[Federal Register Volume 59, Number 54 (Monday, March 21, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-6551]


[[Page Unknown]]

[Federal Register: March 21, 1994]


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Part IV





Environmental Protection Agency





_______________________________________________________________________



Model Standards and Techniques for Control of Radon in New Residential 
Buildings; Notice
ENVIRONMENTAL PROTECTION AGENCY

[AD-FRL-4795-3]

 

Model Standards and Techniques For Control of Radon in New 
Residential Buildings

AGENCY: Environmental Protection Agency (EPA).

ACTION: Notice of publication of final EPA Model Standards.

-----------------------------------------------------------------------

SUMMARY: The Environmental Protection Agency is today publishing final 
``Model Standards and Techniques For Control of Radon in New 
Residential Buildings,'' hereinafter referred to as ``EPA Model 
Standards,'' as required by section 304 of title III of the Toxic 
Substances Control Act. These model standards and techniques are 
designed to prevent or reduce the potential for elevated levels of 
indoor radon in newly constructed residential buildings and are 
provided for use by national code development organizations, states, 
and local jurisdictions as they develop and enforce building codes for 
radon control specifically applicable to their regional and local 
requirements. This publication reflects changes and additions resulting 
from comments received during the public review period on the proposed 
EPA Model Standards.

EFFECTIVE DATE: These EPA Model Standards are effective on March 21, 
1994.

FOR FURTHER INFORMATION CONTACT: David M. Murane, Radon Division 
(6604J), 401 M St., SW., Washington, DC 20460, Telephone: 202/233-9442. 
Requests for copies of this notice and supporting Cost-Benefit Analysis 
should also be directed to this contact.

SUPPLEMENTARY INFORMATION:

I. Introduction

    EPA today publishes its ``Model Standards and Techniques for 
Control of Radon in New Residential Buildings.'' These final EPA Model 
Standards have been modified after consideration of public comments 
received on the proposed EPA Model Standards during the period April 
12, 1993 through June 11, 1993. Title III of the Toxic Substances 
Control Act (TSCA) (15 U.S.C. 2661 et seq.) (also known as the Indoor 
Radon Abatement Act of 1988) was enacted on October 28, 1988. Section 
304 of TSCA requires the Administrator of the Environmental Protection 
Agency to develop model construction standards and techniques for 
controlling radon levels within new buildings. To the maximum extent 
possible, these model standards and techniques were to be developed 
with the assistance of organizations involved in establishing national 
building construction standards and techniques and be made available in 
draft for public review and comment. Section 304 also requires the 
Administrator to work to ensure that organizations responsible for 
developing national model building codes and authorities which regulate 
building construction within states or political subdivisions within 
states, adopt the Agency's model standards and techniques.

II. Background

A. Radon Occurrence and Health Risks

    Radon was first recognized as a cause of lung cancer in underground 
miners in the 1930's. In 1955, the International Commission on 
Radiological Protection established the first occupational health 
standard for radon exposure in mines. In 1970, homes in the United 
States were found to have elevated levels of radon when uranium mill 
tailings were used as fill dirt or when built on reclaimed phosphate 
mining land. Starting in 1984, it became increasingly evident that 
homes could have elevated indoor radon levels caused by naturally 
occurring radium in the underlying soil and rock. In the past 6 years, 
homes with elevated radon levels have been found throughout the United 
States. Surveys indicate that up to 6 million homes may have radon 
levels above the EPA action level guideline established in 1986 of 4 
pico Curies per liter of air (4 pCi/L). Based on studies by the 
National Academy of Sciences and other scientific organizations, EPA 
believes that from 7,000 to 30,000 lung cancer deaths per year can be 
attributed to exposure to elevated levels of indoor radon. There are 
also data that indicate a synergistic effect between radon exposure and 
smoking which places smokers at a higher risk. Several studies are 
underway that could provide new information and insights on the 
magnitude of the radon health risks. Information from these studies 
will be considered and, if appropriate, incorporated by EPA in any 
future revisions of the radon health risk estimates.

B. Initial Steps by EPA To Develop New Construction Guidance

    EPA's initial efforts to reduce public exposure to radon were 
focused on educating the public on the health risk and identifying 
methods for reducing radon levels in existing homes. ``A Citizen's 
Guide to Radon,'' (OPA-86-004, 1986) and ``Radon Reduction Methods, A 
Homeowner's Guide,'' (OPA-86-005, August 1986) were published by EPA in 
1986 to meet those needs. It was also recognized that long-term risk 
reduction would be facilitated if new homes built each year were 
constructed with radon-resistant features. In 1987, EPA and the 
National Association of Homebuilders jointly published ``Radon 
Reduction in New Construction, An Interim Guide,'' (OPA-87-009, August 
1987) to provide initial guidance for builders. At the same time, a 
number of research projects were initiated to validate the interim 
guidance and to identify additional construction techniques that would 
be effective in reducing radon levels in new residential buildings. In 
1988, EPA published its first technical guide on ``Radon-Resistant 
Residential New Construction,'' (EPA/600/8-88/087, July 1988) and, in 
early 1991, published an updated version of this technical guidance 
titled, ``Radon-resistant Construction Techniques for New Residential 
Construction. Technical Guidance,'' (EPA/625/2-91/032, February 1991).

