Jump to main content or area navigation.

Contact Us

Document Display

Page 1 (-1 of 50)
Include current hits

<title>Radon Prevention in the Design and Construction of Schools and Other Large Buildings Third Printing With Addendum  June 1994</title>
<type>single page tiff</type>
<keyword>radon building slab subslab asd system suction pressure walls concrete buildings sealing crawl pipe fan entry air pit hvac aggregate</keyword>

           United States
           Environmental Protection
                  Office of Research and
                  Washington DC 20460
June 1994
      Radon Prevention in the
      Design and Construction of
      Schools and Other Large

      Third Printing with
      Addendum, June 1994
                       SOIL DEPRESSURIZATION
              OUTDOOR AIR
                             POSITIVE PRESSURE

                  RADON SUCTION PIT


                                                           June 1994
Radon Prevention in the Design and Construction of
          Schools and Other Large Buildings

        Third Printing with Addendum, June 1994
                             Prepared by
                       Kelly W. Leovic and A. B. Craig
                     U.S. Environmental Protection Agency
                 Air and Energy Engineering Research Laboratory
                      Radon Mitigation Branch (MD-54)
                      Research Triangle Park, NC 27711
                                                  Printed on Recycled Paper


    The U.S. Environmental Protection Agency (EPA) strives to provide accurate, com-
plete, 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, or for damages arising from, the use of
any information, method, or process in this document. Mention of firms, trade names, or
commercial products in this document does not constitute endorsement or recommendation
for use.



Notice  ii
Figures v
Tables  v
Abstract    vi
Metric Conversion Factors   vii
Acknowledgments viii

1.  Introduction and Overview   1
    1.1  Purpose    1
    1.2  Scope and Content  1
    1.3  Radon and its Sources  2
        1.3.1   Why is Radon a Problem? 2
        1.3.2   How Radon Enters a Building 3
        1.3.3   How to Determine if Radon Prevention is Needed  5
    1.4  Radon Prevention Techniques    6
        1.4.1   Soil Depressurization   6
        1.4.2   Building Pressurization 7
        1.4.3   Sealing Radon Entry Routes  8
    1.5  Why Radon Prevention Should be Considered in Building Design   9
2.  Technical Construction Information  11
    2.1  Active Soil Depressurization (ASD) 11
        2.1.1   ASD Design and Installation 12
       Aggregate   12
      Subslab Walls    13
       Radon Suction Pits  13
       Radon Vent Pipe 16
       Suction Fan 19
      Sealing Major Radon Entry Routes 20
        2.1.2   Operation and Maintenance   20
       Before Occupancy    22
      Weekly   22
       Annually    22
        2.1.3   Additional Instructions for  Basements  22
        2.1.4   Additional Instructions for  Crawl Spaces   22
        2.1.5   ASD Cost Estimates  24
        2.1.6   Summary of Guidelines for ASD Systems   24


                               Contents (continued)
    2.2  Building Pressurization and Dilution   24
        2.2.1   Design Recommendations for HVAC Systems 24
        2.2.2   Standards for Ventilation   26
        2.2.3   Guidelines for Installation and Operation   26
        2.2.4   Maintenance 26
        2.2.5   Summary of Building Pressurization Guidelines   27
    2.3  Sealing Radon Entry Routes 27
        2.3.1   Recommended Sealants    28
        2.3.2   Sealing Concrete Slabs  28
       Slab Joints 28
       Slab Penetrations and Openings  28
       Crack Prevention    29
       Subslab Membranes   29
        2.3.3   Sealing Below-Grade Walls   29
       Wall Types  29
       Coatings for Below-Grade Walls  30
        2.3.4   Sealing Crawl Spaces    31
        2.3.5   Summary of Sealing Recommendations  31
    2.4  Guidelines for Measuring Radon Levels  31

Appendix A:    Case Study   33
Appendix B:    References   35
Appendix C:    EPA Regional Offices and Contacts    37
Addendum    38
        Increasing Pressure Field Extension by Modifying Subslab Walls  38
        Improved Suction Pits   38



1-1     Radon decay chart   2
1-2     Examples of negative pressure sources in a typical building 3
1-3     Typical radon entry routes in slab-on-grade construction    4
l-4a    Typical radon entry routes in concrete block basement walls 4
l-4b    Typical radon entry routes in poured concrete basement walls    5
1-5     Typical crawl space foundation entry routes 5
1-6     Subslab depressurization theory 7

2-1     Typical subslab depressurization system 12
2-2a    Interior footing/foundation wall    14
2-2b    Thickened slab footing  14
2-3a    Outside walls and post load bearing 15
2-3b    Interior walls between rooms and outside walls load bearing 16
2-3c    Hall and outside walls load bearing 17
2-3d    All interior walls load bearing 18
2-4a    Section 1 (corresponds to Figures 2-3a and b)   18
2-4b    Section 1 (corresponds to Figure 2-3c and d)    19
2-5     Radon suction pit   20
2-6     Sealing pipe penetrations through roof. 21
2-7     Submembrane depressurization in crawl space 23
2-8     Building positive pressurization with HVAC system   25
2-9     Example of building depressurization with HVAC system   26
2-10    Every other interior wall block is turned on its side to allow soil gas to pass through 39
2-11    Interior CMU wall   39
2-12    Revised subslab suction pit 40
2-13    Smaller subslab suction  pit    40
2-1     Estimated Costs for Primary ASD Components  24
2-2     Examples of Outdoor Air Requirements for Ventilation in Commercial Facilities   27

A-l     Cost of Mitigation System in Johnson City Hospital  34


    It is typically easier and much less expensive to design and construct a new building
with radon-resistant and/or easy-to-mitigate features, than to add these features after the
building is completed and occupied. Therefore, when building in an area with the potential
for elevated radon levels, architects and engineers should use a combination of radon
prevention construction techniques. To determine if your building site is located in a
radon-prone area, consult your EPA Regional Office or state or local radiation office.

    We recommend the following three radon prevention techniques for construction of
schools and other large buildings in radon-prone areas: (1) install an active soil depressur-
izadon (ASD) system,  (2) pressurize the building using the heating, ventilating, and air-
conditioning (HVAC) system, and (3) seal major radon entry routes. Specific guidelines
on how to incorporate  these radon prevention features in the design and construction of
schools and other large buildings are detailed in  this manual.

    Chapter 1 of this manual is a general introduction for those who need background
information on the indoor radon problem and the techniques currently being studied and
applied for radon prevention. The  level of detail is aimed  at developing the reader's
understanding of underlying principles and might best be used by school officials  or by
architects  and engineers who need a basic introduction.

    Chapter 2 of this manual provides comprehensive information, instructions, and
guidelines about the topics and construction techniques discussed in Chapter 1. The
sections in Chapter 2 contain much more technical detail and may  be best used by the
architects, engineers, and builders responsible for the specific construction details.


                            Metric Conversion  Factors
            Although it is EPA policy to use metric units in its documents, non-metric units have
        been used in this report to be consistent with common practice in the radon mitigation
        field. Readers may refer to the following conversion factors as needed.
     Yields Metric
cubic foot (ft3)
cubic foot per minute (ft3/m)
foot (ft)
gallon (gal.)
horsepower (hp)
inch (in.)
inch of water column (in. WC)
mil (0.001 in.)
picocurie per liter (pCi/L)
pound per square inch (psi)
square foot (ft2)
liters (L)
liter per second (L/s)
meter (m)
liters (L)
watts (W)
centimeters (cm)
pascals (Pa)
micrometers (jun)
becquerels per cubic meter (Bq/m5)
pascals (Pa)
square meter (m2)


    The information contained in this technical document is based largely on research
conducted by the Air and Energy Engineering Research Laboratory (AEERL) of the
Environmental Protection Agency's (EPA's) Office of Research and Development.

    W.A. Turner of the H.L. Turner Group and T. Brennan of Camroden Associates
prepared the initial draft of the document in 1991 under contract number OD2009NCSA.
Scott R. Spiezle of Spiezle Architectural Group prepared the figures under contract number
68-DO-0097.  Technical writing  services  were provided by the Kelton Group under
contract number 2DO682NASA.

    Drafts of this document have been reviewed by a large number of individuals in the
government and in the private and academic sectors. Comments from these reviewers in
addition to those from the individuals listed above have helped significantly to improve the
completeness, accuracy, and clarity of the document. The following reviewers offered
input: William Angell of Midwest Universities Radon Consortium; Timothy M. Dyess and
D. Bruce Henschel of EPA's AEERL; Deane E. Evans of AIA/ACSA Joint Council on
Architectural Research; Kenneth  Gadsby of Princeton University; Patrick Holmes of the
Kentucky Division of Community Safety;  Norman Grant of Quoin  Architects and Engi-
neers; Gene Fisher, Jed Harrison, Dave Murane, Dave Price, and Brian Ligman of EPA's
Office of Radiation Programs; Clifford Phillips of Fairfax County Pubic  Schools; Steve
Sanders of Auburn University; Dave Saum of INFJLTEC; Arthur E. Wheeler of Wheeler
Engineering Co.; Larraine Kohler of EPA Region 2; Bill Bellanger of EPA Region 3; Steve
Chambers of EPA Region 7; Phil Nyberg of EPA Region 8; Michael Bandrowski of EPA
Region 9; Kevin  Teichman of EPA's Office  of Technology Transfer and  Regulatory
Support;  Ruth Robenolt of EPA's Office of Communications; Jerry L. Clement of
Educational Facilities in Houston, TX; and Thomas E. Toricelli of T.E. Toricelli  ALA


                                                 Chapter 1
                                     Introduction and Overview
1.1       Purpose
    Radon is a naturally occurring radioactive gas in ambient
air. It can also  accumulate in varying amounts  in enclosed
buildings. Radon is estimated to cause many thousands of
lung cancer deaths each year. In fact, the Surgeon  General has
warned that radon is the second leading cause of lung cancer
in the U.S. today. Only smoking causes  more  lung cancer
deaths (1).

    Our increased understanding of the risks posed by indoor
radon has underscored the need for construction techniques
that prevent exposure to radon in residential and non-residen-
tial buildings.  The Indoor  Radon Abatement Act  of  1988
states, 'The national long-term goal of the United States with
respect to radon  levels in  buildings is that the air within
buildings should be as free of radon as the ambient air outside
the building." This manual is intended to address this goal in
the new construction of schools and other large buildings.

    The U.S. Environmental Protection Agency (EPA) has
developed construction techniques that are being  used to
reduce radon levels in new buildings. This manual provides
architects, engineers, designers, builders, and school officials
with an understanding of operating principles and installation
instructions for these radon prevention techniques. Research
indicates that many radon prevention features can be installed
relatively easily and inexpensively during building construc-
tion. Installing  these features during construction increases
their effectiveness and involves  less labor, disruption, and
cost than  when these same features are installed after the
building is completed and occupied. Thus, the primary pur-
pose of this manual is to provide information and guidelines
about radon prevention techniques so that they can  be  cost-
effectively incorporated into a building during the design and
construction stages.

1.2       Scope and Content
    This  manual is divided into two parts:

    Chapter 1—Introduction and Overview: Chapter 1 of
this manual is  a general introduction for those who  need
background information on the indoor radon problem and the
techniques currently  being studied and applied for radon
prevention. The level of detail is aimed  at developing the
reader's understanding of underlying principles and might
best be used by school officials or by architects and engineers
who need a basic introduction to radon and radon reduction
techniques. Those who are already familiar with the problems
of constructing radon-resistant  buildings should go  on to
Chapter 2. Chapter 1 contains the following sections:

  1.3 Radon and Its Sources—an introduction to the prob-
      lem of indoor radon.

  1.4 Radon Prevention Techniques—an overview of cur-
      rent construction methods for radon prevention.

  1.5 Why Radon Prevention Should Be Considered in Build-
      ing Design.

    Chapter 2—Technical  Construction  Information:
Chapter 2 of this manual provides comprehensive informa-
tion, instructions, and guidelines about the topics and con-
struction techniques discussed in Chapter 1. The sections in
Chapter 2 contain much more technical detail than Chapter 1,
and may be best used by the architects, engineers, and builders
responsible for the specific  construction details. From  the
information presented in this manual, readers should be able
to select radon prevention techniques that are appropriate to
their particular situation.

    Chapter 2 also briefly covers sources of information on
measuring radon in schools and other large buildings. Appen-
dix  A contains a case study of a step-by-step installation of
radon prevention techniques  in  a recently constructed large
building. Radon levels and  associated costs  of the  radon
prevention features are included. References are in Appendix
B, and Appendix C lists the EPA Regional Offices.

    The recommendations in this manual are based on the
best available information gathered from numerous  research
projects in existing and new construction, and in current field
practice. Most new schools and other large buildings use slab-
on-grade construction; therefore, this manual focuses on ra-
don prevention techniques that  can  be applied to  slab-on-
grade buildings. But because radon can enter a  building
regardless of its foundation type, it also presents techniques
applicable to buildings with basement and crawl space foun-

    As research continues and experience in the application
of radon-resistant construction techniques grows, a variety of
techniques might also prove effective  in reaching radon re-
duction  goals.  These goals are to keep radon  levels in new


construction well below  the currently recommended EPA
action level of 4 pCi/L and as close to the long-term national
goal of ambient radon levels (0.4 pCi/L) as possible. Many of
these radon prevention techniques will eventually prove to be
transferable to the architect's and engineer's common prac-
tices and, it is hoped, will be adopted in national building
codes by the model building code organizations. EPA is
currently working with the American Society of Testing and
Materials (ASTM) to develop a standard for radon prevention
in the construction of large buildings.

 1.3      Radon and its Sources
    The following subsections answer three basic questions
that many people have about radon:

    1)   Why is radon a problem?

    2)   How does radon enter a building?

    3)   How should one evaluate a construction site?

1.3.1     Why is Radon a Problem?
    Radon is a colorless, odorless, radioactive gas produced
by the radioactive decay of radium-226, an element found in
varying concentrations in many soils and bedrock. Figure  1-1
shows the series of elements that begin with uranium-238 and
eventually decay to lead-210. Of all the elements and isotopes
in the decay chain, radon is the only gas. Because radon is a
gas, it can easily move through small spaces between particles
of soil and thus enter a building. Radon can enter a building as
a component of the soil  gas and  reach levels many times
higher than outdoor levels.

    While many of the isotopes in the  uranium-238 decay
series exist for a long time before they decay, radon has a half-
life of only 3.8 days. Radon decay products have even shorter
half-lives than radon and  decay within an hour to relatively
stable lead-210. At each level of this decay process, energy is
released in the form of radiation. This radiation constitutes the
health hazard to humans.

    When radon and radon decay products are present in the
air, some will be inhaled. Because the decay products are not
gases, they will stick to lung tissue or larger airborne particles
that later lodge in the lungs. The radiation released by the
decay of these isotopes can damage  lung  tissue and can
increase one's risk of developing lung cancer. The health risk
depends on how long and at what levels a person is exposed to
radon decay products. Radon and radon decay products cause
thousands of deaths per year in the United States (1).

    Like other environmental pollutants, there is some uncer-
tainty about the magnitude of radon health risks. However, we
know more about  radon risks than the risks from most other
cancer-causing substances. This is because estimates of radon
risks are based  on the studies of cancer in humans (under-
ground miners). Additional studies  of more  typical popula-
tions are underway. Smoking combined with exposure to
elevated levels of radon is an especially serious health risk.

