&EPA
United States
Environmental Protection
Agency
Air and
Radiation
(6604J)
EPA402-R-94-009
March 1994
MODEL STANDARDS AND
TECHNIQUES FOR CONTROL
OF RADON IN NEW
RESIDENTIAL BUILDINGS
Recycled/Recyclable
Printed with Soy/Canola Ink on paper that
contains at least 50% recycled fiber
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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 or
organization 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.
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FORWARD
This document is intended to serve as a model for use by the Model Code
Organizations, States and other jurisdictions as they develop and adopt building codes,
appendices to codes, or standards specifically applicable to their unique local or
regional radon control requirements.
This document is responsive to the requirements set forth in Section 304 of Title
III of the Toxic Substances Control Act (TSCA), 15 U.S.C. 2664, commonly referred to
as the Indoor Radon Abatement Act (IRAA) of 1988. It is anticipated that future editions
of this document will be prepared as additional experience is gained in constructing
new radon-resistant residential buildings.
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TABLE OF CONTENTS
Page#
Forward i
1.0 Scope 1
2.0 Limitations 2
3.0 Reference Documents 3
4.0 Description of Terms 4
5.0 Principles of Construction of Radon-Resistant Residential Buildings 5
6.0 Summary of the Model Building Standards and Techniques 6
7.0 Construction Methods 7
8.0 Recommended Implementation Procedures 8
9.0 Model Building Standards and Techniques 9
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MODEL STANDARDS AND TECHNIQUES
FOR CONTROL OF RADON
IN NEW RESIDENTIAL BUILDINGS
1.0 Scope
1.0.1 This document contains model
building standards and techniques
applicable to controlling radon levels in
new construction of one- and two-family
dwellings and other residential buildings
three stories or less in height as defined
in model codes promulgated by the
respective Model Code Organizations.
1.0.2 The model building standards and
techniques are also applicable when
additions are made to the foundations of
existing one- and two-family dwellings
that result in extension of the building
footprint.
1.0.3 This document is not intended to
be a building code nor is it required that it
be adopted verbatim as a referenced
standard.
1.0.4 It is intended that the building
standards and techniques contained in
section 9.0 of this document, the
construction method in section 7.0, and
the recommended procedures for
applying the standards and construction
method in section 8.0, serve as a model
for use by the Model Code Organizations
and authorities within states or other
jurisdictions that are responsible for
regulating building construction as they
develop and adopt building codes,
appendixes to codes, or standards and
implementing regulations specifically
applicable to their unique local or regional
radon control requirements.
1.0.5 The preferential grant assistance
authorized in Section 306(d) of the Indoor
Radon Abatement Act of 1988 (Title III of
the Toxic Substances Control Act, TSCA,
15 U.S.C. 2666) will be applied for states
where appropriate authorities who
regulate building construction are taking
action to adopt radon-resistant standards
in their building codes.
1.0.6 Model building standards and
techniques contained in this document
are not intended to supersede any radon-
resistant construction standards, codes or
regulations previously adopted by local
jurisdictions and authorities. However,
jurisdictions and authorities are
encouraged to review their current
building standards, codes, or regulations
and their unique local or regional radon
control requirements, and consider
modifications, if necessary.
1.0.7 This document will be updated and
revised as ongoing and future research
programs suggest revisions of standards,
identify ways to improve the model
construction techniques, or when newly
tested products or techniques prove to be
equivalent to or more effective in radon
control. Updates and revisions to the
model building standards and techniques
contained in section 9.0 will undergo
appropriate peer review.
1.0.8 EPA is committed to continuing
evaluation of the effectiveness of the
standards and techniques contained in
section 9.0 and to research programs that
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may identify other more effective and
efficient methods.
practices, and variations in the operation
of buildings.
2.0 Limitations
2.0.1 The Indoor Radon Abatement Act
of 1988 (Title III of TSCA) establishes a
long-term national goal of achieving
radon levels inside buildings that are no
higher than those found in ambient air
outside of buildings. While technological,
physical, and financial limitations currently
preclude attaining this goal, the
underlying objective of this document is to
move toward achieving the lowest
technologically achievable and most cost
effective levels of indoor radon in new
residential buildings.
2.0.2 Preliminary research indicates that
the building standards and techniques
contained in section 9,0 can be applied
successfully in mitigating radon problems
in some existing nnnresidential buildings.
However, their effectiveness when
applied during construction of new
nonresidential buildings has not yet been
fully demonstrated. Therefore, it is
recommended that, pending further
research, these building standards and
techniques not be used at this time as a
basis for changing the specific sections of
building codes that cover nonresidential
construction.