C. EPA's Goals in Preparing a Model Standard

    EPA believes that the ultimate success of the EPA Model Standards 
will be determined by reaching six basic goals:
    1. The Model Standards should meet the requirements established by 
Congress in the 1988 Indoor Radon Abatement Act (Title III of TSCA (15 
U.S.C. 2661 et seq.)).
    2. The Model Standards should result in significant radon risk 
reduction in newly constructed homes in areas of highest radon 
potential and not induce other significant indoor air problems.
    3. The recommended construction techniques should be 
technologically achievable, and readily implementable by the nation's 
builders.
    4. The provisions of the Model Standards should be cost-effective 
for both homebuilders and homebuyers. A significant aspect of all cost 
considerations is the underlying fact that steps taken to reduce radon 
entry during construction are less costly than retrofitting mitigation 
systems into homes after they are built.
    5. The provisions of the Model Standards should be readily 
adoptable and/or adaptable by the national Model Code Organizations and 
by officials who administer building codes at the state and local 
level.
    6. The Model Standards should be targeted for adoption in areas of 
highest radon risk potential.

D. Summary of Public Participation

    On February 1, 1989, EPA convened a Standards and Codes Work Group 
consisting of over 45 representatives of governmental and building 
industry organizations. This Work Group developed the outline and 
essential features for a first draft of the proposed Model Standards. 
EPA then established a cooperative agreement with the National 
Institute of Building Sciences (NIBS) to provide broadly based 
technical assistance in the development and review of the specific 
building standards and techniques. The NIBS Radon Project Committee 
ultimately involved over 90 representatives of Federal Agencies 
(Department of Energy, Department of Housing and Urban Development, 
Department of Defense), building code organizations, state and local 
governmental agencies, and private sector companies. This Committee met 
five times to review and modify the draft document and provided a 
summary report titled, ``Methods and Techniques for Reducing Radon 
Levels within New Buildings,'' April 1990, which was used by EPA as one 
of the sources in developing the model building standards and 
techniques outlined in section 9.0. The NIBS Report is available by 
submitting a request to: The National Institute of Building Sciences, 
1201 L Street, NW., suite 400, Washington, DC 20005, telephone 202/289-
7800. Other support documents, including the ``Analysis of Options For 
EPA's Model Standards For Controlling Radon in New Homes,'' July, 1992, 
(hereinafter referred to as the Cost-Benefit Analysis (CBA)) are 
available through EPA. On April 12, 1993, the proposed EPA Model 
Standards were published for public review and comment as a Notice in 
the Federal Register (58FR, 19097, April 12, 1993). A total of 173 
comments were received from 23 commenters. This Notice responds to the 
comments and contains the final EPA Model Standards.

III. Overview of Technical Analysis

A. Radon Reduction Technology

    The three methods for controlling radon levels in new residential 
buildings involve the use of (1) passive systems, (2) active systems, 
and (3) stack effect reduction systems.
    1. A passive system includes use of all the construction techniques 
that create physical barriers to radon entry, reduce the forces that 
draw radon into a building, and facilitate post-construction radon 
removal if the barrier techniques prove to be inadequate. A ``passive 
system,'' as used in the Model Standards, includes an open vent pipe 
stack that carries radon from the area beneath the slab or from under 
the plastic sheeting covering the crawl space floor to an exit point 
above the roof. It also includes roughed-in electrical wiring to 
facilitate future installation of both a fan in the vent stack and a 
system failure warning device, if radon tests indicate that further 
radon reduction is necessary. The natural convective flow of air upward 
in the vent pipe draws soil gas containing radon from beneath the slab 
and vents it to the outside. Limited research has demonstrated that 
passive systems are effective in reducing indoor radon concentrations 
below the current EPA action level in the large majority of homes where 
post-construction radon levels would otherwise have been slightly 
elevated. EPA believes that radon reductions of about 50 percent are 
achievable using a passive system approach alone (CBA, chapter 4). 
Under certain climatic conditions and in cases where the radon source 
strength in the underlying soil is greatly elevated, the performance of 
the passive stack may not be sufficient to lower indoor radon levels 
below EPA's current action level, but performance can easily be 
improved by adding a fan in the vent stack. The cost to builders of 
installing a passive system, as described above, is in the range of 
$350 to $500 per house depending on its design and size (CBA, chapter 
6). In cases where builders already use passive barrier techniques for 
controlling moisture entry and for energy conservation, the costs to 
install passive radon control systems will be lower.
    2. An active system involves use of all the passive control 
techniques described above plus installation of an electric fan in the 
vent pipe stack and a system failure warning device. The active system 
creates a strong suction on the area beneath the slab or under the 
plastic sheeting covering the crawlspace floor. This results in the 
pressure of soil gas containing radon beneath the slab to be lower than 
the air pressure in the home, creating a pressure barrier to radon 
entry. Because of the active mechanical ventilation of the sub-slab 
space, an active system can reduce indoor radon concentrations to their 
lowest achievable levels and is effective even in the presence of very 
high radon concentrations in the underlying soils. Based on limited 
Agency and independent research, active radon control systems have 
reduced radon levels to below 2 pCi/L in over 90 percent of new homes. 
Levels below 4 pCi/L are achieved in nearly all new homes (CBA, 
appendix B). The cost of installing the additional components of an 
active radon control system (the electric fan and system failure 
warning device) is about $250. The total cost of an active system is 
therefore in the range of $600 to $750. These costs will also vary 
depending on the design and size of the house (CBA, chapter 6). As in 
the passive system, costs applied to radon control may be lower in 
areas where builders are already using barrier techniques and stack 
effect reduction techniques for moisture control and energy 
conservation. There are additional annual costs to homeowners for 
operating and maintaining active radon control systems. EPA estimates 
these costs to be in the range of $40 to $75 (CBA, chapter 6).
    3. Stack Effect Reduction involves installation of features that 
prevent or reduce the flow of warm conditioned air upward and out of 
the building superstructure. This upward movement of air actually can 
draw soil gas containing radon into the lower levels of a building. The 
recommended stack effect reduction techniques include common 
construction practices such as providing adequate makeup air for 
combustion appliances, weather stripping exterior doors and windows, 
sealing openings around attic access doors, and using sealable recessed 
ceiling lights. In some areas, these energy conserving techniques are 
already required by code. Although these techniques, when used alone, 
may not be effective in achieving significant reduction in indoor radon 
levels, when combined with the barrier techniques and a passive or 
active vent stack installation, the stack effect reduction techniques 
can contribute to reducing radon entry through below ground openings in 
the foundation. It is recognized that use of these techniques can also 
reduce the infiltration of dilution air through above ground openings 
in the superstructure of the home. This can lead to some reduction in 
the air change rate. EPA is not aware, however, of any evidence that 
use of the recommended stack effect reduction techniques reduces air 
change rates to a level below the current ASHRAE standard of .35 air 
changes per hour (ACH), or that use of these techniques exacerbates 
problems with other indoor air pollutants. Use of these techniques does 
contribute to the fire resistance of a building, and reduces heating 
and cooling costs. As previously noted, the recommended stack effect 
reduction techniques are already requirements in the Model Building and 
Energy Codes used throughout the U.S. The application of these features 
to the control of radon does not impose additional changes in current 
construction practices.