    Children  have been reported to have greater risk than
adults of certain types of cancer from radiation, but there are
currently no conclusive data on whether children are at greater
risk than adults from radon.

    Radon levels are usually measured in picocuries per liter
of air (pCi/L).  Currently, it is  recommended  that indoor
radon levels be reduced to less than 4 pCi/L. But the lower
the radon level, the lower the health risk; therefore, radon
levels should be reduced to as  close to  ambient levels as
feasible (0.4 pCi/L). For additional information on the esti-
mated health risks from exposure to various levels of radon,
refer to EPA's A Citizen's Guide to Radon, Second Edition (1).

    Architects and engineers should consider the health risks
of radon prior to  constructing new  buildings or renovating
existing buildings  in radon-prone areas. Including radon pre-
Figure 1-1.   Radon decay chart. Time shown in half-life.


vention techniques during building design and construction
will reduce the chance that a building will have a radon
problem and also reduce the cost of reducing radon levels, if

1.3.2    How Radon Enters a Building
    The most common way for radon to enter a building is
from the soil gas through pressure-driven transport Radon
can also enter a building through diffusion, well water, and
construction materials. These modes of radon entry are briefly
explained below.

Pressure-Driven Transport

    Radon can enter a building through pressure-driven trans-
port only if all of the following four conditions exist:

  1)   a source of radium to produce radon

  2)   a pathway from the source to the building

  3)   an opening in the building to permit radon to enter the

  4)   a driving force to move radon from the source into the
       building through the opening

    Pressure-driven transport is the most common way radon
enters  a building. Pressure-driven transport occurs when a
lower indoor air pressure draws air from the soil or bedrock
into the building. This transport happens in many schools and
other large buildings because these buildings usually operate
at an inside air pressure lower than that of the surrounding
soil. Negative pressure inside buildings is due in part to
building shell effects. For example, indoor/outdoor tempera-
ture differences, wind, and air leaks in the shell of the building
can contribute to negative pressures in the building.  The
design and operation of mechanical ventilation systems that
depressurize the building can also  greatly influence radon
entry. Sources of negative pressure in a typical building are
shown in Figure 1-2.

Other Ways Radon Enters a Building

    Radon also can enter buildings when there are no pres-
sure differences. This type of radon movement is  called
diffusion-driven transport. Diffusion is the same mechanism
that causes a drop of food coloring placed in a glass of water
to spread through the entire glass. Diffusion-driven transport
is rarely the cause of elevated radon levels in existing build-
ings. It is also highly unlikely that diffusion contributes sig-
nificantly to elevated radon levels in schools and other large

    Another way radon can enter a building is through well
water. In certain areas of the country, well water  that is
supplied  directly to a building  and that  is  in contact with
radium-bearing formations can  be a source of radon in a
building. At this writing, the only known health risk  associ-
ated with exposure to radon in water is the airborne radon that
is released from the water when  it is used. A general rule for
houses is that 10,000 pCi/L of radon in water contributes
approximately 1 pCi/L to airborne radon levels. It is unlikely
that municipal water supplied from a surface reservoir would
contain elevated levels of radon and, thus, buildings using this
source of water should not need to conduct  radon testing of
the  water.

    Radon can also emanate from building  materials. How-
ever, this has rarely been found to be the cause of elevated
levels in existing schools and other large buildings. The extent
of the use of radium-contaminated building  materials is un-
known but is generally believed to be very small.

    Because pressure-driven transport  is by far  the most
common way radon enters a building, this manual docs not
address the other ways that radon can enter a building.
                                              Roof Exhaust Fan
                                                                   Kitchen Range Exhaust Fan
                                                 = Positive Pressure
                                                 = Negative Pressure
Figure 1-2.    Examples of negative pressure sources In a typical building.



Radon Entry and Substructure Type

    Elevated levels of radon can occur in any building regard-
less of foundation type.  Figures 1-3,  1-4, and 1-5 show
common radon entry routes for buildings constructed on slab-
on-grade, basement, and  crawl space foundations, respec-
tively. Because  a large majority of the new buildings con-
                                                            structed today are slab-on-grade substructures, Section 2.1 of
                                                            this manual emphasizes radon prevention for slab-on-grade
                                                            buildings. However, many of the radon prevention techniques
                                                            usecj for slab-on-grade substructures are also applicable to
                                                            basements and crawl spaces.
                                                                       Wall Cracks and Form Ties
                                                                    Plumbing Pipe  +.

                          Poured Concrete Wall
                                                     © = Positive Pressure

                                                     Q = Negative Pressure
                                                                       Poured Concrete Wall
 Figure 1-3.    Typical radon entry routes In slab-on-grade construction.

                                                                             Soil Gas/Radon Movement
                                                                             through Hollow Core Block
                                                                        Plumbing Pipe
                                              Floor Joist
                 Wall Joints/Cracks

                             Floor Joints/Cracks

             Utility Penetration
                                                                Concrete Floor Slab
                 • Concrete Block Wall
                                                                                   Concrete Block Wall
                                                    •• Positive Pressure
                                                    : Negative Pressure
  Figure 1-4a.  Typical radon entry routes in concrete block basement walls.



                                                                   Wall Cracks and Form Ties
                                             Floor Joist
         Plumbing Pipe

                       Poured Concrete Wall
             Poured Concrete Wall
Positive Pressure
                                                 Q = Negative Pressure

Figure 1-4b.  Typical radon entry routes In poured concrete basement walls.
              Wall Penetration
                                                           Positive Pressure

                                                           Negative Pressure
Figure 1-5.   Typical crawl space foundation entry routes.
    The specific additional requirements for basement sub-
structures (such as sealing of basement walls) are discussed in
Section 2.1.3. The additional recommended requirements for
crawl spaces are discussed in Section 2.1.4  (submembrane

1.3.3    How to Determine if Radon
          Prevention is Needed
    An often-asked question is "Can one determine if radon-
resistant construction techniques are necessary for a given
site?" A simple and inexpensive standardized test that could
conclusively identify problem sites would be very helpful. At
present there are no reliable, easily applied, and inexpensive
methods for correlating the results of radon evaluation tests of
   soils at a building site with subsequent indoor radon levels
   contained in a building built on that site. Bedrock and soils
   interact in complex ways with dynamic building behavior and
   environmental factors. There are too many combinations of
   factors that cause elevated indoor radon concentrations for
   simple correlations to exist.

       In the absence of a simple test to determine when radon
   prevention techniques are needed, the discussion below cov-
   ers various sources  of information to assist architects and
   engineers with site assessment.

   EPA National Radon Potential Map

       One source of guidance is the growing body of radon data
   available at local, state, and regional levels. With  these data,


EPA is compiling a National Radon Potential Map. The map
integrates five factors to produce estimates of radon potential.
These factors are indoor radon screening measurements, geol-
ogy, soil permeability, aerial radioactivity, and substructure
type. All relevant data were collected and carefully evaluated
so that the five factors could be quantitatively ranked for their
respective "contribution" to the  radon potential of a given
area. The map assigns every county of the U.S. to one of three
radon  zones. Zone 1 areas  have the  highest potential for
elevated levels, Zone 2 areas also have potential for elevated
indoor radon levels but the occurrence is more variable, and
Zone 3 areas have the least potential for elevated levels.

    The radon  potential estimates assigned on the map are
stated in terms of predicted average screening levels. They are
not intended to predict annual average measurements, but
rather  to  assess the relative severity of the potential for
elevated indoor radon levels. We recommend you use this
map when it becomes available to help determine when radon
prevention construction techniques might be needed.

Radon Levels in Nearby Buildings

    Radon levels in a sample of existing U.S. school build-
ings were recently surveyed by EPA. Measurements to date
indicate that many schools and other large buildings through-
out the country have rooms or classrooms with radon levels
above 4 pCi/L. Many have been measured at levels in excess
of 20 pCi/L. It is expected that the geographic distribution of
the radon problem in schools and other large buildings will be
similar to that for homes. You can contact regional, state, or
local officials for information about radon levels in nearby
buildings and use this information, together with the National
Radon Potential Map, to help decide if you are in a radon-
prone area.


    Several studies have attempted to  make simple correla-
tions between radon or radium concentrations in the soil and
indoor radon concentrations. No direct correlations have been

Building Materials

    An extremely  small percentage of U.S. buildings with
indoor radon concentrations  greater than  4 pCi/L can be
attributed to building materials. Most of the building material
problems  have  arisen from  the  use of known radium-rich
wastes such as aggregate in block or in fill around and under
houses, or in areas of buildings with no ventilation. None of
the existing large buildings studied in EPA's Air and Energy
Engineering Research Laboratory's research program have
had  any identifiable problem associated with radon from
building materials. However, be aware that building materials
are a potential problem. But unless building materials have
been identified as radium-rich in that region of the country,
the chance of obtaining significant radon levels from building
materials is very small.


    Based on current research and the additional cost of radon
resistant construction  features, the expected impact on the
building budget will probably be much less than $1.00 per ft2
of earth contact floor area in most parts of the country. In most
cases (buildings that are already designed to have subslab
aggregate and plastic vapor retarder), sealing major radon
entry routes and installing an ASD system will add less than
$0.10 - $0.20 per ft2 of earth contact floor area to total costs.
Therefore, it is often more cost-effective to build  using radon
prevention techniques, rather than waiting until the building is
completed and then having to add a radon mitigation system.

1.4      Radon Prevention  Techniques
    Like most other indoor air contaminants, radon can best
be controlled by keeping it out of the building in the first
place, rather than removing it once it has entered. The follow-
ing subsections briefly describe the recommended radon pre-
vention techniques discussed in Chapter 2 of this manual:

  1.4.1     Soil Depressurization. A suction fan is used to
            produce a low-pressure field under the slab. This
            low-pressure field prevents radon entry by caus-
            ing air to flow from Ihc building into the soil.

  1.4.2     Building Pressurization. Indoor/subslab pres-
            sure relationships are controlled to  prevent ra-
            don entry.  More  outdoor air  is supplied than
            exhausted so  that the building is slightly pres-
            surized  compared to both the exterior of the
            building and the subslab area.

  1.4.3     Sealing Radon Entry Routes. Seal major radon
            entry routes to block or minimize radon entry.

    These radon prevention techniques are relatively inex-
pensive and easy to install.  We recommend that  all three of
these techniques be used in new construction to ensure maxi-
mum radon control.

7.4.7    Soil Depressurization
    The most effective and frequently used radon-reduction
technique in existing buildings  is active soil depressurization

How an ASD System Works

    An ASD system creates a low-pressure  zone beneath the
slab by using a powered fan  to create a negative pressure
beneath the slab and foundation. This low-pressure field pre-
vents soil  gas from entering the building because it reverses
the normal direction of airflow where the slab and foundation
meet. If the low pressure zone is extended throughout the
entire subslab area, air will flow from the building into the
soil, effectively sealing slab and foundation  cracks and holes
(2). For a simplified view of the operating principle  of an
ASD, refer to Figure 1-6. A similar system without a fan for
"activation" is referred to as a "Rough-in" of an ASD system,
and is briefly discussed at the end of this section.

    The following are essential instructions  for the design
and construction of a soil depressurization system:

  •    Place a  clean layer of coarse aggregate of narrow
       particle size distribution (naturally occurring gravel or
       crushed bedrock) beneath the slab.


                                           Depressurization Fan
                                                   Low Air Pressure
                  Higher Air Pressure
 Subslab Depressurization System creates low pressure zone
beneath the slab. This prevents radon-containing soil gas from
 entering the building by changing the direction of airflow. Air
  exhausted from under the slab is released above the roof
    where the elevated radon levels can dilute into the
                                                 Low Air Pressure
                                                Radon Suction Pit
Figure 1-6.   Subslab depressurlzatlon theory.
                                                           = Positive Pressure

                                                            Negative Pressure
  •   Eliminate all major barriers to extension of the subslab
      low pressure zone, such as interior subslab walls.

  •   Install radon suction pit(s) beneath the slab  in the
      aggregate (one radon suction pit for each area sepa-
      rated by subslab walls).

  •   Install a vent stack from the radon suction pit(s) under
      the slab to the roof.

  •   Install a suction fan on the vent stack. (The fan should
      be operated continuously, and the system should be
      equipped with  a warning device to indicate loss of
      negative pressure through fan failure or other causes.)

  •   Seal all major slab and foundation penetrations.

Rough-in for an ASD System

    A rough-in for an ASD system is the same as an ASD
system except there is no fan. For new construction where
radon levels are elevated even marginally, the installation of a
rough-in system is a prudent investment and is recommended.
If a building is found to have a radon problem, then a rough-in
can easily be converted into an ASD system by installing a

Passive Soil Depressurization

    Architects and engineers may ask, "Is it possible to install
a soil depressurization system that works passively (that is,
without a fan)?" Although research has shown that passive
systems are sometimes effective in home construction, they
are not  recommended for use in schools and other large
buildings. Many competing negative pressures in large build-
              ings can easily overcome a passive system. Also, the large
              number of radon suction pits  and vent pipes  needed for
              passive systems to be effective in a large building would make
              installation more expensive than an ASD system. Therefore,
              in radon-prone areas we recommend you do not use passive
              soil depressurization systems. We do recommend, as a mini-
              mum, that the design features for an ASD system be roughed-
              in for later activation if needed.

              ASD Costs

                 Several factors affect the cost of an active soil depressur-
              ization system. Incremental installation costs for  a system
              designed into a new large building range from as low as $0.10
              per ft2 of earth  contact area to more than $0.75 per ft2,
              depending on the availability of aggregate and sealing costs
              (3,4,5,6,7,8). If aggregate is already part of the design, the
              costs will be at the low end. Incorporation of the aggregate
              and vapor retarder is considered good architectural practice
              and is  required by code in most areas  of the U.S., and,
              therefore would not be considered a radon-prevention cost.

                 For comparison, a recent EPA. survey showed that the
              average cost for installing ASD in an existing school is about
              $0.50 per ft2 (9). These costs could range from about $0.10 up
              to $3.00 per ft2 of earth contact floor area depending on the
              structure and subslab materials.

              1.4.2    Building Pressurization

                 Building pressurization involves bringing  in more air to
              the building man is exhausted, causing a slightly positive
              pressure inside the building relative to the subslab  area. The
              positive pressure in the building causes air to flow from inside
              the building to the outdoors through openings in the substruc-


lure and building shell; this effectively seals radon  entry
routes. Building pressurization is similar to ASD in that both
methods block radon entry routes using air pressure barriers;
but the systems are different in that, with building pressuriza-
tion, air is pushed out of the building from inside rather than
being drawn out from under the slab, as in ASD. The follow-
ing section explains the principles of building pressurization
using the heating, ventilating, and air-conditioning (HVAC)

How Buildings Typically Operate

    Many buildings (both leaky  and tight buildings) tend to
maintain an indoor air pressure lower than outdoors. It is often
difficult to continuously operate a building to obtain slightly
positive pressure conditions unless the building shell is tight
and the building HVAC system supplies more outdoor air to
each room than  is exhausted. This difficulty is  due to a
complex interaction between the building shell, the mechani-
cal systems, the building occupants, and the climate.