2.0.3 Although radon levels below 4
pCi/L have been achieved in all types of
residential buildings by using these model
building standards and techniques,
specific indoor radon levels for any given
building cannot be predicted due to
different site and environmental
conditions, building design, construction
2.0.4 These model building standards
and techniques are not to be construed
as the only acceptable methods for
controlling radon levels, and are not
intended to preempt, preclude, or restrict
the application of alternative materials,
systems, and construction practices
approved by building officials under
procedures prescribed in existing building
codes.
2.0.5 Elevated indoor radon levels
caused by emanation of radon from water
is of potential concern, particularly in
areas where there is a history of
groundwater with high radon content.
This document does not include model
construction standards or techniques for
reducing elevated levels of indoor radon
that may be caused by the presence of
high levels of radon in water supplies.
EPA has developed a suggested
approach (see paragraph 8.3.2) that state
or local jurisdictions should consider as
they develop regulations concerning pri-
vate wells. EPA is continuing to evaluate
the issue of radon occurrence in private
wells and the economic impacts of testing
and remediation of wells with elevated
radon levels.
2.0.6 While it is not currently possible to
make a precise prediction of indoor radon
potential for a specific building site, a
general assessment, on a statewide,
county, or grouping of counties basis, can
be made by referring to EPA's Map of
Radon Zones and other locally available
data. It should be noted that some radon
potential exists in all areas. However,
EPA recognizes that based on available
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data, there is a lower potential for
elevated indoor radon levels in some
states and portions of some states, and
that adoption of building codes for the
prevention of radon in new construction
may not be justified in these areas at this
time. There is language in paragraph
8.2.3 of this document recommending
that jurisdictions in these areas review all
available data on local indoor radon
measurements, geology, soil parameters,
and housing characteristics as they
consider whether adoption of new codes
is appropriate.
3.0 Reference Documents
References are made to the following
publications throughout this document.
Some of the references do not specifically
address radon. They are listed here only
as relevant sources of additional
information on building design,
construction techniques, and good
building practices that should be
considered as part of a general radon
reduction strategy.
3.1 "Building Foundation Design
Handbook," ORNL/SUB/86-72143/1, May
1988.
3.2 "Building Radon Resistant
Foundations - A Design Handbook,"
NCMA, 1989.
3.3 "Council of American Building
Officials (CABO) Model Energy Code,
1992.
3.4 "Design and Construction of Post-
Tensioned Slabs on Ground," Post
Tensioning Institute Manual.
3.5 "Energy Efficient Design of New
Buildings Except Low-Rise Residential
Buildings," ASHRAE Standard 90.1-1989.
3.6 "Energy Efficient Design of New
Low-Rise Residential Buildings," Draft
ASHRAE Standard 90.2 (Under public
review).
3.7 "Homebuyer's and Seller's Guide
to Radon," EPA 402-R-93-003, March
1993.
3.8 "Guide to Residential Cast-in-Place
Concrete Construction," ACI 332R.
3.9 "Indoor Radon and Radon Decay
Product Measurement Device Protocols."
EPA 402-R-92-004, July, 1992.
3.10 "Protocols For Radon and Radon
Decay Product Measurements in Homes."
EPA 402-R-92-003, June, 1993.
3.11 "Permanent Wood Foundation
System - Basic Requirements, NFPA
Technical Report No.7."
3.12 "Radon Control Options for the
Design and Construction of New Low-
Rise Residential Buildings," ASTM
Standard Guide, E1465-92.
3.13 "Radon Handbook for the Building
Industry," NAHB-NRC, 1989.
3.14 "USEPA Map of Radon Zones,"
Dec. 1993.
3.15 "Radon Reduction in New
Construction, An Interim Guide." OPA-87-
009, August 1987.
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3.16 "Radon Reduction in Wood Floor
and Wood Foundation Systems." NFPA,
1988.
3.17 "Radon Resistant Construction
Techniques for New Residential
Construction. Technical Guidance."
EPA/625/2-91/032, February 1991.
3.18 "Radon-Resistant Residential New
Construction." EPA/600/8-88/087, July
1988.
3.19 "Guide for Concrete Floor and Slab
Construction," ACI 302.1 R-89.
3.20 "Ventilation for Acceptable Indoor
Air Quality," ASHRAE 62-1989.
4.0 Description of Terms
For this document, certain terms are
defined in this section. Terms not defined
herein should have their ordinary
meaning within the context of their use.
Ordinary meaning is as defined in
"Webster's Ninth New Collegiate
Dictionary."