B. Map of Radon Zones

    With the assistance of the U.S. Geological Survey (USGS) and State 
geologists, the Agency has developed a ``Map of Radon Zones'' designed 
to help state and local governments target certain data collection and 
outreach programs. It is also designed to help building code officials 
determine areas where adoption of radon-resistant construction codes 
may be advisable. The methodology for developing the Agency's ``Map of 
Radon Zones'' involved categorization of distinct geologic provinces 
based on indoor radon measurements, geology, aerial radioactivity, soil 
parameters, and house foundation types. These geologic provinces were 
then overlayed on county maps, and each county was assigned to a Zone 
based on the geologic province that is predominant in that county. 
Counties located within a geologic province that had predicted average 
indoor radon screening levels greater than 4 pCi/L were assigned to 
Zone 1. Counties with predicted average screening levels between 2 and 
4 pCi/L were assigned to Zone 2, and counties below an average of 2 
pCi/L were assigned to Zone 3.
    While EPA believes that the Map of Radon Zones and its accompanying 
documentation is useful for setting general boundaries of areas of 
concern, EPA recommends that state and local jurisdictions collect and 
analyze local indoor radon measurements, and assess geology, soil 
parameters and housing characteristics--in conjunction with referring 
to the EPA Map of Radon Zones--to determine specific areas within their 
jurisdictions that should be classified as Zone 1.
    EPA published the ``Map of Radon Zones,'' along with accompanying 
state-specific documentation, in December 1993. Copies of the national 
map and state-specific booklets are available from state radon program 
offices, EPA headquarters, and EPA regional offices.

C. Cost-Benefit Considerations

    The Agency considered a number of approaches for applying the Model 
Standards in the different radon potential zones. The basic approaches 
examined included: Application of active systems nationwide or only in 
Zone 1, application of passive systems nationwide or only in Zone 1, 
and application of some mixture of passive and active systems in Zones 
1 and 2.
    Each of the approaches for applying the Model Standards was 
analyzed in the CBA. The CBA compared costs of installing and operating 
the recommended radon control systems with the benefits in risk 
reduction and energy conservation. This evaluation was done for each of 
the alternative approaches described above.
    Consistent with common EPA practices for estimating annual risk 
reductions from cancer-causing pollutants, EPA estimated the total 
number of lives saved in the population that will occupy new radon-
resistant homes built over the time of the analysis (74 years) and 
converted that total estimate into an average of lives saved per year. 
Such an approach to the analysis allows consistent comparison of cost-
effectiveness of the EPA Model Standards with EPA's pollution control 
decisions in other programs.
    It should be noted that many of the construction standards and 
techniques recommended in this document are included in current model 
building codes, such as The Council of American Building Officials 
(CABO) ``One and Two Family Dwelling Code'' and the CABO ``Model Energy 
Code,'' or in the American Society of Heating, Refrigerating and Air-
Conditioning Engineers (ASHRAE) Standards, as techniques for reducing 
water infiltration or energy loss, or for maintaining acceptable indoor 
air quality. Applying these standard techniques as a means to control 
the levels of indoor radon simply adds a complementary function that 
does not conflict with the objectives of other indoor air quality 
programs within EPA. In addition, applying the recommended radon 
barrier and stack effect reduction techniques will result in 
significant long-term energy savings.
    The provision of radon control systems involves cost considerations 
for both homebuilders and homebuyers. In the passive approach to radon 
control, there are no homeowner costs associated with operation and 
maintenance of a vent fan. The result is long-term radon risk reduction 
at a small initial cost which later results in savings due to improved 
energy efficiency.