    Modern buildings generally are constructed  with fan-
powered HVAC systems to provide outdoor air to the occu-
pants.  Many buildings  also have exhaust fans to remove
internally generated pollutants from the building. If the sys-
tems place the earth contact area under a slightly positive
pressure with respect to the subslab, they will prevent radon
entry and will dilute radon under the slab for as long as the
systems are operating. However, if these fan systems (by
design, installation, maintenance, or adjustment) place any
earth contact area of the building under a negative pressure
with respect to the soil, radon can enter through any openings
in the slab.

Important Features of HVAC Systems to Prevent Radon

    The following HVAC system features and operating guide-
lines should be followed for radon prevention:

       In radon-prone areas, eliminate air supply and return
       ductwork located beneath a slab, in a basement, or in a
       crawl space in accordance with ASHRAE Standard
       62-1989 (10).

  •    Supply outdoor air in accordance with guidelines in
       ASHRAE Standard 62-1989 (10).

  •    Construct a "tight" building shell to facilitate achiev-
       ing a slightly positive pressure in the building.

       Seal slab, wall, and foundation entry points as noted in
       Section 1.4.3, especially in areas of the building planned
       to be  under negative pressure  by design  (such  as
       restrooms, janitor's closets, laboratories, storage clos-
       ets, gymnasiums, shops, kitchen areas).

  •    Ensure proper  training and retraining of the HVAC
       system operators, together with an adequate budget, so
       that the system is properly operated and maintained.
       (This appears to be a major area of neglect in existing
       school buildings.)

  •    In areas with large exhaust fans,  supply more outdoor
       air than air exhausted if possible.
    Once radon has entered a building, another way to reduce
radon levels is by diluting them with ventilation air (outdoor
air). Dilution air should be supplied from outdoors in accor-
dance with ASHRAE Standard 62-1989 (10). To reduce highly
elevated radon levels it may be necessary to supply higher
quantities of outdoor air than those recommended by ASHRAE.
(Note that neither pressurization nor dilution is effective when
the HVAC system is not operating, such as in night and week
end setback.) Additionally, dilution is not an effective stand-
alone radon reduction technique if radon levels are substan-
tially elevated. Dilution is a less reliable and frequently more
costly approach than the other radon prevention techniques.

    In summary, building pressurization with  the HVAC
system can reduce radon levels; however, because of the
difficulty of  properly operating the system in  a way  that
continuously  prevents radon entry, building pressurization is
not recommended for use as a  stand-alone radon-control
system in new buildings. When building pressurization  is
used with the other methods of radon prevention (ASD and
sealing of major radon entry routes), building pressurization
contributes to low radon levels.

    Costs and savings for HVAC systems and a tight building
shell  are not presented because they are considered good
architectural  and engineering  practice,  and moreover, are
mandated by many building and energy codes.

1.4.3    Sealing Radon Entry  Routes
    Because  the greatest source of indoor radon  is almost
always radon-containing soil gas  that enters the  building
through cracks and openings in the  slab and substructure, a
good place to begin when building a radon-resistant building
is to  make the slab and substructure as radon-resistant as
economically feasible.

    However, it is difficult, if not impossible, to seal every
crack and penetration. Therefore, sealing radon entry routes
and constructing physical barriers as a stand-alone approach
for radon control in schools and other large buildings, is not
currently recommended. On the other hand, sealing of major
radon entry routes will help reduce radon levels and will also
greatly increase the effectiveness of other radon prevention
techniques. For example, sealing increases the effectiveness
of ASD by improving the pressure field extension beneath the
slab. Sealing also helps to achieve building pressurization by
ensuring that the building is a "light box" without air leakage.
Many of these sealing techniques are standard good construc-
tion practices.

Sealing Recommendations

    Radon entry routes that should be sealed are:

  •   Floor/wall crack  and other expansion joints. Where
      code permits, replace expansion joints with pour joints
      and/or control saw joints because they are more easily
      and effectively sealed.

  •   Areas around all piping systems that penetrate the slab
      or foundation walls below grade (utility trenches, elec-
      trical conduits, plumbing penetrations, etc.).

  •   Masonry basement walls.


Limitations of Sealing

    Many construction materials are effective air and water
barriers and also retard the transfer of radon-containing soil
gas. In practice however, the difficulties that arise when using
sealing and physical barrier techniques as the only means of
control are virtually insurmountable. Physical barriers  have
proven to be frequently damaged during installation; more-
over, failure to seal a single opening can negate the entire
effort, especially when radon concentrations are high. Never-
theless, you should seal major radon entry routes; not only
will sealing retard radon transfer but sealing will also increase
the effectiveness of ASD and building pressurization.

    The cost of sealing major radon entry routes is dependent
on the building design  and local construction practices. For
one example, refer to the case study in Appendix A.

1.5      Why Radon Prevention Should be
          Considered in Building Design
    Most of the radon prevention techniques covered in this
manual can be applied  to existing buildings, but installation
will cost more than if these techniques were installed during
initial construction. For example, factors  that  increase the
difficulty and  cost to install an ASD system in an existing
building include:
  •    Poor communication below the floor slab (i.e., no
       aggregate or aggregate with many fines or with wide
       particle size distribution range).

  •    Barriers to subslab communication  (internal subslab

  •    Radon entry points at expansion and control joints.

  •    Ease of running the radon vent pipe and power source
       through and/or out onto the building's roof.

       Building depressurization caused by the HVAC sys-
       tem (or other  fans) exhausting more air than is sup-

    All of the above factors can  be controlled in new con-
struction. As further research is conducted, additional infor-
mation on the radon prevention features, or better guidance on
when they are not needed, should become more clear and will
be documented in future updates of this manual.

    Again, we emphasize that it is  important to include
radon prevention features during design. Including these
features during building construction makes their appli-
cation  easier and costs much less than adding them after
the building is completed.



                                                 Chapter 2
                              Technical  Construction  Information
    As outlined in Chapter 1, there are three practical and
cost-effective approaches to preventing elevated radon levels
in new buildings.

  •    Active Soil Depressurization (Section 2.1)

       Building Pressurization (Section 2.2)

       Sealing Radon Entry Routes (Section 2.3)

    EPA recommends using  all three of these methods to
ensure effective and reliable radon control.

    The following three sections present  detailed technical
information for implementing the above approaches. These
sections might best be used by the architects and engineers
who are developing the specifications and construction draw-
ings for the building, and by the contractor who is building the
structure. Guidelines for conducting radon measurements in
schools and other  large buildings are briefly discussed in
Section 2.4.

2.1       Active Soil Depressurization (ASD)
    This section describes how to design, install, and main-
tain an ASD system. The discussion pertains to slab-on-grade
substructures  since most new  schools and other large build-
ings are constructed slab-on-grade. Guidelines for basement
substructures  are similar to slab-on-grade buildings,  except
that basement walls add another potential radon entry point
that must be sealed. The application of ASD to basements is
briefly covered in Section 2.1.3. Radon control in buildings
with crawl space substructures is addressed in Section 2.1.4.

    In most parts of the U.S., design and construction of new
buildings with ASD systems is relatively easy and cost effec-
tive. Incorporating an ASD system into  a new building is
highly recommended in radon-prone areas, since effective
operation of an ASD system is dependent on building  design
factors. Although it is possible  to add an ASD system after the
building is complete, the cost and effectiveness of the system
will be directly influenced by building design parameters that
can be easily controlled during building design and construc-
tion. Certain  parameters, such as aggregate selection and
subslab walls, cannot be practically modified in an existing
Principles of Operation

    An ASD system prevents radon entry by creating a nega-
tive-pressure zone beneath the slab. If the negative-pressure
zone is extended throughout the entire subslab area, air will
flow from the building into the soil, effectively sealing slab
and foundation cracks and holes, and thus preventing the entry
of radon-containing soil  gas. Figure 2-1 illustrates a typical
ASD system.

    To create this negative-pressure zone, a radon suction pit
is installed in the aggregate under the slab. This subslab pit is
then connected to a vent pipe that runs from the pit to the
outdoors. A suction fan is connected to the pipe outside of the
building to produce the negative-pressure zone beneath the
slab, hence the system is "active." A lower air pressure in a
building relative to the surrounding soil is what draws radon-
containing soil gas into a building. The ASD system reverses
the pressure difference—and thus the airflow direction at the
slab — causing the subslab pressure to be lower than the
indoor pressure. This air pressure differential keeps radon-
containing soil gas from entering the building.

    This manual describes  the design and installation  of a
complete ASD system. A soil depressurization system could
also be "roughed-in" and activated with a fan later, if needed.
For new construction, where radon levels may be even mar-
ginally elevated, the installation of a rough-in system is a
prudent investment and  is recommended.  If the completed
building has a radon problem, then the roughed-in soil depres-
surization system can easily be made active at a low cost by
adding a fan.

    Architects and engineers may ask, "Is it possible to install
a soil depressurization system that works passively (that is,
without a fan)?" Although research has shown that passive
systems are sometimes effective in home construction,  they
are not recommended for use in schools and other large
buildings. Many competing negative pressures in large build-
ings can easily  overcome a passive system. Also, the large
number of radon suction  pits and vent pipes needed for
passive systems to be effective in a large building would make
installation more expensive than an ASD system. Therefore,
in radon-prone areas we  recommend you do not use passive
soil depressurization systems. We do recommend,  as a mini-
mum, that the design features for an ASD system should be
roughed-in for later activation if needed.


                                  Roof Exhaust Fan

                Note: Seal All Major Slab Openings,
                     Cracks, or Penetrations  .
                Polyurethane Sealant
                    Radon Exhaust Fan

                    Radon Exhaust Stack
Radon Vent Pipe
Schedule 40 PVC
                                                                              Slab on Grade
                                 Q                              Radon Suction Pit
                             ASTM Size #5 Aggregate or Equivalent

                                                  @  = Positive Pressure

                                                  Q  = Negative Pressure

Figure 2-1.   Typical subslab depressurlzation system. Not to scale.
2.1.1    ASD Design and Installation
    The six essential guidelines for designing and installing
ASD systems in schools and other large buildings are listed
below. The design and construction procedures for each are
discussed in detail in the sections that follow.

  1)   Place a continuous 4- to 6-in. layer of clean, coarse
       aggregate under the slab. (Aggregate, Section

  2)   Eliminate barriers to subslab airflow such as subslab
       walls. (Subslab Walls, Section

  3)   Install a 4- by 4-ft area by 8-in. deep radon suction pit
       (or equivalent) under the slab. (Suction Pits, Section

  4)   Run  a 6-in. diameter PVC radon vent  pipe from the
       radon suction pit to the outdoors. (Radon Vent Pipe,

  5)   Install a suction fan designed for use in ASD systems.
       (Suction Fan, Section

  6)   Seal major radon entry routes including slab and foun-
       dation joints and cracks and utility and pipe penetra-
       tions. (Sealing Radon Entry Routes, Section 2.3)   Aggregate
          Figure 2-1 illustrates how the creation and extension of a
      negative pressure field beneath the slab will cause air to flow
      from  the building into  the  subslab  area. This direction of
      airflow will prevent entry of soil gas into the building. The
      radon-containing soil gas is drawn up  the  vent pipe and
      exhausted outdoors where it will be quickly diluted to ambient

          To extend this negative  pressure field effectively, highly
      permeable material, such as aggregate, should be placed under
      the slab. If the subslab material has low permeability (such as
      tightly packed sand or clay), or  is interrupted by  interior
      subslab walls (as discussed  in Section, the pressure
      field might not extend to all areas of the soil under the slab.
      The building  should be designed so that the pressure field
      extends under the entire building. To ensure the proper exten-
      sion of the pressure field, install a 4- to 6-in. layer of clean,
      coarse aggregate beneath the slab prior to the pour.

      Aggregate Specifications

          In most areas of the U.S., subslab aggregate is routinely
      installed (and frequently required by code) to provide a drain-
      age bed for moisture and a stable, level surface for pouring the
      slab.  The preferred aggregate for ASD  systems is  crushed
      aggregate meeting Size #5 specifications as defined in ASTM
      C-33-90, "Standard Specification for Concrete Aggregates"


(11). This aggregate is in the range of 1/2 to 1 in. diameter
with less than 10 percent passing through a 1/2-in. sieve and
has a free void space of approximately 50 percent.

    In September 1992, the average cost for a ton of crushed
stone was $6.86. This cost represents an average for 20 U.S.
cities, with a range from $4.50 to $11.32 per ton (12). For a
layer of crushed stone 4 in. deep, this would be about $0.10 to
$0.25 per ft2.

Aggregate Placement

    Place a minimum of 4 to 6 in. of aggregate evenly under
the entire slab, taking care not to introduce any fine material.
If the aggregate  is placed on top of a material with a lot of
fines and compaction  of the aggregate is required for struc-
tural or code reasons, a geotextile fabric or an additional
reinforced vapor retarder beneath the aggregate can be used so
that fine  particles from the natural  soil  do  not mix  with the
aggregate. A vapor retarder should also be placed over the
aggregate prior to pouring the slab. Although the vapor re-
tarder probably will not serve as  a stand-alone radon barrier
(due to inevitable holes and tears in the plastic), it will keep
the wet concrete from filling in spaces in the aggregate layer.

Drainage Mats

    In areas where crushed aggregate is not readily available
or is very  expensive, some residential  builders have used
drainage  mats designed for soil stabilization. Drainage mats
cost $0.60 to $0.72 per ft2 and are normally placed under only
part of the  slab. The  use  of  drainage  mats has not been
demonstrated by EPA in any schools or other large buildings.   Subslab Walls
    Because every subslab area isolated by subslab walls will
normally need a radon suction pit and radon vent pipe, limit-
ing subslab barriers to airflow will reduce ASD installation
and operating costs. Figure 2-2a shows how an interior subslab
wall can interrupt the aggregate layer and, hence, the subslab
pressure field. Figure 2-2b, on the other hand, shows how a
continuous aggregate  layer under a thickened slab footing
does not interrupt the subslab pressure field.

    Figures 2-3a through 2-3d illustrate examples of four
subslab wall layouts  that have  been observed in  existing
school buildings. The discussion below  explains the effects
that these example configurations have on ASD system de-

    The  Figure  2-3a design is preferred for radon control
because internal subslab barriers are completely eliminated,
thus maximizing subslab communication and ASD system
performance. This design is  referred to as post-and-beam
construction and is very common in modern construction of
large buildings.  With this type of building  design and the
other ASD design features discussed in this section, one radon
suction pit should provide adequate pressure field coverage
over 100,000 ft2 of ground contact area or larger. The building
in the Appendix A case study has this type of subslab layout.
In another recently constructed building with post-and-beam
construction, one radon suction point depressurized an area of
480,000 ft2.
    Figure 2-3b illustrates the use of subslab walls that are
perpendicular to the corridor but do not cross the corridor. In
this example, the subslab walls would not interrupt the nega-
tive pressure field under the slab unless the subslab wall
extended across the corridor (not shown in Figure 2-3b). As a
result, only one radon suction pit would be needed.

    Figure 2-3c shows two subslab walls each parallel to the
corridor. In this case, the subslab area is divided into three
compartments. For this design, two radon suction pits would
probably be required, or three if one is installed in the corridor

    Figure 2-3d shows  the worst case example for a cost-
effective ASD system design. Subslab walls run both parallel
and perpendicular to the corridor, dividing the subslab area
into many compartments. For an ASD system to be effective
with such a design, one radon suction pit would normally be
required for each subslab compartment.

