construction.
A sampling of subsequent measurement of indoor
radon, adjacent soil gas radon, and soil radium
content is summarized in Table 3 (Mu88b).
The major difference between these data and the
Florida survey data in Table 1 is that this portion of
the NEWHEP data was collected from houses where
only passive radon-resistant construction features
had been incorporated. There are no control data on
houses in the same area that did not have those
built-in features so it is impossible to conclude any
direct correlation between soil measurements and
indoor radon or to accurately predict indoor radon
levels based on these soil measurements. It appears,
however, that passive-only building techniques do
not consistently result in indoor radon levels below 4
pCi/L. All five of the builders in the NEWHEP are
currently experimenting with or are considering the
installation of active, fan-driven sub-slab ventilation
systems. Results are being monitored (Mu88b).
2.3 Variations in Spatial and Temporal
Soil Air Concentrations
Aside from the difficulty in correlating soil radon
measurements with indoor radon measurements,
various field studies have also shown that obtaining a
representative soil gas measurement is difficult. Soil
gas radon measurements were made with a
permeameter in seven central Florida houses in
November 1987 (Pe87). A permeameter is a radon
and permeability measurement device that allows
radon to be measured at various depths. In this study
the radon concentration was the average of samples
collected at depths of 60, 90, and 120 cm. Four to six
samples were collected in the yard of each house at
distances of 0.5 to 4.5 m from the house foundation.
Soil radon concentrations measurements in each of
-------
Table 3. Indoor Radon and Soil
and Michigan
Indoor Radon
House in Basement
No. pCi/L
HECO 7300
HECO 7423
HECO 7423
HECO 7427
HECO 7427
HECO 7425
HECO 7425
HECO 7395
HECO 7395
HECO 7459
HECO 7459
HECO 7456
HECO 7455
HECO 7419
HECO 7448
HECO 7458
5.9
7.9
—
3.0
—
1.5
—
14.5
16.7
0.9
—
2.3
0.7
5.7
11.8
7.2
3.5
Radon Measurements in Colorado
Radium-226
Soil Gas Radon in Soil
pCi/L pCi/g
—
1002
1779
1430
1316
620
—
—
---
1095
1014
996
1240
710
930
2030
388
1.3 (90cm)
1.3 (90 cm)
1 .4 (90 cm)
1.1 (Surface)
1 .4 (90 cm)
1 .3 (Surface)
0.7 (90 cm)
1.3 (Surface)
1 .9 (90 cm)
1 .0 (Surface)
1 .9 (30 cm)
0.6 (90 cm)
0.4 (Surface)
—
...
—
-..
HEM! 30001
HEM) 30002
HEM I 30003
HEMI 30004
HEMI 30005
1.8
0.9
4.2
1.7
3.6
Radium-226 in soil was measured at two lots in this housing development.
One lot measured 0.79 pCi/g and the second lot measured 0.91 and 1.2
pCi/g on two soil samples. These measurements were not made at the same
houses where indoor radon was measured, so no direct correlation is
possible. The soil test results are only indicative of some radon availability in
this same geological area.
the seven yards varied by factors of 1.34 to 6.4, with
an average variation of 3.1.
In another study in the Piedmont area of New Jersey
(Ma87), soil radon was measured in the front, side,
and back yards of seven houses. Grab samples,
taken using a continuous radon monitor (CRM), and
3-month alpha track samples were obtained from a
depth of about 1 m. The grab sample radon
measurements varied by a factor of 50 between
houses and by as much as a factor of 46 between
test sites at a single house with an average variation
for each of the seven houses of 12.9. The alpha track
results showed seasonal variations of approximately
an order of magnitude difference between fall and
winter/spring soil gas levels. The soil alpha track
results did not compare in general with the results
obtained by CRM grab sampling. For example, a
factor of 30 increase in radon from the front to back
yard was observed in one house by grab sample
data, while alpha tracks taken in the front and back
yards were similar. In a second house, the opposite
was observed: grab samples collected in the front
and back yards varied by less than a factor of two,
while alpha track measurements in the same yards
varied by a factor of 14 (Ma87).
As indicated from the data, indoor radon
concentrations cannot yet be predicted from soil
radon values. The possibilities are not promising for
designing a device and/or technique that builders can
rely on to exclude building sites as potential indoor
radon problems. As shown by the Florida and New
Jersey data, multiple measurements would be
required at each building site, and even those
measurements can vary by orders of magnitude. Until
the lot has been cleared, rough grading completed,
and the foundations dug, access to the soil that
actually produces the radon gas in the house is
difficult if not impossible. Few builders would decide
-------
not to build on a lot after they have incurred the costs
of purchasing the lot and digging the foundation. In
addition, many houses use fill dirt brought in from
other locations. Unless the fill dirt is also
characterized, additional radon potential may be
missed or, on the other hand, the actual potential for
radon entry may be overstated.
In summary, at present individual building lots cannot
be characterized reliably for radon potential, and
because of the inherent problems that have been
identified, builders should not expect to be able to
make these measurements or pay someone else to
make them reliably in the near future. Aggregate data
on radon in soils should be evaluated communitywide.
There is hope that these data can be used statistically
to predict large areas with a higher probability of
residential radon problems. Work to enhance the
accurate prediction of radon-prone areas is
continuing within EPA and among other researchers.
2.4 Radon Observed in Nearby Houses
In EPA's Radon Reduction Demonstration Program
for existing houses, those with elevated radon levels
generally have been identified through prior high-
radon measurements in other houses in the
neighborhood. Although it is possible to have isolated
pockets of radon gas in the soil beneath a single
house, most radon-prone houses are located in a
geological setting common to most other houses in
the general vicinity or region. Because of the many
variables that affect radon entry into a house--
radon in soil, permeability of soil, cracks and fractures
in rock, and house construction details—houses
with elevated radon can be found adjacent to houses
with very little radon. However, statistically, the
presence of an elevated radon house in a
neighborhood or a significant number of elevated
houses in an area as large as a county or zip code
area increases the likelihood of other elevated radon
houses in the same area.
A classic example of one elevated radon house
leading to the discovery of other elevated houses in
the area occurred in Clinton, New Jersey, in March
1986. A homeowner in the Clinton Knolls subdivision
read about the radon problem in the Reading Prong
area of Pennsylvania and decided to obtain a
charcoal canister and measure the radon level in his
own house. When he received a very high radon
reading, he notified the New Jersey Department of
Environmental Protection (NJDEP). The NJDEP
surveyed the neighborhood, making charcoal
canisters available to homeowners who were willing to
have the radon level checked in their houses. The
survey showed that 101 out of 103 houses tested had
radon levels above the EPA action level and over half
of the houses had more than 25 times the action level
(Os87a).
The Clinton experience can be contrasted with radon
observations in Boyertown, Pennsylvania, where the
first very high natural radon measurements were
made in existing houses. Houses with radon
concentrations over 500 times the EPA action level
were found adjacent to houses below the action level
(Py88). Therefore, the presence of elevated radon
nouses in a neighborhood is at best only an indication
that the probability of having a radon problem has
increased.
2.5 Radon in Water
Between 2 and 5% of the radon problems found in
the U.S. can be attributed to radon in water
(EPA87a). The most significant radon-in-water
problems observed so far in the United States have
occurred in the New England states. Only houses
with individual or community wells have the potential
of a radon-in-water problem since the water in
these systems is usually not well aerated.
Radon dissolves into groundwater from radon-rich
rocks or soils usually deep in the earth's crust. When
this water is exposed to the atmosphere, some of the
dissolved radon is released. As a rule of thumb, there
is an increase of about 1 pCi/L in the air inside a
house for every 10,000 pCi/L of radon in the
household water (EPA87a). Locally, higher radon
levels have been observed when water is heated or
agitated, such as during shower use (Os87c).
Builders should be aware that houses that require
groundwater as the house water supply could have a
radon problem. The only way to be certain that the
groundwater is not a potential radon source is to have
the water from the well tested. Some states and
private companies provide test kits for this purpose.
If a well has not been drilled, a nearby well may be an
indicator of potential radon problems. Identifying
potential radon-in-water problems by using the
results from adjacent wells is subject to the same
problems that were mentioned in Section 2.2. There
is no guarantee that the neighbor's well is producing
water with the same characteristics as the new well
will produce since it may not be from the same
stratum. The limited data available on houses with
radon-in-water problems indicate that adjacent
houses with similar wells sometimes produce similar
radon-in-water problems and sometimes do not.
However, few isolated radon-in-water problem
houses have been observed.
In summary, because of the small percentage of
houses with radon-in-water problems, few builders
will have to deal with this issue. However, if a house
is being built in an area known to have many houses
-------
with radon-in-water problems, drilling the well and
testing the water supply prior to construction are
advised. If a house is built prior to identifying a
radon-in-water problem, resolving the problem can
be more difficult since space will not have been
allowed for the radon-in-water mitigation
techniques available.
2.6 Radon in Building Materials
Less than 1% of the residential radon problems in the
United States can be attributed to building materials.
Most of the building material problems have arisen
from the use of known radium- or uranium-rich
wastes such as aggregate in block or as backfill
around houses. None of the houses studied in the
EPA Radon Reduction Demonstration program have
had any identifiable problem associated with radon
from building materials.
Builders should be aware that this is a potential
problem but, unless building materials have been
identified as radium- or uranium-rich, the chance of
obtaining radon from building materials is very slim.
-------
Section 3
Radon Entry and Barriers
Three approaches to resolving the radon problem in
the construction of new houses are to 1) prevent
radon entry by using barrier methods, 2) reduce the
radon entry driving forces, and 3) divert the radon
from entering the house by using sub-slab
ventilation. This section addresses the barrier
approach, Section 4 addresses reduction of the
driving force, and Section 5 addresses sub-slab
ventilation.
Radon entry routes of concern in new construction
are the same as those that have previously been
identified for existing houses. Figures 3, 4, and 5
depict the major radon entry routes for simple
basement, slab-on-grade, and crawl-space
houses, respectively. Houses that are combinations
of the above substructures often provide additional
entry routes at the interface between the two
substructures. The following subsections address
each of the potential radon entry routes and suggest
alternative radon-resistant construction techniques
relative to the specific entry routes. Sometimes these
alternatives include barriers that can be used to block
radon entry while continuing to use the traditional
construction methods, while others may require
significant alternative construction methods that avoid
creating the potential radon entry route.
When possible, comments on specific radon-
resistant construction techniques have been obtained
from builders claiming to build radon-resistant
houses. Builders providing input to this report are
identified in Appendix A. Also, building material
average retail prices are quoted when available.
These prices are always in 1988 dollars. THE EPA
DOES NOT ENDORSE ANY OF THE COMPANIES
OR PRODUCTS REFERENCED IN THIS
DOCUMENT.
3.1 Foundation Walls
3.1.1 Construction Materials
Below-grade walls may be constructed of poured
concrete, masonry, or other materials such as all-
weather wood or stone. The materials covered in this
section, poured concrete and masonry block, are the
most common for new construction.
Poured concrete foundation walls are generally
constructed to 3,000 psi compressive strength. The
forms are held together with metal ties that penetrate
the wall and can allow radon entry as they corrode.
Aside from cracks, utility openings, and penetrations
at ties, a poured concrete wall can be a good radon
barrier.
Concrete block foundation walls may have open
cores, filled cores, or cores closed at the top course.
The exterior of masonry walls is frequently coated
with a layer of cementitious material, referred to as
"parging," for water control. Uncoated block walls are
extremely porous and not an effective barrier to
radon.
In many areas of the country, some type of
dampproofing or waterproofing treatment of wall
exteriors is a code requirement that can serve a dual
function of impeding radon movement. This is
discussed at length later in the section on
waterproofing.
There appear to be geographic subareas throughout
the U.S. in which poured walls are in the majority and
other areas where masonry walls predominate.
Poured concrete walls are mostly available only in
areas where contractors have the in-house expertise
to build them and either rent or have invested in
reusable forms. Poured concrete is generally less
expensive than masonry for full-height basements
where 8- or 10-in. poured walls can be used in lieu
of 12-in. block, but masonry can be less expensive
for partial height walls where thinner block can be
used. Recent EPA/AEERL laboratory tests have
confirmed that uncoated concrete masonry walls
allow substantial airflow. Building codes dictate
dampproofing or waterproofing treatment for both
poured concrete and concrete masonry walls. These
treatments inhibit gas movement through the wall as
a unit. Concrete and cinder blocks are much more
porous than poured concrete, although the parge or
waterproofing coats moderate the difference. Block
walls can allow substantial soil gas circulation in the
cores of unfilled blocks, providing an area source of
radon. Various measures are available to alleviate this
11
-------
A. Cracks in concrete slabs
B. Cold joint between two concrete pours
C. Pores and cracks in concrete blocks
D. Floor-to-wall crack or French drain
E. Exposed soil, as in a sump
F. Weeping (drain) tile, if drained to open sump
G. Mortar joints
H. Loose fitting pipe penetrations
I. Open tops of block walls
J. Water (from some wells)
K. Untrapped floor drain to a dry well or septic system
Figure 3. Major Radon Entry Routes in Basement Houses
CM
r-
00
§
12
-------
pfilSi
A. Cracks in concrete slabs1
B. Spaces behind brick veneer walls
that rest on uncapped hollow-block foundation
C. Loose fitting pipe penetrations
D. Open tops of block walls
E. Water (from some wells)
F. Cold joint between two concrete pours
G. Heating duct registers or sub-slab
cold-air return pipes
H. Hole under bathtub and under commode ring
I. Wall/floor joint
hairline cracks probably do not contribute
§
00
CM
Figure 4. Major Radon Entry Routes in Slab-on-grade Houses
13
-------
A. Cracks in subflooring and flooring
B. Spaces behind stud walls and brick veneer walls
that rest on uncapped hollow-block foundation
C. Electrical penetrations
D. Loose-fitting pipe penetrations
E. Open tops of block walls
F. Water (from some wells)
G. Heating duct register penetrations
H. Cold-air return ducts in crawl space
00
(N
Figure 5. Major Radon Entry Routes in Crawl-space Houses
14
-------
problem, including exterior (or interior) gas barrier
membranes and solid or filled block tops.
Officials of several code organizations have indicated
that they strongly favor poured concrete foundation
walls instead of masonry walls because of the
potential for radon penetration through block walls.
On the other hand, many houses with tight slabs have
porous masonry walls that appear to be the major soil
gas entry point. It must be recognized that a bad
batch of poured concrete can also be porous and that
ferrous wall ties rust over time. Recent radon
reduction demonstration projects in existing houses
have included houses with elevated radon levels
including some built with poured concrete foundation
walls and others with laid masonry walls. In general,
poured walls are probably better than block walls in
radon-resistant construction unless special efforts
are made to close the blocks.
Discussions with various builders identified the
following radon-resistant techniques in current use:
1. One builder uses Air-Crete™, a blown-in
insulation, which is also used as a sill sealer, to
fill the top course of masonry blocks. Air-
Crete™ is a magnesium oxisulfate silicate
cement installed by foaming at 2 to 10 Ib/ft3
densities.
2. Some builders use poured concrete foundations
exclusively because of concern over radon
penetrations through block walls. Many masons
are careless about striking all of the joints in
masonry walls, especially at the top course of
block and at the base. To be able to use a
masonry block wall in a radon-prone house, one
builder stated that the wall would have to be
parged both inside and outside.
3. Another builder uses foundation masonry block
walls and concentrates on developing an effective
barrier only at the exterior wall. However, radon
can still enter blocks under the slab and exit
blocks above the slab if the block is not sealed
inside.
One NEWHEP builder in Denver uses an innovative
foundation technique to simultaneously deal with
problems of expansive soil and high soil radium and
radon content. The foundation excavation is over-
dug to a depth of 10 ft. Caisson pilings are driven to
support the 10-ft-tall reinforced poured concrete
walls. Band joists are bolted to the walls 2 ft above
the dirt floor, and a carefully sealed wood subfloor,
supported by steel "I" beams and standard size floor
joists, is installed. The 2-ft-high "buried crawl
space" is actively ventilated by installing a sheet
metal inlet duct in one corner of the basement,
drawing in outside air through an above-ground
vent. A similar duct with an in-line fan is located at
the opposite corner to exhaust air through an above-
grade vent. Soil gas radon at levels from 3,163 pCi/L
to 4,647 pCi/L was measured at three of these
building sites. Soil radium-226 content was
measured at 1.05 to 1.62 pCi/g. Indoor radon
measurements were then taken in the buried crawl
spaces and in the basements. Measurements were
made during the summer of 1987 with the exhaust
fan off, and after 1 day, 1 week, and 2 weeks of
operation. The results are shown in Table 4 (Mu88b).
Table 4. Results Using Vented Crawl Space
Technique
House
No.
1
1
1
2
2
2
3
3
Fan
Operation
Off
2 Weeks
2 Weeks
Off
1 Week
1 Week
1 Day
1 Day
Buried
Crawl-
space Level
pCI/L
9.9
9.9
8.4
27.8
18.6
16.7
26.4
15.5
Basement
Level
pCi/L
1.9
1.4
1.4
1.8
1.2
0.9
1.3
0.9
NOTE: Follow-up measurements were made
in the basements of Houses 1 and 2 in
March 1988 and levels of 0.6 and 0.9
pCi/L were obtained. The continued
effectiveness of this technique is
assumed to be the result of the
combination of both active ventilation in
the crawl space and careful sealing and
caulking of all seams, joints, and
penetrations of the basement floor
(Mu88b).
3.7.2 Masonry Walls with Termite Caps, Solid
Blocks, and Filled Block Tops
Builders may construct a foundation wall with solid,
filled, or sealed block tops for several reasons,
including energy conservation, termite-proofing,
distribution of weight of the structure, and radon-
resistance. If none of these factors is considered
important, the block tops may be left entirely open or
sealed only at anchor points, although some codes
require solid tops. Also, houses have been observed
in which block tops were generally sealed, but open
cores were exposed at access doors to crawl spaces
and around ash pit doors and other openings. The
porosity of some solid blocks may be sufficient to
prevent them from being an adequate radon barrier.
Block tops can be sealed at the top course by stuffing
paper, wire mesh, or some other material into the
block cores and then filling the cores with mortar.
However, the longevity of this technique is doubtful,
and it is easy to leave gaps using this method.
"Termite caps" are cored blocks in which a 2-in.
thick shell closes one end of the cores. They may be
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installed as the top course and may also be inverted
and installed as the bottom course (see Section 6.2).
Termite caps or 100% solid blocks can be expected
to provide a more consistent radon barrier than
blocks whose cores are stuffed with wire mesh and
then filled with grout. On the other hand, it is easier to
install anchor bolts into a block wall whose top course
has open cores than to place the bolts into solid
blocks. The bolts can be set in the mortar between
blocks; however, this technique does not meet
anchorage requirements of some codes. Solid blocks
could also be used as the second course, leaving the
hollow blocks as the top course.