ACTION LEVEL: A term used to identify
the level of indoor radon at which
remedial action is recommended. (EPA's
current action level is 4 pCi/L.)
AIR PASSAGES: Openings through or
within walls, through floors and ceilings,
and around chimney flues and plumbing
chases, that permit air to move out of the
conditioned spaces of the building.
COMBINATION FOUNDATIONS:
Buildings constructed with more than one
foundation type; e.g.,
basement/crawlspace or basement/slab-
on-grade.
DRAIN TILE LOOP: A continuous length
of drain tile or perforated pipe extending
around all or part of the internal or
external perimeter of a basement or
crawlspace footing.
GOVERNMENTAL: State or local
organizations/agencies responsible for
building code enforcement.
MAP OF RADON ZONES: A USEPA
publication depicting areas of differing
radon potential in both map form and in
state specific booklets.
MECHANICALLY VENTILATED
CRAWLSPACE SYSTEM: A system
designed to increase ventilation within a
crawlspace, achieve higher air pressure
in the crawlspace relative to air pressure
in the soil beneath the crawlspace, or
achieve lower air pressure in the
crawlspace relative to air pressure in the
living spaces, by use of a fan.
MODEL BUILDING CODES: The
building codes published by the 4 Model
Code Organizations and commonly
adopted by state or other jurisdictions to
control local construction activity.
MODEL CODE ORGANIZATIONS:
Includes the following agencies and the
model building codes they promulgate:
Building Officials and Code
Administrators International, Inc.
(BOCA National Building
Code/1993 and BOCA National
Mechanical Code/1993);
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International Conference of
Building Officials (Uniform Building
Code/1991 and Uniform
Mechanical Code/1991);
Southern Building Code Congress,
International, Inc. (Standard
Building Code/1991 and Standard
Mechanical Code/1991);
Council of American Building
Officials (CABO One- and Two-
Family Dwelling Code/1992 and
CABO Model Energy Code/1993).
pCi/L: The abbreviation for "picocuries
per liter" which is used as a radiation unit
of measure for radon. The prefix "pico"
means a multiplication factor of I trillionth.
A Curie is a commonly used
measurement of radioactivity.
SOIL GAS: The gas present in soil which
may contain radon.
SOIL-GAS-RETARDER: A continuous
membrane or other comparable material
used to retard the flow of soil gases into a
building.
STACK EFFECT: The overall upward
movement of air inside a building that
results from heated air rising and
escaping through openings in the building
super structure, thus causing an indoor
pressure level lower than that in the soil
gas beneath or surrounding the building
foundation.
SUB-SLAB DEPRESSURIZATION
SYSTEM (ACTIVE): A system designed
to achieve lower sub-slab air pressure
relative to indoor air pressure by use of a
fan-powered vent drawing air from
beneath the slab.
SUB-SLAB DEPRESSURIZATION
SYSTEM (PASSIVE): A system
designed to achieve lower sub-slab air
pressure relative to indoor air pressure by
use of a vent pipe routed through the
conditioned space of a building and
connecting the sub-slab area with outdoor
air, thereby relying solely on the convec-
tive flow of air upward in the vent to draw
air from beneath the slab.
SUB-MEMBRANE
DEPRESSURIZATION SYSTEM: A
system designed to achieve lower sub-
membrane air pressure relative to
crawlspace air pressure by use of a fan-
powered vent drawing air from under the
soil-gas-retarder membrane.
5.0 Principles for Construction of
Radon-Resistant Residential
Buildings
5.1 The following principles for
construction of radon-resistant residential
buildings underlie the specific model
standards and techniques set forth in
section 9.0.
5.1.1 Residential buildings should be
designed and constructed to minimize the
entrance of soil gas into the living space.
5.1.2 Residential buildings should be
designed and constructed with features
that will facilitate post-construction radon
removal or further reduction of radon
entry if installed prevention techniques fail
to reduce radon levels below the locally
prescribed action level.
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5.2 As noted in the limitations section
(paragraph 2.0.2), construction standards
and techniques specifically applicable to
new nonresidential buildings (including
high-rise residential buildings), have not
yet been fully demonstrated. Accordingly,
the specific standards and techniques set
forth in section 9.0 should not, at this
time, be considered applicable to such
buildings. There are, however, several
general conclusions that may be drawn
from the limited mitigation experience
available on large nonresidential
construction. These conclusions are
summarized below to provide some initial
factors for consideration by builders of
nonresidential buildings.
5.2.1 HVAC systems should be carefully
designed, installed and operated to avoid
depressurization of basements and other
areas in contact with the soil.