IV. Summary of the EPA Model Standards and the Implementation 
Approach

A. Summary of the Model Standards

    The EPA Model Standards include a codified presentation of 
construction methods and recommended procedures for their application. 
The EPA Model Standards also include scope and limitations sections, a 
listing of pertinent reference documents and terminology, a discussion 
of the principles for radon-resistant construction, and a summary of 
the construction techniques as applied to basement, slab-on-grade, and 
crawlspace foundations. The recommended construction method and 
recommended procedures for its application are contained in sections 
7.0 and 8.0, and the specific construction techniques are listed in 
section 9.0. Model Code Organizations, states, and local jurisdictions 
are encouraged to adopt those portions of the EPA Model Standards that 
are appropriate for their building code needs.

B. Implementation Approach

    EPA considered five approaches for implementing the EPA Model 
Standards. These include: (1) Active systems in Zones 1 and 2, (2) 
active systems in Zone 1 only, (3) passive systems in Zones 1 and 2, 
(4) passive systems in Zone 1 only, and (5) a combination of active 
systems in Zone 1 and passive systems in Zone 2, plus a requirement to 
test and fix homes above the action level in Zone 2. Based on its 
analysis, EPA selected option (4). EPA believes that the use of passive 
radon control systems in areas of high radon potential (Zone 1), and 
the activation of those systems if necessitated by follow-up testing, 
is the best approach to achieving both significant radon risk reduction 
and cost-effectiveness in construction of new homes. EPA believes that 
this approach best accomplishes the goals identified by the Agency in 
Section II.C. Other approaches and their associated costs and benefits 
are explained in detail in the CBA.
    The EPA Model Standards meet the requirements established by 
Congress in the Indoor Radon Abatement Act. EPA worked to develop the 
Standards in cooperation with the National Institute of Building 
Sciences (NIBS), a Standards and Codes Workgroup, individual home 
builders, and the National Association of Home Builders (NAHB), and 
will work to have the Standards adopted by the Model Code 
Organizations, states, and local jurisdictions.
    EPA believes that the implementation approach selected will result 
in significant risk reduction to the buyers of newly constructed homes 
since about 145,000 of the one million new homes built each year are in 
Zone 1. By applying the selected approach, it is estimated that 
ultimately from 10 to 41 lung cancer deaths could be averted annually. 
In addition, as the EPA Model Standards are adopted across the United 
States, the growing number of new houses equipped with radon-resistant 
features will result in a cumulative increase in the number of lives 
saved each year. For example, after the first five-year period of fully 
implementing the Standards, the Agency estimates that, statistically, 
over 200 lives ultimately will be saved (CBA, Chapter 5).
    These estimates are based only on the risk reduction achieved by 
use of passive radon control systems in Zone 1. If all new homes built 
in Zone 1 with passive radon-resistant features are tested for radon, 
and passive systems activated when elevated radon levels are still 
present, an estimated 3 to 4 additional lives would be saved annually. 
To achieve maximum risk reduction, all new homes should be tested, and 
passive systems activated when necessary.
    The construction techniques are technologically feasible and can be 
readily implemented by builders in the field. Agency research has 
demonstrated the effectiveness of the techniques, and they involve the 
use of standard construction practices and materials readily available 
to builders in all geographical areas.
    The provisions of the EPA Model Standards and the recommended 
implementation program are cost-effective to both homebuilders and 
homebuyers. EPA believes this approach to controlling radon in new 
construction provides a balance between radon risk reduction and the 
cost to both homebuilders and homebuyers. The cost to builders to 
install a passive system is $350 to $500 per house. If applied to all 
new homes in Zone 1 areas, the annual installation cost would range 
from $50 to $70 million (CBA, chapter 6). Even at the higher end of 
this range, a very favorable cost-benefit relationship results when 
these costs are compared to lung cancer deaths that may ultimately be 
averted. Due to the long-term energy savings achieved by using the 
recommended radon reduction techniques, the 10 to 41 lung cancer deaths 
ultimately averted yearly would be at a savings of about $440,000 per 
life saved, using a 3 percent discount rate. At a 7 percent discount 
rate, the savings would be $281,000 per life saved. In a sensitivity 
analysis of this option, in which no credit was taken for energy 
savings, the cost was calculated to be $149,000 per life saved at the 3 
percent discount rate, and $309,000 at the 7 percent discount rate.
    With passive systems, there are no system operation costs to the 
homebuyer. However, if a home is tested, and elevated levels of radon 
are found, the passive system can be made significantly more effective 
in reducing radon levels by the addition of a fan. The installation of 
the fan and a system failure warning device would cost approximately 
$250 and the yearly operation costs of the system to the homebuyer 
would be about $40 to $75 (CBA, chapter 6).
    Building radon-resistant features into a new home during 
construction is extremely cost effective. It should be noted that the 
cost of reducing high radon levels in existing homes that do not 
contain these construction features can range from $800 to $2,500 
(EPA's ``Consumer's Guide to Radon Reduction,'' 402-K92-003, August 
1992).
    Finally, EPA believes the Model Standards can be readily adopted by 
the Model Code Organizations, states, and local jurisdictions that want 
to address the radon problem. The Agency has developed the Model 
Standards with a format and content that will assist in their adoption 
by the Model Code Organizations. The Agency anticipates increasing 
support for this adoption from the building industry. Indeed, the 
National Association of Home Builders passed a resolution (NAHB Radon 
Policy Update, January 22, 1992) that is supportive of the targeted 
approach taken in the EPA Model Standards. The expected acceptance and 
use of the Standards by builders will also contribute to timely 
adoption by the Model Code Organizations and in the building codes and 
regulations of state and local jurisdictions.
    Each of the other implementation options addressed in the CBA 
offers certain advantages and disadvantages. Active radon control 
systems applied in both Zones 1 and 2 would result in greater risk 
reduction. However, these systems would provide limited benefits in the 
large number of new homes that would be below 4 pCi/L without any 
radon-resistant features installed. If targeted only to Zone 1, active 
systems would still be unnecessary in a large percentage of new homes. 
At this time, the Agency believes that the installation, operation, and 
maintenance costs of active systems outweigh the benefit of the greater 
risk reduction achieved by these systems. Similarly, the costs of 
installing passive radon control systems throughout Zones 1 and 2 are 
considered by the Agency to be too great because of the large number of 
homes that would receive no benefit in terms of radon risk reduction. 
EPA also concludes that a ``mixed approach'' (active systems in Zone 1; 
passive systems in Zone 2) would also not be as cost effective as the 
recommended approach. Further explanation of the data leading to these 
conclusions is contained in the CBA. The CBA is available through the 
EPA contact listed at the beginning of this Notice.

