&EPA
United States
Environmental Protection
Agency
Office of Research and
Development
Washington, DC 20460
EPA/625/2-91/032
February 1991
Radon-resistant
Construction
Techniques for New
Residential
Technical Guidance
Mechanical
Barriers
Planned Mechanical
Systems
Sub-slab -
Depressurization
Site
Evaluation
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EPA/625/2-91/032
February 1991
Radon-resistant Construction Techniques
for New Residential Construction
Technical Guidance
By
Mike Clarkin
Terry Brennan
Camroden Associates, Inc.
RD#1 Box 222 East Carter Road
Oriskany, NY 13424
EPA Contract No. 68-02-4287, Task 11
EPA Project Officer: Michael C. Osborne
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, North Carolina 27711
Printed on Recycled Paper
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Notice
The United States 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 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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Table of Contents
Page
List of Figures
List of Tables . """"!!!"!! v
Metric Conversions vi
Section 1
Introduction 1
Section 2
Overview ; ~
2.1 Where Does Radon Come From and Why Is It a Problem? !.."!.. 3
2,2 How Radon Gets into a Home 3
2.3 Radon Control in New Construction 4
2.3.1 Sub-slab Depressurization/Pressurizatidn Systems 5
2.3.2 Mechanical Barriers *
2.3.3 The Site !""""""!!"""".'."".".".' 7
2.3.4 Planned Mechanical Systems 9
2.4 Recommendations n
2.4.1 Sub-slab Depressurization Systems 9
2.4.2 Mechanical Barriers 'JQ
Section 3
Soil Depressurization j~
Introduction .,,
3.1 Sub-slab Depressurization Overview 13
3.2 Sub-slab Depressurization Systems 13
3.2.1 Overall Design Considerations - Active and Passive Systems ".".."I."! 13
3.2.2 Sub-slab Preparation ; 15
3.2.3 Preparation of the Slab 16
3.2.4 Active Sub-slab Depressurization System Materials and Installation Details......."...."....." 16
3.2.5 Passive Sub-slab Depressurization System Components and Installation Details.!...;....."... 16
3.3 A Crawlspace Post-construction Alternative 17
Section 4
Mechanical Barriers _ 19
Introduction ; in
4.2 Foundation Materials 19
4.3 Common Masonry Wall Details and Their Impact on Radon Resistance...."!."] 20
4.3.1 Masonry Walls with Termite Caps, Solid Blocks, and Filled Block Tops !....."..."...."..20
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4.3.2 Masonry Walls with Weep Holes 21
4.3.3 Stemwalls in Slab-on-grade Houses 21
4.3.4 Foundation Walls in Crawlspace Houses 21
4.4 Floors in Basements, Slabs on Grade, and Crawlspaces 21
4.4.1 Crack Prevention : ..." 21
4.4.2 Joints 22
4.4.3 Penetrations 23
4.5 Crawlspaces 24
4.6 Coatings 25
4.6.1 Introduction 25
4.6.2 Dampproofing/Waterproofing to Achieve a Radon Barrier 26
4.7 Membranes 26
4.7.1 Introduction ....- 26
4.7.2 Types of Membranes Available 27
4.8 Mechanical Barriers Applied to the Soil -..- ....28
4.9 Drainage Boards for Soil Gas and Radon Control 28
4.10 Summary of Recommendations for Mechanical Barriers 28
4.10.1 Rules of Thumb for Foundation Walls 28
4.10.2 Rules of Thumb for Slab and Sub-slab Barriers 28
Section 5
Site Evaluation : 31
Introduction 3.1
5.2 Radon in the Soil , . 31
5.2.1 Attempted Correlations Between Indoor Radon and Measurements Made at Sites 31
5.2.2 Indexes Using Permeability and Soil Radon Concentrations 32
5.2.3 Variations in Spatial and Temporal Soil Gas Concentrations 33
5.3 Radon Observed in Nearby Houses 34
5.4 Airborne Measurements ..............34
5.5 Radon in Water 34
5.6 Radon in Building Materials 34
Section 6
Planned Ventilation , 35
Introduction 35
6.2 Interdependence of Mechanical Systems and Climate ....: 35
6.3 Guidelines for Planning the Mechanical System 35
6.4 Two Illustrations 36
6.5 Conclusions .37
References ; ..39
Appendix A
Current Radon-resistant New Construction .Research Efforts ..41
Appendix B
Other Radon-resistant New Construction Guidelines 43
IV
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List of Figures
Figure
2.1 Radon Decay Chart [[[ 4
2.2 Percentage of Radon Contributions by Source from 15 Homes ............................... ...........5
2.3 Typical Radon Entry Routes in Basement Foundations [[[ ..'5
2.4 Typical Crawlspace Foundation Entry Routes ..................... . ................................. 7
2.5 Typical Radon Entry Routes in Slab-on-grade Construction .... ........ . .......... . .................... '.8
2.6 Major Radon-resistant New Construction Topics ...... ............................................. 9
2.7 Sub-slab Depressurization Theory [[[ JQ
2.8 Radon-resistant Barrier Theory . .................... .......................... . . " ..... j j
3.1 Negative Pressure Sources in a Typical Home ........................ ....... ....... .......... ...Z...1.Z 14
3.2 Theory of Operation of a Sub-slab Depressurization System ..... . ........ . ....... 4 ........... ..."" 15
3.3 Typical Sub-slab Depressurization System [[[ 17
4.1 Sealing a French Drain [[[ _ .................... 23
4.2 Sealing a Sump Hole .......................... . ......................... . ...... \ ......... ........... 25
4.3 Summary of Mechanical Barrier Approach for Basement Foundations ..................... .'...."28
4.4 Summary of Mechanical Barrier Approach for Slab-on-grade Foundations ............. ...... 29
4.5 Summary of Mechanical Barrier Approach for Crawlspace Foundations .......... .l."..."."."29
List of Tables
Table D
A 3. £6
3.1 Summary of Radon Concentrations in EPA New Construction Projects ......................... 13
4.3 Results Using Vented Crawlspace Technique .................................. "."'" ..... """25
5. 1 Florida Survey Soil Radon and Corresponding Indoor Radon Concentrations ......".I..." 32
5.2 Swedish Soil Risk Classification Scheme and Building Restrictions ............. . ......... 32
5.3 Geometric Means for Soil Gas Radon-222, Soil Radium-226, Permeability ............
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Metric Conversions
Readers more familiar with the metric system may use the following to convert to that system.
jVonmetric
cfm
ft
ft?
in.
Ib
Ib/ft
mil
psi
pCi/L
Multiplied bv
0.000472
0.305
0.0929
0.0254
0.454
1.488
0.0000254
6.895
37
yields Metric
m3s
m
m2
m
kg
kg/m
m
kPa
vi
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Section 1
Introduction
Growing concern about the risks posed by indoor radon,
a naturally occurring radioactive gas found in varying amounts
in nearly all houses, has underscored the need for dependable
radon-resistant residential construction techniques. In response
to this public health exposure, the U.S. Environmental Pro-
tection 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 could be
applied during construction, involve less labor and financial
investments, and provide greater homeowner satisfaction and
safety than would a radon-reduction technique installed after
the home is built and occupied.
This manual is designed to provide homeowners and
builders with an understanding of operating principles and
installation details of radon-resistant new home construction.
To meet these needs, the manual is divided into four parts.
The first part contains the Introduction, which you are now
reading. The second part containing Section 2 is the Over-
view, which covers techniques being studied or used in the
control of radon in new homes. Underlying operating prin-
ciples, materials, and installation are discussed in Section 2.
The level of detail is aimed at developing an understanding
of basics, not background or details. The overview is quickly
and easily read. The third part, Sections 3-6, contains techni-
cal information which takes the same material to a greater
depth, and covers additional specific construction details.
This part contains far more technical information than the
introduction and overview, and will require more effort to
read and assimilate. The fourth part, the Appendices, contains
background information on the contents of the first three
parts.
The intent of this manual is not to rate similar products
made by different manufacturers, or to provide a stock radon-
resistant package. This manual should provide a basic un-
derstanding of the types of products and systems that are
available and being used. In this way, the reader will be able
to select radon-resistant products and systems that will be
most applicable to a particular situation.
It should be understood that some of the techniques
mentioned in this manual have NOT yet been fully demon-
strated in new home construction. These techniques are
discussed because they have a sound theoretical potential for
effectively precluding radon entry into a home. As research
continues, and experience in the use of radon-resistant new
construction techniques grows, it is expected that some of
these theories will prove to be transferable to the homebuildcr's
list of radon-resistant construction options. The soil ventila-
tion techniques described HAVE been extensively tested in
existing homes and show good potential for application in
new construction and are, therefore, recommended.
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Section 2
Overview
Two areas are addressed in the Overview.
Radon Entry - How radon enters a building
Radon Control - What can be done to lower
indoor radon levels.
2.1 Where Does Radon come from and Why is
it a Problem?
Radon gas is the result of the radioactive decay of
radium-226, an element that can be found in varying concen-
trations throughout many soils and bedrock. Figure 2.1 shows
the series of elements that begin with uranium-238, and, after
undergoing a series of radioactive decays, lead eventually to
lead-210. At the time radium decays to become radon gas,
energy is released. Of all the elements and isotopes illus-
trated in Figure 2.1, radon is the only one which behaves like
a gas and can easily slip through the small spaces between
bits of soil. While many of the isotopes in the uranium-238
decay series exist for a long time before they decay, radon
docs not remain radon for very long. It has a half-life of 3.8
days. If 1 Ib* of radon were put in a jar, 3.8 days later only I/
2-lb of radon would be left; the other 1/2-lb would have
decayed into the short lived decay products polonium, bismuth
and lead. After another 3.8 days only 1/4-lb of radon would
be left in the jar. The radon decay products shown inside the
building have even shorter half lives than radon, and decay
within a few hours to the relatively stable isotope lead-210.
It is this rapid release of energy that causes radon and radon
decay products to pose such a significant health risk.
If radon and radon decay products are present in the air,
they will be inhaled. Because the decay products are not
gases, they will stick to lung tissue or larger airborne particles
which later lodge in the lung. The energy given off as these
isotopes decay, can strike the cells in the lung, damage
tissue, and may eventually develop into lung cancer. The
amount of risk depends on how long a person is exposed to
how high a concentration of radon and radon decay products.
Estimates of the number of lung cancer deaths attributable to
radon and radon decay products ranges from approximately
5,000 to 20,000 deaths per year in the United States.
For simplicity, in the remainder of this manual, radon
and radon decay products will be collectively referred to as
radon, except where the distinction is required.
* For the reader's convenience, nonmetric units are used in this document.
Readers more familiar with the metric system may use the factors in the
front matter to convert to that system.
2 J How Radon Gets into a Home
A house will contain radon if the following four condi-
tions exist:
1) a source of radium exists to produce radon
2) a pathway exists from the radium to the house
3) a driving force exists to move the radon to the
house
4) an opening in the house exists to permit radon
to enter.
If one of these conditions does not exist, then the house
will not have a radon problem. An estimated 10 to 20% of
the existing homes in the United States have annual average
radon concentrations above 4 picocuries per liter of air (pCi/
L). This may seem like a small percentage of problem
homes until one considers that, of the million or so U.S.
houses built each year, 100,000 to 200,000 homes will likely
have radon concentrations higher than 4 pCi/L.
The most common way radon enters a home is when
lower indoor air pressure draws air from th? soil, bedrock or
drainage system into the house. If there is radon in the soil
gas, it will also be drawn in. Just as gravity will make water
flow from a high elevation to a lower elevation, pressure
differences will make radon-laden air move from an area of
higher pressure to an area of lower pressure. For a variety of
reasons, illustrated at length in the Technical Information
section, most buildings tend to maintain an indoor air pressure
lower than outdoor air pressure. If .cracks and holes in the
foundation are open to the soil, radon will be drawn indoors.
Radon movement by pressure differences is called pressure
driven transport.
Radon can also enter buildings when there are no pressure
differences. Place a drop of food coloring in a glass of water
and eventually the coloring will spread out (diffuse) and
color the water - - even without stirring. Radon will do the
same thing - - spread from an area of higher concentration to
an area of lower concentration until the concentrations are
equal. Radon movement in this way is called diffusion
driven transport.
A less common entry mechanism is the outgassing of
radon from well water. A well supplied by groundwater that
is in contact with a radium-bearing formation can transport
the dissolved radon into the home. At the time of this
writing, it is estimated that the health risks associated with
breathing radon gas released from the water are 10 times
higher than the risks associated with ingesting water contain-
ing radon.
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214
Polonium
0.00016
seconds
210
Lead
19.4
years
214
Bismuth
19.7
minutes
218
Polonium
3
minutes
214
Lead
27
minutes
222
Radon
3.8
days
238
Uranium
4.47 billion
years
Figure 2.1. Radon Decay Chart. Radon has a long enough half-life to allow It to move from some distance away from
the house through the soil Into the building. Although some of the radon In the building will be removed
with ventilation air, much will be trapped in the building and decay before it is removed.
Radon can also emanate from the building materials
themselves. The extent of the use of radium contaminated
building materials is unknown but is generally believed to be
small.
Figure 2.2 illustrates the percentages of contribution by
each type of radon entry made to a specific group of study
houses in the Pacific NW (Se89). Any one house can vary
significantly from these figures. However, on a national
basis this is an indication of the relative importance of each
of the contributors.
Figures 2.3, 2.4, and 2.5 illustrate typical radon entry
routes found in basement, crawlspace, and slab-on-grade
construction.
2.3 Radon Control in New Construction
Like most other indoor air contaminants, radon can be
controlled by keeping it out of the house, or reducing the
concentration by mixing it with fresh air after it has already
entered. The following approaches have been tried or sug-
gested:
Prevent Entry
Make provisions for a sub-slab depressurization
or pressurization system during construction
Install mechanical barriers to block soil-gas en-
try
Avoid risky sites
Planned Mechanical Systems
Supply fresh air to reduce radon by dilution
Control pressure relationships to reduce soil-air
entry.
Figure 2.6 illustrates the four major topics to be consid-
ered in this manual - Site Evaluation, Mechanical Barriers,
Sub-slab Depressurization and Planned Mechanical Systems.
All four of these topics are covered in the Overview and
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Figure 2.2. Percentage of Radon Contributions by Source from 15 Homes.