5.2.2 As a minimum, use of a coarse
gravel or other permeable base material
beneath slabs, and effective sealing of
expansion joints and penetrations in
foundations below the ground surface will
facilitate post-construction installation of
a sub-slab depressurization system, if
necessary.
5.2.3 Limited mitigation experience has
shown that some of the same radon
reduction systems and techniques used
in residential buildings can be scaled up
in size, number, or performance to
effectively reduce radon in larger
buildings.
6.0 Summary of the Model Building
Standards and Techniques
The model building standards and
techniques listed in section 9.0 are
designed primarily for control of radon in
new one- and two-family dwellings and
other residential buildings three stories or
less in height.
6.1 Basement and Slab-on-Grade
Foundations.
The model building standards and
techniques for radon control in new
residential buildings constructed on
basement and slab-on-grade foundations
include a layer of permeable sub-slab
material, the sealing of joints, cracks, and
other penetrations of slabs, floor
assemblies, and foundation walls below
or in contact with the ground surface,
providing a soil-gas-retarder under floors
and installing either an active or passive
sub-slab depressurization system (SSD).
Additional radon reduction techniques are
prescribed to reduce radon entry caused
by the heat induced "stack effect." These
include the closing of air passages (also
called thermal by-passes), providing
adequate makeup air for combustion and
exhaust devices, and installing energy
conservation features that reduce non-
required airflow out of the building
superstructure.
6.2 Crawlspace Foundations.
The model building standards and
techniques for radon control in new
residential buildings constructed on
crawlspace foundations include those
systems that actively or passively vent the
crawlspace to outside air, that divert
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radon before entry into the crawlspace,
and that reduce radon entry into normally
occupied spaces of the building through
floor openings and ductwork.
6.3 Combination Foundations.
Radon control in new residential buildings
constructed on a combination of
basement, slab-on-grade or crawlspace
foundations is achieved by applying the
appropriate construction techniques to
the different foundation segments of the
building. While each foundation type
should be constructed using the relevant
portions of these model building
standards and techniques, special
consideration must be given to the points
at which different foundation types join,
since additional soil-gas entry routes exist
in such locations.
7.0 Construction Methods
The model construction standards and
techniques described in section 9.0 have
proved to be effective in reducing indoor
radon levels when used to mitigate radon
problems in existing homes and when
applied in construction of new homes. In
most cases, combinations of two or more
of these standards and techniques have
been applied to achieve desired
reductions in radon levels. Because of
success achieved in reducing radon
levels by applying these multiple,
interdependent techniques, limited data
have been collected on the singular
contribution to radon reduction made by
any one of the construction standards or
techniques. Accordingly, there has been
no attempt to classify or prioritize the indi-
vidual standards and techniques as to
their specific contribution to radon
reduction. It is believed that use of all the
standards and techniques (both passive
and active) will produce the lowest
achievable levels of indoor radon in new
homes (levels below 2 pCi/L have been
achieved in over 90 percent of new
homes). It is also believed that use of
only selected (passive) standards and
techniques will produce indoor radon
levels below the current EPA action level
of 4 pCi/L in most new homes, even in
areas of high radon potential.
7.1 It is recommended that all the
passive standards and techniques listed
in section 9.0 (including a roughed-in
passive radon control system) be used in
areas of high radon potential, as defined
by local jurisdictions or in EPA's Map of
Radon Zones. Based on more detailed
analysis of locally available data,
jurisdictions may choose to apply more or
less restrictive construction requirements
within designated portions of their areas
of responsibility. To ensure that new
homes are below the locally prescribed
action level, in those cases where only
passive radon control systems have been
installed, occupants should have their
homes tested to determine if passive
radon control systems need to be
activated. In addition, it is recommended
that periodic retests be conducted to
confirm continued effectiveness of the
radon control system.
7.2 Any radon testing referenced in
this document should be conducted in
accordance with EPA Radon Testing
Protocols or current EPA guidance for
radon testing in real estate transactions
as referenced in paragraph 3.0. It is
recommended that all testing be
conducted by companies listed in EPA's
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Radon Measurement Proficiency
Program (RMP) or comparable State
certification programs.
7.3 The design and installation of
radon control systems should be
performed or supervised by individuals
(i.e., builders, their representatives, or
registered design professionals such as
architects or engineers) who have
attended an EPA-approved radon training
course, or by an individual listed in the
EPA Radon Contractor Proficiency
Program.
8.0 Recommended Implementation
Procedures
The following procedures are
recommended as guidelines for applying
the model building standards and
techniques and construction methods
contained in this document. These
procedures are based on the rationale
that a passive radon control system and
features to facilitate any necessary post-
construction radon reduction should be
routinely built-in to new residential
buildings in areas having a high radon
potential.