One builder uses solid cap blocks for 8- or 10-in.
thick block walls and filled block cores for 12-inch
block walls. At present, most solid block tops are
intended for energy conservation and are part of
standard construction practice for many builders. In
areas where anchors must be placed into solid
blocks, the anchor penetrations can be sealed or put
into mortar joints.Another builder uses Air-Crete'M
to fill foundation walls and also serve as a sill sealer.
The use of Air-Crete™ as a sill sealer should be
investigated further because of the potential for
shrinkage away from the wood.
Closed block tops enhance soil depressurization and
in many houses are necessary for soil
depressurization to work. Sealing at block tops and
other potential radon entry points may even be
sufficient to maintain radon at an acceptable level in
houses with weak radon sources.
3.7.3 Masonry Walls with Weep Holes
Weep holes at the bottom course of block foundation
walls below the slab are potential radon entry points.
Weep holes are used as a backup system to relieve
water from the block cores when surface
waterproofing barriers fail. Such a connection
between the exterior and interior sub-slab area is an
obvious channel for radon entry allowing soil gas to
pass from the sub-slab to the interior of the block
wall.
The National Concrete Masonry Association (NCMA)
issues technical notes to provide contractors with
guidance in construction practice. The NCMA-TEK
43, Concrete Masonry Foundation Walls (NCMA72),
provides illustrated cross-sections of foundation
walls showing weep holes through the footing. The
NCMA says that weep holes through the footing are
more difficult to install and less common than weep
holes in the bottom course of block. They also serve
a different purpose. Weep holes through the footing
connect exterior drainage systems to interior sumps,
while weep holes through blocks allow accumulated
water to drain from the block cores. Without this
precautionary feature, water may build up and stain
wall interiors. A weep block can also channel water
from the exterior of the foundation toward the sump
system, although this approach is not normally used.
Contractors often create weep holes in the bottom
course of block rather than buying prefabricated weep
block. Some masons open holes in both shells of the
block; others open the block cores to the interior but
leave the exterior shell intact. Some builders prefer
weep holes as an alternative to exterior drainage,
while other builders reportedly use weep blocks in
lieu of backfilling with granular material, although such
backfilling is recommended or required in most areas.
The actual need for weep holes in properly designed
and constructed masonry walls is questionable.
Moreover, a solid block installed as the bottom course
of a foundation wall is recommended to keep radon
from seeping into block cores around the footing. The
NCMA-TEK 160A, Radon Safe Basement
Construction (NCMA87), shows no weep holes in
walls or footings but offers no prediction of the
consequences of eliminating them. A potential
concern is that even properly applied waterproofing
materials may fail over time. New materials discussed
in Sections 3.1.4 and 3.1.5 may help to avoid this
problem.
One builder has suggested that it might be possible to
retain the weep hole while venting the upper blocks
above grade to allow soil gas to escape. This idea
has not yet been tested, and would need to be
combined with an interior barrier such as paint. In
general, weep holes should be avoided and, if
drainage problems are expected, exterior drain tiles
should be installed.
3.1.4 Drainage Boards for Water and Radon
Control
Soil that was excavated from the basement is
commonly used as backfill against foundation walls. In
some cases, a more permeable backfill may be
brought in. If local soils are not appropriate, the
builder may use gravel to backfill, although this is rare
because of the additional cost.
The vendors of EnkadrainTM and comparable
products suggest that their products can be cost-
effective compared to backfilling with gravel. A
drainage board such as EnkadrainTM laid up against a
house wall can provide an air buffer that can break
the pressure connection between the soil and the
house interior. Drainage boards have been used for a
number of years, particularly in commercial projects
and underground nouses. Prices vary widely. Aqua-
ShellTM, a corrugated polyvinyl chloride (PVC)
manufactured and distributed by Brentwood Industries
in Reading, PA, is available for $0.20/ft2 (material
cost). Other products can cost more than $1.00/ft2.
Drainage board can also serve a dual purpose:
Owens-Corning's Warm-n-DrjTM combines an
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insulation and a drainage function, although its
water- and air-channeling capacity is less than that
of some other drainage boards.
EnkadrainTM drainage board has been used in
several radon control applications. EnkadrainTM 9120
is 90% airspace, equivalent to several inches of
gravel. The material cost of Enkadrain™ 9120 is
roughly $1.00/ft2. Strips of EnkadrainTM 9120 have
been used as an alternative to perforated piping with
6-in. gravel to set up prospective sub-slab suction.
Gravel, 2 in. or so, is still needed to support the slab.
EnkadrainTM has also been used with masonry walls
built with cap block. Interior weep holes have been
set up to weep through EnkadrainTM to an interior
drainage system, which links the wall interiors to the
sub-slab pressure field. The material cost for this
system is reportedly less than $300/house (assuming
1200-1500 ft2 of basement), with labor amounting to
3-4 manhours.
EnkadrainTM 9010 is a thinner, lower-cost
($0.60/ft2) material than 9120 and is designed to
relieve hydrostatic pressure against walls. It also can
be used to break the pressure connection between
the soil and the house exterior. The material may be
hung like skirting from a furring strip or fastened to
the walls with Liquid NailsTM. Further, weep holes
can be eliminated if a good foundation drainage
system is provided. Use of EnkadrainTM as a
drainage board against walls is combined with a
standard surface treatment for waterproofing.
According to the manufacturer's representative, the
use of EnkadrainTM 9910 may result in a net savings
under extreme soil conditions when drainage board
can be used in lieu of imported gravel backfill. Many
builders, however, have never needed any significant
amount of gravel backfill for foundation walls. The
incremental cost of EnkadrainTM compared to
traditional construction would vary significantly based
on local soil conditions.
Owens-Corning's Warm-n-DriTM board is a rigid
fibrous glass material available in 3/4, 1-3/16, and
2-3/8 in. thicknesses that can act as a drainage
board, channeling water to foundation drains. The
flow capacity of 2-3/8 in. thick Warm-n-DriTM js
only 30% of that of Enkadrain™ 9010, and 3/4-in.
Warm-n-DriTM has only 8% of the flow capacity of
EnkadrainTM 9010. However, the Warm-n-DriTM
also has an insulating R value of 3.1/in. The material
cost of Warm-n-DriTM js roughly $0.45/board ft,
compared to $0.60/ft2 for EnkadrainTM 9910. The
concept of using drainage board to relieve soil gas to
the atmosphere has not been adequately studied;
therefore, it is not possible to say what flow capacity
is needed to fulfill this purpose.
3.7.5 Dampproofing/Waterproofing to Achieve a
Radon Barrier
The value of radon barriers for foundation walls
appears obvious. If it is possible to identify
waterproofing or dampproofing treatments that are
effective gas barriers, walls can be made radon-
resistant. Acceptable dampproofing or waterproofing
treatments are specifically listed in building codes in
many areas of the United States; these lists are
periodically amended as new materials come into use.
The terms "waterproofing" and "dampproofing" are
often used interchangeably. Briefly, any waterproofing
material can also be used for dampproofing; the
converse is not true. Waterproofing materials must
resist the penetration of water under a hydrostatic
load. Dampproofing materials are not expected to
keep out water under pressure, but do impede water
entry and block diffusive movement of water through
pores.
Any material which provides adequate protection
against water should at least limit convective soil gas
movement. Properly applied waterproofing materials
should help block pressure-driven entry of soil gas.
Barriers against pressure-driven gas flow should
meet the following criteria: good adhesion, crack-
spanning ability, flexibility and elasticity through a
wide temperature range, puncture resistance, and
chemical and structural stability over time.
The radon contribution from diffusion is believed to be
quite small relative to pressure-driven flow, although
there are doubtless house-to-house variations.
Post-mitigation tests at fan discharges have shown
continuing high radon readings, indicating high radon
concentrations under the slab. Moreover, the success
of radon extraction wells at pulling radon laterally
suggests that sub-slab suction might even raise
radon levels beneath the slab. However, sub-slab
depressurization appears to be sufficient to bring
radon under control, independent of the concentration
gradient between the soil and the house interior.
The most common dampproofing treatment for
residential foundation walls is a parge coat covered
with bituminous asphalt. The parge coat is used for
concrete masonry walls but is not necessary for
poured concrete walls. This two-stage treatment has
been superseded by other materials in some areas
(e.g., surface bonding cement in central New York
state). An estimated installed cost for a parge coat
covered with bituminous asphalt is $0.25 -
$0.55/ft2, assuming a single coat of bituminous
material, and $0.75 - $0.85/ft2 when two coats of
bituminous material are used.
Oak Ridge National Laboratory indicates that
bituminous asphalt may be attacked by soil and
groundwater chemicals, specifically acids (ORNL88).
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Bituminous materials may also lose their elasticity and
crack-spanning ability at below-freezing
temperatures. These features render bituminous
asphalt an undependable waterproofing treatment; in
fact, it is listed by code organizations such as BOCA,
CABO, and SBCCI only for dampproofing.
The performance of most dampproofing materials,
including bituminous over parging, can be improved
by the use of a protection board. Almost any rigid
material may be used. The protection function can
also be served by a drainage or insulation board.
A number of dampproofing systems are better gas
barriers than bituminous asphalt. Some are relatively
new to the residential marketplace but have track
records in industrial/commercial settings. Others have
been introduced into the most expensive residential
market or have found applications at problem sites. A
common feature of these alternatives is that they are
generally more expensive than bituminous
dampproofing. However, a 1981 survey of 31,456
households by Owens-Corning Corporation (DA86)
found that 59% of homeowners with basements
reported water leaks. As the supply of trouble-free
building lots dwindles, homebuyers may decide that
additional investment is justified, and improved
dampproofing systems may be developed to address
radon and water problems simultaneously.
The following is a sampling of alternative
waterproofing systems that are readily available to
builders. Some of the materials listed are derived
from other than building waterproofing.
Coal tar modified polyurethane: Coal tar modified
polyurethane is a cold-applied liquid waterproofing
system. The HLMTM system by Sonneborn is an
example of this approach to waterproofing. It is
applied as a liquid at the rate of 10-15 mils/coat;
each coat has a material cost of $0.15 to 0.20/ft2.
The coating dries hard, but has some elasticity. This
material may be attacked by acids in groundwater but
can be defended by a protection board. The
performance of any liquid-applied waterproofing
systems is limited by the capabilities of the applicator,
and it is difficult to achieve even coats on vertical
surfaces.
Polymer-modified asphalt: Polymer-modified
asphalt is a cold-applied liquid waterproofing system.
As with the HLM™ system mentioned above, the
quality of the installation depends on the applicator,
and it is difficult to achieve an even coating on a
vertical surface. High grade polymer-modified
asphalt is superior to coal tar modified polyurethane in
elasticity, crack-spanning ability, and resealability,
but inferior in its resistance to chemicals.
Owens-Corning's Tuff-n-DriTM is a chemically
linked polymer-modified asphalt (as opposed to
other polymer-modified asphalts, which are simply
mixed). It has good crack-bridging ability and
resistance to emulsification and can be applied by
trained contractors to clean walls using high-
pressure airless spray (average thickness 40 mil).
The system is completed by covering the Tuff-n-
DriTM membrane with Warm-n-DriTM? a fibrous
glass drainage/insulation/protection board. The board
can be cut off at grade or run above grade to the sill.
Either way, it breaks the connection between the soil
and the house. Tuff-n-DriTM shows good
durability--the company has exhumed product
samples buried since 1959 and found no decay. The
product has been used for 30 + years in Europe and
10-15 years in Canada. Owens-Corning trains and
certifies its applicators; the product is not available in
the general marketplace. The total applied cost of the
Tuff-n-DriTM/Warm-n-DriTM system is roughly
$0.90 - $1.50/ft2, depending on site location and
the prevailing wage rate.
One builder reports having used the Tuff-n-DriTM
system in radon-resistant construction. He has
attempted to use Tuff-n-DriTM alone (without the
Warm-n-DriTM board), but found that it was not a
successful waterproofing method without the drainage
board. Owens-Corning's warranty requires both
components to be used and supported by a
foundation drainage system.
Membrane waterproofing systems: Waterproofing
applied as a membrane has an advantage over
liquid-applied systems in that quality control over
thickness is ensured by the manufacturing process.
Most membrane systems are also chemically stable
and have good crack-spanning ability. On the other
hand, effective waterproofing demands that seams be
smooth so that the membrane is not punctured.
Some masons apply parging to a half-height level
and then return to finish the upper half of the wall.
This tends to leave a rough section where the two
applications overlap and means that the waterproofing
crew has to grind the wall smooth before applying the
waterproofing membrane. One builder believes that
Aqua-FlexTM fj|m> which he uses as a waterproofing
for both standard and radon-resistant houses,
makes the parging layer unnecessary.
Aqua-Flex™ is a 0.02-in. PVC membrane
developed for settling ponds. It is available at
$0.20/ft2 from Brentwood Industries in Reading, PA.
PolyAmerica's PolyplexTM ($o.i2/ft2) and DuraflexTM
($0.20/ft2) are polyurethane films that also come from
the landfill/lagoon marketplace. These and other
thermoplastic membranes may be applied in various
ways -- affixed to walls, or laid beneath slabs.
Thermoplastic membranes are highly rated for
resistance to chemicals and longevity. Rubberized
asphalt polyethylene membranes have superior
crack-bridging ability, compared to fully adhered
thermoplastic membranes. (Loosely hung
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thermoplastic membranes, by their nature, have
obvious crack-bridging ability in that they are not
bonded to the walls.) Bituthene™, a 60-mil
rubberized asphalt polyethylene membrane which
sells for $0.65/ft2, is substantially more expensive
than Aqua-Flex™, Polyplex™, or Duraflex™.
Seams and overlaps must be carefully and completely
sealed in order for membranes to function as radon
barriers. The choice of seam material varies with the
type of sealant. One builder has been known to use
silicone caulk at the seams of Aqua-Flex.™ A PVC
solvent glue would be more appropriate for this type
of membrane, because silicone does not make a
positive seal. Another builder has expressed concern
over pinhole leaks that solvent glues may create in
curing. This discussion highlights the need for quality
control during installation. Poly America's polyethylene
films are heat-sealed on the job with a proprietary
heat fusion seaming method; however, polyethylene
tape can also be used as a sealant.
Bentonite: Bentonite clay expands when moist to
create a waterproof barrier. Bentonite is sold in
various forms, including panels and mats. Bentonite is
not as resistant to chemicals as the thermoplastic
membranes, nor is it puncture resistant. The major
flaw of bentonite as a radon barrier, however, is that it
is only tightly expanded when wet. This is acceptable
for a waterproofing material, but not for a gas barrier.
Surface bonding cement: Surface bonding mortar or
cement is mentioned in some building codes as an
approved dampproofing treatment, but not as a
waterproofing treatment. A number of manufacturers
produce cements and mortars impregnated with
fibrous glass or other fibers. Some of these may be
chemically unstable in the alkaline environment of
Portland cement. For example, CONPROCO, which
manufactures a variety of fibrous-glass-reinforced
surface bonding cements, contends that some of its
products would qualify as waterproofing, as well as
structural bonding and (potentially) radon-proofing
materials.
One technique of assembly using surface bonding
cement is to dry-stack blocks and apply the cement
on both sides. As an alternative, the block wall is
conventionally assembled with only an outside coating
as a positive-side waterproofing. Cost for one-side
application is roughly $0.25/ft2 for materials, with
labor being equivalent to the standard parge coat
application. If the product is used for a structural
bond, the material cost of the surface bonding
cement would be roughly doubled, but the normal
mortar cost could be deducted and labor cost would
have to be adjusted to account for dry-stacking and
trowelling-on of a surface coating as opposed to
standard masonry work. An exterior coat of surface
bonding cement is now the standard
dampproofing/waterproofing method in central New
York state, although it has never been widely used as
a structural bonding material.
Cementitious waterproofing: A number of additives
can be incorporated into concrete to create
cementitious "waterproofing." This type of water-
proofing is appropriate only for interior applications
because it is inelastic, does not have good crack-
spanning ability, and cannot resist hydrostatic
pressure. ThorosealTM js a cementitious paint for
above-grade applications. It is used as an industry
fix-all for cracked walls and interior patches ($18.00
for a 50-lb bag, $0.07/ft2 of coverage).
Interior paint as a barrier: Morton Thiokol's radon
barrier paint is being tested at EPA/AEERL's
laboratory in Research Triangle Park, NC. Conpro-
LasticTM by CONPROCO, a paint developed for
interior and exterior (above-grade) use, is also being
tested by EPA as a radon barrier. Conpro-Lastic™
costs between $60 and $75 per 5-gal. pail, with
50-125 ft2 coverage per pail. The recommended
application is two coats. As other potential radon
barrier paints are identified, they will also be
evaluated by EPA.
3.2 Slabs
3.2.1 Prevention from Cracking
Plastic shrinkage cracking of concrete is a natural
function of the drying process. Many factors come
into play as concrete cures, including water content,
cement content, atmospheric humidity, temperature,
humidity, air movement over the slab surface, and
aggregate content. The preparation of the sub-slab
area is also important. Reinforcement can be used to
reduce shrinkage cracking. It has not been
traditionally mandatory in residential floor slabs.
Residential builders typically become concerned
about shrinkage cracking and/or slab reinforcement
when they are working in areas with unstable soils or
when they need to ensure slab integrity under
specific finished floor systems (ceramic tile, for
example).
Residential builders in most areas seldom use woven
wire mesh or rebar to reinforce basement floor slabs;
however, builders in some parts of the country use
woven wire mesh or rebar as standard construction
practice.
There are many ways to minimize slab cracking,
although it probably cannot be eliminated entirely.
The following discussion describes a number of
treatments, some of which are familiar to the
commercial/institutional/ industrial construction area
but uncommon to the residential marketplace.
Reinforcement with ferrous metals: The use of metal
reinforcement embedded in the slab increases its
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strength. Woven wire mesh is the most common
material for residential applications. It has been
suggested that 10- or 8-gauge woven wire mesh is
appropriate for a basement slab. Material cost for
10-gauge 6 x 6 in. mesh would be $7.50/100 ft2
(central New York prices), while 8-gauge 6 x 6 in.
mesh would cost $9.50/100 ft2. This translates to
$75 plus labor or $95 plus labor, respectively, for a
1,000 ft2 slab.
Rebar (also called rerod) is most commonly used for
footings or garage slabs and would not generally be
used throughout a basement slab. A No. 4 rebar (1/2
in. bar) runs 0.668 Ib/linear ft and costs $0.30/lb
(central New York) for small quantities. It would
probably be installed in a garage slab 12 in. on
center, leaving 3 in. at each end and running in both
directions. Assuming a 20 x 50 ft slab, this would be
$395 plus labor for the hypothetical 1,000-ft2 slab
mentioned above.
Concrete additives: A number of additives can be
used to change the characteristics of concrete. The
American Concrete Institute (ACI) discusses these
additives in its technical guides. A discussion of the
various fibers used to reinforce concrete is found in
ACI 544 - State of the Art Report on Fiber-
Reinforced Concrete (ACI86).