Technical Information sections. This illustration will also
serve as an index to help you use this manual. The pages in
the Overview and Technical Information sections where they
are covered are listed beneath each topic.
2.3.1 Sub-Slab Depressurization/Pressurization
Systems.
One of the most frequently used radon reduction tech-
niques in existing homes is a sub-slab depressurization system.
Typical installation costs for a system in existing homes
range from $1,000 to $2,000. If the same system is installed
or at least planned for, and roughed in during construction,
the cost is much lower, so a prudent builder who is erecting a
radon-resistant home should include features that will allow
for the easy installation of such a system.
A sub-slab depressurization system creates a low pres-
sure zone beneath the slab using a pipe system to exhaust the
soil-gas from beneath the foundation. This prevents soil-gas
from entering the building by reversing the airflow direction.
Air will flow from the house into the soil, effectively sealing
all the remaining foundation cracks and holes. For a simple
view of the operating principle of a sub-slab depressurization
system, refer to Figure 2.7
A sub-slab pressurization system creates a high pressure
zone beneath the slab. Although this does not reverse the
direction of the airflow ( the air from the system will still
flow into the home through cracks and holes), it does dilute
the radon concentrations beneath the slab and may keep
radon that is being produced in the site from getting to the
foundation. In a number of existing houses it has been found
that this technique performed better than sub-slab depressur-
ization. In buildings where pressurization works best there
are a few common factors. One is the presence of soil or
bedrock that allows air to move very easily through it. So
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Open tops of hollow
core masonry blocks
Diffuses through
interior of wall
Dampproofing or
waterproofing
Cracks in foundation
walls
Loose form ties
Floor drains Cracks in floor
Open pipe
penetrations
and joints
Rgure 2.3. Typical Radon Entry Routes In Basement Foundations.
easily, in fact, that it is difficult to establish a low pressure
field by exhausting 100 cfm or so of air from beneath the
slab. It is this feature that limits the performance of soil
depressurization systems. The other factors that seem im-
portant are either a relatively low concentration of radon in
the soil-gas, or a remote location for the source radium, with
radon transported some distance from the house through the
very permeable soil. It is thought that a positive pressure
created by blowing low radon concentration air under the
slab dilutes the soil-gas near the foundation, and diverts soil-
gas originating farther away. Pressurization has been suc-
cessfully used in buildings built in coarse gravel, shattered
shales, and limestones. This technique has been used in
existing homes to reduce radon concentrations; however,
there has been no major research effort to verify the actual
effectiveness of pressurization. Other factors to consider
when installing a pressurization system are the effect the
introduction of, in some climates, below freezing or high
humidity air will have on the concrete floor slab, and the
effort that must be made to ensure that the air intake does not
become blocked by foreign matter.
Sub-slab depressurization/pressurization systems arc
discussed in detail in Section 3.
23.2 Mechanical Barriers
Knowing that the greatest contributor to indoor radon
concentrations is air from the soil entering the building through
the foundation, it was thought that a good place to begin
building a radon-resistant home is to make the foundation as
radon-resistant as possible. Figure 2.8 illustrates the principle
of a radon barrier. Many materials (concrete, polymeric
coatings and plastic films) are outstanding air barriers and
retard the transfer of radon gas by a large factor. In practice,
the difficulties that arise when using barrier techniques are
numerous. Failure to seal a single opening may negate the
entire effort. Barriers may degrade with time or may be
damaged during installation. The use of barrier techniques
as a stand-alone system is not recommended, but it is rec-
ommended that some amount of effort be made to limit the
entry of radon through the foundation. This can be done by
using :
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n
Pipe penetrations
Bare earth floors
Figure 2.4 Typical Crawlspace Foundation Entry Routes.
foundation materials themselves, sealing cracks,
joints and penetrations
foundation coatings, normally used for
dampproofing
membranes surrounding the foundation.
This section will briefly discuss foundation design and
materials. Methods used to control cracking, treating the
cracks that do form, and ways to seal planned foundation
penetrations will be reviewed. The material presented in this
manual can be easily adapted to buildings with basements,
crawlspaces, or slab-on-grade foundations.
It should be pointed out that attempts to control radon by
making a gaslight barrier around the foundation have not
been completely effective. It is likely they have done some
good, but many newly constructed buildings that relied on
barrier's as the only radon reduction technique have elevated
levels of indoor radon. It is not known, however, what the
indoor radon concentrations would have been if the barriers
had not been installed. This is covered in more detail later in
the manual.
23.3 The Site
The question most often asked by homebuilders is can
one determine if radon-resistant construction techniques should
be applied to a given site?
A simple test that could identify problem sites would be
very helpful. At present, there are no simple, reliable meth-
ods for doing this. The reasons for this are covered in the
Technical Information section. In the absence of a simple
site screening test, guidance can be sought in the growing
body of information developed at regional, state and local
levels. Many researchers, public agencies and private
homeowners are making soil, bedrock and indoor radon
measurements. From these data a picture of the extent of the
problem is emerging. While not yet possible to be certain
about a given site, some idea of where the problem areas are
has been developed. At a recent meeting of several leading
mitigation contractors, the general consensus was to install
radon-resistant techniques rather than spend extra time and
money performing the number of pre-construction tests it
would take to confidently evaluate the site. However, a
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Penetrations and
joints
Figure 2.5. Typical Radon Entry Routes In Slab-on-grade Construction
group of testing contractors may decide just the opposite.
Although no definitive methods for predicting possible in-
door radon concentrations based upon pre-construction soil
measurements exist, it is clear that a building being erected
on a site that is known to contain high concentrations of
radon should have radon-resistant construction techniques
applied. Another concern when evaluating the site potential
for supplying radon to the soon-to-be-constructed home is
the permeability of the soil. A highly permeable soil allows
easy movement of soil gases; therefore, radon can move a
greater distance from the source to the building than in a
tighter, less permeable soil. This can also allow soil-gases
that contain lower concentrations of radon to enter the home
in greater quantities, which can produce elevated indoor
concentrations. Swedish Authorities suggest that a building
site with soil radon concentrations greater than 1350 pCi/L
or with a highly permeable soil should use radon resistant
construction techniques (Ak86).
We do not recommend the avoidance of building sites
that are suspected to contain strong radon sources. We do,
however, strongly recommend that the homes built on those
sites be designed and built with radon-resistant construction
techniques.
Water from wells has been found to be a major source of
radon in some homes in the United States. Radon will
outgas from the rocks into the groundwater. When the water
is exposed to the atmosphere, some of the radon is released.
Builders should be aware that wells can be a potential
problem. The only way to ensure that a well is not a
potential radon source is to have the water tested after the
well is drilled. It is not adequate to make a decision based
upon tests made in wells in the same area or even on adjoin-
ing building sites. A recent research project disclosed two
homes with water radon concentrations of over 400,000 pCi/
L, while the well used at a house between the two had
waterborne radon concentrations of less than 1000 pCi/L
(Ni89). It should be understood that, when considering
waterborne radon, the concentrations that concern us are
much higher than when we are considering radon in the air.
As a rule of thumb, between 8,000 and 10,000 pCi/L of
radon in the water will contribute 1 pCi/L of radon into the
air. There is no standard or guideline for the amount of
radon allowable in the water as yet, but a guideline is expected
to be set soon. Contact your regional EPA office for more
information on pending guidelines.
If radon is present in the water, the current state of
technology offers two possible solutions. Water that is
aerated will release the radon it carries. Several manufactur-
ers have systems designed to aerate the water and vent the
radon outdoors. An alternative system filters the water
through granulated activated carbon which removes the radon
from the water. There are several manufacturers of granulated
activated carbon water filters. It should be noted here that at
high radon levels (greater than 5,000 pCi/L) the buildup of
radon decay products in the charcoal can produce a signifi-
cant level of gamma radiation. Although this can be allevi-
ated by proper shielding, disposal of the charcoal filter media
can be a problem.
A site suspected to contain a waterborne source of radon
should not be avoided solely on the basis of the existence of
radon. Methods can be utilized to alleviate any problem that
may arise from waterborne radon.
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Mechanical Barriers
Overview Page 6
Technical Information
Page 19
Sub-slab Deoressurization
Overview Page 5
Technical Information Page 13
Planned Mechanical
Systems
Overview Page 9
Technical Information
Page 35
Site Evaluation
Overview Page 7
Technical Information Page 31
Figure 2.6. Major Radon-resistant New Construction Topics.
23 A Planned Mechanical Systems
The entry of soil gas into buildings is the result of a
complex interaction between the building shell, the mechani-
cal system, and the climate. Important climatic variables are
the wind velocity, indoor/outdoor temperature differences,
rainfall, and atmospheric pressure changes. Indoor radon
concentrations can be reduced by planning the mechanical
system so that fresh air dilutes the radon that has entered the
building, and by controlling interior air pressures to reduce
soil gas entry. This approach has not been extensively tested
in the EPA Demonstration Projects in existing homes. It also
requires a great deal of insight into the dynamics of building
operation for a given climate. These issues are discussed at
more length in the Technical Information section. If this
method is considered, the following guidance can be used:
Be sure that combustion appliance performance
is not impacted.
Supply fresh air in accordance with ASHRAE
requirements.
Consult ASHRAE (ASHRAE85) ventilation requirements
and the National Fire Protection Association (NFPA1). As a
system is designed, consider the use of:
Power vented combustion devices or combustion
devices that use outside air.
Fresh air supply ventilation systems (heat
recovery or non-heat recovery).
2.4 Recommendations
The following sections contain recommended radon-re-
sistant construction techniques that a builder may wish to
incorporate into the home. It should be understood that these
are recommendations only and should not be construed as
guidelines or regulations. The recommendations are based
upon the best available information gathered from numerous
research projects.
2.4.1 Sub-Slab Depressurization Systems
To facilitate the use of soil depressurization, it is sug-
gested that a permeable layer of material be placed beneath
the slab, all the major foundation penetrations be sealed and
a passive stack be run from the permeable layer up through
the roof like a plumbing vent. Appropriate materials for the
permeable layer are 3/8 to 1-1/2 in. diameter stone pebbles,
or manufactured drainage products (perforated plastic pipe or
drain boards). A passive stack is much easier to add while
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Radium in soil
Figure 2.7. Sub-slab Depressurlzatlon Theory.
Radon gas in soil
building the house, and is easily power vented later if re-
quired. There is evidence that, while not foolproof, a properly
designed passive venting system can sometimes have some
impact on indoor radon levels.
2.4.2 Mechanical Barriers
Below-grade walls may be constructed of poured con-
crete, masonry blocks, or other materials such as all-weather
wood or stone. This manual discusses details for use in
poured concrete and masonry foundations because these are
the most common materials used for new construction. Re-
cently, trade associations such as the American Plywood
Association and the National Forest Products Association
have issued publications on designing radon-resistant perma-
nent wood foundations. Information on these types of foun-
dations can be found by contacting the appropriate trade
association (NFoPASS).
The following is a list of recommendations that builders
can use to utilize the foundation as a mechanical barrier to
radon entry.
Foundation walls and floor slabs are often constructed of
poured concrete. Plastic shrinkage, and therefore cracking, is
a natural function of the drying process of concrete. Many
factors, such as the water/cement/aggregate ratio, humidity,
and temperature, influence the amount of cracking that occurs
in a poured concrete foundation. Cracking may be minimized
by:
Proper preparation, mixture, and curing of
concrete
(ACI302.1R-80, ACI332R-84)
Ferrous reinforcing (rebar rods and woven wire
meshes)
Use of concrete additives to change the
characteristics of concrete
Water reducing plasticizers, fiber-reinforced
cements (ACI212.1R-81).
To help prevent cracking in masonry walls, or minimize
the effects of cracks that do develop:
Using correct thickness of unit for depth of soil
(NCMA71)
Using ferrous reinforcing (corners, joints, top
course) (NCMA68)
Coating interior and exterior of wall with
dampproofing.
Cracks and joints in concrete and concrete block can be
sealed using caulks. Polyurethane caulks have many of the
properties required for durable closure of cracks in concrete.
These features are:
Durability
Abrasion resistance
Flexibility
Adhesion
Simple surface preparation
Acceptable health and safety impacts.
Typical points that should be sealed with caulks are :
Plumbing penetrations (soil pipes and water
lines as minimum)
10
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Radium in soil
Figure 2.8. Radon-resistant Barrier Theory.
Radon gas in soil
Perimeter slab/wall crack and expansion joints
(tool crack or use "zip" off expansion joint
material.
The open tops of concrete block walls are openings
that should be sealed. This can be done by installing a row
of solid blocks, lintel blocks or termite cap blocks at the top
of the wall.
Drainage details that leave openings through the founda-
tion should be avoided or modified. Sump holes and french
drains are widely used examples of this type of detailing. It
is best to avoid them if possible, by using alternate drainage
systems. When these design details are unavoidable, a little
thought can allow the use of these details and still keep radon
from entering the home. The Technical Information section
will discuss these designs in greater detail.
In many areas of the country, some type of dampproofing
or waterproofing treatment is required by code.
The application of dampproofing and waterproofing ma-
terials on the exterior, interior, or both sides of the foundation
that can serve as a radon resistant barrier is recommended to
help control radon entry. It must be understood that a
coating applied to a foundation intended to resist the flow of
radon into the building is in addition to the normal water-
proofing/dampproofing requirements.
Coatings are applied to the outside or inside of the
foundation, creating a radon- resistant barrier between the
source and the inside of the home. They come in a wide
variety of materials including paint-like products that can be
brushed on the interior of the foundation, tar-like materials
that are applied to the outside, and cementitious materials
that can be brushed or troweled on. They cannot be applied
to the underside of the concrete floor slab for obvious reasons,
so must be applied to the inside surface of the slab. The
effective life of an interior coating can be greatly diminished
by damage; therefore, care must be taken to provide protec-
tion to the material used.
Membrane barriers are applied to the exterior of the
foundation and also beneath the floor slab during construc-
tion. Materials used for the membrane barriers range from
co-extruded poly olefin to poly vinyl chloride to foil sheets
with many other materials in between. All membrane barri-
ers must have the edges sealed to prevent radon from mi-
grating around the edges and back into the building.
It is recommended that, as a minimum, a membrane be
placed beneath the slab, and all foundation penetrations to
the soil be sealed or otherwise dealt with in a manner which
will prevent the entry of radon into the home.