8.1 State, county, or local jurisdictions
that use these model building standards
and techniques as a basis for developing
building codes for radon resistant
construction should classify their area by
reference to the Zones in EPA's Map of
Radon Zones or by considering other
locally available data. While EPA
believes that the Map of Radon Zones
and accompanying state-specific booklets
are useful in setting general boundaries
of areas of concern, EPA recommends
that state and local jurisdictions collect
and analyze local indoor radon
measurements, and assess geology, soil
parameters and housing characteristics -
in conjunction with referring to the EPA
radon maps -- to determine the specific
areas within their jurisdictions that should
be classified as Zone 1.
8.2 State, county, or local jurisdictions
that use these model building standards
and techniques as a basis for developing
building codes for radon-resistant
construction should specify the
construction methods applicable to their
jurisdictional area.
8.2.1 In areas classified as Zone 1 in the
Map of Radon Zones, or by local
jurisdiction, application of the construction
method in paragraph 7.1 is
recommended.
8.2.2 In areas classified as Zone 2,
home builders may apply any of the
radon-resistant construction standards
and techniques that contribute to
reducing the incidence of elevated radon
levels in new homes and that are
appropriate to the unique radon potential
that may exist in their local building area.
8.2.3 In those areas where state and
local jurisdictions have analyzed local
indoor radon measurements, geology,
soil parameters, and housing
characteristics and determined that there
is a low potential for indoor radon,
application of radon-resistant construction
techniques may not be appropriate. In
these areas, radon-resistant construction
techniques may not be needed, or limited
use of selected techniques may be
sufficient.
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8.3 It is recognized that specific rules,
regulations, or ordinances covering
implementation of construction standards
or codes are developed and enforced by
state or local jurisdictions. While
developing the model construction
standards and techniques contained in
this document, EPA also developed
several approaches to regulation that
states or local jurisdictions may find
useful and appropriate as they develop
rules and regulations that meet their
unique requirements. For example:
8.3.1 In areas where the recommended
construction method or comparable
prescriptive methods are mandated by
state or local jurisdictions, regulations
would need to include, as part of the
inspection process, a review of the radon-
resistant construction features by
inspectors who have received additional
training, to ensure that the radon-resistant
construction features are properly
installed during construction. It would
also be necessary to establish require-
ments for those building officials who
review and approve construction plans
and specifications to become proficient in
identifying and approving planned radon-
resistant construction features.
8.3.2 In any area where surveys have
shown the existence of high levels of
radon in groundwater, or in areas where
elevated levels of indoor radon have been
found in homes already equipped with
active radon control systems, well water
may be the source. In such areas,
authorities responsible for water
regulation should consider establishing
well water testing requirements that
include tests for radon.
9.0 Model Building Standards and
Techniques
9.1 Foundation and Floor Assemblies:
The following construction techniques are
intended to resist radon entry and
prepare the building for post-construction
radon mitigation, if necessary. These
techniques, when combined with those
listed in paragraph 9.2, meet the require-
ments of the construction method outlined
in paragraph 7.1. (See also the
construction methods listed in ASTM
Standard Guide, E-1465-92.)
9.1.1 A layer of gas permeable material
shall be placed under all concrete slabs
and other floor systems that directly
contact the ground and are within the
walls of the living spaces of the building,
to facilitate installation of a sub-slab
depressurization system, if needed.
Alternatives for creating the gas
permeable layer include:
a. A uniform layer of clean aggregate, a
minimum of 4 inches thick. The
aggregate shall consist of material that
will pass through a 2-inch sieve and be
retained by a 1/4-inch sieve.
b. A uniform layer of sand, a minimum of
4 inches thick, overlain by a layer or strips
of geotextile drainage matting designed to
allow the lateral flow of soil gases.
c. Other materials, systems, or floor
designs with demonstrated capability to
permit depressurization across the entire
subfloor area.
9.1.2 A minimum 6-mil (or 3-mil cross
laminated) polyethylene or equivalent
flexible sheeting material shall be placed
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on top of the gas permeable layer prior to
pouring the slab or placing the floor
assembly to serve as a soil-gas-retarder
by bridging any cracks that develop in the
slab or floor assembly and to prevent
concrete from entering the void spaces in
aggregate base material. The sheeting
should cover the entire floor area, and
separate sections of sheeting should be
overlapped at least 12 inches. The
sheeting shall fit closely around any pipe,
wire or other penetrations of the material.
All punctures or tears in the material shall
be sealed or covered with additional
sheeting.