Water-reducing admixtures: Water-reducing
admixtures, also known as plasticizers, are used to
increase the workability of concrete without adding
water. One example of a plasticizer is WRDA-19, by
Grace Construction Products ($4.50/yd, $55 for a
1,000-ft2, 4-in. slab), which is labeled "an aqueous
solution of a modified naphthalene sulfonate,
containing no added chloride." Chlorides are
frequently added to concrete as antifreezes, but
various codes limit the chloride content of concrete
because of its corrosive effect on ferrous metals and
its reducing effects on concrete strength. American
ATCON's report to the Florida Phosphate Institute
(Sc87) recommends the use of a plasticizer to reduce
the likelihood of water being added on site to produce
more workable concrete. Two builders involved in
radon-prone areas noted that they use plasticizers
for residential construction in Pennsylvania.
Fiber-reinforced concrete: Various fiber additives
are available that can reinforce poured concrete and
reduce plastic shrinkage cracking. Fiber reinforcing is
better than using woven wire mesh because the
fibers are homogeneously distributed throughout the
slab thickness and mesh generally ends up on the
bottom of the slab. The type of fiber used is important
because studies have shown that the alkaline
environment of Portland cement destroys some of the
fibers that are sold for this purpose. Polyester fibers
and glass fibers have been noted by ACI as being
vulnerable in an alkaline environment. Some
companies apply a surface treatment to fibers to
protect them from damage by alkalinity (glass fibers
so treated are known in the trade as "AR fibers"), but
the ends of the fibers are exposed when they are
chopped up during the manufacturing process, and
they can decay from the ends inward. The
polypropylene material used for FibermixTM
($3.75/yd3, $46 for a 1,000-ft2, 4-in. slab) and
FibermeshTM ($7.00/yd3, $86 for a 1,000-ft2, 4-in.
slab) is chemically stable in an alkaline environment.
FibermixTM js designed for the residential market and
uses a smaller dose of fiber than FibermeshTM.
Another polypropylene fiber reinforcement is sold
under the trade name of FortafiberTM ($g.oo/yd,
$111 for a 1,000-ft2, 4-in. slab). The zirconium
glass fibers used in QuikwallTM surface bonding
cement are reportedly also resistant to damage from
alkalinity, so that there are probably other slab-
reinforcing fibers that are not harmed by alkaline
environments. The much higher modulus of elasticity
of glass fibers compared to organic fibers may be an
advantage for the glass since it more nearly matches
the modulus of elasticity of concrete.
The comments above apply to fiber additives used in
surface-bonding mortars as well as those used in
poured concrete slabs.
Curing: Proper curing is critical to the strength and
durability of poured concrete. Many avenues are
available to ensure a good cure, ranging from
watering the slab to covering it with wet sand, wet
sawdust, or a waterproof film [e.g., waterproof paper,
Burlene™ (burlap/polyethylene)] or coating it with a
curing compound. Penetrating epoxy sealer applied to
the slab while it is still wet can act as a curing agent
and slab strengthener. Polyurethane sealants are
applied after the slab is dry, because moisture would
lift them off the slab. There are a number of other
liquid membranes and emulsions, including a number
of solvents which require substantial ventilation as
they dry.
Use of higher strength concrete: Typical residential
concrete slab construction requires a 28-day
compressive strength of only 3,000 psi. Concrete can
be made stronger by reducing the water/cement ratio.
If the water/cement ratio is kept at 0.5 or less, the
minimum 28-day compressive strength will increase
to 3800 psi. Moreover, if the ratio is reduced to 0.45,
the compressive strength increases to 4300 psi. To
achieve compressive strengths of above 3500 psi, the
slump cannot exceed 3 in. The compressive strength
and the slump of the concrete are no more important,
however, than the placeability of the concrete or the
finishability of the surface. Unfortunately, placeability
and finishability are not easily measured quantities
like slump and compressive strength and often do not
receive sufficient emphasis (ACI87).
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3.2.2 French Drains and Floor/Wall Cracks
The French drain (also called a channel drain or
floating slab) is a construction feature that appears to
provoke strong reaction from its defenders and
attackers alike. This slab detail is a standard feature
in new houses in parts of the country as varied as
New York and Colorado, but in other places it is
virtually unknown.
French drains are used in areas with expansive soils,
such as parts of Colorado, to protect the slab from
damage if the wall moves. In central New York state,
the main function of the French drain is purportedly to
drain away water which may seep down the walls.
One national builder has discontinued and now
prohibits the use of French drains in houses because
of the potential for radon problems. This builder
states that French drains also have been found to
significantly increase indoor moisture levels.
Various treatments can be used to seal French drains
against gas entry; some of those treatments have
crack-spanning capability in case of structural
movement. Some builders have attempted to seal a
French drain and preserve its water drainage function
by caulking the channel to a level below the top of
the slab and sloping the trough toward the sump. This
assumes that the sump lid is inset below the surface
of the slab and that a DranjerTM or some other
water-trapped drain in the sump lid drains away
water into the sump.
One Colorado builder, who uses French drains as a
standard construction feature because of expansive
soils, has noted that if a post-construction test
reveals a radon problem, he seals the slab perimeter.
Whether or not a French drain is installed, floor/wall
cracks should be considered in planning radon-
resistant house construction. As a cold joint, this
perimeter crack is always a potential radon entry
point.
Contractors building radon-resistant houses may
deliberately create a significant floor/wall crack so that
it will be easy to work with and seal. One builder
creates a channel at the slab perimeter and fills it with
a perimeter expansion joint - a closed-cell, flexible
foam strip. The expansion joint is presliced so that
the top 1/2 in. can be pulled off to leave room for
caulk; it is a product manufactured by H. Majeske
Company. Another builder tools the floor/wall joint
with an edging tool and seals it with swimming pool
caulk. Still another builder uses Will-SealTM) a
polyester-polyurethane foam impregnated with a
neoprene suspended in chlorinated hydrocarbons.
This material is packaged in a compressed state and
expands in place after installation. Will-SealTM is
very expensive -1/2x1 in. Will-Seal™ costs
$1.25/linear ft. Em-Seal™ is a comparable material
(from Em-Seal Joint Systems Limited, Stamford,
CT). Additional removable plastic materials used to
create a space to aid in future sealing are described
in the following section on cracks and penetrations.
Generally, French drains should be avoided in
radon-resistant construction. However, if they are
installed, one of the aforementioned techniques
should be applied to prevent radon entry.
3.2.3 Cracks and Penetrations
Masonry sealants for radon-resistant applications
must have good adhesion and be durable and elastic.
Polyurethane is the most popular caulk in the radon
mitigation marketplace. Self-leveling polyurethane
caulk sells for $10/qt, while 1-1/2 gal. of
polyurethane paving compound costs $55. Small
tubes of polyurethane caulk for sealing vertical cracks
are available for about $4/tube, with a tube producing
up to 28 linear ft of bead. Silicone is also used;
however, silicones are generally recommended only
for above-grade applications because they may leak
if they get wet. Two silicone products that have been
recommended for excellent durability and exterior use
are DOW 888™ ($80/gal. and $20/qt tube) and
DOW 790™ ($7/10.9 oz tube). The latter DOW
product is for smaller applications such as tooled
joints. Butyl caulk is susceptible to attack by
groundwater acids. Polysulfides have been largely
supplanted by polyurethanes because the former are
more chemically reactive with asphalts. In short, the
popularity of polyurethane appears to be well
founded. This material does give off fumes during the
installation process; therefore, worker protection is
important.
Because some slab cracks may be unavoidable,
some contractors are working to direct cracks into
controlled locations where they can be sealed. Zip-
topTM expansion joints and control Ts™ zip-strips
are both used to direct slab cracking. Both provide
the contractor with a tooled joint ready to be sealed
with caulk. Zip-tops™ at 1/2 x 1/2 in. sell for
$0.22/ft; control Ts™ se|| for $0.15/ft and up,
depending on the desired size. A good mason may
be able to use his tools to create tooled cracks so
that Zip-tops™ and control Ts™ are unnecessary.
Timing is important in this process. To create tooled
joints by hand, the mason must have access to the
slab at the proper point in the cure and be able to
move around to the locations where tooling is
required. Control joints can also be sawed during the
finishing process, before stresses have been
generated but before the concrete has set-usually
the next day.
Three builders in radon-prone areas employ
controlled cracking in their radon-resistant, new
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house construction. Two use control Ts, while the
third tools cracks and joints by hand.
3.2.4 Sub-Slab Barriers
A vapor barrier of polyethylene film is a typical sub-
slab feature in many areas of the country. The cost of
6-mil polyethylene is roughly $0.02/ft2. The intent of
the vapor barrier is to prevent moisture entry from
beneath the slab. They are good convection barriers
for radon, if installed correctly.
Installation of any sub-slab membrane is problematic
because an effective barrier should be both well
sealed and intact. Builders who use polyethylene
under the slab indicate that achieving a complete seal
at all laps and edges and around pipe penetrations is
difficult. It is difficult to seal the polyethylene to the
footing because the weight of the concrete tends to
pull it away from the walls during the pour. There is
also a high probability that the vapor barrier will be
punctured during installation. It has been observed
that even 10-mil polyethylene in a heavy felt
membrane is likely to be punctured during installation.
Another issue is the stability of polyethylene vapor
barriers. Polyethylene is known to be harmed by
ultraviolet (UV) exposure. One radon mitigator has
found polyethylene under slabs in Florida that
deteriorated in less than 15 years; more frequently,
polyethylene of comparable age is in mint condition.
Polyethylene films are manufactured with an array of
additives selected to support specific applications.
Durability varies according to the additives employed,
film thickness, length of UV exposure, temperature
swings, and other factors. Resins used in
polyethylene manufacturing have improved over time,
so that the life expectancy of polyethylene film in
1988 is longer than for the films used in the 1950s,
1960s, and 1970s. The durability of polyethylene films
in current use depends on the contractor's selection
and proper storage of the appropriate film for the job.
On the other hand, there is no evidence to support
the assertion that polyethylene vapor barriers
deteriorate with exposure to soil chemicals.
Construction film is a low-density polyethylene.
High-density polyethylenes are used for storage and
transportation of an array of chemicals. Polyethylene
is chemically stable, but may be adversely affected by
aliphatic hydrocarbons (such as hexane, octane, and
butane) and chlorinated solvents. It does not appear
to be reactive with the acids and salts likely to be
encountered in soil and concrete. No sub-slab
membranes have been identified as manufactured
specifically for radon control. However, several
products are promising alternatives to 6-mil
polyethylene construction film.
Moistop™, from the Massachusetts firm Fortifiber, is
a polyethylene-coated kraft paper vapor barrier
which comes in an 8 x 125 ft roll and sells for
$0.04-0.05/ft2. Overlaps of 6-in are marked on the
paper with a printed line. They can be sealed with
polyethylene tape. This material is attractive to
contractors because it is more puncture-resistant
than 6-mil polyethylene construction film, but less
expensive than many alternative products.
PolyAmerica manufactures polyethylene-based
membranes for use in hazardous waste landfills,
lagoons, and similar applications. Two of their
products have recently been tested by Arix
Corporation to determine their effectiveness as
barriers against radon diffusion. (In most cases,
diffusive flow is considered of little or no significance
as a mechanism of radon entry compared to
convective flow.) PolyAmerica's 20-mil high-density
polyethylene, Polyplex™, tested 99.9% effective in
blocking radon diffusion under neutral pressure
conditions. Its 30-mil low-density polyethylene,
DuraplexTM, tested 98% effective in blocking radon
diffusion under neutral pressure conditions. These
materials are available in rolls 23 ft wide. They are
heat-sealed at overlaps. Polyplex™ costs $0.12/ft2,
and DuraflexTM $o.20/ft2. PolyAmerica's 6-mil
construction film sells for roughly $0.02/ft2. Both
PolyplexTM and Duraflex™ carry a 20-year
warranty.
Energy-Saver Imports (ESI) of Wheat Ridge, CO, is
the U.S. distributor for a number of foil-faced
membranes manufactured in Holland. Foil-Ray™
has been tested as a barrier against diffusive
movement of radon. Soil-FlexTM js used by one
builder as the barrier in multilayered passive sub-
slab ventilation systems.
Foil-RayTM js a double layer of high-strength
bubble-pack with aluminum foil bonded on both
sides. It has a high compression strength and doubles
as an insulator. Concern exists over its fragility and
susceptibility to pinhole punctures. Both foil-faced
membranes can be punctured, but Foil-Ray's™
double bubble-pack offers a defense against
complete penetration. Punctures are easily repaired
with aluminum tape, which is also used at seams. Arix
has found aluminum tape to be almost as resistant to
diffusion as the membrane itself. A well-made seal is
diffusion resistant; however, gas can migrate through
wrinkles in the tape.
Foil-Ray™ can be an effective barrier at floor joists
in crawl spaces, where it can be installed with glue.
The fragility of the material is believed to be a
significant limiting factor in using Foil-RayTM under
the slab or as a perimeter insulation.
Soil-Flex™ has two faces of aluminum foil over a
core of glass scrim webbing; it is coated with asphalt.
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The membrane is 0.012 in. thick. This material has
not been tested as a barrier against diffusive flow of
radon, but its performance should be similar to that of
Foil-Ray™. Seams are sealed with aluminum tape.
The same precautions against puncturing apply to
Soil-FlexTM as to Foil-RayTM.
Foil-Ray™ is available in 75-ft lengths, 48 or 59
in. wide, at a cost of $0.33-$0.38/ft2. Soil-FlexTM
is available in 65-ft lengths, 39 in. wide, and costs
$0.15-$0.17/ft2.
Soil-FlexTM has been found to be in current use as
a sub-slab radon barrier. This highest cost
installation involved placing of the membrane on top
of 18 in. of gravel with EnkadrainTM and perforated
pipe embedded in the gravel, and covering it with 3-
4 in. of sand.
Tro-CalTM has been used as a sub-slab
membrane during mitigation work. This material was
used by Arix Corporation as one phase of its
mitigation of the Stanley Watras house, an often-
referenced radon mitigation site in Boyertown, PA.
Tro-Cal™ is a solvent-sealed PVC material
developed as a roofing membrane. The manufacturer
of Tro-Cal™ has not promoted its use as a radon
barrier and recently stopped distribution. Another
product, EPDM™, has been suggested as an
alternative to Tro-CalTM. (t comes in 60-mil
thicknesses in 100 ft by 61-1/2 in. rolls and costs
$400 per roll plus shipping. EPDMTM also comes in
45-mil thicknesses in 25 by 60 ft rolls for $600 per
roll plus shipping.
In Sweden, sub-slab membranes are not required in
high-radon areas and a tightly sealed slab is
considered to be a more effective radon barrier. The
difficulty of achieving a completely sealed, intact
sub-slab membrane is widely acknowledged;
however, a sub-slab barrier may be worthwhile even
if it is imperfectly installed. Polyethylene construction
film (6-mil) can serve as a backup radon barrier to
the concrete slab, even though it is not a complete
radon barrier by itself. The barrier may continue to
function, even with punctures, if incidental cracks and
holes in the slab are aligned with intact areas of
polyethylene.
Construction film is already in common use as a
sub-slab vapor barrier in many areas of the country.
The current prevalence and low cost of this material
mean that it may be worthwhile to continue its use
even though it is an imperfect barrier. One builder
uses a 6-mil polyethylene vapor barrier under the
slab in radon-resistant houses and takes no
precautions to seal the perimeter or lapped edges. He
is, however, careful to seal slab penetrations and the
perimeter crack. Another builder makes a boot out of
the polyethylene at pipe penetrations and claims to
seal with silicone. Silicone generally does not stick to
polyethylene.
It is possible to seal polyethylene vapor barriers at the
overlapped edges and at the footing. The difficulty in
sealing to the footing can be solved with the use of
an asphalt-based acoustic sealant.
In summary, it is worthwhile to continue the
installation of a vapor barrier that serves the added
valid function of moisture barrier. An inexpensive
alternate material such as Moistop™ offers the
advantage of improved puncture resistance with a
minimal cost penalty. More comprehensive installation
measures and more expensive materials may be
merited in areas where the radon source is strong
resulting from either high radon concentrations in or
high flow rates of soil gas due to high permeability.
3.2.5 Rules of Thumb for Slab and Sub-Slab
Barriers
The following summarizes guidelines to use in
avoiding radon entry through a concrete slab:
• Minimize the number of pours; make as few
joints as possible.
• Pour the slab right up to the basement wall.
• Caulk perimeter crack and control joints with
polyurethane.
• Reinforce slabs with wire mesh to help prevent
large cracks.
• Drain to daylight if possible, or to a drywall or
sewer. If you must use an interior sump pump,
seal it and vent it to outdoors.
• As a precaution, use interior footer drains (in
addition to exterior drains) and 4 in. of No. 2
stone below the slab that drains to the building
exterior. This way, sub-slab ventilation can be
added easily in case a problem is discovered
later (Br86).
3.3 Crawl Spaces
Although the normal spaces between sheets of
subflooring or subfloor boards can contribute to radon
entry from a crawl space to the house, the major
entry points are through numerous electrical, heating,
and plumbing penetrations in the house floor and via
the return air ducting often located in the crawl space.
As the pressure in the house and the return air duct
decreases relative to the pressure in the crawl space,
soil gas containing radon emanating from exposed
soil in the crawl space is easily drawn into the house.
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During construction, all possible penetrations between
the crawl space and the house should be sealed to
simply prevent the passage of radon up into the living
areas. Penetrations can be sealed by using a
combination of expandable closed-cell foam sealants
and a 1-part urethane caulking. Areas of particular
concern include: 1) openings in the subfloor for
wastepipes including openings for tubs, toilets, and
showers, 2) openings for water supply lines, 3)
openings for electrical wiring, and 4) openings for air
ducting for the heating, ventilating, and air
conditioning (HVAC) system. Return air for the HVAC
system should not be supplied from the crawl space.
Return air ductwork should be thoroughly sealed with
duct tape. The use of floor joists and subflooring as
three sides of a return air plenum should be avoided
because of the difficulties encountered in sealing. If
the space between the joists must be used, an
alternative to ducts is to mold sheet metal to fit the
space. If this technique is used, the bottom plate that
is attached to the molded metal between the joists
must be tightly sealed.
If isolation of the crawl space is the primary method
of radon-resistant construction being used, the
number and size of crawl space vents should be
maximized. The March 1988 version of Florida's
proposed interim guideline for radon-resistant
construction (FL88) suggests vents of not less than I
ft2 of vent for each 150 ft2 of crawl space.
Theproposed guideline also requires that vents be
located to provide good circulation of air across the
crawl space and should not include louvers or other
provisions for closure. Such a requirement would
necessitate extremely well-insulated water pipes in
cold climates and probably require the insulation of
subfloors and all heating pipes.
Other radon-resistant alternatives besides simple
isolation of the crawl space should be considered
because of the difficulties encountered in getting an
adequate seal between the house and the crawl
space. These alternatives will be discussed in Section
5.