11
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Section 3
Soil Depressurization
Introduction
The next four sections contain details and references for
those wishing a deeper understanding of radon-resistant con-
struction issues. The four major topics:
Sub-slab Depressurization
Mechanical Barriers
Site Evaluation
Planned Mechanical Systems
are used to organize this portion of the manual.
In theory, the application of radon barriers should be
adequate to avoid elevated radon levels in houses. In prac-
tice, however, a backup radon mitigation system has been
found essential for maintaining indoor radon concentrations
below 4 pCi/L in most homes studied. In recent radon-
resistant residential construction projects conducted by EPA
and/or private builders, several of the homes designed to be
radon-resistant have contained radon concentrations above 4
pCi/L. In each of those houses a backup system consisting
of an active (fan assisted), or passive (wind and stack effect
assisted), sub-slab depressurization system was installed at
the time of construction. When mechanical barriers failed to
adequately control radon, the soil depressurization methods
were made operational.
3.1 Sub-Slab Depressurization Overview
Of the study homes mentioned in the previous section,
some passive systems seemed sufficient to lower the radon
concentrations, while in all cases, active systems resulted in
significantly lower concentrations. However, some of those
projects are on-going and longer term testing may show that
some of the active systems will fail to maintain concentrations
below the guideline for the long term. Table 3.1 summarizes
the findings of these particular projects. See Appendix A for
more information on the data contained in this table.
Table 3.1 Summary of Radon Concentrations In EPA New
Construction Projects.
Soil Depressurization
Project # Houses Barrier Only Passive Active
pCI/L pCI/L pCi/L
EPA-VA1
EPA-NY1
EPA-VA2
EPA-PA1
10
15
2
1
14.5
15.8
1.3
13.4
6.0
13.9
<1
7.0
<1
2.8
<1
1.1
The most common way radon enters a home is when air
pressure differences move soil gases containing radon through
the spaces between soil particles to the foundation of the
home. Just as gravity will make water flow from a higher
area to a lower area, pressure differences will make radon
laden soil gases move from an area of higher pressure to an
area of lower pressure. Most buildings tend to maintain
themselves at an air pressure lower than the surrounding soil.
This characteristic is due to weather driven parameters such
as indoor/outdoor temperature differences and wind. The
use of exhaust fans and combustion devices in a home will
also create a negative pressure in the home. If cracks and
holes in the foundation, are open to the surrounding soil,
radon will be drawn into the building. Figure 3.1 illustrates
the principle of pressure transported radon and also shows
some of the things that produce the differences in pressure.
Refer to the section on planned ventilation for more infor-
mation on pressure differences.
3.2 Sub-Slab Depressurization Systems
As previously mentioned, the air pressure in most homes
is less than the air pressure in the surrounding soil. The
difference in air pressures is what draws radon into the
home. A sub-slab depressurization system alters the pressure
beneath the concrete slab, making the sub-slab pressure less
than the indoor pressure. It is the altered air pressures that
keep radon from entering the home.
Figure 3.2 shows the theory of operation, a simple sys-
tem layout, and the components of a sub-slab depressuriza-
tion system.
Careful attention to detail when in the design stage of a
sub-slab depressurization system will help ensure the easy
installation of a system if it is found to be required. The
proper details are given in the following sub-sections, begin-
ning at the sub-slab area and progressing upward to the
exhaust.
3.2.7 Overall Design ConsiderationsActive and
Passive Systems
When designing an active or passive system, many de-
sign considerations are common to the two systems. For
example, some provision for removal of condensation that
forms in the exhaust pipe will be required. Routing of the
pipes from the basement to the roof must be considered when
the house is being designed. Placement of the exhaust is
extremely important
Removal of condensation is an important consideration.
Water collecting in an elbow or other low point of the system
can effectively block the pipe, and reduce or disable the
system. Builders should strive to design a pipe system that
will allow condensation to run back through the pipe to the
sub-slab aggregate. This can be accomplished by ensuring
13
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Flguro 3.1. Negative Pressure Sources in a Typical Home.
that the pipe run is vertical the entire distance from the
basement to the exhaust. A completely vertical pipe run with
no bends or elbows will also provide a pipe system with
lower static pressure losses which enhances the effectiveness
of both active and passive systems. If elbows or a low point
is incorporated in the design, a condensate pump can be used
to drain the water away. The use of condensate pumps will
increase the cost of the system both in materials and labor, so
the ideal situation is to design a system that does not require
pumps.
Pipe routing should be considered when the home is
being designed. This will ensure that there is an area reserved
for the exhaust pipe and preclude any possibility of having to
build the system with numerous elbows and long horizontal
pipe runs. Ideally, the pipes should be run through an
interior wall of the home or up through closets.
The exhaust should be located above the highest ridge
line. Some builders prefer to exhaust their systems out an
attached garage roof, rather than through the main roof. This
type design does require at least one short horizontal run, and
will not seriously impact the effectiveness of an active system.
When choosing the exhaust point, avoid the reentry of
radon-laden soil-gas into the home through open windows
and doors. Do not exhaust the soil-gas in an outdoor occupied
area such as a porch or patio. Locating the exhaust close to a
chimney that could backdraft and draw the exhausted soil-
gas back into the home should also be avoided. -For a good
discussion on the theory of exhaust design, see the 1985
14
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Medium pressure zone
Figure 3.2. Theory of Operation of a Sub-Slab Depressurization System.
edition of the ASHRAE Fundamentals Handbook, Chapter
14 (ASHRAE85).
3.2.2 Sub-Slab Preparation
Figure 3.2 illustrated that a low pressure area being
developed beneath the slab will draw the radon out of the
soil, up the pipe, and exhaust the gas outdoors. If the sub-
slab material consists of tightly packed soil or contains large
rocks, the pressure field may not extend to all areas of the
soil surrounding the foundation, and allow radon to enter the
home where the pressure field does not exist. One way of
ensuring the proper extension of the pressure field is to
install media beneath the slab prior to the pour that will
allow the easy movement of the air, thus helping to extend
the pressure field.
In areas where it is available, crushed gravel is an
inexpensive material to use. Sub-slab gravel provides a
drainage bed for moisture and a stable, level surface for
pouring the slab. The material preferred for radon reduction
is crushed aggregate with a minimum of 80% of the aggre-
gate at least 3/4 in. in diameter. This stone should have a
free void space above 40 %. One standard specification of
this type of gravel is D.O.T. # 2 gravel. A minimum of 4 in.
of aggregate should be placed under the entire slab. Care
must be taken to avoid introducing fine dirt particles during
and after placement of the aggregate.
In areas where gravel is not readily available, drainage
mats designed for soil stabilization may be used. The use of
these drainage mats may not be cost effective in areas where
gravel is available, but where gravel must be shipped in from
long distances, drainage mats can be cost effective.
Some builders prefer laying perforated PVC piping in
the gravel before the slab is poured, and connecting the
perforated pipe to the exhaust pipe of the system. The use of
perforated pipe may not be necessary in active systems but
probably will assist a passive system.
15
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Membranes beneath the slab help to keep a continuous
radon barrier in the event of slab cracking. For more infor-
mation on this detail see the discussion on membrane barriers.
The use of footing drains for water control can affect the
distribution of the pressure field. Interior footing drains
sometimes terminate in a sump hole. If this is the case and
the sump hole is not sealed airtight, the possibility exists for
air to be drawn into the sump by the sub-slab system and
weaken the pressure field. Make sure all sumps are sealed
airtight. Sometimes interior footing drains extend out beneath
the footing and run to daylight, as shown in the section on
mechanical barriers. If this is the case, provision must be
made to make the ends of the drain airtight while still
allowing water to drain. Reverse-flow valves are ideal for
this application.
To summarize, any opening or connection that allows
the dcprcssurization system to draw air from anywhere but
beneath the slab is detrimental to its effectiveness and must
be avoided.
3.2.3 Preparation of the Slab
A thorough discussion of slabs is included in the section
on foundation materials as mechanical barriers and should be
referred to. However, when installing a soil depressurization
system, it is more important to seal the large openings that
would defeat extension of a low pressure field than it is to
seal every small crack. This is because the airflow through
small cracks from the building into the soil will effectively
seal them against soil gas entry.
32.4 Active Sub-Slab Depressurization System
Materials and Installation Details
As can be seen on Figure 3.3, active sub-slab depressur-
ization systems consist chiefly of a pipe system and a fan.
There are several other components that should be included
in a good system, but are not necessary to make the system
reduce radon concentrations.
Most builders use 4 in. schedule 20 PVC pipe. Other
sizes can be used but 4 in. PVC is readily available and is
commonly used by builders for other purposes. Fans made
for use in sub-slab systems are available in a variety of sizes
from many vendors. The fans normally used are rated in a
range of 90 to 150 cfm at no static pressure. Manufacturers
of fans used for radon reduction are fairly quick to improve
their products on advice from the people who are using their
products. When the radon industry first started, many of the
fans leaked at seams and joints, and required disassembly of
the fan to seal those openings. Most manufacturers now
supply fans that do not leak, but builders should be aware
that this problem did exist and may still exist in some fans.
Additional materials and components that are normally
included in a system satisfy safety needs, system performance
indications, and common sense.
Service switches should be placed within view of the fan
to ensure that the system will not be activated while mainte-
nance is in progress.
Systems should be clearly marked as a radon reduction
device to ensure that future owners of the building do not
remove or defeat the system. An operation manual describ-
ing the system and its purpose should be made available.
Some type of device should be included in the system to
advise the owners on system performance. These devices
may be simple pressure gauges that tap into the pipe and
measure and display the pressure in the exhaust pipe. A
visual check of the gauge will alert the homeowner to
possible system malfunctions. Electronic pressure sensing
devices that illuminate a warning light or sound an audible
alarm when a pressure drop occurs are also used but cost
more than a simple gauge indicator. It is advisable to use a
device that warns of a pressure change rather than something
that warns that the fan is not running because there are
several things that can stop a system from operating effectively
that do not effect the fan.
Rain caps at the end of the pipe are intended to keep rain
from entering the system. Builders use various cap designs
for this purpose. The use of rain caps can cause a loss of air
flow in a system, which may lessen the effectiveness of the
system. It is advisable to use a rain cap that is designed in
such a way as to not seriously impede airflow. For more
information on rain caps and stack design, see the ASHRAE
1985 Fundamentals Handbook, Chapter 14 (ASHRAE85).
Attention to detail during the installation process will
help ensure the proper operation and long life of the system.
Starting at the floor slab, seal the void between the pipe and
the floor slab with a non-shrink grout or a flexible, highly
adhesive sealant. Place a sticker or other labeling device on
the pipe identifying the pipe as belonging to a radon reduction
system. Ideally a label should be placed at regular intervals
along the entire pipe run. A visual system performance
monitoring device should be placed in an area that is often
visited and in plain view of the homeowner. Audible alarms
can be placed in any area, as long as the homeowner can hear
them. It is a good idea to place alarm sensors in easily
accessible areas because they sometimes need adjusting. Run
the pipe as straight as possible to the attic to ensure proper
draining of condensation. The fan should always be located
in a non-living area as close to the exhaust as possible. This
is extremely important because a leak in the fan or in the
piping above the fan will blow the radon back out of the
pipe. If the fan is placed in the basement, and a pipe leak
occurs above the fan, radon laden air will be introduced into
the living area, and can cause radon levels to build to very
high concentrations. Most builders connect the fans to the
pipe system with rubber sewage pipe connectors. This allows
for the easy removal and replacement of the fan if that
should become necessary. Always install a service switch in
sight of the fan. Run the pipe through the roof and flash
well. If desired, cap the pipe with a rain cap.
3.2.5 Passive Sub-Slab Depressurization System
Components and Installation Details
A passive system is much the same as an active system
with the exception of the fan. A passive system relies only
on stack and wind effects to produce the pressure field. As
can be seen on Table 3.1, passive systems do not always
reduce radon concentrations to acceptable levels, but careful
design and installation may improve .the effectiveness of a
passive system.
16
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Flashing
Rain cap
Centrifugal fan
Service
switch
Sewage line
couplers
Alarm system
Identification
label
Caulk joints
and
seams
Figure 3.3 Typical Sub-slab Depressurizatlon System.
4 in. crushed
gravel D.O.T.
#2
It is probably beneficial to a passive system to lay a
network of perforated drainage pipes in the gravel bed beneath
the slab prior to the pour. The use of horizontal pipe runs
and elbows in a passive system may greatly lessen the effec-
tiveness to the system and should be avoided. Some builders
use 6 in. PVC in a passive system to help lessen the pressure
drop.
3.3 A Crawlspace Post-construction Alternative
Due to difficulties often encountered in sealing subfloors
and insulating pipes in crawlspace houses, which rarely have
a poured floor slab, 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 crawlspaces. The polyethylene sheeting can
be used as a gaslight 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 should be set directly
on the earth in a way that produces at least 1-ft overlaps.
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. A good seal is obtained
by spraying both surfaces of the polyethylene, allowing time
for them to get tacky, and pushing the two pieces of poly-
17
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ethylene together. In locations where the soil surface is
exceptionally hard and smooth or the crawlspace is very
large, a drainage material can be placed under the sheeting to
improve airflow. 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 snips. The plastic sheeting may also be
sealed to the foundation walls to reduce air leaks. Some
retrofit applications of this crawlspace 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 with-
out sealing. When this technique is used, a complete sealing
job is recommended for greatest protection. Application of
this technique may not be appropriate in crawlspaces that
receive heavy traffic.
Some builders prefer to concrete the floor of crawlspaces
when site and design conditions permit getting the mix into
the crawlspace. If a crawlspace has a concrete slab, for
radon-resistant construction the crawlspace should be treated
similar to a basement with the advantage of greater ventila-
tion potential.
18
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Section 4
Mechanical Barriers
Introduction
This manual has presented four topics concerning radon-
resistant construction issues. Discussed in this manual are
techniques to:
1) prevent radon entry by using a sub-slab
depressurization system
2) prevent radon entry by using mechanical barriers
3) reduce radon and radon entry with planned
mechanical systems
4) determine the potential for a radon problem by
evaluating the site.
This section addresses the mechanical barrier approach,
Section 3 addresses building in a sub-slab depressurization
system. Section 5 discusses site evaluation. Section 6
addresses a ventilation system planned to supply outdoor au-
to the house, and reduce,the pressure differentials that drive
soil-gas into the building.