    Figures 2-4a and 2-4b illustrate the side view of the effect
of subslab walls on the design of the ASD system. Figure 2-4a
corresponds to a possible ASD system design for the subslab
wall layouts shown in Figures  2-3a  and  2-3b. Figure 2-4b
corresponds to the ASD system design required for the  lay-
outs in Figures 2-3c and 2-3d. For the "worst case" scenario
shown in  Figure 2-3d, this  sideview of  the suction  points
would be required for each area surrounded by subslab walls.
(Note that the radon suction pit shown  in the  corridor in
Figure 2-4b may not be necessary.)

    It is important that the issue of subslab walls be addressed
early  in the  planning  stages so that the building can be
designed with limited subslab  barriers.  Designing subslab
walls as illustrated in Figure 2-3a will significantly reduce the
cost of radon prevention as evidenced  by the  case study
(Appendix A).

    In buildings where subslab walls must be used, the de-
signer should consider "connecting" subslab areas by elimi-
nating subslab walls (Figures 2-4a and 2-4b) under interior
doors. This "connecting or bridging" should allow the nega-
tive pressure  field to extend from a centrally located radon
suction pit to  areas that would have otherwise been isolated.
This approach has had  only limited field testing, but it is
theoretically sound and is undergoing further field testing.
Subslab communication  could also be facilitated  by using
subslab "pipe sleeves" to connect areas separated by subslab
walls. Again,  using "pipe sleeves" is theoretically sound, but
has not yet been field-demonstrated by EPA.  Radon Suction Pits
Purpose and Specifications

    Radon suction pits facilitate communication throughout
the subslab aggregate layer. Figure 2-5 presents an example of
a radon suction pit that has  been successfully field-demon-
strated by EPA in ASD systems in new construction.  The
most important feature of the pit is that the end of the vent
pipe terminates in a large void (or its equivalent exposed
aggregate surface area). We recommend that for a 6-in. diam-
eter vertical stack, you construct a radon suction pit with a 4 ft
by 4-ft void area and 8 in. deep. These dimensions provide a
pit void to aggregate interface of about 7 ft2.


                 Polyurethane Sealant
                                                                      Concrete Block Wall
                                                           Expansion Joint with Backer Rod and
                                                       Polyurethane Pourable Sealant Flush with Slab
                                                                          Aggregate (ASTM
                                                                              Size #5 or
                                                                           Compacted Soil
Figure 2-2a.  Interior footing/foundation wall. Not to scale.
                                                                      Concrete Block Wall
                                                                          Aggregate (ASTM
                                                                             Size #5 or
                                                                            Compacted Soil
Figure 2-2b.  Thickened slab footing. Not to scale.
    A suction pit with a minimum exposed aggregate surface
area about 30 times the cross sectional area of the vent pipe
entrance is very effective. A concrete drainage distribution
box or other structure that meets the 30-1 ratio should also be
effective. However, only the construction detailed in Figure 2-
5 has been field-tested by EPA. As shown in Figure 2-5, the
vent pipe should enter the radon suction pit horizontally so
that the suction pit may be located in a central location and the
vertical vent pipe may be located wherever is most convenient
rather than simply at the pit location.

    Alternatively, the vent pipe can exit the radon suction pit
vertically.  The vertical approach is normally used for ASD
systems in existing buildings because of the ease of installa-
tion. However, new construction provides the designer with
the flexibility for selecting the most convenient and effective
location for the radon suction pit and vent stack. When the
slab is poured over the radon suction pit as shown in Figure 2-
5, be sure to  follow appropriate structural guidelines for
reinforced concrete.

Location of Radon Suction Pits

    The radon suction pit should be centrally located. A
centrally located pit will provide even pressure field extension
in all directions. Do not locate the pit near subslab barriers


                                                             Radon Suction Pit
                             Radon Pipe Riser to be Encased
                                            Subslab Column Footings
                                           111 • • 11111 r
          All Interior Walls  ~\
         Non-Load Bearing     >
                                                 Subslab Footings
Figure 2-3a.  Outside walls and post load bearing. Not to scale.
(such as footings) or near unsealed openings through the slab.
As shown in Figure 2-5, the vent pipe should enter the radon
suction pit horizontally. The vent pipe is then run under the
slab, exiting the subslab in a convenient location.

Number of Radon Suction Pits

    With the use of a properly  designed radon suction pit,
ASTM Size #5  aggregate, the elimination of subslab barriers,
and seating of major radon entry routes, one radon suction pit
per 100,000 ft2 of slab area should result in a very effective
ASD system. This Figure 2-5 approach was recently success-
fully demonstrated by EPA in two large buildings: one build-
ing is  60,000 ft2 in area, and the other is  480,000 ft2. The
60,000 ft2 building is discussed in detail in Appendix A.

Subslab Perforated Pipe

    Instead of a radon suction pit, some designers prefer
laying perforated polyvinyl  chloride (PVC) drainage pipe
under  the slab and connecting the perforated pipe to the vent
pipe. Horizontal perforated pipe is not necessary in ASD
systems  if the  system is designed  as recommended in this
manual.  This is because for a subslab horizontal pipe system
to provide the equivalent exposed surface area to aggregate as
a 4-ft by 4-ft by 8-in. deep radon suction pit, it is necessary to
have approximately 240 linear ft of 4-in. pipe (with ten 3/4-in.
holes per ft).

    One recently constructed school with 50,000 ft2 of ground
contact used 11 suction points with 120 linear ft of perforated
pipe extending from each suction point, totaling over 1300
linear ft. Field testing by EPA demonstrated that only one of
the 11  suction points was needed and that the perforated pipe
was not necessary for an effective ASD system (7).

    Although some designers use systems with perforated
pipe instead of a radon suction pit (7), this type of system can
significantly increase construction costs due to both the quan-
tity of pipe needed and the cost of placement. Therefore, EPA
prefers the radon suction pit approach to  installing subslab
perforated pipe. If perforated pipe is used,  size it so as not to
significantly  reduce the air flow which could normally  be
achieved through the connecting 6-in. vent pipe.

Interaction With  Interior Drainage

    Designers and builders of houses also have tried connect-
ing the ASD system into interior footing  drainage systems.
Although this connection might facilitate the functioning of a


Figure 2-3b.  Interior walls between rooms and outside walls load bearing. Not to scale.
passive system if the system is airtight, this approach has not
been evaluated by EPA in schools or other large buildings.

    Similarly, the use of interior footing drains for water
control can affect the pressure field extension  of an AS D
system. Interior footing drains sometimes terminate in a sump
hole. If this is the case, the builder must seal the sump hole
airtight; if the sump hole is not sealed airtight,  building air
will be drawn into the sump by the subslab system, and the
pressure field will be weakened, and pressure field extension
will be decreased. It is also possible to use the sealed sump
hole as a radon suction pit; this approach is common in houses
(5), but its applicability in schools and other large buildings
has not been demonstrated.   Radon Vent Pipe

    For new construction of schools and other large build-
ings, EPA recommends 6-in. diameter solid PVC pipe. Other
sizes are available; 4-in. pipe is normally used for drainage
systems and plumbing stacks and is easy to route vertically.
However, if you are not planning on sealing expansion joints,
we recommend you use vertical  piping at least 6 in. in
diameter. This size pipe is necessary since greater airflow will
be needed to produce the same level of subslab suction and
pressure  field extension as  a  system with sealed expansion
    If interior footing drains are used and extend out beneath   Building Codes
the footing to daylight or to a sewer, the drain must be airtight
while still allowing water to drain in order for the system to
work. Water traps have been used in houses, but this approach
has yet to be demonstrated or evaluated in schools or other
large buildings.
    PVC radon vent pipes are typically used in existing
buildings because of their ease of handling and cost; however,
building codes in some areas of the country might prevent the
use of PVC piping in some sections of buildings. For ex-
ample, special restrictions sometimes apply  to pipe used in
firewall  penetrations and plenums above dropped ceilings.


                                   -  Interior Walls  -
                                     Non-Load Bearing
                                                                Radon Suction Pit
                                                                  /  Ra
                                                              V.'.   D
            Radon Pipe
            Riser to be
                                          Radon Suction Pit
                                               Load Bearing Walls
Figure 2-3c.  Hall and outside walls load bearing. Not to scale.
Also, building codes in some areas require steel pipe; in most
areas, code requires suitable fire stop details at any location
where the exhaust piping penetrates a fire rated wall, a ceiling
deck, or a floor deck. Generally, PVC pipe can penetrate a
firewall if a material to block fire is used. When installing the
radon vent pipe, make sure  you do not violate applicable
codes.  For example, the building in the Appendix A case
study used Schedule 40 PVC pipe beneath the slab and steel
pipe above the slab in order to meet state codes.

Piping Installation

    Attention to detail while installing the vertical risers will
help ensure the proper operation and long life of the system.
Starting at the floor slab, seal any openings between the pipe
and the floor slab with a high adhesive sealant (polyurethane
is currently preferred). Also, seal all piping joints. An illustra-
tion of sealing pipe penetrations through the roof is shown in
Figure 2-6.  Additional details  on sealants and  sealing are
provided in Section 2.3.

    It is important that all horizontal pipe runs are pitched a
minimum of 1/8 in. per ft so that accumulating condensation
 drains back to the radon suction pit. Accordingly, it is also
 important to avoid any low areas in the horizontal pipe that
 could block airflow if condensation were to accumulate in the
 pipe. One architect has noted that, when piping is installed in
 dropped ceilings that may have a drop in temperature, insula-
 tion of the piping helps to avoid  condensation problems.

 Labeling of System Components

     Label the exposed radon vent pipe to identify the pipe as
 a component of a radon vent system that may contain hazard-
 ous levels of radon. Labels should be placed at regular inter-
 vals (at  least every 10 ft) along the entire pipe run. Clearly
 mark all components of radon  reduction systems as radon
 reduction devices to ensure that future owners of the building
 do not remove or defeat the system. At the roof exit, attach a
 permanent label to the vent with a warning such as "Soil gas
 vent stack may contain high levels of radon; do not place air
 intake within 25 ft." Refer to local codes to determine the
 specific minimum distance for  air intakes.  The suction fan
 discharge location is covered in greater detail in the following



Jf 1 pw

i    1
Radon Suction Pit
/ Radon Pipe
r_/ Riser to be

i_ y.? _ _j
1    1

1 *^' 1
!    JL      i

I^-TI Radon Pipe
! i X i Riser to be

i    1
Radon Suction Pit
1 ^- i — .. L
L JL _   i
Radon Suction Pit ^X5^!?~ Radon Pipe ^
Subslab Footing V^x Riser to be Subslab Footing
L ^ Encased (Typ.)
,    ^   ,
Radon Suction Pit
L.*. _J
i    u   1
x Subslab
i    1
r FT    

r- . . -„_.,    
Footings \
i — -fl      1
i^tt ~*\
1 >s »V
I/ «J ^l
Radon Suction Pit

>f 1 HV.

Figure 2-3d.  All Interior walls load bearing. Not to scale.
                                                                             Radon Exhaust Stack

                                  ASTM Size #5 Aggregate or
 Figure 2-4a.   Section 1 (corresponds to Figures 2-3a and b). Not to scale.



                                                                   Radon Exhaust Stack
               ASTM Size #5
               Aggregate or
Figure 2-4b.  Section 1 (corresponds to Figures 2-3c and d). Not to scale.   Suction Fan
When to Install

    A suction fan can be installed during building construc-
tion or the piping can be terminated and capped at roof level
and the fan installed later. As discussed previously, passive
systems (without a  fan) are not recommended for  radon
control in schools and other large buildings. ASD system fans
should be operated continuously; otherwise elevated levels of
radon may accumulate. The cost of operating the fan continu-
ously is comparable to the cost of operating any other exhaust
fan in the building (such as a restroom exhaust fan).

Fan Selection and Installation

    Use  fans manufactured  specifically for outdoor use in
radon control systems. These are available from many ven-
dors in a variety of sizes. Fans normally used for schools and
other large buildings are in-line duct fans rated from 500 to
600 cfm at zero inches static pressure. Because piping on the
exhaust side of the fan is under positive pressure and might be
subject to leaks, the fan always should be mounted outside the
building. Designers should be aware that leakage inside the
envelope of the building is not acceptable.

    Most installers connect the  fans to the pipe system with
rubber sewage pipe connectors. This connection allows for a
tight seal, quiet operation, and easy replacement of the fan (if
needed). Additional materials and components are normally
included  in a system to satisfy safety needs, system perfor-
mance indications, and noise reduction. Typically code re-
quirements dictate that waterproof electrical service switches
be placed within view of the fan to ensure that the system will
not be activated  during maintenance. If the ASD system is
being roughed-in, with the fan to be installed later if needed,
installation of the waterproof electrical connection above the
roof during construction will facilitate addition of the fan.

Suction Fan Discharge

    The exhaust discharge configuration of an ASD system
should be treated similarly to the discharge of a laboratory
fume  hood or other rooftop exhaust that vents toxic fumes.
Some building codes, for example, specify that any discharge
of pollutants must be located at least 25 ft from any outdoor
air intakes. Examples of suitable discharge configurations are
presented  in  the Industrial Ventilation Manual of Recom-
mended Practices, 19* Edition (13), and the ^959 ASHRAE
Fundamentals Handbook (14).

    We recommend that the vent pipe terminate in a vertical
position above  the roof with sufficient height that the dis-
charge does not re-enter  the building. The discharge  can
contain extremely high levels of radon. If this configuration is
not possible, we recommend that you choose a configuration
that provides at least a 1,000 to 1 dilution ratio to the nearest
air intake or operable window. This dilution ratio is calculated
from the ASHRAE Fundamentals Handbook Chapter 14 equa-
tions (14).

Warning Device

    ASD system designers should include a device that warns
building owners and occupants if the system is not operating
properly. A preferred warning system has an electronic pres-
sure sensing device that activates a warning light or an audible
alarm when a system pressure drop occurs. These are readily
available from several suppliers. We advise installing a device
that warns of a pressure change rather than one that deter-


                                                                            Stack Vented Through Roof
                                     Concrete Slab

                                               Thickened Concrete Slab
                                              3/4" Pressure Treated Plywood

                                                                  8" x 8" x 8" Concrete Block
                                         Pipe Sleeve
                            Clean Coarse Aggregate
                           ASTM Size #5 or Equivalent
                                                          Section A
                                              4'xA'x 3/4"
                                              3/4" Pressure Treated Plywood
                                                                               Stack Vented Through Roof
                                                                           8" x 8" x 8" Concrete Block
Figure 2-5.   Radon suction pit. Not to scale.
mines fan operation. Several things can stop a system from
operating effectively besides fan operation. Additionally, the
fan may still appear to be operating even though air flow is
severely reduced.

    Install the warning device in an area frequently visited by
a responsible person. In some schools, warning devices have
been placed near the HVAC control panels or in the principal's
office. Some schools have chosen to connect the signal from a
warning device into the energy management system computer
for the district.   Sealing Major Radon Entry Routes
    For an ASD system to be most effective, it is important to
seal large openings (such as utility penetrations and expansion
joints) that can defeat extension of a low pressure field. Large
openings in the slab not only reduce system effectiveness, but
also increase operating costs by drawing too much air from
inside the  building. Section 2.3 provides comprehensive in-
structions and guidelines for sealing.