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Section 4
Avoiding Depressurization and Between-Floor Pressure Differences
Given that a pathway exists for radon in the soil to
enter the house, a driving force is still required to
move the radon-containing soil gas from the soil into
the house. That driving force for most soil gas that
enters the house, that which enters by convective
movement, is the pressure gradient between the soil
and the house. Unless a house is at a lower
pressure, or is depressurized relative to the soil, the
only soil radon that can enter is that which enters by
diffusion. Little measurable radon is believed to enter
a house by diffusion. The radon problem is believed
to be almost entirely the product of convective flow
caused by the house's being at a lower pressure than
the soil.
Several factors combine to enhance house
depressurization, including stack effect (rising warm
air), wind, ventilation fans and blowers, and
combustion appliances. House weatherization,
techniques that usually increase the resistance of the
above-grade structure of a house to air infiltration,
can have both positive and negative influences on
these factors influencing house depressurization.
Each influencing factor will be discussed separately;
however, not combining the effects of all contributing
elements may lead to erroneous conclusions about
how to avoid depressurization in a house. Some
limited data on whole-house effects are provided to
help clarify the prevailing factors that influence radon
entry.
4.1 The Stack Effect
As the air in a house becomes heated above the
outside air, it becomes more buoyant and rises. This
rising air creates a negative pressure on the lower
portion of the building cavity, providing a driving force
to suck air in. The air that is sucked in is a
combination of soil gas entering below grade and
outside air entering through cracks in lower level
doors, windows, and above-grade walls. Higher up
in the building cavity, positive pressure created by the
buoyant force tends to push air out through plumbing
chases, gaps around chimneys, pocket doors, attic
hatches, heating duct penetrations, recessed lights,
whole-house fan openings, bathroom and kitchen
ventilation fan openings, and some drop ceilings. In
the absence of all other factors, weatherization of
houses - that is, the closing of all these openings-
reduces the stack effect because it reduces the flow
of air from the lower level of the house to the upper
levels and out. Other factors that cannot be
overlooked, though, include the positive ventilation
effects that may occur if sufficient lower-level,
above-grade openings exist. Such openings, which
may be created as simply as by opening basement
windows, can reduce radon levels by both limiting
overall house depressurization and diluting the radon
levels by house ventilation. In addition, most houses
have forced air ventilation systems which, by design,
tend to depressurize severely weatherized houses
more than those that are leaky. Therefore, although
weatherization can be positive in houses without
forced air systems where extreme care is taken to
seal the upper levels of the houses, for most houses,
ventilation caused by leaks in the building cavity
should be helpful in reducing radon levels.
Negative pressures are a major force in radon entry.
One radon mitigator in existing houses assumes a
rule of thumb of 0.25 Pa stack pressure per ft of
building height, with the neutral pressure plane at the
attic level. He stresses that infiltration reduction
should focus on lowering the neutral pressure plane,
and that the location of the tightening effort is
critically important. His radon-resistant house
construction recommendations include a number of
airtightening details (Ku88).
4.2 Wind
Wind increases air flow into and out of almost all
leaks in the exterior building shell by increasing
pressure differences. Radon diagnosticians have
measured the effects of this phenomenon, known as
the venturi effect. Wind-induced pressure
differentials of 25-50 Pa have been measured
between the interior of a wall and the inside of the
house. Normal wind-related pressure differentials of
5-10 Pa are common.
In some localities, where there is a strong prevailing
wind direction, it is possible to pressurize a house by
facing the side of the house with the maximum
number of openings into the prevailing wind.
Conversely, if the house faces the opposite direction
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it could become depressurized, increasing the
likelihood of radon entry.
Weatherization of a house clearly reduces the effects
of wind-related pressure differentials, if the exterior
side of the shell of the house has been sealed. If only
the above-grade interior side of the shell is sealed,
the air flowing into the inside of the walls may readily
communicate with the sub-slab area and result in
increased depressurization of the house relative to
the soil beneath the house.
In recent studies where wind speed and indoor radon
concentrations have been monitored simultaneously,
no direct correlation could be made between the two
factors by themselves (Ha88). Therefore, except in
the case of building sites that consistently have a
strong prevailing wind from a single direction, builders
can generally ignore wind as a major influencing
factor in radon entry.
4.3 Air Moving Devices
Ventilation fans and blowers that are used to
distribute hot or cold air from furnaces and air
conditioning systems often contribute to house
depressurization. Conventional bathroom and kitchen
ventilation fans, whole-house attic fans, and clothes
dryers exhaust house air and can increase soil gas
entry by causing the house to become depressurized.
When any of these ventilation devices are used, an
equal quantity of outside air should be supplied to the
inside of the house to prevent depressurization.
Activation of an outside air supply should not depend
on the homeowner's action but should be designed to
be activated automatically when the ventilation device
is used. Due to the volume of air being moved, this
approach is practical only for bathroom and kitchen
ventilation fans and for clothes dryers.
Whole-house fans move such large volumes of air
that the addition of that same quantity of outside air
from a single source elsewhere in the house would
probably result in discomfort to the homeowner. Since
whole-house fans are designed for ventilation during
warm weather, the opening of all lower level windows
is the source of the large volume of outside air
needed to offset the whole-house fan. EPA's radon
field studies have shown that 7 to 10 ft2 of window is
needed to neutralize negative pressures of 3 to 4 Pa
(Os87b).
Negative pressures as high as 5 Pa were measured
in one house in New Jersey with a whole-house fan
operating with windows and doors left open. The
increased ventilation, 2,000 cfm, was not sufficient to
prevent increased radon entry. In a similar test in a
house in Maryland, the ventilation from a whole house
fan actually reduced radon levels. Based on these
tests, it is not possible to predict whether whole-
house fans and a large quantity of wall openings can
result in sufficient ventilation to overcome radon entry
since test results depend on factors that may be
peculiar to the individual building's soil gas
characteristics. However, the addition of whole-
house fans is not recommended in the construction of
radon-resistant houses for two reasons: 1)
significant depressurization is possible with whole-
house fans including, increased leakage area in the
winter; and 2) the potential of overcoming that
depressurization effect with ventilation requires
homeowner action (the opening of enough windows
and/or doors).
A more common appliance that often significantly
increases radon entry due to depressurization is the
hot air furnace and its auxiliary ducting. Standard
practice in many parts of the country involves the
installation of hot air furnaces in radon-prone areas
such as crawl spaces. This presents a problem since
furnaces are not generally designed to be airtight and,
even when outside air is supplied as makeup air,
ducts in crawl spaces are usually leaky and difficult to
seal. Even in basements, residential air distribution
ductwork is generally not sealed or insulated, and
leakage can take place, especially at the joints around
the furnace. Some split-level and slab-on-grade
houses have sub-slab ductwork as part of their air
distribution system. The use of sub-slab ducts
should be diligently avoided in radon-resistant
construction for both return air and supply lines.
Sub-slab supply ductwork would not be a radon
entry point while the furnace fan is operating, but
could bring in soil gas between fan cycles.
The proposed guidelines for radon-resistant
construction in Florida expressly forbid any air
handling equipment in crawl spaces bounded by stem
walls, which is the standard crawl space construction
method. Metal ducts are to be sealed at the joints
with mastic or glass fabric and mastic, while fibrous
glass duct joints are to be sealed similarly or with
heat-activated tape. Mitigators of existing radon-
prone houses have emphasized the importance of
sealing leaks in return air systems in basements,
particularly around furnaces, main ducts, panning,
and air cleaning devices like filters and electrostatic
precipitators. The standard material used in this
sealing is duct tape.
Another suggested alternative is to enclose the
furnace and any other combustion appliances in a
separate room isolated from the rest of the basement.
Achieving complete isolation will be very difficult.
Outside ventilation air and careful sealing of the
furnace room from the rest of the basement would be
required.
4.4 Combustion Appliances
Combustion is another contributor to air infiltration.
Furnaces, boilers, gas water heaters, ranges, dryers,
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fireplaces, and woodstoves all consume oxygen from
the air to operate. As the air is used up by
combustion, negative pressure sucks air in through
available passageways, including openings to the soil.
Basement air drawn up through a heated chimney as
draft air is likely to contribute more to
depressurization than combustion air consumption.
Special ducts are used more and more to provide
combustion air and draft air directly to the heating
system or appliance, thereby reducing the infiltration
caused by combustion (MA87). Fireplaces require
tight-fitting dampers to prevent a major loss of air
out the chimney when not in use.
Florida's proposed guidelines for radon-resistant
construction (FL88) require all combustion heating
systems to be supplied with outside combustion air in
accordance with the American Society of Heating,
Refrigerating, and Air-Conditioning Engineers
(ASHRAE) guidelines. The use of direct-duct
furnace air, though not currently common among
builders, was observed to be standard practice
among some builders from such widely varied
geographic areas as Washington, California,
Colorado, and Virginia. Several municipalities are now
requiring direct-ducted combustion air for furnaces.
Due to code restrictions, furnaces should be selected
that use outside combustion air unless the furnace is
being placed in a separate properly vented furnace
room.
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Section 5
Designing for Post-Construction Active or Passive Sub-Slab Ventilation
Although in theory either the application of radon
barriers or the prevention of house depressurization
could be adequate to avoid elevated radon levels in
houses, in practice a backup radon mitigation system
has proven to be essential in radon-resistant
construction. In recent radon-resistant residential
construction projects conducted by EPA and/or
private builders, several of the houses designed to be
radon resistant have actually resulted in radon
concentrations above the EPA action level of 4 pCi/L.
In each of these houses a backup system for active
or passive sub-slab suction had been prepared
during construction and will be activated. These
backup systems are similar to many sub-slab
suction systems applied for radon reduction in
existing houses; however, sub-slab systems in new
construction are always at least as good as, and
usually better than, those applied in existing houses
because good sub-slab communication can be
ensured in new houses with uniform, clean, coarse
aggregate under the slab.
Mitigation contractors of existing houses often
encounter inconsistencies in sub-slab media that
make communication between distant parts of the
slab difficult to impossible. Mitigators then have to
resort to multiple suction points or another radon
reduction technique altogether. With a uniform, clean,
coarse aggregate beneath the slab, sub-slab suction
can often be achieved with a single point and a
smaller fan than would otherwise be required.
The need for a backup mitigation system can stem
from poor quality control during construction. The
radon barrier concept understood by the builder is not
always adequately conveyed to or implemented by
the subcontractor responsible for the installation.
Quality control in the residential construction industry
is as varied as the industry itself. Building inspectors
attempt to influence many aspects of the construction
process but are often rendered ineffective by post-
inspection changes. Since the need for radon-
resistant construction is likely to have little influence
on the level of quality control achievable in residential
construction, a nearly foolproof backup system is
required to ensure low radon levels in new houses.
The elements required in the design of an active or
passive sub-slab suction system for new houses are
described in the following subsections.
5.1 Sub-Slab Suction System
Components
The use of sub-slab aggregate imported to the
construction site depends on soil conditions at the
site and the local availability of suitable aggregate.
Sub-slab gravel or sand provides a drainage bed for
moisture and a stable, leveled surface for pouring the
slab. The material preferred for radon reduction is
crushed aggregate with a minimum of 80% of the
aggregate at least 3/4 in. in diameter. This stone
should have a free void space above 40%. A
minimum of 4 in. of aggregate is required under the
entire slab. To achieve 4 in. throughout, a
specification of 6 in. of aggregate may be required.
Care must be taken to avoid introducing fine dirt
particles during and after placement of the aggregate.
Several builders of radon-resistant houses also
recommend a perimeter loop of 4-in. perforated
drain piping. Another builder includes a sub-slab
manifold of 4-in. perforated drain line that extends
about 75% of the length of the foundation along a line
approximately in the center of the foundation. A
perforated drain line is probably not necessary with
good aggregate beneath the slab and an active sub-
slab ventilation system.
A stub-up of pipe is left to be attached to a sub-
slab ventilation system that would be installed if the
house has elevated radon levels after construction.
The stub-up pipe is capped about 4 in. above the
concrete floor and should be labeled to ensure that it
is not left open. To aid in completing the ventilation
system after construction, a vertical riser of 4-in.
solid PVC pipe should be extended from below the
first floor flooring to 18 in. above the ceiling line into
the attic and capped at both ends. If passive sub-
slab ventilation is being considered, it is preferable for
the vertical riser to be immediately above the stub-
up pipe to eliminate bends and elbows that would
increase the pressure drop and reduce the air flow in
the pipe. A continuous pipe can be extended from the
sub-slab to the attic and left in place if the builder
29
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prefers. The pipe could also penetrate the roof and
be left as a passive sub-slab ventilation system.
Since soil gas is moist, an escape route should be
provided for the condensation that will form.
Insufficient data exist on the effectiveness of sub-
slab ventilation systems using 3-in. pipes (easier to
run through walls); however, in new construction with
excellent sub-slab communication and minimal slab
leakage, the additional pressure drop caused by the
smaller pipe is not likely to have a significant impact
on radon reductions.
5.2 Drainage Considerations
Many residential contractors who build basements
provide exterior footing drainage of gravel and/or
perforated piping. This may be linked to an interior
sump system if the site does not allow drainage to
grade. Sump holes are often installed as a standard
feature, with pumps added as needed. Avoid running
roof drains to exterior perimeter drains if those
perimeter drains are connected to the sump. Sumps
are generally not sealed, although some builders do
seal sump lids.
Radon-resistant construction requires sealed sumps.
Builders may purchase sealed units or field-fabricate
sealed lids. Sealed sump systems are available from
HanCor and AK Industries for about $50 per unit.
Some builders are using the more expensive sewage
ejector systems since they have well-sealed sump
crocks. Both plywood and sheet metal sump covers
have been field fabricated. Sub-slab suction
systems can be vented through sumps instead of
using stub-up pipes. Figure 6 depicts a
disconnected sub-slab sump suction application that
is suitable for accessing the sub-slab aggregate and
perimeter drains.
The only gas-trapped drain known at present is the
DranjerTM> manufactured in Winnipeg, Manitoba.
DranjerTM units can provide a positive seal even
when water traps are dry, although debris can
interfere with ball seating and active suction can lift
the ball out of its seat. Some builders prefer to field-
fabricate oversized water traps and report having no
trouble with them..
Condensate lines can allow soil gas entry when water
traps dry during the winter months. Condensate
pumps may be required to alleviate this problem.
5.3 A Crawl Space Post-Construction
Alternative
Due to difficulties often encountered in sealing
subfloors and insulating pipes in crawl-space
houses, another radon-resistant alternative that can
be applied after construction should be considered.
This mitigation technique is a variation of the
successful sub-slab depressurization methods used
in basements. Polyethylene sheeting is often used as
a moisture barrier applied directly over the soil in
crawl spaces. The polyethylene sheeting can be used
as a gastight barrier that forms a small-volume
plenum above the soil where radon collects. A fan
can be installed to pull the collected soil gas from
under the sheeting and exhaust it outside the house.
The wide-width polyethylene sheets can be laid
directly on the earth in a way that produces at least
1-ft laps. Some field applications have included a
bead of caulking to seal between sheets of
polyethylene. A better seal has been achieved by
using an aerosol spray, Touch n StickTM by
Convenience Products, Inc., of St. Louis, MO
($5.65/12-oz can).
A good seal is obtained by spraying both surfaces of
the polyethyene, allowing time for them to get tacky,
and pushing the two pieces of polyethylene together.
In locations where the soil surface is exceptionally
hard and smooth or the crawl space is very large, a
drainage material (Enkadrain Type 9010, BASF
Corporation, Fibers Division, Enka, NC) can be placed
under the sheeting to improve air flow. If a large
number of support piers exist or if the suction point is
located close to support piers, the polyethylene
sheeting should be sealed to the piers with caulking
and wood strips. The plastic sheeting may also be
sealed to the foundation walls to reduce air leaks.
Some retrofit applications of this crawl-space radon
mitigation technique have worked well without
attempting to seal the sheets of polyethylene together
or sealing the polyethylene to piers or walls. Many
others have not been successful without sealing.
Therefore, for radon-resistant construction, when
this technique is used, a complete sealing job is
recommended. An example of a complete sub-
polyethylene suction design for a crawl space is
shown in Figure 7. Application of this technique may
not be appropriate in crawl spaces that receive heavy
traffic.
Some builders prefer to concrete the floor of crawl
spaces when site and design conditions permit
getting the mix into the crawl space. If a crawl space
has a concrete slab, for radon-resistant construction
the crawl space should be treated similar to a
basement with the advantage of greater ventilation
potential.
30
-------
r
Capped
Airtight sump cover
sealed to allow access.
Sump drains interior and/or
exterior footing drains.
Sub-slab
aggregate
Submersible sump pump
Water exit line
can also be
connected via a
trapped seal
to the sewer
CC
m
3
§
Figure 6. Incomplete Sub-slab Sump Suction Design for New Houses
31
-------
Polyethylene
Air Barrier
Figure 7. Complete Sub-polyethylene Suction Design for Crawl Space I
32
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Section 6
Current Practice in Radon-Resistant Construction
In Sections 3, 4, and 5, each element of radon-
resistant construction was discussed independently.
In this section each of these elements will be
synthesized into a variety of techniques that have
been or are being evaluated in the construction of
new houses. Unfortunately, at present, there is a
scarcity of data validating the effectiveness of these
designs in reducing the radon levels in new houses.
The factors listed below have each contributed to the
lack of available evaluations of radon-resistant
designs:
• An elevated radon level in a house is still a
relatively new problem. Few houses have been
built to date with radon resistance being
considered before the construction.
• Without actually building the houses on the lot
using standard construction procedures, with
what can the results of radon-resistant
construction be compared? In other words, there
is a lack of non-radon-resistant baseline data
to compare with radon-resistant data on the
same house.
• Laboratory data are not yet available on sealants
and caulks to verify their ability to resist radon
penetration.
• Good quality control is essential to success in
the application of radon barriers, the avoidance
of depressurization, and the preparation for
post-construction sub-slab ventilation
systems. Inspections of residential construction
projects that were intended to be radon resistant
have revealed many quality control problems.
In spite of these problems, some attempts have been
made to verify the effectiveness of some radon-
resistant designs. All available data have been
included in the description and assessment of the
designs given in the following subsections.
6.1 Radon-Resistant Construction
Practice in Sweden
Contractors building basement houses in high-radon
areas (Section 2) often install gravel and perforated
piping under the basement floor slab to prepare for
sub-slab suction, in case it proves necessary. Floor
slabs are often poured double-thick (8 in. instead of
the normal 4 in.) and with double reinforcement. A
waterproof membrane may be installed under the
slab, although reports are that such a membrane is
not generally as effective as other radon-resistant
measures.
Houses constructed in normal radon areas (Section
2) tend to be designed with minimal departure from
traditional practice. The measures commonly used
are: sealing of leaks and openings through the
substructure, and increased ventilation of crawl
spaces.
Silicone and epoxy are identified as sealants used for
radon control in Sweden. Polyurethane is not widely
used there for radon-related sealing, even though it
is the sealant preferred by leading U.S. mitigators. As
previously noted, polyurethane adheres better than
silicone. Epoxies vary, but some of the types readily
available in the United States are inferior in elasticity
and crack-spanning ability. Epoxy is not widely used
by U.S. contractors in the field of radon control.