Theoretically, a gaslight barrier could be placed between
the soil and foundation to eliminate radon entry from the
soil. Like many other building details, it is much easier to
draw such a detail than to actually install it. Many materials
form effective retarders to gas transport. The problem is
effectively sealing cracks, joints and penetrations. As any-
one who has tried to build an airtight house can tell you, it is
not as easy as it seems.,
The types of mechanical barriers that have been tried or
suggested for radon control, fit into one of the following
categories:
foundation materials themselves
coatings
membranes
possibility of a "site" barrier.
Ongoing EPA research on radon-resistant new construc-
tion has encountered numerous difficulties in making a
gaslight mechanical barrier effective enough to confidently
keep indoor radon levels below 4 pCi/L. The types of
problems encountered included quality control on the job;
incomplete communication between researchers, contractors
and subcontractors; reluctance of builders to change drainage
detailing; and the smallness of the radon atoms.
The first problems on the list are not specific to radon
control but are encountered on nearly every construction job.
In spite of quality control and communication problems, and
the understandable wariness builders show when asked to
build something in a different way, the residential construc-
tion industry has responded to new techniques, materials and
public demands. The average house being built today is very
different than a home built 10 years ago. If a product or
method can be demonstrated to reliably keep radon out with-
out presenting significant problems with cost, scheduling or
installation, many builders would learn to use it The major
difficulty faced by mechanical barrier approaches is the thor-
oughness that seems lo be required to ensure that no radon
problem will occur.
In 1988 and 1989, EPA projects studied newly con-
structed houses which incorporated mechanical barriers and
provisions for active and passive sub-slab depressurization to
determine the effectiveness of each approach. Preliminary
results from these five studies found that, when there was a
source of radon beneath the houses, the mechanical barriers
were not adequate to ensure basement levels below 4 pCi/L.
However, there is no way to judge how high the radon
concentrations in these buildings would have been had the
mechanical barriers not been employed. These data should
not be used as evidence that the barriers used (or that me-
chanical barriers in general) do not reduce radon levels in-
doors. In fact there are good reasons to employ barriers to
enhance the performance and reduce the energy penalty of
soil depressurization techniques.
When trying to make a barrier to soil gas entry, the
routes of concern in new construction are the same as those
that have previously been identified for existing houses.
These entry routes are covered in Part 2, the Overview.
Houses that are combinations bf the above substructures
often provide additional entry routes at the interface between
the two substructures. The following subsections address the
types of mechanical barriers (foundation materials, coatings
and membranes), the potential radon entry routes associated
with common foundation detailing, and suggestions for de-
tails that reduce the risk of elevated indoor radon. When
possible, these alternatives include barriers that can be used
to block radon entry while continuing to use traditional
construction methods. Depending on current local or regional
building practices, some of the suggestions may require sig-
nificantly different construction methods.
4.2 Foundation Materials
The materials used to construct a foundation can often
be used as an effective barrier to the entry of radon laden soil
gas. Below-grade walls may be constructed of poured con-
crete, masonry, or other materials such as pressure treated
wood or stone. The materials covered in this section, poured
concrete and masonry block, are the most common for new
19
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construction. Details for radon protection in permanent wood
foundations can be found in a National Forest Products
Association publication entitled "Radon Reduction in Wood
Floor and Wood Foundation Systems" (NFoPA88).
In residential buildings, foundation walls made of poured
concrete are generally constructed to a compressive strength
of 2,500 to 3,000 psi. The forms are held together with
metal ties that penetrate the wall. A poured concrete wall is
a good barrier to radon transport. The major weaknesses in
this regard are cracks, joints and penetrations. It is these
openings in the walls that allow soil gas to enter the building
without actually having to diffuse through the concrete. It is
recommended that concrete walls be built in compliance with
guidelines established by the American Concrete Institute
(ACI332R-84). Such concepts as cover mix, reinforcing,
slump, temperature, vibration and a variety of other factors
help to keep the foundation from cracking.
Residential foundation walls built of concrete masonry
units may have open cores, filled cores or cores closed at the
top course. Masonry walls are frequently coated with an
exterior layer of cementitious material, referred to as "parg-
ing," for water control. This coating is usually coved at the
bottom of the wall to make a good exterior seal at the joint
between the footing and the block wall. Uncoated block
walls can range in porosity depending on the type of aggre-
gate used. Uncoated blocks are neither an effective water
nor radon barrier. It is recommended that concrete block
walls be built according to guidelines issued by the National
Concrete Masonry Association (NCMA72). Their publica-
tions cover thickness of block, reinforcing, pilaster location,
control joints, sequencing and other issues that prevent
cracking or foundation failure.
There are geographic areas throughout the U.S. in which
the majority of foundation walls are poured concrete and
other areas where masonry walls predominate. Poured con-
crete walls are generally available only in areas where con-
tractors have the in-house expertise to build them and either
rent or have invested in reusable forms. In areas where both
types of construction are found, the costs of each seem
competitive.
There are building codes that dictate dampproofing or
waterproofing treatment for both type foundations. The
treatments can also inhibit gas movement through the wall.
Concrete blocks are much more porous than poured concrete,
although the parge or waterproofing coats moderate the dif-
ference. Recent laboratory tests have confirmed that uncoated
concrete masonry walls allow substantial airflow, but that
there is a great deal of variation in the porosity of blocks, due
mainly to the use of different aggregates by the block manu-
facturer. Block walls can allow substantial soil gas circula-
tion in the cores of unfilled blocks, providing an area source
of radon. Various measures are available to alleviate this
problem, including exterior (or interior) gas barrier membranes
and solid or filled block tops.
Although it is clear that concrete blocks are more porous
than poured concrete, some studies reveal no strong correla-
tions concluding that a home built with a concrete block
foundation is more likely to have a radon problem than one
built with a poured concrete foundation. A New Jersey study
(Ru88) found mean radon concentrations in 581 basements
with poured concrete walls of 6.3 pCi/L ± 14.1 % and that the
mean concentration in 3408 basements built with concrete
block walls was 5.7 pCi/L ±11.1%. There is no statistical
difference between the two means. A survey conducted in
Connecticut (Si90) in a smaller sample population revealed a
geometric mean radon concentration of approximately 1.7
pCi/L in 755 homes with poured concrete foundations. The
same study revealed a mean concentration of approximately
2.0 pCi/L in 129 homes with block foundations. The
amount of error in the two means is not known at the time of
this writing; however, it is suspected to be significantly high
enough to show no statistical significance between the two
means. It is one more example of a variable that would seem
to have an effect on indoor radon concentrations not meeting
those expectations. The expected effect is lost in the com-
plex interaction of the far more important factors that affect
radon source strength and transport. It is interesting to note
that the 639 stone foundations tested had mean basement
radon concentrations of 6.2 pCi/L ± 10.1%, virtually identical
to the other two types of foundation walls.
4.3 Common Masonry Wall Details and Their
Impact on Radon Resistance
4.3.1 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
termite-proofing, energy conservation, distribution of weight
of the structure and radon-resistance. The National Concrete
Masonry Association (NCMA72) recommends that a solid or
grouted top course be installed to distribute the loads of
joists and beams. Some building codes require solid tops to
block hidden termite entry. In spite of this, the block tops in
many residences are left open except at anchor points. Houses
have been observed in which block tops were generally
sealed, but cores were left unsealed at access doors to
crawlspaces, around ash pit doors and other openings. Seal-
ing hollow cores at or near their tops can prevent soil gas
from entering the basement, but more importantly might
make the building easier to mitigate in the event that it has
elevated radon. Sealing the bottom course might prevent air
beneath the slab from entering the block wall, but if the wall
cores are used as part of a water control method it may not
be possible.
It is recommended for potential radon control to seal
open blocks at the time of construction.
Block tops have been successfully sealed using :
mortar mixed with plastic binder to fill the top
cores (quality control and shrinkage can be
problems)
"Termite caps" - cored blocks with a 2-in. thick
solid cap as the top course
solid or lintel blocks to seal one of the top
courses.
When solid blocks or termite caps are used, anchor bolts
must be placed in the joints between the blocks. Lintel
20
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blocks and grouted top courses allow for more flexible place-
ment
43.2 Masonry Watts with Weep Holes
Weep holes are used to drain water from the block cores
into the sub-slab area 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 srb-slab to the interior of the block
wall. Openings from the sub-slab into the block wall would
also make it more difficult to apply active sub-slab depres-
surization at a later date. If the block tops are sealed and the
interior of the block wall is sealed, then weep holes would be
much less of a problem as radon entry points or as barriers to
sub-slab depressurization.
The National Concrete Masonry Association (NCMA)
issues technical notes to provide contractors with guidance in
construction practice. The NCMA-TEK 43, Concrete Ma-
sonry Foundation Walls (NCMA72), provides illustrated
cross-sections of foundation walls showing weep holes through
the footing. These run from the exterior of the wall to the
sub-slab area, connecting an exterior drainage system to an
interior drainage system. This system does not directly drain
the block wall, but the combination of dampproofing and
exterior drainage should make it unnecessary.
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.
It has been 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, an exterior drainage system
should be installed.
It is recommended that, if weep holes are used, care
be taken that they do not present a radon entry path or a
barrier to later sub-slab depressurization. At this time the
best approaches appear to be either avoiding weep holes by
carefully planning and installing a drainage system that would
prevent water from entering the block walls or sealing the
block tops and interior of the block wall.
43.3 Stemwalls in Slab-on-Grade Houses
Stemwalls, also called frost walls, are below grade foun-
dations that support the load of the above grade walls and
thereby the roof. There is usually a footing beneath them at
some depth below the frost line. The major radon related
issue for these walls is the geometry of the slab/stemwall
joint This will be covered in the section on floors. If
stemwalls are constructed of concrete blocks then the block
tops should be sealed. See Sections 5.3.1 and 5.3.2.
43.4 Foundation Walls in Crawlspace Houses
Foundation walls in ventilated crawlspaces are substan-
tially different than walls in basements and unventilated
crawlspaces. In basements and slab-on-grade buildings it is
clear that barriers should be applied between the soil and the
foundation or be the foundation itself. With ventilated
crawlspaces there are two locations that present themselves
for the application of barriers. First, as in the other, barriers
can be placed between the soil and foundation. Secondly, a
barrier effort can be made between the crawlspace and the
upstairs living area at the floor deck. The second option will
be treated in Section 4.5. If the first option, making a barrier
between the soil and the crawlspace, is selected, then the
basement wall details that apply to sealing open blocktops
and preventing the foundation from cracking also apply to
the crawlspace walls.
4.4 Floors in Basements, Slabs on Grade, and
Crawlspaces
Concrete slabs are the only floors considered for this
sub-section. As already pointed out in the beginning of
Section 3.2, poured concrete is a good retarder for radon gas
and soil gas. The major problems will be cracks, joints and
penetrations. The focus of this sub-section will be on crack
prevention and sealing joints and penetrations. A good deal
of this material applies to both poured concrete and masonry
walls.
4.4.1 Crack Prevention
Plastic shrinkage cracking of concrete is a natural func-
tion of the drying process. Many factors come into play as
concrete cures, including water content, cement content, at-
mospheric humidity, temperature, humidity, air movement
over the slab surface and aggregate jntent. The preparation
of the sub-slab area is also important. Reinforcement can be
used to reduce shrinkage cracking. It has not been tradition-
ally mandatory in residential floor slabs. Residential build-
ers 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 ex-
ample).
There are many ways to minimize slab cracking, al-
though it probably cannot be eliminated entirely. The
American Concrete Institute (ACT) publishes a number of
documents outlining standard practice for building concrete
and concrete masonry structures. A number of these apply to
crack prevention. Specifically the reader is referred to
21
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ACI302.1R-80 Guide for Concrete Floor and Slab Construc-
tion, and ACI332R-84 Guide to Residential Cast in Place
Concrete. 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 re-
inforcement embedded in the slab increases its strength.
Woven wire mesh is the most common material for residen-
tial applications. For slabs on grade, the Council of Ameri-
can Building Officials (CABO86) One and Two Family
Dwelling Code recommends 6 x 6 in. - W2.9 x W2.9 woven
wire mesh. To help control cracking it has been suggested
that this is appropriate for a basement slab as well.
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/fL It would probably be installed in a garage slab
12 in. on center, leaving 3 in. at each end and running in both
directions.
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 titled State of the Art Report on Fiber
Reinforced Concrete (ACI544).
Water-reducing admixtures: Also known as plasticizers,
these admixtures reduce the amount of water used in the
concrete. This reduces shrinkage and cracking while in-
creasing the workability of the concrete. One example of a
plasticizcr is WRDA-19, by Grace Construction Products,
which is labeled "an aqueous solution of a modified naph-
thalene 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. See ACI212.1R-81, Ad-
mixtures for Concrete.
Fiber-reinforced concrete: Various fiber additives are
available that can reinforce poured concrete and reduce plas-
tic shrinkage cracking. Fiber reinforcing has the advantage
over woven wire mesh in that the fibers are homogeneously
distributed throughout the slab thickness. The type of fiber
used is important because studies have shown that the alka-
line 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 fi-
bers"), 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 in some fiber products is chemically stable in an alkaline
environment. 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. See ACI212.1R-81, Admix-
tures for Concrete.
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 cover-
ing it with wet sand, wet sawdust, or a waterproof film [e.g.,
waterproof paper, BurleneTM (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 2,500 to 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 in-
creases to 4300 psi. To achieve compressive strengths of
above 3500 psi, the slump cannot exceed 3 in. The com-
pressive strength and the slump of the concrete are no more
important, however, than the placability of the concrete or
the finishability of the surface. Unfortunately, placability
and finishability are not easily measured quantities like slump
and compressive strength, and often do not receive sufficient
emphasis.
4.4.2 Joints
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 de-
fenders and detractors alike. French drains are only a con-
cern in basement foundations. 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 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. French
drains can be sealed airtight and still preserve their 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 water-trapped drain in the sump lid drains
22
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Backer rod Self leveling urethane caulk
Sealed sump with
drainage channel
Water still free to move from blpck
core to sub-slab drainage layer
Figure 4.1 Sealing a French Drain.
water into the sump.
treatment.
Figure 4.1 shows a French drain
It is recommended that French drains be avoided if
possible because of the difficulty in sealing them at the time
of construction and the expense and difficulty of sealing
them after construction.