9.1.3 To minimize the formation of
cracks, all concrete floor slabs shall be
designed, mixed, placed, reinforced,
consolidated, finished, and cured in
accordance with standards set forth in the
Model Building Codes. The American
Concrete Institute publications, "Guide for
Concrete Floor and Slab Construction,"
ACI 302.1 R, "Guide to Residential Cast-
in-Place Concrete Construction," ACI
332R, or the Post Tensioning Institute
Manual, "Design and Construction of
Post-Tensioned Slabs on Ground" are
references that provide additional
information on construction of concrete
floor slabs.
9.1.4 Floor assemblies in contact with
the soil and constructed of materials other
than concrete shall be sealed to minimize
soil gas transport into the conditioned
spaces of the building. A soil-gas-
retarder shall be installed beneath the
entire floor assembly in accordance with
paragraph 9.1.2.
9.1.5 To retard soil gas entry, large
openings through concrete slabs, wood,
and other floor assemblies in contact with
the soil, such as spaces around bathtub,
shower, or toilet drains, shall be filled or
closed with materials that provide a
permanent air-tight seal such as non-
shrink mortar, grouts, expanding foam, or
similar materials designed for such
application.
9.1.6 To retard soil gas entry, smaller
gaps around all pipe, wire, or other
objects that penetrate concrete slabs or
other floor assemblies shall be made air
tight with an elastomeric joint sealant, as
defined in ASTM C920-87, and applied in
accordance with the manufacturer's
recommendations.
9.1.7 To retard soil gas entry, all control
joints, isolation joints, construction joints,
and any other joints in concrete slabs or
between slabs and foundation walls shall
be sealed. A continuous formed gap (for
example, a "tooled edge") which allows
the application of a sealant that will
provide a continuous, air-tight seal shall
be created along all joints. When the slab
has cured, the gap shall be cleared of
loose material and filled with an
elastomeric joint sealant, as defined in
ASTM C920-97, and applied in
accordance with the manufacturer's
recommendations.
9.1.8 Channel type (French) drains are
not recommended. However, if used,
such drains shall be sealed with backer
rods and an elastomeric joint sealant in a
manner that retains the channel feature
and does not interfere with the
effectiveness of the drain as a water
control system.
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9.1.9 Floor drains and air conditioning
condensate drains that discharge directly
into the soil below the slab or into
crawlspaces should be avoided. If
installed, these drains shall be routed
through solid pipe to daylight or through a
trap approved for use in floor drains by
local plumbing codes.
9.1.10 Sumps open to soil or serving as
the termination point for sub-slab or
exterior drain tile loops shall be covered
with a gasketed or otherwise sealed lid to
retard soil gas entry. (Note: If the sump is
to be used as the suction point in an
active sub-slab depressurization system,
the lid should be designed to
accommodate the vent pipe. If also
intended as a floor drain, the lid shall also
be equipped with a trapped inlet to handle
any surface water on the slab.)
9.1.11 Concrete masonry foundation
walls below the ground surface shall be
constructed to minimize the transport of
soil gas from the soil into the building.
Hollow block masonry walls shall be
sealed at the top to prevent passage of
air from the interior of the wall into the
living space. At least one continuous
course of solid masonry, one course of
masonry grouted solid, or a poured
concrete beam at or above finished
ground surface level shall be used for this
purpose. Where a brick veneer or other
masonry ledge is installed, the course
immediately below that ledge shall also
be sealed.
9.1.12 Pressure treated wood
foundations shall be constructed and
installed as described in the National
Forest Products Association (NFPA)
Manual, "Permanent Wood Foundation
System - Basic Requirements, Technical
Report No. 7." In addition, NFPA
publication, "Radon Reduction in Wood
Floor and Wood Foundation Systems"
provides more detailed information on
construction of radon-resistant wood
floors and foundations.
9.1.13 Joints, cracks, or other openings
around all penetrations of both exterior
and interior surfaces of masonry block or
wood foundation walls below the ground
surface shall be sealed with an
elastomeric sealant that provides an air-
tight seal. Penetrations of poured
concrete walls should also be sealed on
the exterior surface. This includes
sealing of wall tie penetrations.
9.1.14 To resist soil gas entry, the
exterior surfaces of portions of poured
concrete and masonry block walls below
the ground surface shall be constructed in
accordance with water proofing
procedures outlined in the Model Building
Codes.
9.1.15 Placing air handling ducts in or
beneath a concrete slab floor or in other
areas below grade and exposed to earth
is not recommended unless the air
handling system is designed to maintain
continuous positive pressure within such
ducting. If ductwork does pass through a
crawlspace or beneath a slab, it should
be of seamless material. Where joints in
such ductwork are unavoidable, they shall
be sealed with materials that prevent air
leakage.