A tight slab and minimal underpressure in the house
are generally sufficient to keep radon progeny below
the Swedish limit of 70 Bq/m3 (Sw87). (Using the
standard assumption of 50% equilibrium of progeny
to radon gas, the Swedish standard for radon as
progeny is equivalent to the EPA action level of 4
pCi/L for radon as gas.) Some new houses with
concrete block foundation walls have measured in
excess of that level despite being built with thick
slabs; it is suspected that the blocks were too porous
to keep radon out of the houses. Sealing of block
walls has not been very successful.
Of 782 newly built houses constructed using radon-
protective designs, 6% tested above the Swedish
33
-------
limit (based on radon progeny, not radon gas); 0.5%
tested above 400 Bq/m3. By comparison, 11% of
1,165 newly built houses tested above 70 Bq/m3, and
20% of the 383 houses that were not radon-
protective in design showed radon levels above 70
Bq/m3. Swedish research showed that access to
expertise was important to success in choosing
appropriate designs and installing them effectively.
Municipalities in which local authorities were actively
involved produced the best results.
Swedish techniques of radon-resistant construction
are generally similar to those used in the United
States. The most significant differences are:
1) Sweden has compiled geological and radon
survey data to map areas of high, normal, and
low radon risk. These are used to direct builders
toward appropriate construction techniques.
2) The Swedish regulatory model avoids prescribing
specific construction techniques; instead, it
establishes testing requirements and sets radon
limits above which occupancy permits cannot be
issued. The builder has the freedom and the
responsibility to choose design features that will
meet the goal of limiting radon entry. The
regulators have the responsibility of working with
and educating the builders about radon-resistant
construction techniques.
3) Radon extraction wells, tested in at least two
locations in Sweden, have not yet been tested in
the United States. This technique is evidently
limited in application to areas of highly permeable
soil and horizontal stratification; however, such
areas are often associated with elevated radon
levels. Swedish experience supports the theory
that high indoor radon concentrations are often
found in houses built on glacial eskers, which are
long narrow ridges or mounds of sand, gravel,
and boulders deposited by a stream flowing on,
within, or beneath a stagnant glacier.
6.2 New York State Energy Research
and Development Authority
(NYSERDA) Project Plans
In September 1986, the Environmental Protection
Agency signed a cooperative agreement with
NYSERDA to evaluate radon reduction options on
existing houses and radon-resistant construction
options on new houses in a limited number of houses
in the state of New York. The new construction phase
of the project was limited to 15 full-basement
houses. A contractor, W.S. Fleming and Associates,
was employed to develop radon-resistant new
construction designs, see that these designs were
built in radon-prone areas of New York, and monitor
the completed houses for radon. The incremental
cost for radon-resistant construction was paid for by
NYSERDA and EPA and not by the builder. At least
five additional new houses of similar construction and
in the vicinity of the radon-resistant houses would
serve as control houses to compare with the houses
built using the radon-resistant construction
techniques.
Currently only 5 of the 15 houses employing radon-
resistant construction techniques have been built,
although radon-resistant designs have been
developed for all 15 houses. Data have not yet been
collected on the effectiveness of the radon-resistant
designs. The following are the builder's directions for
applying radon-resistant techniques in the
construction of these new houses with full basements
(FI87):
Task 1: Install a continuous airtight plastic film (6-
mil polyethylene or equivalent) over the
sub-slab aggregate before the slab is
poured.
• Discharge footing drains to daylight or dry
well, whenever possible, to avoid
introducing radon into an interior sump. If
footing drains discharge into an interior
sump, provide the sump liner with an
airtight lid (that still allows access to
service the sump pump).
• Seal airtight any tears, punctures, slits, or
penetrations of the plastic film with
builder's tape (3M 8086TM Or equivalent).
Overlap the edges of any joining of the
plastic film by at least 3 in. and seal
airtight with builder's tape (3M 8086™ or
equivalent).
• Affix the plastic film to the footing under
the expansion board with a troweled-on
asphalt coating (Hydrocide 700™ mastic
or equivalent) to prevent radon entering
the basement from cracks in the footing
and from gaps between the footing and
plastic film. (Application of Hydrocide
700™ mastic requires washing the
surface with water, then removing any
standing water.) Position the plastic film
between the expansion board and
foundation wall and trim the plastic film
below the slab level after the expansion
board is removed. (If water collects in the
foundation wall, as shown by wet lower
surfaces, weeping holes may be
introduced into the bottom course of
concrete blocks to allow water to flow
from the foundation wall into the floor/wall
gap-)
• Provide a strip of asphalt coating on the
top of the plastic film, under the slab
around the footing, and around any
penetrations to prevent radon entering the
34
-------
basement from gaps between the plastic
film and the slab.
• Install a 2-in. pipe over the plastic film
from the floor/wall gap to the inside of the
sump liner. If the footing drains discharge
into the sump and not to daylight, the 2-
in. pipe is capped to prevent radon from
the sump entering the floor/wall gap and
basement. (If water from the foundation
wall collects in the floor/wall gap, the pipe
is uncapped and a small water trap is
installed allowing the flow of water from
the floor/wall gap to the sump, while not
allowing the flow of radon from the sump
to the floor/wall gap and basement.)
• Use the recommended water content in
the concrete mix to minimize drying time
and reduce shrinkage and cracks in the
slab.
• Minimize the number of pours. Seal any
control joints with polyethylene foam
backer rod and polyurethane caulk.
• Ensure that steel reinforcing mesh, if
used, is embedded in (and not under) the
slab to help reduce major floor cracks.
Reducing major cracks in the slab (as
well as footings, block foundation walls,
and poured-concrete walls) will reduce
the rate of radon entry.
For construction details, see Figures 8, 9, 10, and 11.
Task 2a: Install a continuous airtight plastic film (6-
mil polyethylene or equivalent) around the
exterior of the foundation wall from finished
grade level to the bottom of the footing.
• Affix the plastic film to the foundation wall
and footing using a troweled-on asphalt
coating (Hydrocide 700™ mastic or
equivalent).
• Seal airtight plumbing, electrical, or any
other penetrations through the plastic film
with builder's tape (3M 8086™ or
equivalent) and/or troweled-on asphalt
coating (Hydrocide 700™ mastic or
equivalent).
OR
Task 2b: Install a continuous layer of surface
bonding cement (Foundation Coat™ or
equivalent) around the exterior foundation
wall and footing.
• Ensure that plumbing, electrical, or any
other penetrations are sealed airtight.
For construction details, see Figures 8, 9, 10, and 11.
Task 3: Install two courses of termite blocks at the
top and bottom of the concrete block
foundation wall, one course directly on the
footing (cap up).
For construction details, see Figures 8, 9, 10, and 11.
Task 4a: Provide for venting the footing drains (and
sump, if any) to the outside using 4-in.
PVC pipes from the footing drains, along
the outside of the foundation wall, to
finished grade level. Initially, these PVC
pipes are to be capped. At least two, and
up to four, vents are to be used on
opposite sides of the building, venting at
least 10 ft from the nearest window, door,
or other opening into the building.
For construction details, see Figures 8 and 9.
OR
Task 4b: Provide for venting the interior footing
drains (and sump, if any) directly through
the roof with the largest PVC pipe possible
(4-in. diameter minimum). The PVC pipe
is to be initially capped at the slab surface,
the basement ceiling surface, and on the
outside roof surface.
For construction details, see Figures 10 and 11.
OR
Task 4c: Provide for venting the interior footing
drains and/or sump with at least a 4-in.
PVC pipe through the rim joist, venting at
least 10 ft from the nearest window, door,
or other opening into the building. The PVC
pipe is to be initially capped at the slab
surface.
For construction details, see Figures 10 and 11.
6.3 National Association of
Homebuilders' New Jersey Project
Plants
During the summer of 1987, the Environmental
Protection Agency, the New Jersey Department of
Community Affairs, and the New Jersey Builders
Association (NJBA) jointly funded a cooperative
agreement with the National Association of
Homebuilders-National Research Center (NAHB-
NRC) to develop and apply radon-resistant
35
-------
Trim plastic
film after
removing
expansion
board
Note:
Sump hole, plumbing.
Plastic film
^S
AV » ." Slab;'/.** V
f ,. * ./-._.»•>» « «'»^
">,. l
?^\
A &' *\
» " " 0 » S*.
" J * * a 4 A
*'-"*" »\
^ Termite ,\
,' block • \
];:-:--/ii
fe^v:^:-:-?:::^:^
\? Vv&tf.vtv'
n ys-* °,,°,?Tli°?|* » » • *"<
\ — E& «**'' * '
HI j£=||i|l|=
Asphalt coating
over and under
plastic film
Airtight sum
sealed to all
Sump drains
exterior fool
Airtight plastic
film to prevent x.
soil air from >v
entering basement
g
^
Clean, coarse
sub-slab
aggregate
Footing , » » /
« « » » • »
7V ./
'.%%::;/
EJHip^
'=±lr
Termite block -+•
floor/wall gap to
sump -
i
p cover \
ow access. 1 —
> interior and/or 1
ing drains \
N. j
yfcx^
0 o°»°o° « o° °,o° l__ | (\ J
tz^llllt=d|llll= n]|fnfei
^^^>^_ cicuuiv^ai, ui any uuic
^^^ penetrations through
the wall or sub-slab
plastic film should be
sealed airtight using
builder's tape and/or
asphalt coating
Capped passive air
vents on opposite
sides of building.
Locate at least 1 0 ft
from nearest
window or other
opening. Minimum of two
s|-ft1ttj=;| cement or airtight
T — "" plastic film
1 — arihprpri with a^nhalt
- — coating to prevent
1 — [||| soil air from
11 mrllll enterinq basement
= 1111 =
11 — -lljl
- [Jll^-^ Floor/wall gap
' ~S HU - No. 2 stone covered
14 '.* — by filter paper
™3^^^ or straw
•Sllllsll|l^-4P^ra^FXlll^TermitB block
/ Interior and/or
Submersible sump pump exterior 4-in.
footing dram
Figure 8. Radon Prevention Details —
Vented Footing Drains Technique No. 1
£
00
-------
Trim plastic
film after
removing
expansion
board
Plastic film
Asphalt coating
over and under
plastic film
Termite block ~*
Pipe from
floor/wall
gap to sump
Airtight plastic
film to prevent'
soil air from
entering basement
Clean, coarse
sub-slab
aggregate
Airtight
sump liner for
discharge from
floor/wall gap
Note:
Sump hole, plumbing,
electrical, or any other
penetrations through
the wall or sub-slab
plastic film should be
sealed airtight using
builder's tape and/or
asphalt coating
Capped passive air
vents on opposite
sides of building
at least 10 ft from
nearest window or
other opening. Minimum
of two
J
Surface bonding
cement or airtight
plastic film
adhered with asphalt
coating to prevent
soil air from
entering basement
JE^. Floor/wall gap
No. 2 stone covered
3="" by filter paper
or straw
Termite block
Interior and/or
exterior 4-in.
footing drain
to daylight
Figure 9. Radon Prevention Details —
Vented Footing Drains Technique No. 2
DC
CO
00
37
-------
Trim plastic
film after
removing
expansion
board
Capped
Flashing
Note:
Sump hole, plumbing,
electrical, or any other
penetrations through
the wall or sub-slab
plastic film should be
sealed airtight using
builder's tape and/or
asphalt coating
Asphalt coating
over and under
plastic film
Capped pipe from
floor/wall gap to
sump
Airtight plastic
film to prevent
soil air from
entering basement
Clean, coarse
sub-slab
aggregate
Airtight sump cover
sealed to allow access.
Sump drains interior and/or
exterior footing drains
Largest diameter
PVC pipe possible
Optional rim joist vent
location:
Locate at least 10 ft from
window or other penetration
Termite block
Surface bonding
cement or airtight
plastic film
adhered with asphalt
coating to prevent
soil air from
entering basement
Termite block
Floor/wall gap
Pj^^a^im- No. 2 stone covered
— by filter paper
or straw
Submersible sump pump
Interior and/or
exterior 4-in.
footing drain
Figure 10. Radon Prevention Details —
Roof Venting Technique No. 1
oo
§
38
-------
Trim plastic
film after
removing
expansion
board
Capped
Flashing
Plastic film
Note:
Sump hole, plumbing,
electrical, or any other
penetrations through
the wall or sub-slab
plastic film should be
sealed airtight using
builder's tape and/or
asphalt coating
Asphalt coating
over and under
plastic film
Capped PVC pipe
connected to interior
and/or exterior footing
drains
Airtight sump
liner for discharge from
floor/wall gap. Pipe connects
floor/wall gap with sump
Airtight plastic
film to prevent
soil air from
entering basement
Clean, coarse
sub-slab
aggregate
Largest diameter
PVC pipe possible
Optional rim joist vent
location:
Locate at least 10 ft from
window or other penetration
Termite block
. Surface bonding
cement or airtight
plastic film
adhered with asphalt
coating to prevent
soil air from
entering basement
• Termite block
Floor/wall gap
No. 2 stone covered
by filter paper
or straw
Interior and/or
exterior 4-in. footing
drain discharge to
daylight
Figure 11. Radon Prevention Details —
Roof Venting Technique No. 2
00
CM
39
-------
construction techniques in a two-phase project in
New Jersey. The first phase was to include
application of the techniques to 25 houses, while the
second phase was to include 75 houses.
Obtaining builder participation has been difficult even
with the assistance of NJBA. Currently, construction
has begun on only 14 of the initial 25 houses, and
collection and analysis of radon data are not complete
for any of the houses.
The study includes the three basic foundation types:
basement (including poured concrete and block
walls), slab-on-grade (including conventional and
monolithic slabs), and crawl space. A baseline radon
prevention system is suggested for each foundation
type. These systems include provisions that would
enable active or passive sub-slab ventilation
systems to be fitted at a later date, if required.
The baseline system, designed to seal entry routes
and provide an air/gas barrier around the foundation,
is shown in Figures 12, 13, 14, 15, and 16 (NAHB87).
The objective of the baseline system is to prevent
radon from entering the house.
Techniques for making poured concrete basements
radon resistant are relatively straightforward and
require less change from conventional practice.
Details include a polyethylene vapor barrier under the
slab sealed firmly to the inside of each wall,
polyethylene film or equivalent barrier affixed to
exterior walls, and a drainage system to relieve
hydrostatic pressure. A clean, uniformly graded stone
base (minimum 6-in., No. 57 stone) is also included
with the baseline recommendations. The stone base,
required by most building codes and generally
considered good building practice, is actually provided
to accommodate the active or passive sub-slab
ventilation systems.
Crawl-space foundations are treated similarly to
basements, with one exception. The floor of the crawl
space is covered with a barrier applied directly over
the soil and held in place by a 2-in. layer of sand.
Slab-on-grade foundations are treated in the same
way as basement floors, with a polyethylene barrier
and a stone base beneath the slab.
Details for masonry block construction were more
difficult to develop, due to a local (New Jersey)
practice of providing an interior perimeter drain at the
wall/slab interface. This is a carryover from a time
when effective waterproofing techniques were not
widely known or practiced. However, research and
experience in other damp regions of the United
States and Canada indicate that dry, block-wall
basements can be routinely constructed with proper
precautions. Generally, the methods suggested for
radon control should be at least as effective for
waterproofing. Quality control was considered an
absolute necessity to ensure the effectiveness of the
methods suggested for baseline radon control.
Builders not convinced of the effectiveness of these
techniques were allowed to install a perimeter drain
for block walls. However, this drain differed from the
currently used drain in that it did not completely
penetrate the slab. Builders were instructed to check
local codes and warranty programs before installing
this type of drain.
Active or passive sub-slab ventilation systems were
considered necessary in houses in which baseline
techniques prove insufficient. A 6-in. base of No. 57
stone was installed under slab floors of all test
houses in anticipation of the possible need for sub-
slab ventilation. Each test house was fitted with an
advanced sub-slab ventilation system capable of
being easily engaged. This allows for testing of the
baseline system as well as the incremental value of
the advanced system.
A passive sub-slab ventilation system, as shown in
Figure 17, is designed for all houses with a slab-
on-grade or basement foundation. The system is
initially made inoperative by cutting the stack
approximately 6 in. above the slab and sealing the
pipe with a standard plug. The stack is temporarily
supported by resting on the sealed section, and
secured with a standard elastomeric adaptor fitting.
The plug can be removed and the adaptor fitting used
to join the two sections in order to activate the
passive stack. In addition, provisions are made for
installation of an in-line fan at a later date should the
passive system prove insufficient (Figure 17).
Stronger radon reduction methods for crawl-space
foundations rely primarily on increased exterior
venting. This is illustrated in Figure 16.
Test data will be reviewed at the end of a year to
determine if further action is necessary. Houses with
average annual levels above 4 pCi/L will then be
upgraded to the next level (i.e., a baseline system will
be upgraded to a passive stack or a fan will be
installed on passive systems). Test houses with
upgraded systems will be monitored for an additional
year.
Approximately one house for each five test houses is
selected as a control house. Ideally, control and test
houses are of similar construction, located in the
same subdivision or area, and on similar soil types.
6.4 Ryan Homes Project Plan
Ryan Homes, one of the nation's largest
homebuilders, has developed a set of construction
guidelines for all of their residential construction
projects underway in Virginia and Maryland (near
Washington, DC) during the 1987-88 construction
year. The average increased cost of applying these
40
-------
Carefully placed
clean backfill
Air barrier2
(6 mil polyethylene
or equivalent)
Tool joint and caulk
(See Detail in Figure 14)
Air barrier1 (cross-laminated or
6-mil polyethylene)
Optional weep hole
Drainage system
(install as specified
by code)
Minimum 6-in. - No. 57 stone
Notes
1 Install a continuous barrier under the slab, attached to
the wall with an approved adhesive at point A. Seal all
penetrations and joints with contractor's tape (3M-3086
or equivalent) or urethane foam.
2 Apply a continuous wall barrier extending from the top
of the footing to finished grade and secured to the wall
with an adhesive or as specified in the CABO OTFDC or
the New Jersey State Uniform Construction Code. Seal
all penetrations and joints.
fC.
O)
00
CM
Figure 12. Baseline Radon Reduction Techniques — Poured Concrete Wall
41
-------
Carefully placed
clean backfill
Solid cap block or termite block
(or fill cells)
Air barrier1 (6-mil
polyethylene or equiva-
lent over parging, if
required by local build-
ing official)
Fill and strike. Cove bottom /^l^g?
or mortar joint on both sides f^-^
Drainage system
(install as specified
by code)
Solid bottom course or termite block
(or fill cells)
Air barrier1
-r .. . . . „ (cross-laminated or 6-mil
Tool joint and caulk polyethylene)
(see Detail in Figure 14)
Perimeter drain (optional)
V »*«<». »««k > < < A - * * »
^*» « » » »V » v * * »«V*. * «
i « « » «««*<«*« « * * » »>.