Perimeter Crack: The perimeter crack is located be-
tween the edge of the floor slab and the foundation wall.
This applies to slabs in basements, crawlspaces and slab-on-
grade foundations. 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.
A perimeter expansion joint is made of a closed-cell, flexible
foam strip. The expansion joint is presliced so that die top I/
2 in. can be pulled off to leave room for caulk. Another
approach is to tool the floor/wall joint with an edging tool
and seal it with caulk. Particular attention should be paid to
sealing this crack in slab-on-grade houses because the joint is
often inaccessible after the house walls are raised.
Control Joints: When large areas of slab are poured,
some cracks are unavoidable. There will be cold joints
because the slab was poured in small sections to avoid
cracks, or the slab will crack because the pours were too
large. To direct the inevitable cracking that will occur in
either case, a control joint can be made by grooving the
surface of the slab. The groove should be large enough to
seal with caulk. Cold joints can make use of the same
expansion joint materials that have a "zip off top that was
described for the slab edge crack.
4.4.3 Penetrations
Every house has some minimum of penetrations through
the slab or foundation walls. The ones always present are :
water pipe entry
sewer pipe exit.
Common additional penetrations are:
floor drains
sump holes
air conditioner condensate drains.
Openings around water pipe entries and sewer exits that
pass through concrete can be easily sealed using caulks.
Many builders use plastic sleeves to protect metal pipes from
corrosion when they pass through concrete. In this case an
effort can be made to leave a space around the pipe that can
be sealed with caulk or backer rod and caulk. The same
techniques can be used for pipes passing through block
walls.
Depending on the details of a. floor drain, a great deal of
soil gas can enter through large openings to the drainage
matrix. This is true not only of slop drains that are simply
holes through slabs into the sub-slab area, but also of other
types of drains. Even water trapped drains with water in the
traps can allow radon an entry passage where the dish shaped
bottom of the drain seats into the drain pipe. It is recom-
mended that floor drains connect to pipe that drains to day-
light using solid PVC pipe glued at the joints, or that water
trapped drains or mechanical traps be installed that do not
have unsealed joints on the room side of the water trap.
Sump holes are usually a collection point for the drain-
age system. Almost by definition this is a terrifically good
radon collection system. It must have access to large areas
of soil beneath the foundation so it is easier for water to run
into the sump than to penetrate the foundation. It is better if
there is no open sump at all. A sub-slab drainage system that
can drain by gravity to a daylight opening serves the same
purpose as a sump hole but offers no fewer radon entry
routes. If this is not possible then the sump hole must be
sealed (a code item in some places to keep children from
23
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playing in them). Sumps can be sealed airtight and still
function as a water collection and removal system by routing
the interior and/or exterior drainage pipes or layer into the
sump. The sump hole is then sealed with a corrosion resis-
tant lid that is recessed a few inches to create a shallow
sump. The lid is fitted with a water trapped drain so water
that happens across the floor will end up in the sump.
Lastly, a low profile sump pump is installed to eject any
water collected in the sump through a check valve to ap-
proved disposal. This detail is illustrated in Figure 4.2.
Air conditioner condensate lines are sometimes installed
so that they penetrate the slab to dispose of the water in the
sub-slab area. Even when water is trapped, this can be a
problem because the traps often dry up during the heating
season. At this point they become radon entry routes. It is
recommended that air conditioning condensate lines run to a
drain that will not dry out or that a condensate pump be
installed that collects the condensate and disposes of it through
a water trap. Often a washing machine drain is located in a
basement near enough to use it
Sealants for Cracks, Joints and Penetrations: Masonry
sealants for radon-resistant applications must have good ad-
hesion and be durable and elastic. Polyurethane comes in
gunnable grades, and one- and two-part self leveling types.
Self-leveling urethanes can be used only on level surfaces as
they are very mobile. In fact if there is even a small crack at
the bottom of a joint being sealed, the self leveling caulk
may drain out. The popularity of polyurethane is based on a
combination of good adhesion even under difficult condi-
tions, long service life, good elasticity and easy availability.
Copolymer caulks have very similar properties to the poly-
urethancs. Recently some copolymer caulks have been pack-
aged as sealants specific to radon control. Silicone caulks
have also been used in radon control but require more ex-
tensive surface preparation for good adhesion. Many radon
mitigators have adopted the use of silicone caulks for sealing
sump lids and access ports because they make a tight-fitting
gasket that can be removed more easily than polyurethane at
a future date. 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.
Surfaces should be clean and dry when caulk is applied.
Bear in mind that the idea is to get a flexible membrane to
bridge between the two surfaces that the crack divides. It is
a poor practice to simply fill every crack. Manufacturers
usually specify appropriate dimensions for their caulks. Of-
ten this is a minimum 1/4 x 1/4 in. For small cracks, it may
be necessary to grind them larger to meet the caulk manufac-
turers' specifications. For cracks much larger than 1/4 in., a
backer rod should be used to support the caulk so that it can
be applied correctly.
CAUTION: Caulks give off organic compounds. Some
of these are carcinogenic. Users are reminded here that they
should have the Manufacturers Data Sheets for any chemi-
cals they use. These sheets identify hazardous aspects in the
use of the products. OSHA requires that contractors have
these sheets available for employees and that a safety training
program be in effect for these products.
4.5 Crawlspaces
Crawlspaces are being treated here as a special case of
using the foundation materials to make a mechanical barrier.
In this sub-section isolating the living space from the
crawlspace by sealing the floor between the two spaces will
be discussed. A sheet of plywood is a relatively good barrier
to radon laden crawlspace air and, as with the other material
barriers, it is the joints and penetrations that are the prob-
lems. The major entry points are through numerous electri-
cal, heating, and plumbing penetrations in the house floor
and via the return air ducting often located in the crawlspace.
Lower air pressure in the house and the return air duct than
in the crawlspace draws radon laden crawlspace air into the
living space of the house.
During construction, all possible penetrations between
the crawlspace and the house should be sealed to simply
prevent the passage of radon up into the living areas. At-
tempts to seal penetrations can be made by using expandable
closed-cell foam sealants and urethane caulk. Sealing these
areas can be difficult because of limited access even during
construction. Areas of particular concern include:
1) openings in the subfloor for waste pipes
including openings for tubs, toilets, and showers.
2) openings for water supply lines.
3) openings for electrical wiring.
4) openings for air ducting for the heating,
ventilating, and air conditioning (HVAC)
system.
5) openings around hot water heating pipes --
Check on code requirements for clearance
between hot water pipes and wood floors. These
may require a special sealant.
6) joints between sheets of plywood.
Any sealing around plumbing traps must be done so that
the trap can still be reached and serviced.
Return air for the HVAC system should not be supplied
from the crawlspace. It is best to avoid routing return air
ductwork through the crawlspace, but if it must be, then it
should be thoroughly sealed with duct tape at a minimum. It
should be understood, however, that duct tape may dry out
and fall off. A better approach would be to use seamless
ductwork in these areas. 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 use a rectangular duct to fit the space.
If isolation of the crawlspace is the primary method of
radon-resistant construction being used, the number and size
of crawlspace 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
1 ft2 of vent for each 150 ft2 of crawlspace. The proposed
guideline also requires that vents be located to provide good
circulation of air across the crawlspace and should not in-
clude registers or other provisions for closure. This require-
ment would be impractical in cold climates with water pipes
in the crawlspace. If there were no water pipes to worry
24
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Slab
Water
trapped
drain
Sump
pump
Check valve
Cover sealed to
shallow sump
i Drainage
layer :':. "'
Figure 4.2 Sealing a Sump Hole to a Shallow Yet Operable Sump.
about, then the floor would need to be well insulated in order
to ensure that a large energy and comfort penalty was not
incurred.
Other radon-resistant alternatives besides simple isola-
tion of the crawlspace should be considered because of the
difficulties encountered in getting an adequate seal between
the house and the crawlspace. These alternatives will be
discussed in Section 5.
A NEWHEP builder in Denver uses an innovative foun-
dation 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. Cais-
son 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 crawlspace" is actively ven-
tilated by installing a sheet metal inlet duct in one corner of
the basement, drawing in outdoor air through an above-
ground vent. A similar duct with an in-line fan is located at
the opposite comer to exhaust air through an above-grade
vent Soil gas radon at levels from 3,163 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 crawlspaces 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 4.3 (Mur88).
4.6 Coatings
4.6.1 Introduction
If waterproofing or dampproofing treatments that are
effective gas barriers and that can be sealed at joints and
penetrations could be identified, then walls could be made
radon-resistant Acceptable dampproofing or waterproofing
treatments are specifically listed in building codes in many
Table 4.3. Results Using Vented Crawlspace Technique
Burled Crawl- Basement
House Fan space Level Level
No. Operation pCi/L pCi/L
1
1
1
2
2
2
3
3
Off
On 2 Weeks
On 2 Weeks
Off
On 1 Week
On 1 Week
On 1 Day
On 1 Day
9.9
9.9
8.4
27.8
18.6
16.7
26.4
15.5
1.9
1.4
1.4
1.8
1.2
0.9
1.3
0.9
NOTE: Followup 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 crawlspace and careful seal
ing and caulking of all seams, joints, and penetrations of
the basement floor (Mur88).
areas of the United States; these lists are periodically amended
as new materials come into use. These coatings apply prima-
rily to basement walls.
The terms "waterproofing" and "dampproofing" are of-
ten used interchangeably. Briefly, any waterproofing mate-
rial 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.
The most common dampproofing treatment for residen-
tial 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-
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stage treatment has been replaced by surface bonding cement
in some areas.
Oak Ridge National Laboratory indicates that bitumi-
nous asphalt may be attacked by soil and groundwater
chemicals, specifically acids (ORNL88). Bituminous materi-
als may also lose their elasticity at belowrfreezing tempera-
tures. 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.
A number of dampproofing systems are better gas barri-
ers 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 house-
holds by Owens-Corning Corporation (Da86) found that 59%
of homeowners with basements reported water leaks. As the
supply of trouble-free building lots dwindles, home buyers
may decide that additional investment is justified, and im-
proved dampproofing systems may be developed to address
radon and water problems simultaneously.
4.6.2 DampprooJing/WaterprooJing to Achieve a
Radon Barrier
The following is a sampling of alternative waterproofing
systems that are readily available to builders.
Coal tar modified polyurethane: Coal tar modified poly-
urcthane is a cold-applied liquid waterproofing system. The
HLMTM system by Sonnebom is an example of this ap-
proach to waterproofing. It is applied as a liquid at the rate
of 10-15 mils/coat. 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 (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
HLMTM system mentioned above, the quality of the instal-
lation depends on the applicator (it is difficult to achieve an
even coating on a vertical surface). High grade polymer-
modified asphalt is superior to coal tar modified polyure-
thane in elasticity, crack-spanning ability, and resealabilky,
but inferior in its resistance to chemicals.
Membrane waterproofing systems: Waterproofing ap-
plied 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 purging 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. Thermoplas-
tic membranes may be applied in various waysaffixed to
walls, or laid .beneath slabs. Thermoplastic membranes are
highly rated for resistance to chemicals and longevity. Rub-
berized asphalt polyethylene membranes have superior crack-
bridging ability, compared to fully adhered thermoplastic
membranes. (Loosely hung thermoplastic membranes, by
their nature, have obvious crack-bridging ability in that they
are not bonded to the walls.)
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.
Manufacturers' recommendations for sealant, procedure and
safety precautions should be followed.
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 environ-
ment of Portland cement
One technique of assembly using surface bonding ce-
ment 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.
Cementitious waterproofing: A number of additives can
be incorporated into concrete to create cementitious "water-
proofing." This type of waterproofing is appropriate only for
interior applications because it is inelastic, does not have
good crack-spanning ability, and cannot resist hydrostatic
pressure.
Interior paint as a barrier: A variety of interior applied
masonry paints are available. Some of these have been tested
by the AEERL laboratory at the EPA. Results of these tests
are given in a paper presented at the 1988 Symposium on
Radon and Radon Reduction Technology (Har88).
4.7 Membranes
4.7.1 Introduction
Membranes of plastics and rubbers that are used to
control liquid water penetration and water vapor diffusion
are effective at controlling air movement as well. If they can
be adequately sealed at the joints and penetrations and in-
stalled intact, then they could also provide a mechanical
barrier to radon entry.
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
26
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barrier. It is possible to seal polyethylene vapor barriers at
the overlapped edges, at penetrations, and at the footing; but
it may be that the extra effort will not be rewarded with
improved radon resistance.
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 ac-
knowledged; 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.
In summary, it is worthwhile to continue the installation
of a vapor barrier that serves the added valid function of
moisture barrier. More comprehensive installation measures
and more expensive materials may be merited in areas where
the radon source is strong because of either high radon
concentrations or high soil gas flow rates.
4.7.2 Types of Membranes Available
Polyethylene film: A vapor barrier of polyethylene film
is a typical sub-slab feature in many areas of the country.
The intent of the vapor barrier is to prevent moisture entry
from beneath the slab.
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 indi-
cate 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 con-
crete tends to pull it away from the walls during the pour.
There is also a high probability mat 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 bar-
riers. 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. Durabil-
ity varies according to the additives employed, film thick-
ness, length of UV exposure, temperature swings, and other
factors. Resins used in polyethylene manufacturing have
improved over time, so that the life expectancy of polyethyl-
ene 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.
Polyethylene-coated kraft paper vapor barrier is avail-
able in 8 x 125 ft rolls. Overlaps of 6 in. are marked on the
paper with a printed line. They can be sealed with polyethyl-
ene tape. This material is attractive to contractors because it
is more puncture-resistant than 6-mil polyethylene construc-
tion film, but less expensive than many alternative products.
Polyethylene-based membranes are manufactured for use
in hazardous waste landfills, lagoons, and similar applica-
tions. Two of these products have recently been tested to
determine their effectiveness as barriers against radon diffu-
sion. (In most cases, diffusive flow is considered of little or
no significance as a mechanism of radon entry compared to
convective flow.) A 20-mil high-density polyethylene tested
99.9% effective in blocking radon diffusion under neutral
pressure conditions. A 30-mil low-density polyethylene tested
98% effective in blocking radon diffusion under neutral pres-
sure conditions.