V. Response to Comments

A. Comment Review Process and General Responses

    1. Comments were reviewed and similar or related comments were 
grouped within one of the following 7 topical categories:
    (1) Syntax, Language, General Editorial.
    (2) Radon Measurement and Risk Assessment.
    (3) Training, Certification, Proficiency Rating.
    (4) Referencing Existing Standards and Requirements.
    (5) Technical Standards and Requirements.
    (6) Cost-Effectiveness of Proposed Standards.
    (7) Comments Pertaining to EPA's ``Significant Issues.''
    2. The following general responses address each of these 7 
categories of comments. Specific responses to individual comments are 
contained in section B below.
    (1) In general, a review of the 22 comments recommending editorial, 
syntax, or modified language changes resulted in improvements in the 
text of the Model Standards. These changes were adopted and no further 
response was considered necessary.
    (2) The 14 comments relating to radon measurement and risk 
assessment reflected a broad spectrum of divergent views, ranging from 
total rejection of the Model Standards (due to an alleged failure to 
substantiate the risk), to recommendations that the 4 pCi/L Action 
Level be lowered to achieve greater risk reduction. Specific responses 
to comments in this category are included in section B, below.
    (3) There were 6 comments that focused on the need to clarify 
provisions in the Model Standards relating to Training, Certification, 
and Proficiency Rating. Appropriate editorial changes were made to 
clarify those provisions. More detailed responses to the 6 comments in 
this category were not considered necessary.
    (4) There were 21 comments citing a need to include additional 
references to Existing Codes or ASTM Standards, or to include more 
detailed specifications on construction techniques. The majority of 
these comments were accommodated by adding appropriate building code or 
ASTM references to sections 9.1.3, 9.1.6, 9.1.7, 9.1.12, 9.1.14, 9.2.1, 
9.2.4, and 9.2.5 of the Model Standards. Specific responses to several 
of the comments in this category are included in section B, below.
    (5) Many of the comments (69 out of 173) were categorized as 
addressing Technical Standards and Requirements. As in the previous 
category, the majority of these comments were accommodated since they 
enhanced the clarity and completeness of the Model Standards. Specific 
responses to suggested changes that were rejected are included in 
section B, below.
    (6) There were 14 comments categorized as addressing Cost-
Effectiveness of the Proposed Standards. All of these comments were 
directed toward the introductory material contained in the preamble to 
the Model Standards and did not recommend specific changes in the body 
of the Standards. However, specific responses to this category of 
comments have been included in Section B, below.
    (7) There were 17 responses to EPA's request for comments on the 7 
``Significant Issues'' listed in the preamble to the Proposed EPA Model 
Standards. Responses to these comments are included in Section C, 
below.