9.1.16 Placing air handling units in
crawlspaces, or in other areas below
grade and exposed to soil-gas, is not
recommended. However, if such units
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are installed in crawlspaces or in other
areas below grade and exposed to soil
gas, they shall be designed or otherwise
sealed in a durable manner that prevents
air surrounding the unit from being drawn
into the unit.
9.1.17 To retard soil gas entry, openings
around all penetrations through floors
above crawlspaces shall be sealed with
materials that prevent air leakage.
9.1.18 To retard soil gas entry, access
doors and other openings or penetrations
between basements and adjoining
crawlspaces shall be closed, gasketed or
otherwise sealed with materials that
prevent air leakage.
9.1.19 Crawlspaces should be ventilated
in conformance with locally adopted
codes. In addition, vents in passively
ventilated crawlspaces shall be open to
the exterior and be of noncloseable
design.
9.1.20 In buildings with crawlspace
foundations, the following components of
a passive sub-membrane
depressurization system shall be installed
during construction: (Exception: Where
local codes permit mechanical
crawlspace ventilation or other effective
ventilation systems, and such systems
are operated or proven to be effective
year round, the sub-membrane
depressurization system components are
riot required.)
9.1.20.1 The soil in both vented and
nonvented crawlspaces shall be covered
with a continuous layer of minimum 6-mil
thick polyethylene sheeting or equivalent
membrane material. The sheeting shall
be sealed at seams and penetrations,
around the perimeter of interior piers, and
to the foundation walls. Following
installation of underlayment, flooring,
'plumbing, wiring, or other construction
activity in or over the crawlspace, the
membrane material shall be inspected for
holes, tears, or other damage, and for
continued adhesion to walls and piers.
Repairs shall be made as necessary.
9.1.20.2 A length of 3- or 4-inch diameter
perforated pipe or a strip of geotextile
drainage matting should be inserted
horizontally beneath the sheeting and
connected to a 3- or 4-inch diameter "T"
fitting with a vertical standpipe installed
through the sheeting. The standpipe
shall be extended vertically through the
building floors, terminate at least 12
inches above the surface of the roof, in a
location at least 10 feet away from any
window or other opening into the
conditioned spaces of the building that is
less than 2 feet below the exhaust point,
and 10 feet from any adjoining or
adjacent buildings.
9.1.20.3 All exposed and visible interior
radon vent pipes shall be identified with at
least one label on each floor level. The
label shall read: "Radon Reduction
System."
9.1.20.4 To facilitate installation of an
active sub-membrane depressurization
system, electrical junction boxes shall be
installed during construction in proximity
to the anticipated locations of vent pipe
fans and system failure alarms.
9.1.21 In basement or slab-on-grade
buildings the following components of a
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passive sub-slab depressurization system
shall be installed during construction.
9.1.21.1 A mimimum 3-inch diameter
PVC or other gas-tight pipe shall be
embedded vertically into the sub-slab
aggregate or other permeable material
before the slab is poured. A "T" fitting or
other support on the bottom of the pipe
shall be used to ensure that the pipe
opening remains within the sub-slab
permeable material. This gas tight pipe
shall be extended vertically through the
building floors, terminate at least 12
inches above the surface of the roof, in a
location at least 10 feet away from any
window or other opening into the
conditioned spaces of the building that is
less than 2 feet below the exhaust point,
and 10 feet from any adjoining or
adjacent buildings. (Note: Because of
the uniform permeability of the sub-slab
layer prescribed in paragraph 9.1.1, the
precise positioning of the vent pipe
through the slab is not critical to system
performance in most cases. However, a
central location shall be used where
feasible.) In buildings designed with
interior footings (that is, footings located
inside the overall perimeter footprint of
the building) or other barriers to lateral
flow of sub-slab soil gas, radon vent pipes
shall be installed in each isolated,
nonconnected floor area. If multiple
suction points are used in nonconnected
floor areas, vent pipes are permitted to be
manifolded in the basement or attic into a
single vent that could be activated using
a single fan.
9.1.21.2 Internal sub-slab or external
footing drain tile loops that terminate in a
covered and sealed sump, or internal
drain tile loops that are stubbed up
through the slab are also permitted to
provide a roughed-in passive sub- slab
depressurization capability. The sump or
stubbed up pipe shall be connected to a
vent pipe that extends vertically through
the building floors, terminates at least 12
inches above the surface of the roof, in a
location at least 10 feet away from any
window or other opening into the
conditioned spaces of the building that is
less than 2 feet below the exhaust point,
and 10 feet from any adjoining or
adjacent buildings.