A material composed of a double layer of high-strength
bubble-pack with aluminum foil bonded on both sides is
available. It has a high compression strength and doubles as
an insulator. Concern exists over its fragility and suscepti
bility to pinhole punctures. Both foil-faced membranes can
be punctured, but the double bubble-pack offers some defense
against complete penetration. Punctures are easily repaired
with aluminum tape, which is also used at seams. A well-
made seal is diffusion resistant; however, gas can migrate
through wrinkles in the tape. The fragility of the material is
believed to be a significant limiting factor in using it under
the slab or as a perimeter insulation.
Another available product has two faces of aluminum foil
over a core of glass scrim webbing; it is coated with asphalt.
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 other foil faced
products. Seams are sealed with aluminum tape.
PVC membranes have been used as a sub-slab mem-
brane during radon mitigation work in existing houses. PVC
membranes are usually sealed with solvents and were devel-
oped as roofing membranes.
Another product, EPDAf is a rubber-like material. It
comes in 60-mil thicknesses in 100 ft by 61-1/2 in. rolls.
EPDM also comes in 45-mil thicknesses in 25 by 60 ft rolls.
This product has gained popularity as a ground cover in
crawlspaces because of its durability qualities.
Note: EPA does not endorse any brand names or products mentioned in
this manual
27
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4.8 Mechanical Barriers Applied to the Soil
It has been suggested that mechanical barriers could be
applied to the soil beneath the foundation that would prevent
the migration of radon into the building. As of this writing
this is an untried approach. If it works it would have the
benefit of being less susceptible to occupant behavior, future
remodeling activities and mechanical failure of fans. Two
approaches have been brought forward. One would use an
injection of slurry composed of clay to dramatically reduce
the permeability of the soil. This technique is used in the
construction of lagoons, landfills and dams. The second idea
is to spray the soil surface with a polymer modified asphalt.
This technique has been used to cap landfills to control the
release of methane and other organic compounds.
4.9 Drainage Boards for Soil Gas and Radon
Control
Soil that was excavated from the basement is commonly
used as backfill against foundation walls. This should not be
the case where the site material contains clays and silts,
particularly organic clays and silts. If local soils are not
appropriate, the builder may use gravel to backfill.
Drainage boards are a substitute to backfilling with gravel.
Drainage boards have been used for a number of years,
partieularlyirrcommercial projects and underground houses.
Depending on the cost of hauling sand and gravel, a drainage
board may be a cost effective alternative.
It has been hypothesized that a drainage board which is
laid up against a house wall might provide an air buffer that
can break the pressure connection between the soil and the
house interior. This is rather like having a hole in your straw
when drinking through it. No systematic research has been
done on this topic.
4.10 Summary of Recommendations for
Mechanical Barriers
4.10.1 Rules of Thumb for Foundation Walls
Use reinforcing to limit cracking.
Seal pipe penetrations.
Cap masonry walls with bond beam or solid
blocks.
Dampproof walls (interior as well as exterior
on masonry walls).
4.10.2 Rules of Thumb for Slab and Sub-Slab
Barriers
Make a slab edge joint that is easy to seal
(tooled joint or zip-off expansion joint material).
Caulk perimeter crack and control joints with
polyurethane.
Reinforce slabs with wire mesh to help prevent
large cracks and use control joints - - caulk the
control joint.
Drain to daylight if possible, or to a drywell or
sewer. If you must use an interior sump pump,
seal it.
As a precaution, use interior footing 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).
These suggestions are illustrated in Figures 4.3,4.4 and
4.5.
Bond beam or
solid cap block
Reinforce walls and slabs
to reduce cracking
Coat interior wall
Dampproofing or
waterproofing
Exterior parge coat
and dampproofing
Membrane beneath
slab
Gravel drainage
layer i
Seal around pipe
penetrations
and at joints
Interior and/or
exterior footing
drain
Rgure 4.3 Summary of Mechanical Barrier Approach for Basement Foundations.
28
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Seal penetrations.
, and joints
Install membrane beneath slab
Permeable aggregate or
drain strip network
Figure 4.4 Summary of Mechanical Barrier Approach for Slab-on-grade Foundations.
Foam insulation
Install vents in
unvented
crawlspace
Stone pebbles under " *
slab
Vented Crawlspace
Unvented Crawlspace
Figure 4.5 Summary of Mechanical Barrier Approach for Crawlspace Foundations
29
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Section 5
Site Evaluation
Introduction
When siting new residential construction, builders would
like to determine the potential for radon problems associated
with each building site. Unfortunately, at present there are
no reliable, easily applied methods for correlating the results
of tests made at a building site with subsequent indoor radon
levels contained in a house built on that site. Houses vary
significantly in their ability to resist radon entry. Bedrock
and soils interact in complex ways with dynamic house
behavior and environmental factors. There are too many
combinations of factors that cause elevated indoor radon
concentrations for simple correlations to exist.
In an effort to evaluate the risk of an indoor radon
problem occurring in a home built on a particular site, re-
searchers have made many types of measurements. The mea-
surements commonly made include:
soil and bedrock radium concentrations
radon measurements in the interstitial soil and
bedrock pores
permeability of the soil or bedrock
airborne radiation measurements.
In addition to the above measurements, indexes using
soil concentrations in combination with permeability mea-
surements have been suggested by some researchers (Ku88,
Pe87). As elaborated on later in this section, these methods
have been successful in establishing relationships between
some of the site measurements and indexes, and indoor radon
concentrations for specific areas and regions.
Although substantial progress has been made by investi-
gators using geologic, radiation and other site data to predict
areas of high radon risk, it still requires many site measure-
ments to adequately assess a particular site. The judgement
that needs to be made is whether or not it is more cost
effective to make the building radon-resistant to begin with,
or to put the money into site evaluation and possibly avoid
the need for radon-resistant construction techniques.
5.2 Radon in the soil
In buildings with indoor radon concentrations greater
than 4 pCi/L, the majority of the radon is produced in the soil
and enters the building through foundation openings. The
radon gas found in soils is a product of the decay of radium-
226, a radioactive chemical element present in trace levels
in many types of soils and rocks. Radium and radon are
elements that are part of the uranium-238 (U-238) decay
series. See Figure 2.1 for details. Uranium-238 decays
through a chain of radioactive elements. Radiation is re-
leased as each element decays. Radon will move through the
porous soil or shattered bedrock by convection and diffusion
because it is a gas. The other elements in the U-238 series
will not easily move through the soil because they are par-
ticles and not gases. The amount of radon that enters the
house depends on the amount of radon gas or radon parent
compounds 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 along path-
ways into the house also contribute to the total radon levels.
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.
5.2.1 Attempted Correlations Between Indoor
Radon and Measurement Made at Sites
Several studies have attempted to make simple correla-
tions between radon or radium concentrations in the soil and
indoor radon concentrations (ERDA85, Na87). No signifi-
cant correlations were made between these variables.
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.
The two highest soil radon values were 6587.0 and 6367.2
pCi/L. Interestingly, corresponding indoor radon levels for
the two highest sites 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.
The Florida data reported by Geomet have been evalu-
ated and the houses listed in order of highest measured
indoor radon levels. This analysis is shown in Table 5.1
(Pu88 and Na87).
It is clear from Table 5.1 that soil radon measurements
which varied over an order of magnitude produced signifi-
cantly 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 high,
normal, or low radon risk potential based on soil radon
concentration and soil permeability. The soil radon values
and permeability characteristics used to establish the soil
31
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classifications and the corresponding construction require-
ments are given in Table 5.2 (Sw82). Factors other than soil
radon that are considered before classification in Sweden are
permeability, ground humidity, and soil thickness. Clearly
Sweden has decided that a number of factors must be ad-
dressed to evaluate the radon problem potential of a site.
Using the suggested soil radon concentrations but not the
permeability guidelines included in the Swedish soil classifi-
cation scheme, no building restrictions would have been
required for many of the houses surveyed in Florida with
indoor radon measurements greater than or equal to 4 pCi/L.
Fifteen of the houses in the Florida study with measure-
ments greater than or equal to 4 pCi/L had soil radon con-
centrations less than or equal to 200 pCi/L. This corresponds
to 13.5% of the houses with soil gas less than 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.
Table 5.1 Florida Survey Soil Radon and Corresponding Indoor
Radon Concentrations.
Indoor Radon Concentration
pCI/L
Soil Radon Concentration
pCi/L
32.4 1591.1
29.5 1846.9
28.0 786.9
25.3 555.9
25.3 200.1
25.0 353.9
24.1 439.7
22.9 3561.3
22.9 2144.5
Table 5.2 Swedish Soil Risk Classification Scheme and Build-
Ing Restrictions.
Soil Radon Permeability
Concentration of Soil
pCI/L
Risk Building
Classification Restrictions
<270
270-1350
>1350
Very low permeability
(e.g., clay and silt)
Low
Use conventional
construction
Average permeability Normal Use radon-protec-
tive contruction
High permeability
(e.g. gravel and
coarse sand)
High
Use radon-safe
construction
The Florida survey was an ideal opportunity to compare
soil radon and corresponding indoor radon levels in slab-on-
grade construction. By looking exclusively at slab-on-grade
houses, additional variables, including depth below grade of
basements, and height and ventilation rates of crawlspaces,
are eliminated. These variables, which are inherent in com-
mon construction techniques used throughout much of the
rest of country, exaggerate the difficulty correlating indoor
air radon and soil radon levels.
The major drawback in using the Florida study to sup-
port the correlation between indoor and soil measurements
was that the 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 de-
ployment of alpha track detectors 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.
5.2.2 Indexes using Permeability and Soil Radon
Concentrations
By making an index from the product of soil radon
concentrations and soil permeabilities, a better assessment
can be made of the risk of a problem on a given site. A
Radon Index Number (RIN) has been applied to three areas
in New York state that have sandy, gravelly soils and pre-
dicted with some confidence the geometric mean of indoor
radon concentrations using the geometric mean of the soil
radon concentrations and the geometric mean of the square
root of the soil permeability (Ku88). The results of this
effort are summarized in Table 5.3. This research also points
out barriers when applying this technique more widely with-
out a substantial amount of additional work. First, the index
must be modified by a depth factor when the soil depth to an
impermeable layer (water table, some bedrock, clay) is less
than 10 ft. Second, the soil radon concentrations in all three
areas were typical of most soils in New York state only. They
ranged from slightly below to slightly above the statewide
average for radon levels in gravel.
Using the permeability and soil radon measurements for
the gravel soils in New York state to compare to the Swedish
guidelines would result in a recommendation for radon-resis-
tant techniques to be used in a large fraction of new houses
in all the areas listed except Long Island.
Table 5. 3 Geometric Means for Soil Gas Radon-222, Soil
Radium-226, Permeability, RIN and Indoor
Radon- 222.
Study Area Soil Gas Soil Permeability RIN* Basement
(Soil Type) Rn-222 Ra-226 Rn-222
pCi/L pCi/g cm2 x 10-6 pCi/L
Cortland Co.
(Gravel)
Albany Co.
(Gravel)
Rensselear Co.
(Gravel)
State Wide
(Gravel)
Long Island
(Sand)
Onondaga Co.
551
675
1,003
602
164
1,671
NA
1.0
1.0
1.2
0.4
2.8
12.0
6.7
1.1
4.1
0.22
0.12
19.0
18.0
11.0
12.0
0.8
9.0
17.2
20.2
9.4
NA
1.0
6.1
* RIN = 10 [soil gas radon (pCi/L)](permeability) 0.5
32
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In EPA Office of Radiation Program's New House
Evaluation Program (NEWHEP), two builders in the Denver
area, two in Colorado Springs, and one in Southfield, Michi-
gan, installed various radon-resistant features in houses dur-
ing construction. A sampling of subsequent measurements
of indoor radon, adjacent soil gas radon, and soil radium
content is summarized in Table 5.4 (Mur88).
The major difference between these data and the Florida
survey data in Table 5.1 is that this portion of the NEWHEP
data was collected from newly constructed houses where
passive radon-resistant construction features were being tested.
There are no data on control houses in the same area that did
not have those built-in features, making it difficult to com-
pare soil radon measurements to indoor radon concentrations.
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 experi-
menting with or are considering the installation of active,
fan-driven sub-slab ventilation systems. Results are being
monitored (Mur88).
Table 5.4 Indoor Radon and Soil Radon Measurements In
Colorado and Michigan.
Indoor Radon
House In Basement
No. pCi/L
HECO 7300
HECO 7395
HECO 7395
HECO 7419
HECO 7423
HECO 7423
HECO 7425
HECO 7425
HECO 7427
HECO 7427
HECO 7448
HECO 7455
HECO 7456
HECO 7458
HECO 7458
HECO 7459
HECO 7459
HEMI 30001
HEMI 30002
HEMI 30003
HEMI 30004
HEMI 30005
5.9
14.5
16.7
5.7
7.9
1.5
3.0
11.8
0.7
2.3
7.2
3.5
0.9
1.8
0.9
4.2
1.7
3.6
Radium-226
Soil Gas Radon In Soil
pCi/L pCi/g
710
1002
1779
620
1430
1316
930
1240
996
2030
388
1095
1014
.
__
_,_
1.3 (90 cm)
.3 (Surface)
.9 (90 cm)
.3 (90 cm)
.4 (90 cm)
.3 (Surface)
0.7 (90 cm)
1.1 (Surface)
1.4 (90 cm)
0.4 (Surface)
0.6 (90 cm)
1.0 (Surface)
1.9 (30 cm)
* Radium-226 in soil was measured at two lots in this housing devel-
opment. 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 existence in this same geological area.
52.3 Variations in Spatial and Temporal Soil
Gas Concentrations
Aside from the difficulty correlating soil radon measure-
ments 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 soil-gas and
permeability measurement device that allows soil-gas to be
sampled at various depths. In this study the radon concentra-
tion 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 concentration measurements in each
of the seven yards varied by factors of 1.3 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
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. The average
variation for each of the seven houses was 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 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). In another
seven home study in the Piedmont area (Se89) large variabil-
ity in permeability measurements and soil gas radon concen-
trations was seen. Spatial variation in soil permeability at
individual homes ranges from a factor of 10 to 10,000.
Temporal variations in soil permeability at a given test hole
ranged from a factor of 2 to a factor of 90. Spatial variations
in soil gas radon ranged from less than a factor of 2 to a
factor of 200 for a given site. Temporal variations in soil gas
radon from less than a factor of 3 to a factor of 40 for a given
test hole.