B. Responses to Specific Comments

    The following responses are related to comments on the radon 
measurement and risk assessment aspects of the Model Standards.
    (1) One commenter questioned the need for Model Standards for 
radon-resistant new construction by stating that ``without conclusive 
evidence that radon increases the risk of lung cancer, is such 
protective action warranted?'' EPA believes that there is clear 
evidence to support the radon risk assessment that resulted in a 
Congressional mandate to develop the Model Standards. The 
carcinogenicity of radon has been well established by the scientific 
community, including the World Health Organization's International 
Agency for Research on Cancer (IARC 1988), the Biological Effects of 
Ionizing Radiation (BIER IV) Committee of the National Academy of 
Sciences (NAS 1988), the International Commission of Radiological 
Protection (ICRP 1987), and the National Council on Radiation 
Protection and Measurement (NCRP 1984). These concerns were also 
affirmed in the ``Comparative Dosimetry of Radon in Mines and Homes'' 
(NAS 1991), by the National Academy of Sciences. EPA's discussion of 
the aforementioned findings and other data is contained in the 
``Technical Support Document for the 1992 Citizen's Guide to Radon'' 
(USEPA 1992).
    (2) One commenter requested that EPA's Map of Radon Zones be 
included as an appendix to the Model Standards. EPA believes that the 
Map of Radon Zones and the more detailed state-specific booklets that 
accompany the map should be published separately from the Model 
Standards. The lack of precise definition of zone boundaries on a 
single page map of the U.S. would limit its usefulness to home builders 
or to state and local building officials as they make decisions 
regarding the specific application of the Model Standards to their 
local requirements. The state-specific booklets are considered an 
essential element in interpreting the Map of Radon Zones, and it would 
not be feasible to also include the booklets in an appendix to the 
Model Standards. EPA recommends that parties interested in the Map of 
Radon Zones consult with their state radon office to obtain information 
specific to their locality or area of interest.
    (3) One commenter stated that EPA has not substantiated its action 
level with any studies showing that radon poses a risk at that level. 
The Agency disagrees with this statement. EPA's estimates of lung 
cancer risks to the general population due to radon are based on human 
exposure-response data from epidemiologic studies of underground 
miners. These studies show excess cancer risk in miners whose 
cumulative exposure overlaps those exposures expected in residential 
settings at 4 pCi/L. The Agency has provided a detailed discussion of 
the exposure, risk, and uncertainty issues in the ``Technical Support 
Document for the 1992 Citizen's Guide to Radon,'' (EPA 400-R-92-011, 
May, 1992).
    (4) The same commenter suggested that ``even if one accepts EPA's 
radon action level, the standards are not cost-effective. It is more 
cost-effective to retrofit only those homes testing above the EPA 
action level, than to install passive systems in all homes in Zone 1.'' 
This assumption is incorrect on several counts. EPA estimates that 
144,808 new homes are constructed in the 12 Zone 1 states each year 
(CBA, chapter 6). If passive radon control systems, at a cost of $500 
each, were installed in each of these homes, the total installation 
cost would be $72,400,000. However, the costs of post-construction 
mitigation of homes in Zone 1 that would be expected to test above 4 
pCi/L would be almost double that amount. Based on federal and state 
radon surveys, the Agency estimates that 55,585 of the 144,808 new 
homes built annually in Zone 1 would have radon levels above 4 pCi/L. 
If those homes were mitigated, at a cost of $2,500 per home, the total 
costs of mitigation would be $139,000,000. Actually, the difference 
between these two approaches is even greater due to the energy savings 
that result when passive radon control systems are installed during 
construction. Over the typical 74 year life of the 144,808 homes, the 
installation of passive systems will result in energy savings to 
homeowners of $7,045,000. On the cost issue, another factor must also 
be considered. In its evaluation of rates of voluntary radon testing by 
owners of existing homes across the country, EPA has found that 
approximately 9 percent of the homes have been tested. The rate of 
radon testing by owners of new homes is not expected to be any higher. 
Therefore, the approach suggested by the commenter would result in very 
little risk reduction, when compared to installation of passive systems 
by builders during construction.
    (5) The same commenter also stated that ``given the uncertain basis 
for EPA's action level, EPA must consider the full social cost of the 
standards before acting.'' The Agency's CBA contains an extensive 
analysis of the lives to be saved through implementation of the Model 
Standards as well as the costs incurred through this and other 
approaches. It is calculated that the installation of passive systems 
in new homes in Zone 1 and the associated energy savings derived, will 
result in an overall savings of $442,000 per life saved, at a 3 percent 
discount rate, or $281,000 at a 7 percent discount rate. As discussed 
earlier, if no credit is taken for energy savings, the cost was 
calculated to be $149,000 per life saved at a 3 percent discount rate, 
or $309,000 at a 7 percent discount rate. These calculations did not 
factor in the additional significant savings to society resulting from 
not having to treat cancers that have been avoided.
    (6) One commenter stated that ``if, according to EPA's 
calculations, these measures save only 16 deaths per year, then they 
are not worth the cost of installing.'' As stated earlier, if the Model 
Standards are fully implemented, it will result in an overall savings 
of $442,000 per life saved at a 3 percent discount rate. The cost per 
life saved indicates how cost-effective an alternative is in providing 
health benefits to the public. It should be compared to the cost the 
public is willing to pay to save a ``statistical life,'' i.e., buy risk 
reductions. In the past, EPA's 1983 Regulatory Impact Analysis (RIA) 
Guidelines indicated that the public appears to value a risk reduction 
that saves a life (in statistical terms) for between $600,000 to 
$9,900,000. A more recent study titled, ``The Value of Reducing Risks 
of Death: A Note on New Evidence,'' by Fisher, et al. 1989, suggests 
that the public places the value of saving a statistical life between 
$2,000,000 and $10,500,000 in 1991 dollars.
    (7) One commenter stated that ``EPA has failed to consider studies 
that contradict its linear no-threshold theory for radon-induced lung 
cancer.'' The Agency has considered these studies but continues to 
believe the evidence available supports the no-threshold approach. In 