2.1.2    Operation and Maintenance
    ASD  system operation and  maintenance concerns  fall
into three time frames:

  •    Before Occupancy

  «    Weekly

  •    Annually


                                                                                          Top of Stack
                                                                                     25' from Any Air Intake
 Polyurethane Sealant Applied Behind
 Turnup and on Top of the Draw Band
       Approved Fasteners and Disc
        (Min. of 4) Around Vent Pipe
                                                                                           Radon Exhaust Fan
Draw Band, Required
 Minimum 1" Turnup

Figure 2-6.   Sealing pipe penetrations through roof. Not to scale.

 image:   Before Occupancy
    Measure radon levels in the building at least 24 hours
after the ASD fan is turned on. (Guidelines for measuring
radon levels are briefly covered in Section 2.4 of this manual.)
If you have roughed-in an ASD system without a fan, then
these radon measurements will determine if it is necessary to
activate your system with a fan. Many building owners con-
tinuously operate ASD systems even if radon levels without
the system are below 4 pCi/L. Continuous operation of the
system will further reduce radon exposure to building occu-

Measure Subslab Pressures

    If the building has elevated radon levels, it is important to
confirm that the ASD system is achieving an adequate nega-
tive pressure field under all areas of the slab. Measurement of
the subslab pressure field is commonly referred to as pressure
field extension (PFE) or subslab communication.

    To measure PFE, it is necessary to drill about 10 small
holes (approximately 1/4 to 1/2 in. diameter) through the slab
at various distances and directions from the suction pit. Be
sure to carefully determine the locations of all subslab utility
lines before drilling through the slab. Then, with the ASD fan
off, measure the subslab pressure in each of the holes. This
should  be done using  a sensitive  device  such as  a
micromanometer; however, something as simple as a chemi-
cal smoke stick could be used to determine if air flows into the
slab. These measurements should then be repeated with the
ASD fan turned on. Once the PFE tests are complete, the holes
should be carefully sealed with concrete patching material.

    The purpose of PFE measurements is to confirm that the
ASD system maintains an adequate negative pressure under
the slab. A minimum subslab pressure  of -0.002 in. water
column (WC) is required at all test holes for an effective ASD
system.  If all of the recommendations for ASD discussed in
this section are followed, then the  pressures at even the
farthest test holes should be at least -0.01 in. WC. If measure-
ments indicate that there is inadequate pressure field under the
slab, troubleshoot the system by confirming fan operation,
sealing major radon entry routes, locating potential subslab
barriers, inspecting type of aggregate used, and inspecting the
operation of the HVAC system. (See Section 2.2 for informa-
tion on how an HVAC system can overcome ASD.)

    Some builders express concern about drilling holes in a
newly constructed building; however, measurement of PFE is
the only way to determine if the negative pressure is being
extended.  Detailed guidelines for measuring PFE are de-
scribed in numerous EPA publications (2,3,9,15) and are also
discussed in the Appendix A case study. The holes do not
compromise the structure of the building and are normally
covered with finished floor such as carpet or vinyl.

Provide ASD Operating Manual

    An  operating manual describing  the system and its pur-
pose should be provided to building owners. The manual
should include a discussion of system components, how to
interpret the system failure warning device, and the other
important maintenance needs of an ASD system as explained
in this section.  Weekly
    Check the pressure gauge(s) in the radon vent pipes and
the system alarm to ensure that the fan is maintaining ad-
equate negative pressure to depressurize the subslab area.  Annually
    Inspect  the fan for bearing failure  or signs  of other
abnormal operation, and repair or replace if required.

    Inspect the discharge location of the vent pipe to ensure
that no air intake has been located nearby, and that a building
usage change has not placed the exhaust near operable win-

    Check the HVAC system to determine if it  is  being
maintained and operated as designed. Even though the ASD
system may be functioning as designed, excessively powered
exhaust without adequate makeup air might overcome an
ASD system.

    If building settling is  noted, check for slab, floor, or
basement wall cracks and perform radon testing (and addi-
tional sealing, if needed) to ensure the continued effectiveness
of the system. (Refer to Section 2.4 for guidelines on radon

2.1.3    Additional Instructions for
    Instructions for designing and installing an ASD system
in buildings with basement foundations are similar to instruc-
tions for slab-on-grade buildings. The primary  difference is
that basement walls provide additional radon entry routes.

    Below-grade walls and stem walls are normally con-
structed of either poured concrete or masonry blocks. Section
2.3.3 discusses the different types of below-grade walls and
the coatings that can be used to seal these walls.

2.1.4    Additional Instructions for Crawl
    This section describes two techniques for radon reduction
in crawl space  buildings:  submembrane depressurization
(SMD) and crawl space depressurization. SMD is typically a
much more  effective approach for  maintaining low  radon
levels; consequently, construction of crawl space buildings in
radon prone areas should include provisions for SMD.

Submembrane Depressurization (SMD)

    Since ASD cannot be used in crawl spaces  with dirt
floors, and difficulties are often encountered in isolating a
crawl space from the occupied area above, builders must use
alternate radon prevention techniques in crawl spaces. SMD is
an effective technique for reducing radon levels in  crawl
spaces. This technique is a variation of the successful ASD
method, and is shown in Figure 2-7. Research in schools and
houses has shown SMD to be the most effective year-round
approach for reducing radon levels in crawl space buildings

    To  install a SMD system in a crawl space, 6 mil (or
thicker) polyethylene sheeting is used as a vapor retarder that
forms a small-volume plenum above the soil. A suction fan


and vent stack are used to pull radon from under the mem-
brane and exhaust it outside the building. Active SMD has
been widely applied in houses; limited experience indicates
that it is also effective in schools (16). This approach may be
expensive in large crawl spaces due to the need for large
amounts of polyethylene sheeting; however, because build-
ings often use polyethylene sheeting as a vapor retarder, the
sheeting would not necessarily be considered an additional
mitigation cost.

    To install a SMD system, place wide polyethylene sheets
(with at least 1 ft overlaps between the sheets) directly on the
earth. Be sure to remove any  large rocks, broken concrete
blocks, or other obstructions before placement. After the sheet
is placed, we recommend  that you seal the seams in the
polyethylene in the vicinity of the suction point to increase
system effectiveness. Use the special sealants recommended
by the  manufacturers of the sheeting for gluing polyethylene
together. Where the soil surface  is exceptionally hard and
smooth or the crawl space is very large, use a radon suction pit
or perforated piping manifolded under the sheeting to improve
the pressure field extension. In large crawl spaces with many
support piers it might be more difficult to install SMD. If
many support piers exist, or if  the radon suction point has to
be located close to support piers, seal the polyethylene sheet-
ing to the piers.

    The polyethylene sheeting can also be sealed  to the
foundation walls to reduce air leaks; however, this additional
sealing has proved to be unnecessary in some existing build-
ings. Currently, research is being done to determine exactly
how much sealing of the membrane is necessary.

Crawl Space Depressurization

    Crawl space depressurization is another method for con-
trol of indoor radon. For crawl space depressurization, a fan is
used to depressurize the entire crawl space area. The negative
pressure in the crawl space relative to the building interior
keeps the radon from  entering the building.  However, the
negative pressure in the crawl space will increase radon levels
in the crawl space, so  this technique should not be used if
people need to enter the crawl space frequently. Because of
the potential for high radon levels in the crawl space, it is very
important that the area between the crawl space and building
interior is thoroughly sealed. This sealing is also important to
reduce energy loss from air flowing from the building interior
into the crawl space.

    To achieve a sufficient negative pressure in the crawl
space, the vents should be closed. Research has shown that
closing the  crawl  space  vents will not create a moisture
problem if a vapor retarder is placed over the ground (17).

    A forthcoming EPA manual on radon mitigation of exist-
ing schools will have a more detailed section on crawl space
mitigation.  Call  your  state radon office or EPA Regional
Office for more information.
            Attic/Roof Fan Creates Lower Air
            Pressure Beneath the Membrane
                                                                      Exhaust Stack Above Roof
                                                                 Install Groundcover over
                                                                   Permeable Material
                                        Permeable Material  or
                                        Perforated Pipe Network
                                                                       Pit or Perforated Pipe System
                                                     Positive Pressure
                                                     Negative Pressure
Figure 2-7.   Submembrane depressurization In crawl space.


2.1.5    ASD Cost Estimates
    Estimated typical cost ranges for the materials needed for
an ASD system are presented in Table 2-1. Material costs and
labor costs can vary widely by region. Also, remember that
because many buildings normally use aggregate and a rein-
forced  vapor retarder under the slab,  they  are not usually
considered an additional cost of radon prevention.

    The average total cost of conducting diagnostics and
installing an  ASD system in  an existing  building is about
$0.50/ft2 (9). The total cost of an  ASD system for a new
60,000 ft2 building was $5,000 (see Case Study, Appendix A).

2.1.6    Summary of Guidelines for ASD
    In  areas  where radon is known to be a problem, as a
minimum, it is advisable to rough-in a soil depressurization
system that can easily be made active with a fan. Attention to
detail in the design stage of the soil depressurization system
will  help ensure its success. The following is  a review of
important  guidelines  for building  and designing  an ASD

  •    Place  a continuous 4-  to 6-in. layer of the specified
       aggregate under the slab. (Aggregate, Section

  •    Eliminate barriers to subslab airflow such as subslab
       walls. (Subslab Walls, Section

  •    Install a 4 by 4 ft suction pit under the slab. (Radon
       Suction Pits, Section

  •    Run a 6-in. diameter radon vent pipe from the radon
       suction pit to the outdoors. (Radon Vent Pipe, Section

       Install a suction fan designed for use in ASD systems.
       (Suction Fan, Section

  •    Seal major radon entry routes including slab and foun-
       dation joints and cracks and utility and pipe penetra-
       tions. For  basement substructure, also seal the base-
       ment walls. (Sealing Radon Entry Routes, Section 2.3)
            •    For  crawl space substructures, provide for  a
                submembrane depressurization system. (Section 2.1.4)

            •    Install an alarm system and, to ensure ASD system
                effectiveness and longevity, follow all operation and
                maintenance recommendations. (Section 2.1.2)

         2.2      Building Pressurization and
             The heating, ventilating, and air-conditioning (HVAC)
         system  in a modern building has many functions; it must
         regulate temperature, humidity, air movement, and air quality
         inside the facility. A properly designed and operated HVAC
         system can be used to reduce radon levels by building pressur-
         ization and dilution.

             New construction offers the opportunity to  design and
         install the HVAC system so that it produces a slightly positive
         air pressure inside all areas of the building. Pressurization is
         accomplished by bringing more outdoor air into the building
         than is removed. This has been shown to reduce radon levels
         in existing schools. The outdoor air also increases building
         ventilation, and thus dilutes radon and other indoor contami-

             The following subsections contain design recommenda-
         tions, standards for ventilation, and guidelines for installation,
         operation, and maintenance of HVAC systems. As discussed
         in the overview of this document, in radon-prone areas we
         recommend a combination of ASD, HVAC pressurization and
         dilution, and sealing of major radon entry routes.

         2.2.1    Design Recommendations for
                   HVAC Systems
             Building pressurization is accomplished by bringing in
         more outdoor air than is removed by mechanical exhaust
         systems. Excess air not removed by the exhaust system is
         forced out of the building through cracks and unsealed open-
         ings in the building shell, and is referred to as exfiltration.

             The concepts  of  building pressurization  and building
         depressurization are illustrated in Figures 2-8 and 2-9, respec-
         tively. In both examples  the building HVAC  system has a
         supply of 100,000 cfrn and an exhaust fan that withdraws
Table 2-1.    Estimated Costs for Primary ASD Components

ASD Feature                                         Material Cost
Crushed stone (4 in. deep

Radon suction pit (4 x 4 ft)

Vent stack (6 in. diameter PVC)

Vent stack fittings (6 in. diameter PVC)

6 mil poly vapor retarder under slab

Suction fan


Sealing joints in concrete
(typical 40 x 40 ft slab sections)
$0.10 to $0.25 per ft2
($4.50 to $11.32 per ton)


$2.00 to $3.00 per ft

$20.00 to $30.00 each

$0.10 to $0.30 per ft2

$300 to $500 each

$100 to $150 each

$0.40 to $1.50 per linear ft
(includes material and labor)
If aggregate is normally used, do not
include as additional cost.

As shown in Figure 2-5.

Total cost depends on pipe run length.

Total cost depends on system design.

Normally included in construction.

As discussed in Section

At least one per stack and pit.

Highly variable, depending on building
 design and location.


15,000 cfm. However, in Figure 2-8 there is an outdoor air
supply of 20,000 cfm, or 20% of the total supply. As a result,
the building  illustrated  in Figure  2-8 is  under a positive
pressure and 5,000 cfm of air will exfiltrate from the building.
This positive pressure will keep radon from entering the
building while the HVAC system is operating. On the other
hand, the scenario in Figure 2-9 shows an outdoor air supply
of only 5,000 cfm, or 5% of the total supply. In this case, the
building is depressurized by 10,000 cfm. This depressuriza-
tion will cause air to infiltrate  into the building and can
exacerbate radon  entry into the building. The natural "stack
effect" can also contribute to building depressurization.

    To minimize the amount of outdoor air needed to pressur-
ize a building, the shell of  the building must be tightly
constructed. In addition to facilitating building pressurization,
a tight building shell will reduce energy costs and allow for
improved environmental control. For details on measuring air
leakage rates, refer to ASTM E779 "Standard Test Method for
Determining Air Leakage Rate by Fan Pressurization (18)."
Note that large buildings may be difficult to test by this
method because of the larger leakage area.

    Measurements  in existing schools  show that a slight
positive pressure (as little as +0.001 in. WC relative to subslab
and outdoors) reduces radon levels by preventing radon entry.
So, radon entry should be prevented while the HVAC system
is operating if the building is pressurized.

    The  supply  of outdoor air also helps to reduce radon
levels by dilution. For a given constant  rate of entry, radon
concentrations in a building are inversely proportional to
ventilation rates. Thus, for example, to reduce radon levels by
a factor of 10, one would have to increase the air exchange
rate by that same factor (19). In most  cases, such a  large
exchange rate may be neither practical nor desirable.
                    Although building pressurization and dilution can reduce
                radon levels and improve indoor air quality, they do present
                some concerns  as  a stand-alone radon control technique.
                These include:

                  •    If total building exhaust capacity is not balanced with
                      an equal or greater amount of conditioned makeup air
                      (outdoor  air), the pressure in the building interior will
                      be negative with respect  to the subslab area. This
                      negative  pressure acts as a driving  force for radon-
                      containing soil gas to be drawn into the building.

                  •    Open windows and doors make it  very difficult to
                      achieve a consistent positive pressure in the building.

                  •    Start/stop operation of the HVAC system for-various
                      occupancy modes does not allow for continuous build-
                      ing pressurization. If the HVAC system is turned off or
                      set back during unoccupied periods, then the specific
                      hours of preoccupancy start-up to reduce radon levels
                      that have built up while the system was off should be
                      determined on a building-by-building basis.