As indicated from the data, indoor radon concentrations
cannot yet be predicted from soil radon values. The possi-
bilities are not promising for designing a device and/or tech-
nique 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 re-
quired 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 foundation hole
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 can only be evaluated on a
community wide basis at this time. There is hope that these
data can be used statistically to predict large areas with a
33
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high probability of residential radon problems. Work to
enhance the accurate prediction of radon-prone areas is con-
tinuing within EPA and among other research organizations.
5.3 Radon Observed in Nearby Houses
Another approach to estimating the risk of a radon prob-
lem on a particular site is to examine measurements from
nearby existing houses. In EPA's Radon Reduction Demon-
stration Program for existing houses, those with elevated
radon levels generally have been identified through prior
high-radon measurements in other houses in the neighbor-
hood. 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,
homes 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 Pro-
tection (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 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 houses in a neigh-
borhood is at best only an indication that the probability of
having a radon problem has increased.
5.4 Airborne Measurements
The State of New Jersey has been able to correlate
airborne radiation measurements to clusters of buildings with
elevated indoor radon (Mu88). In this study, researchers
compared airborne gamma-ray spectrometer data to indoor
radon data to see if any trends emerged. For the conditions
in New Jersey it was found that areas with airborne anoma-
lies of 6 ppm equivalent uranium or greater were likely to
have clusters of homes with elevated radon. This could be a
valuable tool for health officials who are trying to make the
greatest public health impact for the most reasonable cost.
Inasmuch as it alerts a region to be wary, it is helpful, but it
is probably not of much benefit in the assessment of an
individual site.
5.5 Radon in Water
Between 2% and 5% of the radon problems found in the
U.S. can be attributed to radon in water (EPA87). The most
significant radon-in-water problems observed so far in the
United States have occurred in the New England states.
Houses with individual or community wells seem to have the
greatest potential for a problem since the water in those
systems is usually not well aerated.
Radon dissolves into groundwater from rocks or soils.
When the 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 (EPA87).
Higher radon levels have been observed in individual rooms
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. It should also be noted that radon
concentrations in water, like, radon concentrations in the air,
can vary significantly.
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 2.3.3. 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 con-
struction 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.
5.6 Radon in Building Materials
A small percentage of the buildings in the United States
with indoor radon concentrations in excess of 4 pCi/L can be
attributed to building materials. Most of the building mate-
rial 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 ra-
dium- or uranium-rich, the chance of obtaining radon from
building materials is very slim.
34
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Section 6
Planned Ventilation: Mechanical Systems
Introduction
New construction offers the opportunity to plan and
install mechanical equipment so that fresh outdoor air is
supplied to the living space and so that the air pressure
relationships between the inside of the building and the
outdoors reduce the influx of soil gas. This approach requires
a better understanding of moisture and airflow building dy-
namics than the others covered in this manual. For example,
it is important to understand what effect manipulating
interzonal air pressure differences will have on the risk of
condensation in the building shell, the entry rate of soil gas,
the comfort of the occupants or the risk of increased spillage
and downdrafting of combustion devices. By careful plan-
ning, the risk of these and other potential problems can be
reduced; however, no systematic research has been done to
evaluate this approach for radon control. Many variables
come into play in trying to design a mechanical system and
building shell that interact with the environment in the ways
best for the health of the occupant and the building itself.
6.2 Interdependence of Mechanical Systems and
Climate
Traditionally, residential mechanical equipment has been
treated as independent devices which have little or no impact
on the rest of the building other than the obvious stated
purpose. Bath fans, dryers and kitchen ranges are assumed
to exhaust moisture, lint and cooking by-products, but to
have no impact on the performance of chimneys. Instances
have been reported that show this is not the case, that in
some houses fireplaces and other combustion appliances
backdraft (CHMC84) when one or more of the exhaust fans
are in operation. Houses have been reported in which the
operation of exhaust devices increases the radon concentra-
tion (Os87b). Houses have been found in which pressure
differences between different rooms of the house caused by
HVAC distribution fans have increased energy costs (To88),
occupant discomfort (To88, Ne88), condensation in the
building shell (Ne88) and radon concentrations in parts of
the houses (Hu88, Ru88). All of these effects are the result
of air pressure relationships created by the interaction of
mechanical equipment, indoor/outdoor temperature differ-
ences, wind velocity, and moisture and radon availability.
To a large extent wind, temperature, moisture and radon
are beyond the control of the residential designer or builder.
True, good drainage practice and the techniques outlined
earlier in this manual can divert moisture and radon from a
building, but the amount of rainfall or radon produced is
independent of anything a builder can do. The pieces of this
house dynamics puzzle that the builder or designer can affect
are the mechanical devices used in the building.
6.3 Guidelines for Planning the Mechanical System
Specific guidelines for planning mechanical systems so
that they minimize problems resulting from their interaction
with each other and other climate-driven building dynamics
are impossible to determine at this point. The major reason
for this is that buildings constructed on different sites in
different climates have very different behavior. For an ex-
ample, a ranch house built in Florida has a warm, humid
climate with which to work. This means that the space
conditioning system is probably dominated by air condition-
ing and may also incorporate dehumidification. If the same
house were located in Arizona, the cooling need would be
there but there would be no need for dehumidification. If the
same house were built in Minnesota the space conditioning
would be a heating system and might require dehumidifying
in the summer and humidifying in the winter. In the Florida
house a case can be made for locating a vapor barrier on the
outside skin of the building because the risk of condensation
in the building shell is near the cooler indoor surface. In
Arizona, fliere is seldom the risk of condensation because of
the small amount of water present in the environment. In
Minnesota, the risk of condensation in the building shell
would be at the cool outside surface near the siding. In terms
of risk of condensation it would be acceptable to pressurize
the Florida house to control radon, because, as the outgoing
cool interior ah- is warmed up, the risk of condensation
decreases. Pressurizing the house in Minnesota is almost
certain to result in condensation during the winter months, as
the warm interior air cools down on the way through the
building shell.
At this time a cohesive body of knowledge that has
enough depth to make recommendations for different site
conditions within the several U.S. climatic regions does not
exist. However, many individuals do have enough insight to
design intelligently for their own regions, and there are
guiding principles that are general enough to apply for all
situations.
Guidelines: Preserve the intended purpose of all me-
chanical devices. A heating system should still deliver the
required amount of heat in a short amount of time. Exhaust
fans should remove the moisture, fumes and contaminants.
Be sure applicable codes and standards are followed:
Begin with the life and safety codes. The intent of this
manual is to reduce the risk resulting from radon, but not in a
way that increases other risks. Especially important in this
35
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regard are the National Fuel Gas Code (NFPA54), National
Fire Protection Code (NFPA1) and the National Electric
Code (NFPA70). Also the CABO One and Two Family
Dwelling Code (CABO86) will be very helpful. There are
thousands of code jurisdictions in the U.S., therefore many
issues will have to be dealt with locally.
Plan to reduce soil gas entry: If possible, plan the me-
chanical systems so that soil gas is not drawn in by lower
air pressure in the basement or ground floor rooms (slab-on-
grade and crawlspace). Efforts along these lines can be
made by minimizing the amount of air drawn from those
rooms by exhaust fans, conditioned air return ductwork leaks
and grills and sealing bypasses that penetrate floors. Air can
also be supplied to these spaces to make up for the amount of
air exhausted. If the exhaust air rate equals the supply air
rate for a single zone, then pressure differences should be
minimized. Supply air can cautiously be increased to pres-
surize these spaces and prevent soil gas entry, but the effect
on moisture dynamics, combustion equipment and code ac-
ceptability must be kept in mind. An example of this is the
relatively common practice of opening warm or cool air
supply grills in a conditioned basement. This uses condi-
tioned air and the air circulation blower to pressurize the
basement (or at least reduce the negative pressures).
Plan to supply air to the areas of the house that need
fresh air: A-planned mechanical system also allows the
builder to direct fresh air into the living spaces. This will
reduce radon concentrations by diluting it with outdoor air.
Depending on how it is supplied, it may also reduce the
driving forces that draw soil gas into the building. Supply
air will be drawn in by the mechanical devices, stack effect
and wind pressures that exhaust air from the building. The
incoming air will enter either through the unintentional cracks
and holes left in the building or through passive vents that
can be installed in the building shell. Passive vents allow the
builder to let the fresh air in where it is wanted. Bedroom
closets are a typical location. Supply air can also be powered
by a fan and ducted to the areas where it is wanted. Heat
recovery ventilators are a well established method of doing
this. In either case fresh air will be added and the pressure
difference between inside and outdoors will be reduced.
Caution: Take no risks with carbon monoxide. This is a
special warning to carefully ensure that combustion products
are properly exhausted from the house. Of course the place
to begin is with the appropriate codes (UMC, NFUC, CABO,
NFC) but keep in mind that even though something is not
against code it may still be dangerous. For example, a
system that backdrafts a fireplace because it removes air
from the upstairs of a house might not violate any codes, but
is certainly a hazard. Many new heating plants either are
power vented or have dedicated outdoor combustion air.
The two most generally applicable and useful guidelines
for planning are:
Air moves from higher to lower pressures
Lowering temperature increases relative
humidity
These two rules help to predict the effect of air exhaust
and supply on the transport of radon and moisture and whether
or not to expect increased or decreased risk of condensation.
6.4 Two Illustrations
Here are two situations illustrating the issues involved in
trying to understand the interactions between the mechanicals
and the climate. These are illustrations. They do not apply to
every house in the climates described.
First, consider a house in a cold, humid climate. The
way it ordinarily operates is as follows. The warm inside air
exits through cracks and holes at the top of the building. The
warm air leaving through these cracks and holes is cooling
down as it leaves, increasing the possibility of condensation.
The suction placed on the lower part of the building in-
creases the flow of radon laden soil gas into the basement
where it is drawn into the leaks in the cold air return and
distributed to the rest of the house by the warm air circulation
system. All of the pieces in this scenario are likely to occur.
Other things that could present problems might be bathroom
fans that do not have much airflow or are vented into the
attic.
If the upstairs portion of the house had the area of cracks
and holes into the attic and walls reduced, then exhausting a
small amount of air from the house would draw outdoor air
in through the remaining cracks and holes. This would
jeduce the risk of condensation in the building shell because
the air being pulled in would become warmer, lowering its
relative humidity. However, exhausting air from a tighter
house might increase the amount the furnace downdrafts and
the influx of radon.
Using a furnace that draws combustion air from out-
doors, or that is power-vented, solves the downdraft problem
and probably has little effect on the radon influx when
compared to a furnace that uses indoor air for combustion
purposes. If it is desirable for the upstairs part of the house
to run slightly negative to eliminate moisture, ensure that the
heating system has been designed so that backdrafting will
not occur when bathroom, laundry, and kitchen fans are
used. If a centralized exhaust ventilation system is used,
remember to vent dryers and kitchen ranges separately. It is
poor practice to have grease soaked lint with a fan blowing
air over it in the event of a fire.
If the air exhausted from the upstairs part of the house is
diverted into the basement, the basement might be slightly
pressurized and the influx of soil gas stopped. If the air leaks
between the basement and upstairs and the basement and
outside have been sealed, then a smaller volume of air will
be able to pressurize the house. If the basement is insulated
along the perimeter walls, it would be possible to use the air
distribution ductwork to pressurize the basement and depres-
surize the upstairs. This could be done by planning the
distribution ductwork so that it is easy to seal the joints and
then opening grills in the supply ductwork. For this to be an
effective radon control, the fan would have to run all the
time. A two speed distribution fan could be used that would
run on low speed all the time and be boosted to high speed
when heating or cooling is called for.
Ventilation systems could further reduce indoor radon
levels by dilution with outdoor air, and, depending on how it
is distributed, could reduce driving forces that draw in soil
gas. If outdoor supply air is added to the return-air side of
the ductwork then some (50 to 100 cfm) ventilation air
36
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would be introduced and distributed to the house whenever
the fan was running. Some new heating systems combine
heat recovery ventilation (HRV) with warm air space condi-
tioning. This would add about 200 cfm of fresh air when-
ever the HRV was operating and 50 cfm whenever the
circulation fan was running. The American Society of Heating
Refrigeration and Air Conditioning Engineers is currently
revising their residential ventilation guidelines to recommend
the capability of providing one-third of an air change per
hour (ACH) for residences. An HRV would provide that for
a 4500 ft2 house with 8 ft ceilings, and makeup air for the
return ductwork would meet that for an 1100 to 2200 ft2
house with 8 ft ceilings. In addition to radon control this
amount of ventilation has the benefits of control of the
unavoidable contaminants released by washing, cooking and
body functions. In a heating climate where there is moderate
to heavy rainfall, powered ventilation in the winter can be
used for humidity control.
Summarizing, a mechanical system that is planned to
control indoor air contaminants (including humidity, radon,
combustion gases and body odors) and reduce the risk of
condensation in the building shell in a cold humid climate
should include:
power-vented or dedicated outdoor combustion
air heating systems
dcprcssurized upstairs / pressurized basement
(possibly using the distribution system)
air supplied to the building with or without heat
recovery
tightened building shell to minimize the amount
of air needed to pressurize the basement and to
lower neutral pressure plane
Situation Two is a house constructed in a warm humid
climate. It is a single story slab-on-grade house with air
conditioning in the attic. There is a single return air grill
located in the hallway that leads to the bedrooms. When the
air handler is not moving air, the conditioned indoor air mass
tends to create a reverse stack effect preventing soil gas from
entering. When the air handler is running the house at 2 Pa
negative pressure, it overwhelms the reverse stack effect
because the supply ducts in the attic are far more extensive
than the returns and have more leaks. When the bedroom
doors are closed the entire living area goes to about 10 Pa
negative pressure. In both of these lower indoor air pressure
conditions soil gas is drawn in through the many cracks and
penetrations of the floor slab. Space heat, when it is needed
is supplied by a heat pump cycle through the air conditioning
ductwork. In the summertime when it is warm and humid
outdoors, the negative pressure in the building draws air in
through the cracks and holes in the building shell. As the air
gets closer to the cool interior, the relative humidity in-
creases, and the risk of condensation in the building shell
near the interior sheetrock increases.
Pressurizing the house would reduce both the soil gas
entry and the chance of condensation occurring. This could
be accomplished by planning the ductwork so that it could be
easily sealed to reduce losses, running a more extensive
return air system, and using dampers so more air is supplied
to the house than is exhausted. The difference between
supply and exhaust will be lost through the building shell.