order for there to be a threshold, all non-lethal genetic damage from 
alpha radiation which would lead to cancer would have to be repaired 
perfectly. Research has established that even at low doses, only a 
fraction of the damage caused by alpha radiation is effectively 
repaired. Because of the tendency toward double stranded rather than 
single stranded DNA breaks with alpha radiation, there is high 
probability of extensive damage and a high probability of ``mis-
repair.'' Any repair that is evident indicates only cell survival, and 
may not indicate continued DNA integrity. The findings of the National 
Academy of Sciences BEIR IV report (p. 426) suggest that ``carcinogenic 
damage induced by high-LET radiation (e.g., alpha radiation) in 
mammalian cells is very inefficiently repaired'' and ``the 
intracellular effect of exposures to high-LET radiation can be 
cumulative.'' Mis-repaired cells can survive, multiply, and reproduce 
the mis-repair (i.e., mutation) that may lead to cancer. Although a 
threshold cannot be definitively ruled out, there is currently no 
scientific evidence of a threshold for cancer induction from exposure 
to radon or any other ionizing radiation.
    (8) One commenter stated that ``EPA has overlooked a significant 
body of scientific literature which suggests that low levels of 
radiation are not only harmless, but possibly beneficial.'' The Agency 
has considered ``ecologic studies'' which have shown lower lung cancer 
rates in some states with a high incidence of radon, and some 
experimental evidence in animals. Ecologic studies are preliminary 
studies which examine groups of people rather than individuals; the 
relationship between individual lung cancer cases and their exposure to 
radon or other cancer causative agents such as smoking cannot be 
studied. Also the mobility of the individuals cannot be assessed. A 
sensitivity analysis of ecological studies by Dr. Jonathan Samet showed 
that they had little value. Based on the considerable limitations of 
this type of study design, the scientific community, including 
participants in a recent international epidemiologist's workshop, has 
recommended against further use of ecologic studies for examining 
residential radon risk. Some studies conducted in laboratory animals 
kept under sub-optimal conditions have shown a stimulatory effect of 
low levels of radiation. However, these studies have found no change in 
the expected risk of lung cancer induced by radiation exposure. Given 
the strong a priori understanding of the carcinogenicity of radon 
(National Research Council, BEIR IV, 1988) an inverse association of 
radon with lung cancer is not biologically plausible.
    (9) One commenter stated that ``EPA's proposed action guideline of 
4 pCi/L is not safe,'' and indicated that ``the Standard should be 
based on 2 pCi/L instead.'' Another commenter inquired as to ``why EPA 
does not go As Low As Reasonably Achievable, ALARA?'' Average levels of 
radon outdoors are about 0.4 pCi/L. The Agency believes that there is 
some risk associated with human exposure to any level of radon. In 
assessing residential radon risk, EPA assumes that the exposure-
response relationship is linear at low exposures and exposure rates. 
This assumption is consistent with the evidence for linearity at a wide 
range of cumulative exposures in the radon epidemiologic studies of 
underground miners. There is no evidence of a threshold for lung cancer 
response from radon exposure, that is, a level of radon exposure below 
which no increased risk of lung cancer would exist. EPA's action level 
of 4 pCi/L is based on the mitigation capabilities of existing 
technology. This technology reduces radon levels to below 4 pCi/L in 
almost 95 percent of the existing homes mitigated, and below 2 pCi/L in 
75 to 80 percent of these homes (CBA, Appendix B). The Agency believes 
a construction standard for builders should target builders to the more 
readily achievable 4 pCi/L, while also acknowledging that as builders 
follow the techniques of the Model Standards they will in fact be 
achieving levels below 4 pCi/L in 75 to 80 percent of the cases. The 4 
pCi/L level is also consistent with EPA's action level for existing 
homes, as stated in the Citizen's Guide To Radon.
    The following responses are related to comments on specific 
sections of the EPA Model Standards.
    Section 1.0.1  Two commenters recommended amending this section to 
more clearly restrict the scope of the Model Standards to specific 
kinds of residential dwellings and to avoid including buildings such as 
high rise apartment buildings and others. EPA concurs with this 
amendment. Restricting the Model Standards to one- and two-family 
dwellings and other residential buildings three stories or less in 
height has been the intent throughout development of the Standards. 
This intent was already reflected in the Limitations section 2.0.1 and 
in the Summary section 6.0, and is now specifically stated in section 
1.0.1.
    Section 1.0.2  Two commenters questioned the need to apply the 
Model Standards when modifying the foundations or central air handling 
systems of existing buildings. This provision was not considered 
appropriate for inclusion in standards for new construction. It was 
believed to be more appropriately covered in EPA's Radon Mitigation 
Standards. EPA concurs with deleting the provision related to 
modification of central air handling systems. This section has also 
been modified to more clearly define applicability of the Model 
Standards when additions to the foundations of existing one- and two-
family dwellings result in extension of the building footprint.
    Section 2.0  One commenter recommended including a statement in 
this section that ``all homes should be tested in order for the 
Standard to accomplish its goal of reducing the risks from radon.'' EPA 
has consistently recommended that all homes, including new homes, be 
tested for radon. However, in developing the recommended passive 
approach to radon reduction in new homes as set forth in section 7.1 of 
the Model Standards, it was determined that the recommendation for 
post-construction testing should be applied only to those new homes in 
which passive radon control systems were installed. This approach would 
identify homes where activation of the passive system is needed to 
achieve radon levels below the locally prescribed action level. In new 
homes, where builders install active radon control systems during 
construction, research has shown that radon concentrations below the 
EPA Action Level of 4 pCi/L are achieved in almost all cases (CBA, 
appendix B). While EPA continues to recommend testing of all new homes, 
inclusion of that recommendation as a specific provision of the Model 
Standards was not considered appropriate.
    Section 7.2  One commenter disagreed with the recommendation that 
EPA Protocols be used for any radon testing referenced in the Model 
Standards and expressed a preference for ``use of prescriptive 