^gJVJ-LUJL t*uLii J u« i Saflrfurfii L
Minimum 6-in. - No. 57 stone
Optional weep hole2
Notes:
1 Apply a continuous wall barrier extending from the top
of the footing to finished grade and secured to the wall
with an adhesive or as specified in the CABO OTFDC or
the New Jersey State Uniform Construction Code. Seal
all penetrations and joints.
2 The sealing method is independent of the drainage
system. However, weep holes installed between the
under-slab area and exterior footing drains should be
recessed into the footing.
Figure 13. Baseline Radon Reduction Techniques — Block Wall
00
§
42
-------
Tool and caulk
Expansion material (cut back Vi-in. at top)
Detail "A"
Tool and caulk
Alternate Detail "A"
Figure 14. Baseline Radon Reduction Techniques — Floor/Wall Joint
Sealing Options (Detail from Figures 12 and 13)
43
-------
Solid (FHA) block
(or grout-filled
header block)
Air barrier1 applied
as specified for
basement slab
Minimum 6-in. - No. 57 stone
A. Conventional
Minimum 6-in. - No. 57 stone
Air barrier1 folded down into trench before
pouring foundation
B. Monolithic
Note:
1 Seal all penetrations and joints with contractor's tape
(3M-8086 or equivalent) or urethane foam.
oc
Si
CM
§
Figure 15. Baseline Radon Reduction Techniques — Slab-on-grade Options
44
-------
Air barrier - cover with
2 in. of sand or 1 in. concrete
mud slab
Notes:
1 Cross-laminated or 6-mil polyethylene applied as for
basement wall construction.
2 Provide 25% of vent area to face in each
direction. Vents may be placed on three sides if
positioned as close as possible to building corners.
Minimum aggregate vent area should not be less than
0.6% of total square feet of crawl space floor area.
cc
8
CN
Figure 16. Baseline Radon Reduction Techniques — Crawl Space Option
45
-------
Alternative
inclined
stack v / /
In-line fan located
'in attic space
Perimeter drain
Perimeter drain
Notes:
The stack:
a. should run vertically without change of direction
from the slab to the roof.
b. may change direction, but should not be inclined
greater then 45 degrees from vertical.
c. should be located in an interior wall.
d. should terminate in the gravel and not bottom out on
the soil.
e. may terminate in an interior drain tile or sump crock
if all penetrations are sealed.
f. should be caulked at the slab penetration.
g. should extend above the peak.
h. may require wind induction hood.
Figure 17. Baseline Radon Reduction Techniques
Slab-below-grade Option
CM
CO
8
46
-------
radon-resistant features in Ryan homes built in the
area is $200. The EPA has signed a Memorandum of
Understanding with Ryan Homes, whereby EPA's
contractor, COM Corporation, monitors radon levels in
newly completed and occupied houses built by Ryan
if the homeowner requests a free radon mea-
surement.
Ryan Homes' radon-resistant construction
procedure for full basements and houses with
kneewall foundations includes (Tr88):
Sealants - Finish floor-to-wall joints squarely
(no excess concrete splash on walls) to accept a
bead of urethane caulking around the entire
perimeter. (Garages are not included.) Seal
around all floor and wall penetrations; e.g.,
stanchion posts.
Plumbing - Pour concrete tight to any plumbing
pipes that pass through the basement floor. Apply
an additional bead of urethane sealant around
pipes. Use no forms or open pits for plumbing
connections unless the form or pit area is filled
with asphalt or urethane sealant when fixtures are
installed. Use above-floor rough-in to avoid
need for trap pits for bathtubs used for slab-
on-grade construction.
Sump Crock - If a sump crock would normally
be installed, use the Jackal EjectorTM (or equal)
crock with gasketed lid. Do not install a crock if it
is not needed for water control.
Sub-Slab Manifold - For a sub-slab manifold
use a 4-in. perforated, drain line (flexible or
solid) extending approximately 75% of the length
of the foundation, approximately in the center of
the foundation. On foundations with interior or
exterior drain systems that do not drain to daylight
(assumed to drain to a sump), connect the
manifold to the drain system. Connection may be
at the sump or by a tee in the interior drain line.
With foundation drainage systems that drain to
daylight or to a storm sewer, use an independent
section of 4-in. perforated pipe for the sub-slab
manifold.
Provide either a tee or an elbow in the manifold
where the vertical riser passes through the building.
(Use an ell if the riser is at the end of the manifold.)
Extend a short, capped pipe stub from the tee or ell
to approximately 4 in. above the finished concrete
floor. NOTE: If it is practical to place a sump crock
under the vertical riser, no additional ell or tee is
required.
Vertical Riser - Extend a 4-in. solid PVC pipe
(capped at both ends) from below the first floor
flooring to 18 in. above the ceiling line. For
cathedral ceilings, where the top of the rough-in
pipe is inaccessible or when less than 2 ft of
space is available between the top of the
insulation and the roof line, extend the pipe
(capped only at the bottom) through the roof into
a roof jack, suitable for exhaust fan installation.
GENERAL
• Aggregate (4 in. of No. 57 stone) is
required under the slab.
• Slab must meet the wall; weep space is
not acceptable.
• The 6-mil polyethylene vapor barrier must
have a minimum of 12-in. lapped joints
and must lap 2 in. up the wall. All openings
for plumbing must be neatly fitted.
• All stakes must be pulled from concrete
during finishing.
• All joints in basement supply and return air
ducts must be taped.
Full crawl-space houses will use a nonconditioned,
ventilated crawl space with 6-mil polyethylene
ground cover. All floor penetrations, including rough
cuts around heating registers, will be completely
sealed. Any duct work within the crawl space will
have taped joints. If exterior duct insulation is used on
metal ducts, the duct joints will be taped prior to
insulation.
Attached crawl spaces (e.g., Columbia split level)
may be conditioned if a concrete wash coat is
provided on the floor. Nonconditioned, attached crawl
spaces require the same procedures as outlined for
full crawl spaces. The walls between crawl spaces
and basements must be tightly sealed and access
panels must be gasketed with sill sealer or similar
material.
Initial results from the first 92 houses built to be radon
resistant (where homeowners have asked for radon
measurements) show that 30% of the houses had
radon concentrations above 4 pCi/L in the lowest
inhabitable area of the house (includes basements).
Site visits to 19 of the houses included in the study
resulted in the following observations (Ro88):
• Floor/wall joint sealing. It appears that all floor
slabs are floated with a powered rotary device
that causes some of the concrete to wash onto
the foundation walls. The floor/wall joint is then
tooled and sealed with polyurethane. Upon
curing (and shrinking) of the floor slab, the
excess concrete on the foundation wall, along
with the sealing material, is pulled away from the
foundation wall, leaving the floor wall crack,
47
-------
which was intended to be sealed. In some
instances, however, the floor slab edge
(interface with the foundation wall) is tooled to
remove the excess concrete. In these cases
floor/wall joint sealing is very effective.
• Air conditioning (AIC) condensate drain line. A/C
condensate lines contain traps and drain either
into the sanitary sewer via floor drains or to a
dry well beneath the slab (or to daylight) via
PVC pipe through the floor slab. Samples from
the PVC pipes have yielded significant radon
gas concentrations. To compound the concern,
as long as no water is in the A/C drain line trap,
the heating, ventilation, and air conditioning
(HVAC) systems are drawing soil gas from the
PVC drain pipe and ventilating it through the
house. The magnitude of this contribution is not
known.
• Sump covers. In several instances sump covers
were found to be unsealed around the cover and
the electric power cord ports.
• Sump discharge pipes. Since the sump pump
discharge pipes are actively ventilated, a check
valve allows proper operation of the sump
ventilation system.
• Pipe stub connected to sub-slab manifold. In
two instances, caps to the pipe stub were
missing. In several other instances, caps were
cracked around the edges. Improper capping
allows gas to enter the house directly from the
sub-slab, via the pipe stub.
• Companion pipes. A few of the houses visited
did not have upper companion vent pipes
(vertical risers). This may have been intentional
or because these houses were built very early in
the program when this feature was not included.
• Water service pipes. Water service pipes are
sleeved in flexible PVC pipe before they
penetrate the floor slab. This allows for gas
entering through the angular space between the
water service pipe and the PVC pipe. Not
enough sampling has been done to evaluate the
magnitude of this entry route.
Ryan Homes has intensified their inspection
procedures to reduce future quality control problems.
Measurements in 19 of the houses have included
radon grab samples in the lowest inhabitable area of
the house (includes basements) and soil gas radon
samples from 1) inside the sealed sub-slab
ventilation pipe, 2) inside a sealed air conditioning
condensate drain pipe that penetrated the slab, 3)
inside a sealed sump hole, or 4) a drilled hole through
the slab. Using a uniform soil radon measurement
location in all of the houses was impossible because
of house-to-house variations in construction.
Ten of the 19 houses had soil gas radon
measurements uniformly taken from the bottom of a
sealed sub-slab ventilation pipe. Five of these
houses had indoor radon levels of less than 4.0 pCi/L,
and five had indoor radon levels above 4 pCi/L. As
shown in Table 5, the average indoor radon
concentration in the elevated radon houses was over
three times the average of the non-elevated houses,
and the sub-slab radon concentrations were almost
1.5 times higher in the elevated radon houses
compared to the non-elevated radon houses.
Although these ratios are not uniform from house to
house, the averages do suggest that higher radon
levels in the soil beneath some of the houses likely
contributed to higher indoor radon levels in those
houses.
The individual house results demonstrate again how
difficult it is to project indoor radon levels based on
sub-slab radon measurements. House 53 had 9.4
pCi/L, the highest indoor radon concentration shown
in Table 5, but had a sub-slab radon concentration
of only 470 pCi/L. House 65 had only 3.9 pCi/L,
slightly less than the EPA action level, and had 2160
pCi/L in the soil. The ratio of sub-slab radon to
indoor radon in house 65 was over an order of
magnitude higher than the same ratio in house 53.
Prediction of indoor radon levels based on sub-slab
measurements clearly becomes complicated by
variations in the uniformity of application of the radon
barriers.
6.5 Garnet Homes Project Plan
Garnet Homes is a relatively new residential house
construction company that builds between 100 and
200 houses per year in northern Virginia near
Washington, DC. Their president, Regis Skeehan, has
developed a "Radon Abatement Package" (RAP) for
application in every Garnet house. The Garnet RAP
includes 1) sealing radon entry routes through
basement floors and walls, 2) reducing opportunities
for negative pressure spikes in basements, and 3)
installing an active sub-slab suction system. The
Garnet RAP represents the most complete radon-
resistant package currently being marketed in the
United States. The following radon-resistant design
specifications are provided to each sub-contractor
involved in the construction of a Garnet house
(Ku88):
A. CONCRETE
1. Tool edge of slab perimeter to accept
continuous bead of caulk.
48
-------
Table 5. Corresponding Indoor and Sub-Slab Radon Measurements in
Maryland Houses Built to be Radon Resistant
Houses greater than 4
House
No.
40
43
49
53
64
Average
Indoor Radon
pCi/L
8.7
9.0
5.0
9.4
4.4
7.3
pCi/L
Sub-slab
Radon
pCi/L
960
595
505
470
2,040
918
Houses less than 4
House
No.
19
36
65
67
83
Indoor Radon
pCi/L
0.1
1.0
3.9
3.4
-------
E. Frame Carpentry
1. Use sill sealer below bottom plates and above
top plates on all exterior walls.
2. Glue and nail edge of subfloor to ring joists.
3. Repair any holes in exterior sheathing.
F. Drywall Installation
1. Make every attempt to cut openings for
heat/electrical penetrations as tightly as
possible, especially in ceilings and high on
walls.
2. Seal at tops of skylight tunnels to prevent air
exfiltration.
G.Trim Carpentry
1. Install door sweep under door from first floor
to basement. This inhibits air leakage from
the basement to the upper stories of the
house.
2. Make every attempt not to leave gaps around
window casings.
3. Install rigid ledge on attic access door and
install weatherstripping.
H. Insulation/Air Sealing
1. Caulk basement slab perimeter and any
control joints using single-component
urethane caulk.
2. Caulk all pipe and post penetrations through
basement floor and walls.
3. Caulk and seal any visible cracks in basement
floor.
4. Caulk heavily around sub-slab suction stack
penetration through basement floor.
I. Painting
1. Caulk tops of window and door casings
before painting.
2. Caulk gap at fireplace where trim surrounds
perimeter of masonry.
J. Roofing
1. Flash extension of sub-slab suction stack
through roof.
Radon measured by Garnet Homes on the first 22
houses installed with the RAP averaged 0.67 pCi/L,
with a range of 0.0 to 1.4 pCi/L. These
measurements have not been verified by EPA testing
nor have there been any attempts by EPA to verify
that the houses were built in a radon-prone area.
The costs of the RAP program are provided in
Section 7.1.
6.6 New Construction House Evaluation
Program (NEWHEP)
The EPA's Office of Radiation Programs (ORP) has
extended its House Evaluation Program (HEP), which
is focused on diagnosing and recommending to the
homeowner mitigation options for radon problems in
existing houses, to include a new program of
evaluating and validating the effectiveness of the new
construction techniques contained in the brochure,
"Radon Reduction in New Construction, An Interim
Guide" (EPA 87b). The new program was begun in
1987 with seven builders from four states and is
being expanded in 1988 to include builders from a
broader cross section of geological locations. The
following outlines the NEWHEP procedures (Mu88a):
• ORP selects general locations for new house
and building site evaluations.
• Builder participation is solicited both directly and
through state homebuilders associations.
• Builders make sites available for preconstruction
soil sampling.
• ORP conducts soil sampling tests at selected
building sites (tests for radon in soil gas,
uranium/radium content in soil, and soil
permeability).
• Builders will use selected construction
techniques outlined in the "New Construction
Guide" and are encouraged to develop
additional innovative techniques and materials
for building radon-resistant houses that may be
effective adaptations in their particular building
location.
• Builders make completed houses available for
indoor radon testing and place charcoal
canisters in the houses.
• Radon tests are made before occupancy. If
active radon reduction systems are installed,
tests will be made with the system operating and
with the system shut down.
• Follow-up radon testing after occupancy will be
made, with homeowners' consent. The number,
type, and timing of follow-up tests will be
coordinated between builder and homeowner,
50
-------
with the objective of obtaining test results during
both winter and summer.
• ORP will provide charcoal canisters for both
pre- and post-construction radon tests and
will analyze exposed canisters.
• Results of both soil and indoor radon tests will
be made available to participating builders.
• Confidentiality of all test results will be at the
discretion of the builder.
• Results of the soil tests will be used by EPA to
assess the potential for developing a baseline
soil characterization by which building sites
might be classified by need for radon-resistant
building techniques.
• Results of indoor radon tests will be used to
identity effective construction techniques and to
refine and revise radon-resistant new
construction guidance.
• Results will also aid regulators in their analysis
of appropriate changes to building codes.
During the 1987-1988 heating season, radon was
measured in 135 houses in the New House
Evaluation Program. Results in the 19 houses where
both indoor measurements and related soil tests were
made were covered in Tables 3 and 4. The following
summary includes data from indoor
radonmeasurements in all 135 houses. Five of the
houses are in Michigan; the remainder are in Denver
(114) and Colorado Springs (16).
In the 111 Denver area houses, in which radon
prevention building techniques were limited to passive
measures, the average basement measurement was
6.11 pCi/L and the average first floor measurement
was 3.64 pCi/L. In the three Denver area houses
where active subfloor ventilation was used in addition
to passive sealing, the average basement
measurement was 1.35 pCi/L. From these limited
data, it appears that, in the presence of a moderate-
to-high radon source, radon prevention techniques
that are passive only may not produce indoor radon
levels consistently below the 4 pCi/L EPA action level.
In Colorado Springs, three builders participated in the
NEWHEP with measurements taken in 16 houses. As
in Denver, the building techniques were all passive
and results were similar. In 10 houses, the average
basement measurement was 3.75 pCi/L and first-
floor measurements averaged 2.64 pCi/L. In two other
houses where radon source strength was relatively
high, the average basement measurement was 28.7
pCi/L and first-floor measurements averaged 8.35
pCi/L. The final four houses were built in widely
dispersed and geologically different locations but used
the same basic house design and construction. One
house that was measured at 12.3 pCi/L was in a
subdivision where other surveys have identified
elevated indoor radon levels (Mu88b).
51
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Section 7
Cost of Radon-Resistant Construction
The costs of many radon-resistant construction
materials and practices have been presented
throughout the text. In some cases, however, the
substitution of a radon-resistant material involves a
change in application procedure that makes cost
difficult to estimate. For example, the labor and cost
of parging may be deducted when a waterproof
membrane is used on a masonry wall; however, most
masons do not break out the cost of parging when
they quote prices on building a wall.
Homebuilders are mindful of the final cost of their
product as they evaluate new materials and
techniques. Innovations that can be shown to reduce
labor or material cost gain easier acceptance than
those that increase cost. Changes which will increase
the final cost of the house must be justified on the
basis of increased consumer appeal or decreased
liability. Construction practices vary according to the
market for which the house is intended. Energy-
conserving housing insulated beyond code
requirements could be sold at a premium because of
projected savings in operating costs. Radon-
resistant construction techniques may evolve to fit
market slots as well. Standard houses might be set
up for active mitigation if radon levels dictate the
need, while passive designs requiring more expensive
preparation may be reserved for custom and luxury
houses.
Expensive control measures may be justified if they
serve multiple purposes, such as radon control
combined with water control or if a high initial cost
eliminates the need for constantly operating a
mechanical control system. Unless barrier systems
can achieve passive radon control when installed by
commercial enterprises as well as research teams,
then the value of investing in the relatively expensive
materials necessary for this approach is questionable.
It may be that perfect barriers are impossible and
imperfect barriers are ineffective. If that is the case,
then sealing of obvious openings, a moderate effort to
maintain slab integrity, and preparatory work for sub-
slab suction may be the most cost-effective
approach to radon-resistant new construction.
7.1 Example Costs
The added cost of the Garnet Homes' RAP (Ku88)
referred to in the previous section, including materials
and extra labor for a 2,000-ft2 house, was $1,361.
Incremental costs were $260 for sealing entry routes
through basement floors and walls, $664 for standard
airtightening measures common in energy-
conserving construction and direct vent appliances
using only outside air for combustion, and $437 for
installing a complete active sub-slab suction system.
A breakdown of the specific components that
contribute to these costs is provided in Table 6
(Ku88).
Table 6. Cost Attributed to Radon Abatement
Item
Concrete
Plumbing*
Electrical
Heating-
Caulking
Roofing
Fan
Weatherstripping
Sealing
Basement
$140
0
0
0
120
0
0
0
Negative
Pressure
Control
$ 0
155
0
395
80
0
0
34
Sub-slab
Suction
System
$ 50
125
60
0
0
30
172
0
Total
$ 190
280
60
395
200
30
172
34
Totals
$260
$664
$437 $1,361
Includes extra cost for direct vent water heater.
-Includes extra cost for direct vent furnace or boiler.