By making the building shell as airtight as possible, the
amount of air it takes to do this will be smaller. If more air
is supplied to the building than is removed by the return air
ducts then the difference must come through leaks in the
return air ductwork. It is possible that an outdoor air supply
duct will have to be run to the return air side of the air
handler to make the pressurization (and coincidentally venti-
lation) air available. The incoming air must be cooled down
to house temperature resulting in a sensible and latent heat
gain energy penalty. In this case two approaches could be
made to reducing the cooling energy penalty. A high effi-
ciency cooling coil using dchumidifying heat pipe technol-
ogy could be used to precondition the incoming air. Second,
a heat pump domestic hot water heater could be used to pre-
cool the incoming air and heat the hot water at the same
time.
The bathroom, laundry and kitchen exhausts would have
to operate as normally installed and enough pressurization air
would have to be added so that the intermittent operation of
these exhausts would not overcome the time averaged ben-
efits of house pressurization.
Combustion products are probably not an issue because
there is no combustion device in the house.
Summarizing the system :
Pressurize the house using the air handling
system (concurrently adding ventilation air)
Reduce the cooling load penalty by
preconditioning the incoming air (reducing
the indoor humidity and/or heating the domestic
hot water)
6.5 Conclusions
It is obvious that an approach in new construction that
matches mechanical system design and installation to the
multiple needs of occupant health, safety, and comfort and to
building longevity requires an understanding of how the
climate and building interact. This approach is both more
comprehensive in effect and complex in design and installa-
tion than the other techniques outlined in this manual. This
line .of attack should only be pursued by qualified people
who have training and experience in mechanical systems,
because it is too easy to overlook an important aspect of the
interconnections involved. In many ways it is a more sophis-
ticated control strategy than soil depressurization or me-
chanical barriers.
37
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References
ACI - American Concrete institute, Detroit, MI
ACI332R-84 - Guide to Residential Cast in Place Concrete
Construction
ACI302.1R-80 - Guide for Concrete Floor and Slab
Coinforced Concrete Construction
ACI212.1R-81 - Admixtures for Concrete
ACI544 - State of the Art Report on Fiber-Reinforced
Concrete Construction
Ak86 - Akerblom, G., Investigation and Mapping of Radon
Risk Areas, International Symposium on Geological
Mapping in the Service of Environmental Planning,
Trondheim, Norway, May 6-9,1986.
ASHRAE85 - American Society of Heating, Refridgeration,
and Air Conditioning Engineers, 1985 Fundamentals
Handbook, Atlanta, GA
Br86 - Brennan, T., and W. Turner, Defeating Radon, Solar
Age, p. 34, March 1986.
CABO86 - CABO One and Two Family Dwelling Code/
1986, Council of American Building Officials, Falls
Church, VA, 1986.
CMHC84 - Scanada Consultants Ltd., The Thermal
Performance of Furnace Flues in Houses, Canada
Mortgage and Housing Corporation, Ottawa, Canada,
1984.
Da86 - D'Alesandro, W., Foundation Drainage Mats,
Progressive Builder, 11:10, pp. 12 - 13, September
1986.
EPA87 -U.S. Environmental Protection Agency, Removal of
Radon from Household Water, OPA-87-011, September
1987.
ERDA85 - Nitschke, I.A., G.W. Traynor, J.B. Wadach, ME.
Clarkin, and W.A. Clarke, Indoor Air Quality, Infiltration
and Ventilation in Residential Buildings, NYSERDA
Report 85-10, March 1985.
FL88 - Proposed Interim Guidelines for Radon Resistant
Construction, Tallahassee, FL, March 1988.
Har88 - Harris, D.B., J.S. Ruppersberger, and M. Walton,
Radon Wall Coatings Test Facility Design and
Development Phase, in Proceedings: The 1988
Symposium on Radon and Radon Reduction Technology,
Vol. 2, EPA-600/9-89-006b (NTIS PB89-167498), March
1989.
Hu88- Hubbard, L.M., B. Bolker, R.H. Socolow, D.
Dickerhoff, and R.B. Mosley, Radon Dynamics in a
House Heated Alternately By Forced Air and by Electric
Resistance, in Proceedings: The 1988 Symposium on
Radon and Radon Reduction Technology, Vol. 1, EPA-
600/9-89-006a (NTIS PB89-167480), March 1989.
Ku88 - Kunz, C., C.A. Laymon, and C. Parker, Gravelly
Soils and Indoor Radon, in Proceedings: The 1988
Symposium on Radon and Radon Reduction Technology,
Vol. 1, EPA-600/9-89-006a (NTIS PB89-167480), March
1989.
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.
Mu88 - Muessig, K.W., Correlation of Airborne Radiometric
Data and Geologic Sources with Elevated Indoor Radon
in New Jersey, in Proceedings: The 1988 Symposium on
Radon and Radon Reduction Technology, Vol. 1, EPA-
600/9-89-006a (NTIS PB89-167480), March 1989.
Mur88 - Murane, D. U.S. Environmental Protection Agency,
Office of Radiation Programs, Washington, D.C. personal
communication, June, 1988.
Na87 - Nagda, N. L., Florida Statewide Radiation Study,
GEOMET Technologies, Inc., Report IE-1808,
November 1987.
NCMA - National Concrete Masonry Association, Hemdon,
VA
NCMA68 - Specification for the Design and Construction of
Load Bearing Concrete Masonry, 1968.
NCMA71 - Reinforced Concrete Masonry Design, 1971.
NCMA72 - Concrete Masonry Foundation Walls NCMA-
TEK 43, 1972.
NCMA87- Radon Safe Basement Construction NCMA-TEK
160A, 1987.
Ne88 - Nelson, G., Finding the Flaws, Energy Design
Update, Cutters Information Corporation, February 1987.
NFoPA88 - Radon Reduction in Wood Floor and Wood
Foundation Systems, National Forest Products
Association, 1988.
NFPA - National Fire Protection Association, Quincy, MA
NFPA1 - Fire Protection Code, 1987.
NFPA54 - National Fuel Gas Code, 1984.
NFPA70 - National Electric Code, 1981.
Ni89 - Nitschke, L, Radon Reduction and Radon Resistant
Construction Demonstrations in New York, U.S.
Environmental Protection Agency, EPA/600/8-89/001
(NTIS PB89-151476), January 1989.
39
-------
ORNL88 - Oak Ridge National Laboratory, Building
Foundation Design Handbook, Oak Ridge, TN, 1988.
Os87a - Osborne, M.C., Resolving the Radon Problem in
Clinton, New Jersey, Houses in, Indoor Air '87:
Proceedings of the 4thlnternational Conference On
Indoor Air Quality and Climate, Vol. 2, pp. 305-309,
Berlin, West Germany, August 1987.
OsSTb - Osbome, 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.
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.
Ru88 - Rugg. M., House Age, Substructure and Heating
System: Relationships to Indoor Radon Concentrations,
in Proceedings : The 1988 Symposium on Radon and
Radon Reduction Technology, Vol. 2, EPA-600/9-89-
006b (NTIS PB89-167498), March 1989.
Sc87 - Scott, A.G., and W.O. Findley, Production of Radon
Resistant Foundations, American ATCON, Inc.,
September 1987.
Se89 - Sextro, R.G., W.W. Nazaroff, and B.H. Turk, Spatial
and Temporal Variation in Factors Governing the Radon
Source Potential of Soil, in Proceedings: The 1988
Symposium on Radon and Radon Reduction Technology,
Vol. 1, EPA- 600/9-89-006a (NTIS PB89-167480), March
1989.
Si90 - Siniscalchi, M.S., L.M. Rothney, B.F. Toal, M.A.
Thomas, D.R. Brown, M.C. van der Werff, and C.J.
Dupuy, Radon Exposure in Connecticut: Analysis of
Three Statewide Surveys of Nearly One Percent of Single
Family Homes, presented at the 1990 International
Symposium on Radon and Radon Reduction Technology,
Atlanta, GA, February 1990.
Sw82 - Translation of Statens planverk, report 59, 1982 -
Stockholm, Sweden, p. 3.
To88 - Tooley, J.J., Mechanical Air Distribution and
Interacting Relationships, Natural Florida Retrofit, Inc.,
1988.
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Appendix A
Current Radon-resistant New Construction
Research Efforts
There are several U.S. EPA, AEERL radon-resistant
research projects that are ongoing or recently completed.
Some of these are in cooperation with other research agencies,
for example the New York State Energy Research and De-
velopment Authority and the U.S. EPA jointly pursued a
research effort involving 15 newly constructed houses with
radon-resistant features and 5 control houses.
The lack of a reliable method to estimate indoor radon
concentrations in a new house before it is built makes the
results of radon-resistant new construction research difficult
to interpret. Without pre-test data, how can a new house with
a successful radon control method be distinguished from the
9 out of 10 new houses that are below the EPA Action
Guideline of 4 pCi/L ? Several approaches have been made
to develop confidence in the results of projects. They are :
1) Make measurements in a large number of
experimental and control houses so reliability
can be estimated using statistical methods.
2) Build the test houses in neighborhoods known
to have elevated indoor radon levels in a large
fraction of the existing houses. In some
neighborhoods >50% of the houses are over 4
pCi/L.
3) Study a small number of new buildings with
radon control features in detail. Phase the study
to separate the radon control features and
establish how effective they are. For example,
a soil depressurization method can be testedb y
monitoring indoor radon with the vent stack
open and the blower off, with the vent stack
open and the blower on, and with the vent stack
blocked off. Tracer gases can be used to test the
effectiveness of mechanical barriers or the
amount of airflow through a soil depressurization
system that comes from inside the basement.
Lastly, and as it seems to be turning out, if buildings
with radon-resistant new construction features end up having
elevated indoor radon concentrations, then the features didn't
work well enough. There is no way to tell if the features
were partially successful and the elevated indoor radon would
have been higher yet had they not been used.
Table A1. Current EPA/AEERL Radon-resistant New Construction Projects.
Walls Site Methods Tested
Project
EPA1b
NYSERDA
NAHB-NRC
(NJ)
EPA2
(VA/PA)
Block
0
15
4
0
Pour
10
0
6
4
Char. Barrier
10
Highly 8
perm.
Highly 0
varied
2 day 4
2 perm.
Pass.SSD
10
8
0
4
Act.SSD Comments
5
8 controlhouses
averaged
34.4 pCi/L
0
4 % indoor air
in exhaust
estimated
(NY)
EPA1b - Passive and Active Soil Depressurization
NYSERDA (NY) - Barrier/Active/Passive
NAHB-NRC (NJ) - Passive and Active Soil Depressurization
EPA2 (VA/PA) - Barrier/Active/Passive/Energy Penalty
41
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Table A2. Preliminary Results from Current EPA Research Projects.
Average Basement Radon (pCi/L)
Project Barrier Passive
Active
# of Houses
EPA1b 14.5
NYSERDA (NY)
EPA2 (PA)
EPA2 (VA)
6.0
15.8
1.3
1.4
13.9
0.7
7.0
10
2.8
1.1
1.1
15
2
1
EPA1b - Passive and Active Soil Depressurization
NYSERDA (NY) - Barrier/Active/Passive
EPA2 (VA/PA) - Barrier/Active/Passive/Energy Penalty
It should be kept in mind that the results of these research
projects are preliminary. However, it is clear that in all the
projects at least some of the buildings that had radon resistant
features built in also ended up with elevated radon levels.
Whether this is the result of failure of the systems at con-
ceptual, design or installation levels is unknown at this point.
42
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Appendix B
Other Radon-resistant New Construction
Guidelines
Several other groups are currently working on or have
already issued guidelines to control radon in new buildings.
These groups are usually either Professional or Trade Asso-
ciations or government agencies.
There are thousands of local, state and national codes
jurisdictions in the United States. It is their job to enforce
existing codes. Many legal, enforceable codes are based on
model codes that have been developed by model codes asso-
ciations. The model codes often reference standard practice
as recommended by industry associations.
Developed and Available:
DOE, Oak Ridge National Laboratories, ORNL/Sub/86-
72143/1, "Building Foundation Handbook," 1988. An im-
pressive publication that addresses nearly all imaginable as-
pects of foundation design and construction. Chapter 10 is
devoted to radon control in new construction.
National Forest Products Association, "Radon Reduction
In Wood Floor and Wood Foundation Systems," 1988 - A
20-page booklet describing radon control strategies for per-
manent wood foundations. National Forest Products Asso-
^ciation is a trade association for the producers of wood
products.
U.S. EPA, Office of Radiation Protection - National
Association of Homebuilders Research Foundation, "Radon
Resistant New Construction - An Interim Guide," August
1987, OPA-87-009 - A 10-page pamphlet that covers funda-
mentals and recommendations.
In Process, Not Yet Available :
American Society for Testing and Materials (ASTM),
"DRAFT-Standard Guide for Radon Control Options For
New Home Construction, "White Paper," - Currently in pro-
cess. ASTM is an organization composed of users, producers
and interested parties who work together via a consensus
process to produce voluntary industry guidelines. All publi-
cations go through extensive peer review. This document is
being developed by Committee E-06.41.08, Reduction of
Radon Intrusion Into Buildings. Contact Bion Howard at the
National Association of Homebuilders Research Center, 400
Prince George Blvd., Upper Marlboro, MD 20772. Ph. (301)
249-4000.
Florida - The State Legislature mandated in 1988 that
the Florida University system develop a model building code
for radon control methods in new and existing buildings. The
preliminary planning has occurred for this effort. Contact
Thomas Pugh at the Florida A & M University School of
Architecture, Tallahassee, FL 32308. Ph. (904) 599-3000.
U.S. EPA, Office of Radiation Programs - Currently
mandated by Federal legislation to develop a model code for
radon resistant new construction, ORP is in the process of
writing a draft of a radon resistant new construction code.
Contact Dave Murane, U.S. EPA, ORP, 401 M St. S.W.,
Washington, DC 20460. Ph. (202) 475-9623.
Washington Energy Extension Service, "Northwest Radon
Ordinance" - In process. This is a model radon resistant new
construction code being developed by the Washington Energy
Extension Service with extensive review by interested parties.
Contact Mike Nuess, WEES, N. 1212 Washington St., Spo-
kane, WA 99201. Ph. (509) 456-6150.
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