                  •    The design and operation limitations of different types
                      of HVAC systems must be considered when designing
                      a system to pressurize the building. For example, the
                      design of variable air volume (VAV) systems must
                      take into consideration the effects of minimum flow
                      conditions on ventilation  and pressurization of the

                    For additional  information on the effects  that different
                types of HVAC systems have on radon levels in schools, refer
                to the recent EPA report "HVAC  Systems in the Current
                Stock of U.S. K-12 Schools" (20).
                                                                         Exhaust Fan
                   I        1        i  I   T
                Total Supply 100,000 CFM Includes
                    Recycled Air 80,000 CFM
Positive Pressure From
5,000 CFM Excess (ft

                                                   : Positive Pressure
                                                   : Negative Pressure
 Figure 2-8.    Building positive pressurization with HVAC system.


                                                                       Exhaust Fan
                             r~m    r   i
              Total Supply 100,000 CFM Includes
                  Recycled Air 95,000 CFM
                    Unit Ventilator
                                        Negative Pressure From
                                        10,000 CFM Deficiency (
                15,000 CFM
                                             10,000 CFM
          10,000 CFM
                                                  Positive Pressure
                                                  Negative Pressure
Figure 2-9.   Example of building depressurization with HVAC system.
2.2.2    Standards lor Ventilation
    For many years it has been common practice to design
large buildings with approximately 10% more supply air than
return air in order to reduce drafts from infiltration. Following
this same procedure in a building with a tight shell is likely to
produce a net positive pressure in the building during normal
operation. Examples  of recommended ventilation standards
for commercial buildings, from ASHRAE Standard 62-1989:
"Ventilation for Acceptable Indoor Air Quality" (10), are
summarized in Table  2-2. The ASHRAE guidelines are being
adopted by  many  states and national building codes as a
standard in new construction. The application of this standard,
coupled with "tight" construction, is expected to reduce entry
of soil gas and increase dilution of building contaminants.
Both the increased ventilation and the pressurization should
help to reduce indoor radon levels.

2.2.3    Guidelines for Installation and
    It is not practical to provide specific radon control guide-
lines for designing and operating every type of HVAC system.
However, the following basic guidelines for achieving build-
ing pressurization should be discussed with the design engi-
neers during the planning stage.

       Plan the HVAC systems so that the building interior in
       all ground contact rooms is at least slightly pressurized
       (for example,  0.005 to 0.010 in.  WC). Any effect on
       moisture dynamics and code acceptability must also be
       addressed by the building designers.

  •    Avoid subslab supply and/or return ductwork.

  •    In radon-prone areas, do not locate air supply or return
       ductwork in a crawl space (10).
  •    Seal all supply and return ductwork at all seams and

      Seal all floor and wall penetrations (especially under
      through-wall units and in mechanical rooms, see Sec-
      tion 2.3).

  •    Construct the building "tightly."

  •    Control operation of the HVAC relief dampers so that
      they modulate to maintain a positive building pressure
      of 0.005 to 0.010 in. WC. Relief dampers should be
      controlled by sensing the differential pressure across
      the building shell and modulating the relief damper to
      maintain positive pressure in the building.

  •    Be sure all applicable building and safety codes,  stan-
      dards, and guidelines are followed. Especially impor-
      tant in this regard are fire codes, fuel use codes, the
      National Electrical Code, and other safety and me-
      chanical codes.

  •    Be sure to preserve the intended indoor air  quality
      purposes of mechanical ventilation devices. Exhaust
      fans should remove the moisture, fumes, and other
      contaminants generated within the building. Supply air
      systems should provide tempered air, free of objec-
      tionable quantities of contaminants.

2.2.4    Maintenance
    Proper HVAC system maintenance is essential to ensure
continued reduction of radon levels and adequate indoor air
quality. This is especially important in areas known  to have
radon problems. The following items are intended for build-
ing owners and operators to assist in proper operation and
maintenance of HVAC systems.


Table 2-2.    Examples of Outdoor Air Requirements for Ventilation In Commercial Facilities (Source: ASHRAE Standard 62-1989)
Type of Facility
Conference Rooms
Assembly Rooms
Dormitory Sleeping Areas
Office Spaces
Reception Areas
Smoking Lounges
Barber Shops
Beauty Shops
Ballrooms & Discos
Transportation Waiting Rooms
School Classrooms
School Laboratories
School Auditoriums
Hospital Patient Rooms
Operating Rooms
Correctional Cells
Note: For complete listing refer to
Estimated Occupancy,
Persons per 1000 ft2 of Roor Area
ASHRAE Standard 62-1989 (10).
Outdoor Air Requirements
(cfm/Person) Non-smoking Area


  •   Replace air filters at least twice a year if high quality,
      medium efficiency pleated air filters are used and
      more frequently if non-pleated or disposable low effi-
      ciency filters are used.

  •   Check the HVAC system and exhaust fans to deter-
      mine if they are being operated as designed. Excessive
      exhaust without adequate makeup air will depressurize
      the building, rendering building pressuri/ation inef-

  «   Inspect the HVAC system components and controls
      for failure or signs of faulty operation (such as loss of
      damper control) that would restrict the supply of out-
      door air. Note:  two states, California and Maine, cur-
      rently require annual inspections for correct operation
      of the ventilation systems in schools; other states are
      considering similar requirements.

  •   If an ASD system is also installed, inspect  the dis-
      charge location of the ASD vent pipe to ensure that an
      air intake has not been located nearby, or building
      usage change has not placed the exhaust near operable

Once Every 5 Years

  •   Test and  balance the HVAC system. Rebalance the
      system as renovations and usage changes occur.

2.2.5    Summary of Building
          Pressurization Guidelines
    In a building with  a tight shell, slight positive pressuriza-
tion can be achieved by supplying about 10% more outdoor
air than is mechanically exhausted when the building is oper-
ating under minimum outdoor air conditions. This positive
pressurization will reduce radon entry, and the additional
outdoor air  will help to dilute radon that does enter the

    A building designed to control indoor air contaminants
(including radon) should include:

  •   Pressurized ground contact rooms

  •   A well-balanced air distribution system

  •   Adequate makeup air

      A tight building shell (less than 1.0 ach at 25 Pa)

    Mechanical systems should be designed and installed to
meet the needs of occupant health, safety, comfort, energy
conservation, and building longevity. Meeting  these needs
requires an understanding of how the climate, the building,
and the occupants interact. Building pressurization alone,
however, cannot always consistently prevent radon entry. For
example, operable windows can make it very difficult to
achieve pressurization. A  properly designed and operated
mechanical system, in conjunction with an ASD system and
sealing of major radon entry routes, should provide cost-
effective radon prevention in new buildings.

2.3      Sealing  Radon Entry Routes
    This section on  sealing radon entry  routes covers the
following topics:

  •   Recommended Sealants (2.3.1)

      Sealing Concrete S labs (2.3.2)

      Sealing Below-grade Walls (2.3.3)

      Sealing Crawl Spaces (2.3.4)


    Recommended sealants for radon-resistant new construc-
tion are briefly covered in Section 2.3.1. Sections 2.3.2,2.3.3,
and 2.3.4 cover sealing the most common radon entry routes.
Section 2.3.2 is applicable to all three substructure types —
slab-on-grade, basement, and crawl space — that are con-
structed with poured concrete slabs.  Section 2.3.3 is appli-
cable to basement substructures. Section 2.3.4 provides addi-
tional sealing recommendations for limiting radon entry from
the crawl space into the building interior.

    On-going EPA research on radon-resistant new construc-
tion in homes has encountered numerous difficulties in achiev-
ing a reliable, gaslight physical  barrier between the soil gas
and the building (5). This research indicates that a near perfect
sealing job is necessary to achieve high radon reduction in
homes using sealing as a stand-alone radon reduction tech-
nique in  radon-prone areas. Because of the difficulties of
achieving complete sealing, it is normally much more cost
effective to include ASD (Section 2.1) and adequate HVAC
system design and operation (Section 2.2) in the design of
new buildings in radon-prone areas. However,  sealing of
major  radon entry  routes  (as  discussed below) and good
construction practice will enhance the performance of both
ASD and HVAC radon prevention techniques.

2.3.1    Recommended Sealants
    Sealants used for radon-resistant  applications must have
good adhesion to concrete and  be durable and elastic. The
popularity of polyurethane as a  suitable elastomeric joint
compound is based on a combination of strong adhesion to
concrete under difficult conditions, long service life, and good
elasticity  (5). Avoid  silicone caulks because  they  do not
adhere to concrete well.

    When you apply sealants, be sure surfaces are clean, dry,
and free  of grit and that the surface temperature is  above
freezing. Apply sealants in accordance  with the manufacturer's
recommended practice. Typical dimensions for caulk beads
are 1/2 in. deep by 1/4 in. to 1/2 in. wide. It may be necessary
to use backer rod when applying sealant in wide gaps.

2.3.2   Sealing Concrete Slabs
    This section covers all buildings constructed with con-
crete slabs: slab-on-grade, basement, and crawl space.

    Concrete is  normally a good radon barrier.  The major
problems with concrete slabs are joints, slab penetrations, and
cracks. The following subsections provide guidance on avoid-
ing these problems by: 1) sealing slab joints, penetrations, and
openings; 2) preventing random cracks in slabs; and 3) using
subslab membranes. For additional information, refer to Con-
crete Floors  on Ground (21) and Guide for Concrete Floor
and Slab Construction (22).   Slab Joints
    Slab joints of concern for radon  entry include the floor/
wall joint, pour joints, and control saw joints.


    The floor/wall joint (also called perimeter crack) of a slab
is located between the edge of the floor slab and the interior or
exterior load bearing walls. As a cold joint, the floor/wall joint
is always a potential radon entry point. To facilitate sealing of
this joint after construction, contractors have deliberately
created a significant floor/wall joint detail so that it will  be
easy to work with and seal. One approach is to install  an
expansion joint with the top  1/2 to 3/4 in. of the joint remov-
able after the concrete sets. This approach leaves enough
space for sealing with a suitable polyurethane caulking before
floor covering is installed. Another approach is to round the
slab at the floor/wall joint with an edging tool and seal it with
polyurethane joint compound. The expansion joint should be
as thin as possible (or eliminated if code permits) to make
sealing easier. It is important  to seal this joint during construc-
tion because the joint is often inaccessible after the building's
walls are raised and floor covering is laid.

    Architects and engineers should also be aware that build-
ings constructed with a combination of different substructures
may have additional  entry routes at the interface between the
two types of substructures.

Pour Joints and Control Saw Joints

    Cracks are difficult to avoid when large concrete slabs are
poured. To minimize cracking, builders either use pour joints
because the slab was poured in sections, or  saw-cut the slab
(control saw joints) to control where a crack will occur,  or
both.  If neither of these techniques nor post-tensioning has
been employed, larger slabs will crack unevenly in unpredict-
able locations.  To facilitate  sealing these cracks, make the
joint or saw-cut large enough to seal with polyurethane caulk
after the slab sets. To seal properly, both sides of cold joints
should be tooled when poured and then sealed when cured.   Slab  Penetrations and Openings
    Major slab penetrations and openings should be sealed to
reduce radon entry and to improve ASD and building pressur-
ization system performance. These slab penetrations and open-
ings include utility penetrations and sump holes.

Utility Penetrations

    Examples of utility penetrations through the slab include
water and sewer lines, utility lines to unit ventilators and
radiators, electrical service entries, subslab conduits, air con-
ditioner condensate  drains,  and  roof drains. The openings
around these slab penetrations should be sealed with polyure-
thane caulks. Many builders use plastic sleeves to protect
metal pipes from corrosion when they pass through the con-
crete slab. These sleeves can be removed after the concrete is
set, and the space around the pipe can then be sealed with
polyurethane caulk. The same techniques should be used for
pipes passing through block  walls.

    In most construction, floor drains empty  into a sewer pipe
rather than the  soil.  In these cases, the drain itself is not  of
concern  as a radon entry route. The  only concern is the
opening around the pipe penetration as discussed above. Where
the floor drain does drain  into  the  soil, the  drain  should
include a filled water trap to prevent soil gas from entering the


Sump Holes

    Although sump holes are rare in new construction of
large buildings, they are occasionally used as collection points
for a subslab drainage system. The sump hole can create a
radon collection system that should not be open to the build-
ing interior. An alternative subslab drainage system is one that
drains by gravity to daylight, serving the same purpose as a
sump hole without the radon entry  routes. If draining to
daylight is not possible, then seal the sump hole so that there
are no air leaks to  the building interior. Seal the sump hole
with a gasket and lid, and vent the sump to the outdoors using
plastic pipe  (as discussed in Section Also install a
submersible sump pump to remove any water collected in the
sump through a  check valve to approved disposal. Sealed
sumps have been used as suction pits for ASD systems in
houses by attaching a fan to the PVC pipe (15); however, this
approach has  not  been field-tested in  schools and is  not

    Radon mitigators sometimes use silicone rather than poly-
urethane caulks for  sealing sump lids and access ports because
they make a tight fitting gasket that can be removed at a future
date. This is satisfactory if the sump cover is bolted down and
the seal is airtight.   Crack  Prevention
    Cracking  of concrete is a natural result of the curing
process. Factors that affect the curing process include water
content, cement content, aggregate content, humidity, tem-
perature, carbon dioxide levels, air movement over the slab
surface, and preparation of the subslab area. Reinforcement is
one of the methods typically  used in large slabs to reduce
cracking. Concrete  should be reinforced and placed in accor-
dance with American  Concrete Institute (ACI) codes and
standard  practice.  ACI  publishes  a number of documents
outlining standard practice. A number of these apply to crack
prevention. Specifically, the reader is referred to ACI 302.1R-
89, Guide for Concrete Floor and Slab Construction (22).

    The builder should treat the slab in one  or more of the
following ways to reduce slab cracking.

    Reinforce with ferrous metals: Imbed a combination of
rebar and woven wire mesh in the slab to increase its strength.

    Reinforce with fibers: Various fiber additives are avail-
able to reinforce poured concrete and reduce cracking. These
fibers are discussed in ACI 544, State-of-the-Art Report on
Fiber-Reinforced Concrete.

    Use water-reducing admixtures: These admixtures (also
known as plasticizers) retain workability at a lower water
content, increasing  the strength of the concrete slab. See ACI
212.1R-89, Admixtures for Concrete, for more information

    Cure properly: Proper curing is critical to the strength
and durability of poured concrete. Stronger concrete can be
achieved by  slowing  the drying rate. Approaches include
watering the slab during drying, covering it  with wet sand,
wet sawdust, or a waterproof film, or coating it with a curing
    Use higher strength concrete: Typical school concrete
slab construction uses concrete with a 28-day compressive
strength of 3,000 to 3400 psi. Concrete can be made stronger
by  increasing the cement content, by reducing the water/
cement ratio, or both.  Subslab Membranes
    Membranes of plastics used to control liquid water pen-
etration and water vapor diffusion also are effective in con-
trolling air movement. If they can be adequately sealed at the
joints and penetrations and installed intact, membranes can be
used in conjunction with the sealed concrete slab to help
provide a physical barrier to radon entry. The use of a polyeth-
ylene vapor retarder will also enhance the effectiveness of an
ASD system by keeping  wet concrete out of the aggregate
during pouring.