An analysis of the cost of Garnet Homes' RAP-
program shows that providing direct vent appliances
contributes nearly 50% of the cost of the whole
program. With an active sub-slab suction system,
the addition of negative pressure controls may not
ultimately change the reduced radon concentration
achievable in the house. Therefore, the actual cost
attributable to radon control in the RAP program may
be significantly less than projected by Garnet Homes.
In 1983 in Sweden, the projected costs for radon-
safe (Swedish term) construction were those provided
53
-------
in Table 7 (Sw87). Radon-safe construction included
covering the ground and the below-grade walls with
an impermeable layer and preparing the sub-slab
area for soil depressurization. No attempt has been
made to reduce the cost figure in Table 7 to reflect
the material and labor costs normally incurred in
preparing the sub-slab area.
Table 7. Radon-Safe Construction Costs in Sweden
Type of House
Detached houses
Basement
Slab-on-Grade
Crawl Space
1983 Cost
(Krona)
20,000
2,000
0
U.S. Dollars at 8.5
Krona/$
$2,350
235
0
7.2 Hidden Costs
Concerns over publicity and potential liability have
constrained many builders from participation in radon
research projects. It is easy to understand their
reluctance. Once radon-resistant construction
techniques have been initiated within an existing tract,
a future plaintiff may argue that the builder was aware
of a potential problem in that tract. The initial
techniques tested may be subsidized by the research
project, but the builder will be essentially committed
to continue radon-resistant construction throughout
the remainder of the property at his own expense.
Traditionally constructed houses in the tract may be
more difficult to sell due to local awareness of the
research project. Residents of traditionally
constructed houses in the same tract may become
anxious and/or demand that radon problems in their
houses be remedied by the builder. Current
experience by Ryan Homes does not bear out this
concern since sales have not slowed after public
notification of radon problems.
Some builders are worried that radon reduction
techniques have not been tested over time and that
some currently recommended techniques could
backfire. One concern is that a sub-slab suction
system, drawing radon toward the house that would
otherwise have exited the soil at grade, might leak or
malfunction and raise the house radon level. Other
concerns include potential for sub-slab suction to
cause water condensation on slab bottoms, resulting
in the swelling of soils. This swelling could cause
cosmetic damage, cracking, or even structural
failures. Sub-slab suction can also remove soil
moisture from below grade, particularly in silt and clay
soils. The loss of soil moisture can result in shrinkage
of soils, causing additional cosmetic damage,
cracking, and structural failure. The history of radon
reduction systems (particularly sub-slab suction
systems) is short. The actual potential for each of the
aforementioned potential problems is currently
unknown. Within the next year, the EPA plans to
begin research on potential problems encountered
when using active and passive sub-slab suction
systems in existing houses.
54
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Section 8
References
ACI85 - American Concrete Institute, Guide to
Residential Cast-in-Place Concrete
Construction, Detroit, Ml, May 1985.
ACI86 - American Concrete Institute, ACI 544-
State of the Art Report on Fiber-Reinforced
Concrete, Detroit, Ml, May 1986.
ACI87 - American Concrete Institute, Guide for
Concrete Floor and Slab Construction, Detroit, Ml,
May 1987.
BOCA86 - BOCA National Building Code/1986,
Building Officials and Code Administrators
International, Country Club Hills, IL, 1986.
BPA87 - Northwest Energy Code, Bonneville Power
Administration, Portland, OR, 1987.
Br86 - Brennan, T., and W. Turner, Defeating
Radon, Solar Age, p. 34, March 1986.
CABO86a - CABO One and Two Family Dwelling
Code/1986, Building Officials and Code
Administrators International, Country Club Hills,
IL, 1986.
CABO86b - Model Energy Code/1986, Council of
American Building Officials, Falls Church, VA,
1986.
DA86 - D'Alessandro, W., Foundation Drainage
Mats, Progressive Builder, 11:10, pp. 12-13,
September 1986.
EPA87a - U.S. Environmental Protection Agency,
Removal of Radon from Household Water, OPA-
87-011, September 1987.
EPA87b - U.S. Environmental Protection Agency,
Radon Reduction in New Construction, An Interim
Guide, OPA-87-009, August 1987.
EPA88 - U.S. Environmental Protection Agency,
Radon Reduction Techniques for Detached
Houses, Technical Guidance (Second Edition),
EPA-625/5-87/019, January 1988.
FI87 - W.S. Fleming and Associates, Inc.,
Demonstration of Radon Resistant Construction
Techniques in New Houses, prepared for New
York State Energy Research and Development
Authority and U.S. Environmental Protection
Agency, Assistance ID Number CR-355001-0,
June 1987.
FL88 - Proposed Interim Guidelines for Radon
Resistant Construction, Tallahassee, FL, March
1988.
Ha88 - Harper, J.P., N.L. Nagda, P.A. Joyner, and
C.S. Dudney, Radon Entry and Control: Influence
of Building Factors, presented at the 15th Energy
Technology Conference, Washington, DC,
February 1988.
ICBO85 - Uniform Building Code, 1985,
International Conference of Building Officials,
Whittier, CA, 1985.
Ku88 - Kurent, H., How to Build a "Radon-safe"
House - The Garnet Homes RAP Program,
Energy Design Update, 7:8-13, January 1988.
Ma87 - Matthews, T.G., et al., Investigation of
Radon Entry and Effectiveness of Mitigation
Measures in Seven Houses in New Jersey:
Midproject Report, Oak Ridge National
Laboratory, Report ORNL/TM-10671, December
1987.
MA87 - Massachusetts Audubon Society,
Contractor's Guide to Finding and Sealing Hidden
Air Leaks, Lincoln, MA, 1987.
Mu88a - Murane, D., U.S. Environmental Protection
Agency, Office of Radiation Programs,
Washington, DC, personal communication,
February 1988.
Mu88b - Murane, D., U.S. Environmental Protection
Agency, Office of Radiation Programs,
Washington, DC, personal communication, June
1988.
55
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Na87 - Nagda, N.L., Florida Statewide Radiation
Study, Geomet Technologies, Inc., Report IE-
1808, November 1987.
NAHB87 - NAHB National Research Center,
Construction Techniques for New Homes in
Radon-prone Areas of New Jersey, Upper
Marlboro, MD, November 1987.
NCMA72 - National Concrete Masonry Association,
Concrete Masonry Foundation Walls - NCMA-
TEK 43, Herndon, VA, 1972.
NCMA85 - National Concrete Masonry Association,
Radon in Buildings, NCMA-TEK 153, Herndon,
VA, 1985.
NCMA87 - National Concrete Masonry Association,
Radon Safe Basement Construction, NCMA-TEK
160A, Herndon, VA, 1987.
ORNL88 - Oak Ridge National Laboratory, Building
Foundation Design Handbook, Oak Ridge, TN,
1988.
Os87a - Osborne, M.C., Resolving the Radon
Problem in Clinton, NJ, Houses, in Indoor Air '87:
Proceedings of the 4th International Conference
on Indoor Air Quality and Climate, Vol. 2, pp.
305-309, Berlin, West Germany, August 1987.
Os87b - Osborne, M.C., T. Brennan, and L.D.
Michaels, Monitoring Radon Reduction in Clinton,
New Jersey, Houses, presented at the 80th
APCA Annual Meeting, New York, NY, June
1987.
Os87c - Osborne, M.C., Four Common Diagnostic
Problems That Inhibit Radon Mitigation, JAPCA,
37:5, pp. 604-606, May 1987.
PCA80 - Portland Cement Association, Concrete
Basements for Residential and Light Building
Construction, IS208.01B, Skokie, IL, 1980.
Pe87 - Peake, T., EPA Office of Radiation
Programs, unpublished data November 1987.
Pu88 - Pugh, T.D., Literature Search: Radon
Resistant Construction, Institute for Building
Sciences, Florida A&M University, Tallahassee,
FL, January 1988.
Py88 - Pyles, M., Pennsylvania Department of
Environmental Resources, Harrisburg, PA,
personal communication, April 22, 1988.
Ro88 - Rosa, D., COM Federal Programs
Corporation, unpublished data under EPA
Contract 68-02-4268, March 1988.
SBCCI85 - Standard Building Code/1985, Southern
Building Code Congress International,
Birmingham, AL, 1985.
Sc87 - Scott, A.G., and W.O. Findlay, Production of
Radon-resistant Foundations, American ATCON,
Inc., September 1987.
Sw82 - Translation of Statens planverk, rapport 59,
1982 - Stockholm, Sweden, p. 3.
Sw87 - Swedjemark, G.A., H. Wahren, A. Makitalo,
W. Tell, and E. Melander, Experience from Indoor
Radon-Daughter Limitation Schemes in Sweden,
in Indoor Air '87: Proceedings of the 4th
International Conference on Indoor Air Quality and
Climate, Vol. 2, pp. 427-428, Berlin, West
Germany, August 1987.
Tr88 - Tracy, R., Ryan Homes, Products Division,
Pittsburgh, PA, February 8, 1988.
56
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Appendix A
Examples of Standard Construction Practice and Current Adaptations to Radon fora
Sampling of U.S. Homebuilders
The EPA does not endorse any of the specific combinations of
construction techniques included in this Appendix.
Page
Buffalo 58
Camperlino and Fatti 58
Garnet 59
Levitt 60
Lewis 60
Masters 60
Pulte 61
Richmond 62
Ryan 63
Simon 64
Stafford 64
U.S. Homes 65
Jim Walter 65
Sources of Information 66
57
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Buffalo Homes, Riegelsville, PA (215) 346-8004
Contact: William Brodhead
Brodhead describes his approach to radon-
resistant construction as two-pronged--
prevention and remediation. Construction elements
are chosen and applied to hold radon entry to a
minimum. At the same time, preparatory work is
included to facilitate sub-slab ventilation, if it
proves necessary.
Slab - 4 in. slab
Shrinkage cracking is minimized using the following
techniques:
-Plasticizer ($4.00/yd) to eliminate the need for
added water.
-Slab is partitioned into sub-areas for
manageable shapes and controlled cracking;
embedded metal strip ("control T") forces a crack
at the desired location, for easy caulking.
-Reinforcement - rebar at corners and other
strategic locations.
-Flexible foam bond breaker is used at the slab
perimeter; presliced to make space for
polyurethane caulk.
-A curing agent is used to seal the top of the
slab and reduce differential drying.
-Brodhead does not recommend fiber
reinforcement additives.
At least 1 month is allowed between pouring the slab
and caulking the joints.
If concrete is poured over fill, the fill should be
mechanically tamped every 8 in.
Where pipes penetrate the slab, they are wrapped in
ArmaflexTM to protect from corrosion. The
ArmaflexTM is stripped back and caulked to seal at
the slab surface.
Sub-slab aggregate - At
or larger clean stone.
least 4 in. of 1/2-in.
Sub-slab vapor barrier - Brodhead feels that a
well-constructed slab is a much better radon
barrier than 6-mil poly construction film. He does
use a 6-mil poly vapor barrier, but thinks of it as
a vapor barrier only, and does not attempt to seal
it at the overlaps or the perimeter.
Crawl Space - 3-4 in. of gravel and at least 1
length of perforated pipe, then poly vapor barrier
topped with a slab at least 2 in. thick. Insulate and
seal from living spaces.
Drainage - 4 in. perforated drain piping around the
interior of the footing, draining to daylight or to sealed
sump. Sump cover is pressure-treated plywood,
field fabricated, sealed. No pipe penetrations through
the sump lid. Sump pump is submersible.
Dranjers™ used where appropriate, and condensate
pumps for condensate lines.
4-in. PVC runs to attic in preparation for sub-slab
suction, if needed. Can also try passive wind-driven
suction, with wind directional roof cap by Artis
Products, or equivalent.
NOTE: If exterior drainage system drains to
daylight, don't hook exterior and interior
drains, or it will short-circuit future sub-
slab suction.
Walls - Poured concrete, 3,000 psi (standard),
shortened spans. Reinforced with rebar at potential
crack locations. Sometimes coats pins with hydraulic
cement to eliminate leakage.
Dampproofing/waterproofing
Tuff-n-DriTM/Warm-n-DriTM
- Owens-Corning
system. He has
tried the Tuff-n-DriTM without the Warm-n-DriTM
and had water problems. Sometimes uses two 1 in.
layers of Warm-n-DriTM and sometimes one 1-in.
layer Warm-n-DriTM.
Cost of waterproofing:
Tough-n-DriTM . $o.80/ft2 installed.
Warm-n-DriTM . $o.45/board ft installed.
Combustion air - All combustion appliances have
ducted fresh air supply. Rule of thumb for sizing is
that fresh air supply should be the same size as the
flue. Down-draft range hoods (e.g., Jenn-AirTM)
not recommended.
Added cost - $1,200 for 1,725-ft2 basement.
Camperlino and Fatti, Syracuse, NY
(315) 488-2923
Contact: Frank Fatti, Jr.
Camperlino and Fatti is working with W.S.
Fleming on a NYSERDA/U.S. EPA project that is
testing radon-resistant construction elements.
Area served - Central New York State.
Foundation style - Basement, combination
basement/crawl space
Traditional construction details
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Slab - No reinforcement, expansion joint around
perimeter (1/2 in. material is pulled to create void -
French drain). Control of slab shrinkage through
keeping tight control over addition of water. Sub-
surface preparation is important - grading,
compacting, wetting the sub-surface to create a
moist atmosphere. Coating the slab the day after
pouring using Uco™ floor coating.
Sub-slab aggregate - Clean, coarse gravel.
Sub-slab vapor barrier - Not standard.
Drainage - Interior perimeter drain connects to sump
well; no exterior footing drain.
Walls - masonry block.
Block tops - Termite block at 7th course of 11
course basement (at grade).
Weep holes - No weep block; weep holes at
footing.
Dampproofing/waterproofing - Portland cement
parging covered with bituminous asphalt. They have
tried surface bonding mortar, but it is more expensive
and does not offer any noticeable advantage. Fatti is
concerned that a wall treated with surface bonding
mortar would still be porous and not waterproof.
Combustion air - Masonry-built fireplaces are
provided with direct-ducted combustion air, but
furnaces or domestic water heaters are not.
Adaptations to radon
The following approaches are being evaluated in
Camperlino and Fatti's work with W.S. Fleming &
Associates:
French drain 1) Poured directly to wall, poly-
sealed membrane at the slab
(brought up along wall, with the
slab poured to the wall).
2) Floor-wall joint sealed with 1/2
in. foam, covered with asphalt
caulking sealer or silicone caulk.
Sump hole Sink sump well 1/2-in. below the
surface of the slab, close with
plywood lid, and cover with
concrete.
Sub-slab Poly construction film (6 mil) taped
barrier at overlaps and sealed at the
perimeter with acoustical sealer.
Pipes are taped or sealed to
membranes at penetrations. The
membrane is sealed at overlaps
and perimeter - roughly 3 man-
hours, less than $200 material
cost for sealants.
Mechanical systems:
Venting - Builder prefers venting radon out
through box joists; does not think that fan
discharge is likely to be dangerous in central New
York.
He has looked into air exchangers a bit. If radon
becomes a real issue, he envisions offering a
variety of choices to the homebuyer, including air
exchangers.
Garnet Homes, Fairfax, VA (703) 591-4663
Contact: Regis Skeehan or Lyn Amaral
NOTE: David Saum of Infiltec and NAHB are
involved with this program.
Slab - Slabs are reinforced with wire mesh. Rebar is
extended from basement overdig to dry-stacked
block piers to reduce cracking potential.
The edge of the slab is tooled to accept a continuous
bead of caulk. Control and expansion joints are also
tooled and caulked. Lolly columns and posts are
installed before the slab is poured to avoid patching.
The perimeter area around columns is tooled and
caulked. Utility penetrations are sleeved with PVC.
The interior of the sleeve is filled with caulk, and the
slab is poured carefully to surround the sleeve.
Single-component polyurethane caulk is the sealant
used.
Sub-slab aggregate - 4 in. of No. 57 stone.
Sub-slab vapor barrier - 6-mil polyethylene
construction film.
Drainage - Interior footing drain tile is extended into
the center of the slab, and a PVC stub-up is
provided for attachment to sub-slab suction system.
Where sumps are needed, an AK Industries or
equivalent ejector pit is used (price is similar to
normal sump crock; perhaps $10.00 more than
standard item). This is a sealed system.
Condensate drains are provided with a "P" trap
instead of an "ell" fitting.
Walls - Poured walls are used, and wall-tie holes
are sealed with polyurethane caulk.
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Dampproofing/waterproofing - No particular brand,
spray-on bituminous. NOTE: They are using only
poured walls, not block walls.
Combustion air - Ducted outdoor combustion air is
supplied to furnaces and domestic water heaters.
Design equipment is a Rheem direct-vent water
heater.
Reducing stack effect - Garnet uses numerous
sealing and gasketing details to reduce stack effect
and air infiltration. These include: gasketed attic
access door, sealing around recessed light fixtures
and light fixture boxes, caulking around doors and
windows, and sealing around all plumbing and wiring
penetrations.
Sub-slab suction system - A 4-in. PVC vent stack
is installed through the roof, and a sub-slab vent fan
is installed in the attic.
Levitt Corp., Boca Raton, FL (407) 482-5100
Contact: Steve Fike
Levitt is listed in the May 1987 Builder magazine
as one of the 100 largest residential builders in the
United States - 977 detached for-sale units in
1986.
Area served - South Florida (also builds in other
areas; this information includes construction details
for South Florida only).
Foundation style - Slab-on-grade.
Traditional construction details
Slab - 4 in. slab, monolithic pour, wire mesh
double-lapped with three No. 5s; poured tight
around piping with no additional sealing.
Sub-slab aggregate - They bring in fill and
compact it; aggregate is basically rock ("coal rock")
maximum size - 3 in.
Sub-slab vapor barrier - 6-mil poly construction
film.
Combustion air - Direct-ducted combustion air to
fireplaces is standard.
Adaptations to radon - None.
Lewis Homes, Upland, CA (714) 985-0971
Contact: Doug Martin
Lewis is listed in the May 1987 issue of Builder
magazine as one of the 100 largest residential
builders in the United States - 2,561 detached
for-sale units in 1986.
Area served - California.
Foundation style - Slab-on-grade.
Traditional construction details
Slab - The slab is a separate pour from the footing.
Poly (6-mil) laid under the slab is brought up at
edges to above level of top of slab. Poly is covered
with sand, then slab is poured. Mesh or steel
reinforcement may be necessary; it depends on soil
conditions. No plasticizers.
Sub-slab aggregate - Generally compacted on-
site materials, mostly sand. Rarely brings in gravel,
except on expansive soils.
Sub-slab vapor barrier - Covers entire sub-slab
area and is brought up around the edges of the slab
(trimmed back after slab is poured). No sealing at
overlaps, but membrane is taped at pipe penetrations.
An effort is made to keep the membrane intact.
Builder has masons protect it by distributing the
weight of their screens.
Drainage - Graded site; no underground drainage.
Combustion air - Ducted fresh air is provided for
fireplaces and all other combustion equipment.
Adaptations to radon - No activity in relation to
radon.