9.1.21.3 All exposed and visible interior
radon vent pipes shall be identified with at
least one label on each floor level. The
label shall read: "Radon Reduction
System."
9.1.21.4 To facilitate installation of an
active sub-slab depressurization system,
electrical junction boxes shall be installed
during construction in proximity to the
anticipated locations of vent pipe fans
and system failure alarms.
9.1.21.5 In combination basement/-
crawlspace or slab-on-grade/crawlspace
buildings, the sub-membrane vent
described in paragraph 9.1.20.2 may be
tied into the sub-slab depressurization
vent to permit use of a single fan for
suction if activation of the system is
necessary.
9.2 Stack Effect Reduction
Techniques.
The following construction techniques are
intended to reduce the stack effect in
buildings and thus the driving force that
contributes to radon entry and migration
through buildings. As a basic principle,
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the driving force decreases as the
number and size of air leaks in the upper
surface of the building decrease. It
should also be noted that in most cases,
exhaust fans contribute to stack effect.
9.2.1 Openings around chimney flues,
plumbing chases, pipes, and fixtures,
ductwork, electrical wires and fixtures,
elevator shafts, or other air passages that
penetrate the conditioned envelope of the
building shall be closed or sealed using
sealant or fire resistant materials
approved in local codes for such
application.
9.2.2 If located in conditioned spaces,
attic access stairs and other openings to
the attic from the building shall be closed,
gasketed, or otherwise sealed with
materials that prevent air leakage.
9.2.3 Recessed ceiling lights that are
designed to be sealed and that are Type
1C rated shall be used when installed on
top-floor ceilings or in other ceilings that
connect to air passages.
9.2.4 Fireplaces, wood stoves, and other
combustion or vented appliances, such
as furnaces, clothes dryers, and water
heaters shall be installed in compliance
with locally adopted codes, or other
provisions made to ensure an adequate
supply of combustion and makeup air.
9.2.5 Windows and exterior doors in the
building superstructure shall be weather
stripped or otherwise designed in
conformance with the air leakage criteria
of the CABO Model Energy Code.
9.2.6 HVAC systems shall be designed
and installed to avoid depressurization of
the building relative to underlying and
surrounding soil. Specifically, joints in air
ducts and plenums passing through
unconditioned spaces such as attics,
crawlspaces, or garages shall be sealed.
9.3 Active Sub-Slab/Sub-Membrane
Depressurization System.
When necessary, activation of the
roughed-in passive sub-membrane or
sub-slab depressurization systems
described in paragraphs 9.1.20 and
9.1.21 shall be completed by adding an
exhaust fan in the vent pipe and a
prominantly positioned visible or audible
warning system to alert the building
occupant if there is loss of pressure or air
flow in the vent pipe.
9.3.1 The fan in the vent pipe and all
positively pressurized portions of the vent
pipe shall be located outside the
habitable space of the building.
9.3.2 The fan in the vent pipe shall be
installed in a vertical run of the vent pipe.
9.3.3 Radon vent pipes shall be installed
in a configuration and supported in a
manner that ensures that any rain water
or condensation accumulating within the
pipes drains downward into the ground
beneath the slab or soil-gas-retarder.
9.3.4 To avoid reentry of soil gas into the
building, the vent pipe shall exhaust at
least 12 inches above the surface of the
roof, in a location at least 10 feet away
from any window or other opening into
the conditioned spaces of the building
that is less than 2 feet below the exhaust
point, and 10 feet from any adjoining or
adjacent buildings.
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9.3.5 To facilitate future installation of a
vent fan, if needed, the radon vent pipe
shall be routed through attics in a location
that will allow sufficient room to install and
maintain the fan.
9.3.6 The size and air movement
capacity of the vent pipe fan shall be
sufficient to create and maintain a
pressure field beneath the slab or
crawlspace membrane that is lower than
the ambient pressure above the slab or
membrane.
9.3.7 Under conditions where soil is
highly permeable, reversing the air flow in
an active sub-slab depressurization
system and forcing air beneath the slab
may be effective in reducing indoor radon
levels. (Note: The long-term effect of
active sub-slab depressurization or
pressurization on the soil beneath
building foundations has not been
determined. Until ongoing research
produces definitive data, in areas where
expansive soils or other unusual soil
conditions exist, the local soils engineer
shall be consulted during the design and
installation of sub-slab depressurization
or pressurization systems.)
•U.S. Government Printing Office: 1994 — 515-003/01026
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