    Many types of membranes are available including: poly-
ethylene film, reinforced polyethylene film, polyethylene-
coated kraft paper, PVC membranes, and EPDM membranes.
Polyethylene sheeting is commonly used as a subslab vapor
retarder in most areas of the country. The current prevalence
and low cost of this material  indicate it is worthwhile to
continue its  use  even though it is an imperfect barrier for

2.3.3    Sealing Below-Grade  Walls
    Below-grade walls and  stem walls  are normally con-
structed of either poured concrete or masonry blocks. Because
these walls are in direct contact with the soil, they can be
major radon entry routes. This section discusses the different
types of below-grade walls and the coatings that can be used
to seal these walls. Penetrations and openings through below-
grade walls into the soil can also be major radon entry routes.
These penetrations and openings should always be sealed as
discussed in Section   Wall  Types
Poured Concrete Walls

    In schools and other large buildings, foundation  walls
made of poured concrete are generally constructed to a mini-
mum compressive strength of 3,500 psi.  A poured  concrete
wall can be  an excellent barrier to radon; however, as with
concrete slabs, the major problems  are  cracks, joints, and
penetrations. We recommend that concrete walls be built in
compliance with guidelines established by ACI to  ensure a
strong foundation and to minimize cracking (24,25).

Masonry Block Walls

    Foundation walls built of concrete masonry units can be
designed with open cores, filled cores, or cores closed at or
near the top course or at slab level. In addition, masonry walls
are frequently coated with an exterior cementitious material
(referred to as "parging") for water control. This coating is
usually covered at the bottom  of the wall to make a good
exterior seal at the joint between the footing and the block
wall. Other types of coatings are discussed below in Section Uncoated blocks  are not effective water or soil-gas


    Concrete blocks are more porous than poured concrete,
although the parge or waterproofing coats can moderate the
difference. Recent EPA laboratory tests have confirmed that
concrete masonry walls can allow  substantial airflow, al-
though there  is a great deal of variation in the porosity of
blocks (26).

    When masonry construction is used, it is mandatory that
concrete block walls be built according to guidelines issued
by the National Concrete Masonry Association (NCMA) and
American Concrete Institute/American Society of Civil Engi-
neers. Their publications cover thickness of block, reinforc-
ing, pilaster location,  control joints, sequencing  and other
issues that influence cracking and foundation strength (5).

Stemwalls and Interior Walls

    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 a footing beneath Stemwalls below
the frost line. The sealing of the slab/stem wall joint is covered
under Section

    If Stemwalls are constructed of concrete  blocks, then the
top blocks must be solid. This solid block can help prevent
radon from entering the building; it will also  make the build-
ing easier to  mitigate  if it has elevated radon. Sealing  the
bottom course should prevent soil gas beneath the slab from
entering the block wall.   Coatings For Below-Grade Walls
    There are building codes that dictate dampproofing or
waterproofing treatments for foundations. Any waterproofing
material that provides adequate protection against water should
greatly reduce convective soil  gas movement Properly  ap-
plied waterproofing materials will help block  the pressure-
driven entry of soil gas. Waterproofing barriers against pres-
sure-driven gas flow should meet the following criteria: good
adhesion, crack-spanning ability, flexibility and elasticity
through a wide temperature range, puncture resistance, and
chemical and structural stability over time. The advantages
and disadvantages of various types of coatings for exterior
and interior below-grade walls are discussed below.

Exterior Wall Coatings

      Bituminous asphalt: the most common exterior
      dampproofing treatment for foundation walls is a parge
      or  spray coat cover using bituminous  asphalt. The
      parge coat is most often used for concrete masonry
      walls. However, data from Oak Ridge National Labo-
      ratory indicate that bituminous asphalt can be attacked
      by soil and groundwater chemicals, specifically acids
      (5). Bituminous materials may also lose their elasticity
      at below-freezing temperatures. These features render
      bituminous asphalt an undependable waterproofing
      treatment;  thus, builders should not  use bituminous
      asphalt for sealing radon entry routes. Bituminous
      asphalt is listed by code organizations such as Build-
      ing Officials and Code Administrators  (BOCA), Coun-
      cil of American Building Officials (CABO), and South-
      ern Building Code Congress International (SBCCI)
      only for dampproofing.
  •    Coal tar modified polyurethane: coal tar modified
       polyurethane is a cold-applied liquid waterproofing
       system. The coating dries hard but has some elasticity.
       One problem with this material is that it can be at-
       tacked by acids in groundwater, but it can be defended
       by a protection board. The performance of any liquid-
       applied waterproofing system is limited by the capa-
       bilities of the applicator,  and it is difficult to achieve
       even coats on vertical surfaces  (5).

  •    Polymer-modified asphalt: polymer-modified asphalt
       is another cold-applied liquid  waterproofing system.
       As with the system mentioned above, the quality of the
       installation depends on the applicator, and it is difficult
       to achieve an even coating on a vertical surface. High
       grade polymer-modified asphalt is superior to coal tar
       modified polyurethane in elasticity, crack-spanning
       ability, and re-sealability, but inferior in its resistance
       to chemicals (5).

  •    Membrane waterproofing systems: membrane water-
       proofing is advantageous  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. Effective waterproofing demands that concrete
       seams be smooth so  the membrane is  not punctured.
       Reinforced thermoplastic membranes can be applied
       in various ways: affixed to walls, laid beneath concrete
       slabs, or on a layer of sand. Thermoplastic membranes
       are rated highly for resistance  to chemicals and lon-
       gevity. Rubberized asphalt polyethylene membranes
       have superior crack-bridging ability, compared to fully
       adhered thermoplastic membranes (5). However, seams
       and overlaps must be carefully  and completely sealed
       for membranes to function as complete radon barriers.
       Manufacturers' recommendations for sealant, applica-
       tion procedures, and safety precautions should be fol-

  •    Surface bonding cement: surface bonding mortar or
       cement is approved by  some  building  codes as
       dampproofing treatment,  but not as  a waterproofing
       treatment.  A number of  manufacturers produce ce-
       ments and mortars impregnated with fibrous glass or
       other fibers. Some of these may be chemically un-
       stable in the alkaline environment of Portland cement

Interior Wall Coatings

  •    Cementitious waterproofing: a number of additives
       can be  mixed  with  concrete  to create  cement-like
       "waterproofing." This type of waterproofing is appro-
       priate only for interior applications because it is inelas-
       tic, 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 EPA's Air and Energy Engineering Research
       Laboratory. Results of these tests show that a number
       of interior paints can be effective radon barriers if
       properly applied (26).


2.3.4    Sealing Crawl Spaces
    Elevated levels of radon can also build up inside a crawl
space, especially if the crawl space has an earthen floor rather
than a poured concrete slab. Radon in the crawl space can then
enter the occupied area above the crawl space through cracks
and openings in the floor. Thorough sealing of these cracks
and openings will help to reduce radon entry into the occupied

    In schools and other large buildings, the floor above the
crawl space is typically a suspended concrete slab rather than
a wood floor (as in houses). A poured concrete floor slab is a
good barrier to radon; however, as discussed in Section 2.3.2,
joints and cracks in the slab are potential radon entry routes
and must be sealed. Sealing and crack prevention techniques
for slabs, covered in Section 2.3.2, should be followed.

    Openings and penetrations between the crawl space and
the occupied area above should be eliminated where possible.
All other openings and penetrations should be carefully sealed
during  construction. Openings and penetrations of particular
concern are  similar  to those covered in Section and

       water and sewer lines
  •    utility lines to unit ventilators and radiators
  •    electrical service entries

    In areas with a high potential for elevated radon levels, it
may also  be necessary to take a more direct approach by
installing a submembrane depressurization system in the crawl
space.  This  technique actually reduces radon levels in  the
crawl space rather than reducing radon entry from the crawl
space into the building and is covered in Section 2.1.4.

    Radon in the crawl space can also enter the occupied area
above if duct work  for the HVAC  system is located in  the
crawl space. Therefore, in radon-prone areas, neither air sup-
ply nor return duct work should be located in the crawl space.
For additional information, refer to ASHRAE Standard 62-
1989 (10).

2.3.5    Summary of Sealing
    While physical barriers and sealing entry routes will
reduce radon levels, the primary  importance of sealing is to
enhance the effectiveness of ASD systems and building pres-
surization. The following lists summarize guidelines for rec-
ommended sealants and for sealing concrete slabs, below-
grade walls, and crawl spaces.

Recommended Sealants

  •    Use polyurethane sealants since they adhere well to
       concrete, have a good service life, and good elasticity.

       Sealants should be applied, according to manufactur-
       ers' recommendations, onto a clean dry surface.

Sealing Concrete Slabs

  •    Slab joints (floor/wall joints, pour joints, and control
       saw joints) should be tooled when poured and sealed
       with polyurethane caulk after curing.
  •    Openings around utility penetrations that pass through
       the slab should be thoroughly sealed.

  •    Drain footing and interior drainage systems to day light
       if possible. If a sump hole is necessary, a submersible
       pump should be used, the hole sealed airtight to  the
       building, and the sump vented to the outdoors.

  •    To reduce slab cracking the builder can reinforce  the
       concrete with ferrous metals or fibers, use water reduc-
       ing admixtures, use higher strength concrete, and make
       sure that the concrete is cured properly.

  •    Subslab membranes can be used under the slab to help
       provide a physical barrier to radon entry; however,
       their most useful purpose is probably to prevent wet
       concrete from seeping into the aggregate during con-

Sealing Below-grade Walls

  •    Poured concrete walls are good barriers to  radon as
       long as cracks and openings around utility penetrations
       are sealed.

  •    If masonry block walls  are used, select blocks with
       low air flow permeability and apply exterior and/or
       interior coatings to the walls.
  •    If stem walls and interior walls are constructed of
       concrete blocks, the top blocks should be solid.

Sealing Crawl Spaces

  •    Thoroughly seal all cracks and openings in  the floor
       above the crawl space.

  •    Crawl space buildings constructed in radon-prone ar-
       eas should use suspended concrete floors (rather than
       wood) above  the crawl space and a  submembrane
       depressurization system.

2.4      Guidelines for  Measuring  Radon
    EPA is currently revising their guidelines for conducting
radon measurements in schools. Contact your local, state, or
EPA Regional Office for a copy of these updated guidelines
for radon measurements in schools  and for radon measure-
ment guidelines for large buildings.

    In addition to measuring radon after the building is con-
structed, EPA recommends that schools be retested sometime
in the future. This is particularly important if there are any
changes to  the building structure or HVAC system. A sug-
gested schedule for retesting is:

       If the results of the initial testing were all below 4 pCi/
       L, retest all frequently occupied ground-contact rooms
       sometime in the future. As a building settles, cracks in
       the substructure or other structural changes may  in-
       crease radon entry.

       If any areas initially tested above 4 pCi/L, requiring
       radon mitigation, retest these areas periodically. Spe-
       cific guidelines on post-mitigation testing will be pro-
       vided in an updated EPA manual on radon mitigation
       in schools.


If major renovations to a building or HVAC system
are planned, retest the building beforehand. If elevated
radon levels are detected, incorporate radon-resistant
features as part of the renovation.


                                               Appendix A
                                               Case Study
                Application  of Radon Prevention Design Features to a
                      Johnson  City Rehabilitation Hospital Building
Background Information
    In late 1990  and 1991, EPA  had the  opportunity to
demonstrate ASD in a large hospital building under construc-
tion in Johnson City, Tennessee (6, 7). The hospital building
is one story with  a floor area of about 60,000 sq ft. The
building  is slab-on-grade construction with  no foundation
walls penetrating the slab. Mechanical piping, electrical con-
duit, and structural columns penetrate the slab with the col-
umns sitting on footings beneath the slab. These columns
support steel beams overhead which in turn carry the bar joists
for the roof (post-and-beam construction).

    This type of construction is used in most commercial and
industrial buildings currently being built in the U.S. where
dimensions are large in both directions (length and width). All
internal  walls are gypsum  board on metal  studs,  and the
exterior walls are metal stud supporting gypsum board on the
inside surface and  an exterior insulation finish system on the

    The 4-in. thick slab was poured over a 6 mil vapor barrier
underlain with a 4-in. layer of coarse, crushed aggregate that
was continuous under  the entire slab. The slab was divided
into about 15 ft squares by a combination of pour joints (1,000
linear ft) and control saw joints (5,000 linear ft). No expansion
joints were used. Turned down exterior foundation walls were
used, eliminating  an exterior floor-to-wall joint.  In  other
words, the slab, exterior foundation walls, and footings were
poured monolithically.

    EPA was requested to review the plans and specifications
and to recommend a radon mitigation system since the region
was known to have high radon potential. After this review,
five recommendations  were  made to the architect designing
the building and incorporated in the plans and specifications.

  1.   Good compaction of the clay soil under the aggregate
      to decrease permeability of the material under the

  2.   Minimum of 4 in. of crushed aggregate—meeting Size
      #5 specifications as defined in ASTM C-33-90 (11)—
      carefully placed so as not to include any soil. The
      stone was not tamped after it was placed, and a  vapor
      retarder was placed on top of the aggregate prior to
      pouring the slab.

  3.  Sealing of all pour and control saw joints and any slab
      penetrations with a polyurethane caulking. (No expan-
      sion joints were used in the building.)

  4.  Installation of one subslab radon suction pit, as shown
      in Figure 2-5. The pit was located in the approximate
      center of the slab  and had a 6-in. stack leading to the
      roof. If a radon problem were found when the building
      was completed, plans were to install a turbo fan ca-
      pable of moving  500 cfm of soil gas at zero static

  5.  Continuous operation of the HVAC fans in order to
      pressurize the building in all areas except those where
      negative pressure  is necessary to control odors, nox-
      ious chemicals, or infectious diseases (toilets, kitchen,
      pharmacy, soiled linens area, isolation wards, etc.).

    All  of the above recommendations  were accepted and
incorporated into the building design. Upon completion of ihe
shell of the building and  sealing of  the slab, EPA made
diagnostic measurements to determine effectiveness of the
ASD system in depressurizing the entire subslab area. (Refer
to "Measure Subslab Pressures" in Section Test holes
were drilled through the  slab at varying distances from the
radon suction pit, including a scries around the entire perim-
eter about 6 ft from the slab edge. Radon levels below the slab
were measured by "sniffing" with a continuous monitor and
ranged from about 200 to 1,800 pCi/L.

    A suction fan was attached  to the radon vent slack in
order to determine the subslab pressure field. The suction fan
moved about 200 cfm of soil gas at a vacuum of about 1.5 in.
WC. Subslab pressure measurements were  made using a
micromanometer. Negative pressure was 0.47 in. WC in the
radon suction pit, 0.22 in.  WC 50 ft from the radon suction pit,
and 0.18 in. WC at the  farthest point on  the  perimeter (a
distance of 185 ft). This is considered extremely good exten-
sion of the negative pressure field. Extrapolation of these dala
indicates that the mitigation system could mitigate a slab as
large as  1,000,000ft2.


    Upon completion of the building, radon levels were mea-
sured in half of the building using open-faced charcoal canis-
ters. The HVAC and the ASD systems were off for this first
set of measurements. Radon levels ranged from less than 0.5
pCi/L (lowest detectable level with the open-faced canisters
used) to 53 pCi/L. The highest levels were in the bathrooms,
particularly those attached to the patient rooms. The patient
room with the  highest bathroom radon level had a radon
reading of 10 pCi/L. This was the highest radon level found in
any non-bathroom area in the building.

    To determine the effect of the HVAC system alone, the
entire building was then measured with the HVAC system on
and the ASD system off. Again, some of the bathrooms had
elevated radon levels as did some of the patient rooms. The
bathroom with the highest radon reading was again the high-
est in the building with the HVAC operating, testing 6 pCi/L.