Masters Corporation, New Canaan, CT
(203) 966-3541
Contact: Paul Bierman-Lytle
Bierman-Lytle is an experienced designer of
passive solar houses and of hypoallergenic houses
for environmentally sensitive individuals. The firm's
knowledge of airflow through passive solar
rockbeds has been applied to develop a radon-
resistant house design involving creation of a
pressurized air envelope around the house. The
design is proprietary; Masters is preparing to write
a book with the National Association of
Homebuilders that will cover nontoxic building
materials and radon-resistant design.
Foundation style - One principle of Masters' designs
is the minimization of ground contact. Basements are
eliminated whenever possible. Crawl spaces are
elevated at least 4 ft above grade.
Slab - The floor slab is reinforced with rebar or
woven wire mesh. No additives or plasticizers are
60
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used because of Masters' avoidance of toxic
materials.
Sub-slab aggregate - Sub-slab aggregate
employed in Masters' radon-resistant houses is
much deeper than that of most builders. From the
slab downward, the following layers of material are
used:
4 in. slab
3 - 4 in. of sand
1 in. Soil-Flex™ reinforced foil groundsheet
6 in. gravel
Enkadram™ drainage board
6 in. perforated pipe in bed of gravel, 6 in. deep
6 in. gravel
Compacted soil
Drainage - All drains are run to daylight. The
drainage system is used for the radon control system,
as the sub-slab aggregate is flushed with outside air.
Walls - Where below-grade foundation walls are
used, Masters uses masonry filled with Air-Crete™,
a blown-in insulation which also serves as a sill
sealer.
Dampproofing/waterproofing - The exterior of the
wall is waterproofed with 1/2 in. parging, covered by
1/2 in. bentonite board, with 1/2 in. Enkadrain™ as a
final outer layer.
Sealants - The choice of sealants is quite limited
when toxic materials are eliminated. Masters uses
Will-Seal™, which is manufactured by Illbruck
Corporation. Will-Seal™ is a neoprene foam tape
which expands as it warms. It is an open-cell foam
which is saturated with never-hardening silicone
goo.
Combustion air - Combustion appliances are
avoided in Masters' house designs, so that space
conditioning and cooking are electric. Heating and
cooling are provided by a heat pump, and makeup air
by a Van-EE™ heat recovery system. When clients
require fireplaces, woodstoves, or other combustion
appliances, direct-ducted fresh air is supplied to
each appliance.
Pulte Homes, West Bloomfield, Ml (313) 644-7300
Contact: Larry Lawson, risk manager
Pulte Homes is listed in the May 1987 issue of
Builder magazine as one of the 100 largest
residential builders in the United States - 6,600
detached for-sale units in 1986.
Radon testing is being integrated into the standard
geotechnical site evaluation procedures as Pulte
acquires land for development. Pulte does not dictate
tests for their sites, but sites are tested at the
engineers' recommendation.
All Pulte sales contracts have a disclaimer mentioning
radon as a naturally occurring substance that is found
in various areas of the country and stating that they
have tried to construct the house accordingly. In
certain areas where soils suggest radon risk, they
provide vented slabs (preparatory work for mitigation)
and attempt to make the slab resistant to water and
radon penetration.
There are 16 different operating groups around the
country, operating with considerable local autonomy.
The following is a sample of Pulte's regions .
Pulte Homes, Illinois Division (312) 843-0500
Contact: Dave Dugger
Area served - Chicago area.
Foundation style - Roughly 30% each style:
basement, slab-on-grade, crawl space.
Traditional construction details
Slab - 4 in., no reinforcement, no plasticizers.
Sub-slab aggregate - 4 in. pea gravel.
Sub-slab vapor barrier - Poly (6 mil) construction
film.
Drainage - Exterior footing drains to sump hole, no
interior footing drain, no French drain.
Walls - Poured walls.
Waterproofing - Emulsion-type fibrous glass and
bituminous ($0.32/ft2) sealant, liquid-applied, does
not know brand name (done by subcontractor).
Combustion air - No direct-ducted combustion air.
Adaptations to radon - Has not heard of any radon
in the area; only reference to radon is in disclaimer in
Pulte sales contracts.
Pulte Homes, Michigan Division, Detroit, Ml
(313) 647-9300
Contact: Rocco Pigneri, vice president
61
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Area - Detroit metro area. The construction
practices described here are also typical for Pulte's
midwest construction.
Foundation style - Basements are standard in
Michigan.
Traditional construction details
Slab - Slabs are sealed at basement walls. No
reinforcement and no plasticizers are felt to be
necessary. The slab is poured all the way to the wall.
No deliberate sealing at the wall. Contractor checks
back after 28 days to take care of cracking.
Sub-slab aggregate - Sand or pea gravel, 4 in.
minimum
Sub-slab vapor barrier - Sometimes used, when
required by municipality.
Drainage - 4 in. drain tile around foundation - this
is an exterior loop bleeding beneath footing to sump
system. The sump lid is sealed as a standard
practice.
Walls - Mainly poured walls, block only used rarely.
Dampproofing/waterproofing - Parging (if masonry);
single coat, sprayed-on bituminous.
Combustion air - No direct-ducted outside air.
Adaptations to radon - There has been discussion of
potential response to radon; however, specific
changes have not been institutionalized. There is no
identified radon problem in the Detroit area at
present.
Pulte Homes, Texas Division, Dallas, TX
(817) 640-7227
Contact: Zelda McGriff, construction secretary
Area - Texas.
Foundation style - All slab-on-grade.
Traditional construction details
Slab - Post-tensioned, using tensioning cables.
Slab and footing are a single pour.
Sub-slab aggregate - No gravel; they use a sand
cushion.
Sub-slab vapor barrier - Poly (6-mil) construction
film.
Drainage - Grading of lots only.
Combustion air - Combustion air draws from space;
no ducted fresh air.
Adaptations to radon - At present, no identified
radon problems in Pulte's Texas region.
Richmond Homes, Denver, CO (303) 355-8000
Richmond handles house construction for M.D.C.
Holdings, listed in Builder magazine's May 1987
issue as one of the 100 largest residential builders
in the United States - 4,000 detached for-sale
units in 1986.
Area - Colorado: Ft. Collins, Denver, Longmont,
Colorado Springs.
Foundation style - crawl space, basement.
Traditional construction details
Slab - 4 in. floating slab poured at 3,000 psi, woven
wire mesh reinforcement. Concrete mix has flyash
added to make it more workable.
Sub-slab aggregate - Varies depending on soil
conditions.
Sub-slab vapor barrier - No vapor barrier under the
slab; it's not a typical feature in this area.
Drainage - Perimeter gravel. Interior footing drains
are typical, draining to sump pits.
Walls - 9 in. poured concrete walls at 3,000 psi,
reinforced with rebar.
Dampproofing/waterproofing - Spray-on tar, single
layer of bituminous material.
Combustion air - Ducted fresh air to fireplaces and
furnaces.
Adaptations to radon - Houses are tested for radon
at homeowner's request. The sales contract may or
may not include clause contingent upon an
acceptable level of radon (such a clause would be
introduced at the purchaser's initiative, not suggested
by Richmond). If it does, there is a dollar limit the
contractor would be willing to spend; then they would
give the buyer the right to void the sales contract. So
far in 1988, they have not reached the dollar limit.
Slab Seal at edges with silicone at all
penetrations and at edge of slab.
62
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Sump pits - Seal lid and vent outside.
Crawl space - Install exhaust and intake vents
and exhaust fan; cover floor with
vapor barrier.
Ryan Homes: Pittsburgh, PA (800) 245-6652
Ryan is listed in the May 1987 issue of Builder
magazine as one of the 100 largest residential
builders in the United States - 4,787 detached
for-sale units in 1986.
Area - Radon program applies to houses in FL, NY,
OH, PA, and Baltimore/ Washington area. Ryan also
builds houses in CA, CT, GA, IL, IN, KY, Ml, MN, NC,
NH, SC, TN, and TX.
Foundation style - Varies with area.
Traditional construction details
Slab - Considering use of fibrous glass binder for
concrete mix, which would add $5-10/yd, but permit
elimination of wire mesh.
Sub-slab aggregate - In most areas, minimum 4 in.
clean aggregate (crushed rock). Until 1987, Ryan
used unwashed aggregate in the Dayton, OH, area,
but they have changed to washed aggregate because
of radon (to develop better sub-slab com-
munication). Sand is used in FL.
Sub-slab vapor barrier - Poly (6-mil) construction
film used everywhere except under garage slab; no
attempt to seal.
Drainage - No drainage direct to earth. All piped
direct to storm sewer or sump.
Drainage varies with area. In the Washington/MD
area, exterior drain is tied to interior sump. Interior
drain is added in wet areas. In upstate NY, interior
drain tile is standard. In the Pittsburgh area,
exterior drain and an interior drain channel are
linked.
French drains have been discontinued. They were
very common in upstate NY. NOTE: Ryan tested
the effect of French drains and found that they
increased indoor humidity significantly.
Walls • Local availability of poured concrete walls for
residential applications varies. Poured walls can be
less expensive in full-height situations; partial-
height masonry walls are usually less expensive than
partial-height poured walls.
Block tops • Solid cap block is used for 8 or 10 in.
block walls; filled cores for 12-in. block walls. These
are standard details adopted for energy conservation.
Dampproofing/waterproofing - Bituminous coating:
sometimes sprayed, sometimes brushed or troweled.
Crawl spaces: In a full crawl-space house, the floor
is covered with vapor barrier, and the crawl space is
vented. In an attached crawl space (combination
crawl space/basement), the crawl space is treated as
a conditioned space with a full floor slab. Until 2 years
ago, all crawl spaces were treated as conditioned
spaces. This has been changed due to concern over
radon entry.
NOTE: It is difficult to pour a slab in a full crawl-
Space house, especially in winter. The slab is usually
poured after the framing is complete.
Combustion air -
Fireplaces - Ducted combustion air is standard
for all fireplaces. Ryan states that it is often
insufficient when the fire is really roaring.
Masonry fireplaces are provided with two 5-in.
round inlets; manufactured fireplaces come with
one 4-in. inlet.
Other combustion appliances - Ducted fresh air
is required in a number of cities in OH. Ryan
installs it wherever required by code. Their
standard forced-draft furnace is suitable for
direct venting.
Other features - Laundry facilities are usually located
on above-grade levels.
Standard energy conservation package includes
sealing openings between conditioned and
unconditioned spaces. Sealants: Duct-SealTM (a
waterproof green putty-type material which is
pushed into the space), or - less commonly -
canned poly foam (doesn't necessarily work well;
must be applied very carefully).
Adaptations to radon
Slab - Considering fibrous glass binder.
Sub-slab aggregate • Changed to exclusive use of
washed gravel where available.
Drainage - Eliminated the use of French drains.
Considering the problem of weeping block in
foundation walls. Perhaps weep holes could be
eliminated by providing a deeper gravel base on
exterior drain or by using a drainage board.
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Condensate pumps are used where there is a
concern about radon entry through dried-out water
traps during summer. Incremental cost: about
$40.00/system.
Sealed sump - $35-40 per house.
Preparatory work for sub-slab suction - Rough-in
of sub-slab ventilation system. PVC duct is run up
through the building. The ventilation manifold is tied
into the drainage system. Added cost: $100-150 per
house. Cost to homeowners to finish: $400.00.
Ron Simon, Barto, PA (215) 754-6455
Slab - Plasticizer is used to keep up the strength
of the slab, and water content is
minimized to limit shrinkage cracking.
Control joints to direct cracking - embed
metal U-bar in concrete deep enough to
allow tooling above, making room for
caulk.
Caulk - Swimming pool caulk; flowable
polyurethane.
Perimeter of slab is tooled to accept
caulk.
Penetrations - Undersize hole in membrane so that
it stretches around pipe; make boot out of membrane.
Sub-slab aggregate - Stone and perforated pipe
under slab - "the standard setup."
Sub-slab vapor barrier - Used to put PVC
membrane under the slab, but no longer does so. 6-
mil poly used instead.
Drainage - Interior perimeter footing drain of
perforated pipe, as mentioned above. If a sump is
necessary, builder uses the Han-CorTM sealed
sump unit ($50, comes with all necessary hardware).
Builder fabricates his own water-trapped drains.
Walls - Wall type was not specifically discussed, but
builder uses parging, so it is assumed that he works
with masonry walls.
Dampproofing/waterproofing - Aqua-Flex™
membrane (PVC) is used as a barrier. It costs
$0.35/ft2 for the material, and is easy to apply.
Builder adopted it as his standard, not just for radon-
resistant construction. Aqua-FlexTM is caulk-sealed
with silicone. Builder used to use Tro-CalTM, but it
was much more expensive. Note that lots of materials
are probably gas-impermeable; the failure point is
the seam.
Parging can be a problem because masons
sometimes leave very rough areas which have to be
ground smooth before the Aqua-FlexTM js applied.
Builder believes that Aqua-FlexTM js so good that
the parging could be eliminated.
It is important to cover the Aqua-Flex™ membrane
with a protection board, to avoid punctures. Anything
will do. 1/2-in. building board would add about
$120-150 to cost for a typical house.
Incremental costs for radon-resistant construction:
Setup for sub-slab suction - $400.
Tooled joints for caulk - negligible added cost.
Plasticizer for slab - standard practice.
Aqua-FlexTM . standard practice.
Stafford Homes, Tacoma, WA (206) 488-2222
Contact: Pat Brown
Stafford handles house construction for
Weyerhauser Real Estate Co., listed in the May
1987 issue of Builder magazine as one of the 100
largest residential builders in the United States -
3,339 detached for-sale units in 1986.
Area - Washington state.
Foundation style - Crawl spaces.
Crawl-space floor - No concrete slab; 6-mil poly
vapor barrier laid on earth.
Slab - Slabs (other than garage) are only used
where plan requires it; in tri-level, for example.
Sub-slab aggregate - May use gravel or rock; it
depends on site conditions.
Sub-slab vapor barrier - Beneath habitable space.
They would also insulate beneath the slab in this
situation.
Drainage - Footing drains (exterior usually;
sometimes interior).
Walls - Poured concrete.
Dampproofing/waterproofing - Bituminous, used only
if required at site.
Combustion air - Ducted fresh air to all combustion
appliances except water heaters.
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Adaptations to radon - No current anxiety about
radon in their area; no changes in traditional
construction.
U.S. Homes Corp., Houston, TX (713) 877-2311
Contact: Larry Wagner (X530)
U.S. Homes is listed in the May 1987 issue of
Builder magazine as one of the 100 largest
residential builders in the United States - 5,174
detached for-sale units in 1986.
Area - AZ, CO, FL, GA, MD, MN, NJ, NM, TX, VA.
NOTE: NJ houses are not in radon hot spots.
Masonry walls - Parging and bituminous, sealed
(filled, may have termite cap).
Foundation style - Varies with area.
Traditional construction details
Slab - Limit added water and require proper
finishing. Don't use plasticizers. Sometimes coat top
of slab during cure. Thin layer of sand or watered
blankets over concrete after pour are recommended
by the State of Florida; they're thinking about it.
U.S. Homes' Arizona office is considering testing
Fiber-MeshTM additive ($5-8/yd added cost;
average basement is 30-50 yd); supposedly
eliminates cracking in basement slabs. Contact Bob
Berwick, at the Phoenix, AZ, office of U.S. Homes,
(602) 345-0077.
Concern over limiting slab cracking has more to do
with consumer preference (aesthetics) than with
radon.
Sub-slab aggregate - Varies with area.
Sub-slab vapor barrier - 6-mil construction film.
Drainage - Perimeter drain in basement areas,
draining to sump.
Walls - Poured vs. masonry - that depends on
what is available; block tops - sealed, sometimes
with termite cap.
Waterproofing - Varies with local practice and
foundation style.
Combustion air - Ducted fresh air to fireplaces.
Adaptations to radon - U.S. Homes attempts to
bring its construction practices into line with
governmentally recommended practices. (No time to
discuss details.)
Jim Walter Homes, Tampa, FL (813) 621-3585
Contact: Scott Wiersma
Area - West central Florida.
Foundation style - Some slab-on-grade,
occasional crawl spaces, mostly wood pilings, pads,
and piers.
Traditional construction details
Crawl spaces - Exposed earth, no barrier, sealed
around pipe penetrations with caulk (wood and caulk
at large cutout).
Slab - Not monolithic, reinforced with welded wire
mesh.
Sub-slab aggregate - Sand, on-site material.
Sub-slab vapor barrier - 6-mil poly.
Drainage - Nothing needed.
Walls - Masonry.
Block tops - Termite shield - galvanized - lies under
pressure-treated plate.
Dampprooftng/waterproofing - None needed.
Combustion air - No fireplaces, no direct-ducted
outside air.
Adaptations to radon - Most of their construction is
piers and pads; he has heard of radon but they have
not made any changes in relation to it.
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Sources of Information
If you would like further information on or explanation of any of the points mentioned in this booklet, you should
contact your State radiation protection office or homebuilders association.
If you have difficulty locating these offices, you may call your EPA Regional Office listed below. They will be
happy to provide you with the name, address, and telephone number of these contacts.
STATE-EPA REGION
Alabama-4
Alaska-10
Arizona-9
Arkansas-6
California-9
Colorado-8
Connecticut-1
Delaware-3
District of
Columbia-3
Florida-4
Georgia-4
Hawaii-9
ldaho-10
EPA REGIONAL OFFICES
lllinois-5
lndiana-5
lowa-7
Kansas-7
Kentucky-4
Louisiana-6
Maine-1
Maryland-3
Massachusetts-1
Michigan-5
Minnesota-5
Mississippi-4
Missouri-7
Montana-8
Nebraska-7
Nevada-9
New Hampshire-1
New Jersey-2
New Mexico-6
New York-2
North Carolina-4
North Dakota-8
Ohio-5
Oklahoma-6
Oregon-10
Pennsylvania-3
Rhode lsland-1
South Carolina-4
South Dakota-8
Tennessee-4
Texas-6
Utah-8
Vermont-1
Virginia-3
Washington-10
West Virginia-3
Wisconsin-5
Wyoming-8
EPA Region 1
Room 2203
JFK Federal Building
Boston, MA 02203
(617)565-3715
EPA Region 6
1445 Ross Avenue
12th Floor, Suite 1200
Dallas, TX 75202
(214)655-6444
EPA Region 2
26 Federal Plaza
New York, NY 10278
(212) 264-2525
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913)236-2800
EPA Region 3
841 Chestnut Street
Philadelphia, PA
19107
(215)597-9800
EPA Region 8
Suite 500
999 18th Street
Denver, CO 80202
(303)293-1603
EPA Region 4
345 Courtland St., NE
Atlanta, GA 30365
(404) 347-4727
EPA Region 9
215 Fremont Street
San Francisco, CA
94105
(415)974-8071
EPA Region 5
230 South Dearborn
St.
Chicago, IL 60604
(312)353-2000
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(206)442-5810
& ENVIRONMENTAL PROTECTION AGENCY
REGIONAL ORGANIZATION
o
•S-GOVERNMENT PRINTING OFFICE! 1988- 548-158-87926
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