    The final series of tests were made with both the HVAC
and  ASD systems  operating. The 20 bathrooms with the
highest radon levels in the second series of tests and many of
the patient rooms were remeasured. No measurable radon
levels were found in any of the rooms tested. This is not
surprising in  view of the relatively high negative pressure
under the entire slab with the ASD system in operation.

    In the Indoor Radon Abatement Act of 1988, the U.S.
Congress set a long-term goal of reducing the radon level in
all buildings in the U.S. to a level as low as that surrounding
the buildings (i.e., ambient). This building, built in a radon-
prone area, appears to meet the long-term ambient goal.

    Incremental costs of these radon prevention features were
easily tabulated since the contract for the building had been let
before the ASD system was added to the design. Hence, the
cost of the ASD system  and sealing  was covered by four
change orders for which the construction contractor charged
an additional $5,300. This is less than $0.10 per sq ft of floor
space. Specifications had already called for 4 in. of aggregate
under the slab,  and there was no charge for the change in
aggregate size used. The other three change orders covered
installation of the radon suction pit and stack to the roof,
sealing of all pour and control saw joints with a polyurethane
caulking, and installation of the suction fan and alarm system.

    The costs of the four change orders are summarized in
Table A-l. A survey of eight  recently constructed school
buildings showed that the cost of installing radon mitigation
systems during construction ranged from $0.30 to over $1.00
per sq ft (8). Hence, the mitigation  system installed during
construction in this  new building cost  only a fraction of the
cost of systems installed in the eight schools.
Table A-1.    Cost of Mitigation System In Johnson City
    Change Order Description
Cost ($)
Change aggregate to ASTM Size #5 stone
Seal all slab cracks and penetrations
  with polyurethane caulking
Install subslab suction pit and stack to roof
Install suction fan and alarm system

  Total cost


    A low cost, single point ASD system, installed during
construction, has lowered radon levels in a one-story 60,000
ft1 hospital building to near ambient levels. Levels as high as
53 pCi/L were measured in the building with both the HVAC
and ASD systems off, and levels as high as 16 pCi/L were
measured with the  HVAC system operating and  the ASD
system off.

    The features of this radon-prevention system are:

  1.   Slab-on-grade post-and-beam construction with no bar-
       riers to soil gas flow below the slab.

  2.   Continuous layer of coarse, narrow particle size range
       crushed aggregate a minimum of 4 in. thick.

  3.   Careful sealing of all slab cracks and penetrations and
       the use of a 6-mil plastic film between the slab and the

  4.   Low permeability layer beneath the aggregate. (In this
       case, the compacted clay beneath the aggregated itself
       was highly impermeable.)

  5.   A subslab radon suction pit having a void to aggregate
       interface area of 5 to 7 ft2 and a 6-in. diameter stack to
       the roof.

  6.   An exhaust fan (on the stack) capable of exhausting a
       minimum of 500 cfm at no head.

    For additional details on this and other case studies, refer
to References 3,4,6,7,8, and 16.


                                           Appendix B
1.  U.S. Environmental Protection Agency, U.S. Depart-
    ment of Health and Human Services, and U.S. Public
    Health Service. A Citizen's Guide to Radon (Second
    Edition), May 1992.

2.  U.S. Environmental  Protection Agency.  Radon Re-
    duction Techniques  in  Schools—Interim Technical
    Guidance. U.S. EPA Office of Radiation Programs.
    EPA-520/1-89-020 (NTIS PB90-160086). October

3.  Leovic, K.W. Summary of EPA's Radon Reduction
    Research in Schools During 1989-90. U.S. EPA, Of-
    fice of Research and Development. EPA-600/8-90-
    072 (NTIS PB91-102038). October 1990.

4.  Craig, A.B., K.W. Leovic, and D.B. Harris. Design of
    radon resistant and easy-to-mitigate new school build-
    ings. Presented at the 1991 International  Symposium
    on Radon and Radon Reduction Technology, Philadel-
    phia, PA, April 1991.

5.  U.S. Environmental Protection Agency. Radon-resis-
    tant Construction Techniques for New Residential Con-
    struction—Technical Guidance. Office of Research
    and Development. EPA/625/2-91/032. February 1991.

6.  Craig, A.B., K.W. Leovic, and D.B. Harris. Design of
    New Schools and Other Large Buildings Which  are
    Radon-Resistant and Easy to Mitigate. Presented at the
    Fifth International Symposium on the Natural Radia-
    tion Environment, Salzburg, September 1991.

7.  Craig,  A.B., D.B. Harris, and K.W. Leovic.  Radon
    Prevention in Construction of Schools and Other Large
    Buildings—Status of EPA's Program. Presented at the
    1992 International Symposium on Radon and Radon
    Reduction Technology, Minneapolis, MN, September

8.  Craig, A.B., K.W. Leovic, and D.W. Saum. Cost and
    Effectiveness  of Radon Resistant Features in New
    School Buildings, Healthy Buildings—IAQ'91, Wash-
    ington, D. C., September 4-8,1991.

9.  Leovic, K.W., H.E. Rector, and N.L. Nagda. Costs of
    Radon  Diagnostics and Mitigation in School Build-
    ings. Presented at the 85th Annual Meeting and Exhi-
    bition of the Air and Waste Management Association,
    Kansas City, MO, June 21-26,1992.

10.  ASHRAE1989. Ventilation for Acceptable Indoor Air
    Quality. Standard 62-1989. American Society of Heat-
    ing,  Refrigerating and Air-Conditioning Engineers,
    Inc., Atlanta, 1989.

11. American Society of Testing and Materials (ASTM
    C-33-90), Standard  Specification for Concrete Ag-
    gregates, 1990.

12. Engineering News Record, September 7,1992, pg 45.

13. Industrial Ventilation 19th Edition: A Manual of Rec-
    ommended Practices, Committee on Industrial Venti-
    lation, Lansing, MI, 1986.

14. 1989 ASHRAE Fundamentals Handbook, Chapter 14,
    page 14.4, Figure 17.

15. U.S. Environmental  Protection Agency. Radon Re-
    duction Techniques for Detached Houses—Technical
    Guidance (Second Edition). EPA-625/5-87-017, Janu-
    ary 1988.

16. Pyle, B.E. and K.W. Leovic. A Comparison of Radon
    Mitigation Options for Crawl Space School Buildings.
    Presented at the 1991 Symposium on Radon and Ra-
    don  Reduction Technology, Philadelphia,  PA, April

17. Dutt, G.S., D.I.  Jacobson, R.G.  Gibson, and D.T.
    Harrje. Measurement of Moisture in Crawl Space Ret-
    rofits for Energy Conservation. Presented at the Build-
    ing Thermal Envelop Coordinating Council, Ft. Worth,
    TX,  1986.

18. American  Society of Testing and Materials (ASTM
    E779), Standard Test  Method for Determining Air
    Leakage Rate by Fan Pressurization, 1987.

19. Cavallo, A., K. Gadsby, and T.A.  Reddy. Natural
    Basement  Ventilation as a Radon Mitigation Tech-
    nique. EPA-600/R-92-059 (NTIS PB92-166958). April

20. Parker, J.D. HVAC Systems in the Current Stock of
    U.S. K-12 Schools. EPA-600/R-92-125 (NTIS PB92-
    218338). July 1992.

21. Portland  Cement  Association, Concrete  Floors on
    Ground, Skokie, IL, 1990.

22. American Concrete Institute (ACI 302.1R-89), Guide
    for Concrete Floor and Slab Construction, Detroit, MI,

23. American  Concrete Institute  (ACI 212-1R-89), Ad-
    mixtures for Concrete, Detroit, MI, 1989.


24.  American Concrete Institute (ACI 318-89), Building     26.  Ruppersberger, J.S. The Use of Coatings and Block
    Code Requirements for Reinforced Concrete, Detroit,         Specification to Reduce Radon Inflow Through Block
    MI, 1989.                                              Basement Walls. In: Proceedings: The 1990 Interna-
             „          .    f.m~  „ , „„,, „ ....           tional Symposium on Radon  and Radon Reduction
25.  American Concrete Institute (AC  3  8.1-89), Building         Technology. Volume 2: Symposium Oral Papers (Ses-
    Code Requirements for Structural Plain Concrete, De-         slons V.IX)  EPA-600/9-91-026b (NTIS  PB91-
    troit, MI, 1989.                                          234450), July 1991.


Region 1
               Appendix C
EPA Regional Offices and Contacts
                                 Region 6
    (CT, ME, MA, NH, RI, VT)
    JFK Federal Building
    Boston, MA 02203
    Attention: Radiation Program Manager
    (617) 565^502
Region 2
    26 Federal Plaza
    New York, NY 10278
    Attention: Radiation Program Manager
    (212) 264-4418
Region 3
    (DE, DC, MD, PA, VA, WV)
    841 Chestnut Building
    Philadelphia, PA 19107
    Attention: Radiation Program Manager
    (215) 597-8320
Region 4
    (AL, FL, GA, KY, MS, NC, SC, TO)
    345 Courtland St. N.E.
    Atlanta, GA 30365
    Attention: Radiation Program Manager
    (404) 347-3907
Region 5
                                     (AR, LA, NM, OK, TX)
                                     1445 Ross Ave.
                                     Dallas TX, 75202
                                     Attention: Radiation Program Manager
                                     (214) 655-7223
                                 Region 7
                                     (IA, KS, MO, ME)
                                     726 Minnesota Ave.
                                     Kansas City, KS 66101
                                     Attention: Radiation Program Manager
                                     (913) 551-7020
                                 Region 8
                                     (CO, MT, ND, SD, UT, WY)
                                     999 18th SL
                                     Denver Place, Suite 500
                                     Denver, CO 80202-2405
                                     Attention: Radiation Program Manager
                                     (303) 293-1709
                                                 Region 9
                                     (AZ, CA, HI, NV)
                                     75 Hawthorne SL
                                     San Francisco, CA 94105
                                     Attention: Radiation Program Manager
    (IL, IN, MI, MN, OH, WI)
    77 West Jackson Blvd.
    Chicago, IL 60604
    Attention: Radiation Program Manager
    From: IN, MI, MN, OH & WI:
    (800) 621-8431
    From: IL:
    (800) 572-2515
                                                 Region 10
                                     (AK, ID, OR, WA)
                                     1200 Sixth Ave.
                                     Seattle, WA 98101
                                     Attention: Radiation Program Manager
                                     (206) 442-7660


    This addendum to the technical guidance manual, "Ra-
don Prevention in the Design and Construction of Schools and
Other Large Buildings," is included in this printing of the
manual in order to make available new technology which has
been developed and field-verified since the manual was ini-
tially printed. In the future, the entire manual will be revised
and all new technology,  including this addendum, will be
incorporated into the body of the manual.

Increasing Pressure Field Extension by
Modifying Subslab Walls

    Section describes the effect of subslab barriers on
pressure field extension (PFE). It states, "...the designer should
consider  'connecting' subslab areas by eliminating subslab
walls—under interior doors....Subslab communication could
also be facilitated by using subslab 'pipe sleeves'  to connect
areas separated by subslab walls."

    Another technique, now field-tested, has been shown to
be extremely effective in improving PFE through block walls.
Every other concrete masonry unit (CMU) is turned on its side
in the first row of block below the slab  in interior walls.  This
allows soil  gas to pass through the subslab wall, significantly
improving  PFE. PFE tests have shown that this  essentially
makes the  wall disappear  as far as PFE is concerned.  This
technique is shown in Figures 2-10 and 2-11. In one field test,
adequate negative  pressure was still  maintained after the
pressure field had passed through four successive walls  with
CMUs turned on their sides. In the school where this was first
demonstrated, the contractor made the change to all interior
walls at no extra cost. Based on these results, we recommend
that blocks be turned on all interior walls in buildings in which
ASD is installed except toilet walls serving as pipe chases.
These should not be turned and should be sealed from any
open contact with the subslab aggregate.

Improved Suction Pits
    The suction pit recommended in the manual is described
in Section (page 13) and illustrated in Figure 2-5 (page
20).  Since the manual was issued, two new suction pits  of
improved  design have been developed and field-tested. The
first is shown in Figure 2-12. It is constructed from angle iron
which supports a covering of expanded metal decking. This
new  suction pit is smaller (3 by 3 ft in area and 12 in. deep) but
has the same void-to-aggregate interface (7 ft2)  as the one
shown  in Figure 2-5.

    The second new suction pit is smaller and much simpler
to construct. It is shown in Figure 2-13. It is constructed from
a rolled cylinder of expanded metal decking with a sheet metal
top and bottom. When it is 8  in. tall  and fitted with a 6 in.
stack, it will exhaust an area of at least 20,000 ft2. When the
area  to be covered is less than about 10,000 ft2, the pit can  be
6 in. tall and fitted with a 4 in. stack and a smaller fan if the
distance between the pit and the fan is  not too great (less than
about 20 ft).


                                                        Slab level
Figure 2-10.  Every other Interior wall block Is turned on Its side to allow soil gas to pass through.
                                                                          CMU Wall
                            4" Concrete Slab on
                            10 mil Vapor Barrier
      Turn Every Other 8"x8"x16"
     CMU Horiz. So Soil Gas Can
            Pass Through
                                                                          Seal All Slab Joints & Pipes
                                                                                        Lintel Block Filled with Concrete
Figure 2-11.  Interior CMU wall.


                                       1 1/2" x 18 Ga-TypeB
                                          Galv. Mtl. Deck     6 - #4 Rebar x 8' 0" Long
                                               ,              E.W. Centered Over Pit
              Angle 2x2x1/4" cont.    Angle 2x2x1/4" Vert.
                 T & B Around          @ ea. Comer
                Perimeter of Pit
                                                        Expanded Metal on
                                                       All 4 Sides Welded to
                                                          Angle Supports
                                                                                                             6" Suction Pipe
                                                                       Poured Concrete
Figure 2-12.   Revised substab suction pit
Rigici        6"or8"x48"#13
8"x48" #13 Expanded Metal Decking (1/2°:
Rolled into Cylinder and Overlap Welded
                                                                       Steel Plate
                                                                       Welded to
                                                                        Top and
                                        4 1/2" Hole for 4" Suction Pipe (6" Pit)
                                        6 1/2" Hole for 6" Suction Pipe (8" Pit)
Figure 2-13.  Smaller subslab suction pit.
                                                                           U.S. GOVERNMENT PRINTING OFFICE: 1094— 550-001 /00160


   9e-o -ON
QlVd S33d * SOVlSOd
                                                                                •J9UIOO puEg-uai jeddn
                                                      egi u| ssaippe em 01 ujniaj pue 'JOAOO smi Adoa jo 'goeiep
                                                    ! [] 3U3H >1O3HO sjjodaj asagi BAjeoej oj I)S!M |ou op noA H
 jaddn em u| ssejppe em o| tuniai pue 'Adoo jo yoeiap
'\aqe\ M0|aq eqi uo saBueip Ajessaoeu ||E BI\BUJ osea\d
                                                   uoijBuiio|U| qojeassy

    iBAIJd JO} Aj|EU8d
    sseujsng IBIOI^Q

     Aug JQJ jajuao


Page 1 (-1 of 50)

of 50

Area Navigation

Jump to main content.