Standards.'' It was suggested that prescriptive standards ``allow less 
latitude in interpretation and less variance in test results 
obtained.'' EPA believes that the rigorous requirements for gaining 
approval of all types of radon test devices (under the Radon 
Measurement Proficiency (RMP) Program), combined with the demonstrated 
and proven effectiveness of the procedures for use of those test 
devices in homes (as prescribed in EPA's ``Indoor Radon and Radon Decay 
Product Measurement Device Protocols'' and ``Protocols For Radon and 
Radon Decay Product Measurements In Homes''), results in consistent, 
easily interpreted, and accurate radon testing.
    Section 7.3  There were 6 comments on this section recommending 
changes or additions to improve clarity in describing the individuals 
and qualifications needed to design and install radon control systems. 
Additions were made in this section to include registered design 
professionals (architects or engineers) and contractors listed in EPA's 
Radon Contractor Proficiency (RCP) Program as being qualified to 
perform or supervise radon control system installations in new homes.
    Section 8.2.3  This section states that radon-resistant features 
may not be needed, or that limited use of selected techniques may be 
sufficient in areas identified as having a low potential for indoor 
radon (Zone 3). One commenter recommended that in Zone 3, the Model 
Standards ``should specify instead that radon protection measures would 
not be needed unless analysis indicated otherwise.'' The difference in 
these two approaches appears to be largely semantic. EPA believes that 
by establishing a Zone of low radon potential (Zone 3), an analysis has 
already been made which provides state and local jurisdictions with an 
adequate basis for deciding what, if any, radon-resistant features may 
be appropriate for inclusion in their building codes. The original 
wording has been retained.
    Section 8.3.1  This section was designed to provide an example of 
how states or local jurisdictions might approach the development of 
rules, regulations, or ordinances for implementing provisions of the 
Model Standards. It also suggested the related training that might be 
appropriate for local building inspectors and officials. One commenter 
stated that, ``Given no criteria for training or resources specified, 
it is inappropriate to recommend such training.'' EPA believes that it 
is appropriate and desireable to provide an Agency assessment of the 
general type of training that may be necessary in jurisdictions where 
the Model Standards are adopted in building codes. EPA has agreed to 
work with the National Association of Home Builders and with the Model 
Code Organizations to develop appropriate training programs and 
materials. Funding for this type of activity is expected to be 
available through grants to states, as authorized by current 
legislation.
    Section 9.1.1  Two commenters recommended changes in this section 
to more clearly define the alternatives and specifications for creating 
a gas permeable layer under slab floors. EPA concurs with this 
recommendation and modified the language to include more detailed 
specifications for alternative sub-slab materials.
    Section 9.1.2  Three commenters recommended changes in this section 
to more clearly define specifications and placement requirements for 
sub-slab soil-gas-retarder membranes. EPA believes that the current 
specifications for membrane type (polyethylene) and thickness (6-mil or 
3-mil cross laminated), provides sufficient definition to ensure that 
effective soil-gas-retarders are installed by builders nationwide. At 
the local level, jurisdictions may decide to add more detailed, locally 
approved membrane specifications when they adopt provisions of the 
Model Standards in their building codes. This would facilitate 
enforcement of the requirement by local building inspectors. On the 
question of membrane placement, EPA concurs with the need for more 
specific guidance and revised this section accordingly.
    Section 9.1.3  This section provides guidance for construction of 
concrete floor slabs and makes reference to several guides and manuals 
published by the American Concrete Institute (ACI). One commenter 
recommended that the Model Standards refer instead to existing Model 
Building Code standards for construction of concrete floors. EPA 
concurs with this recommendation but has also retained the ACI 
publications as ``references that provide additional information on 
construction of concrete floor slabs.''
    Section 9.1.5  Three commenters recommended changes in this section 
to establish a performance standard for sealing large openings through 
floors that are in contact with the soil. EPA concurs. The section has 
been revised to require the use of sealant materials that ``provide a 
permanent air-tight seal.'' Examples of materials that may be used to 
achieve that performance standard are also included in this section.
    Sections 9.1.6, 9.1.7, 9.1.8, 9.1.13, 9.1.15, 9.1.17, and 9.1.18.  
Four commenters recommended changes in one or more of these sections to 
more clearly define the characteristics and specifications of sealants 
used to retard soil gas entry. EPA concurs with the need to provide 
more specific guidance on use of sealants and has made appropriate 
changes in each of these sections. The changes have either established 
a performance standard (such as air-tight sealing), or have referenced 
an ASTM Standard, or have included both a performance standard and 
samples of ASTM approved sealant materials.
    Section 9.1.9  This section includes specific procedures for 
routing the discharge from floor drains and air conditioning condensate 
drains so as to prevent radon entry through those openings. One 
commenter indicated a preference for applying the procedures for floor 
drain discharge that are contained in current model building codes. EPA 
concurs with using existing building or plumbing codes as references 
when they provide guidance that is also applicable to radon control 
techniques. This section was changed to reference local plumbing codes.
    Sections 9.1.8, 9.1.11, 9.1.12, and 9.1.14.  Each of these sections 
contained references to one or more publications of the National 
Concrete Masonry Association, the National Forest Products Association, 
or the American Concrete Institute. One commenter suggested that if 
these publications are included in the Model Standards, they would not 
be enforceable since they are not consensus documents and are not 
referenced in Model Building Codes. As in the previous comment, EPA 
concurs with use of existing, applicable building codes whenever 
possible and has either deleted references to the Trade publications or 
listed them as additional sources of valuable information to builders.
    Section 9.1.15  This section covers the placement of air handling 
ducts beneath slabs or in other areas exposed to earth. Two commenters 
recommended elimination or prohibition of sub-slab ducting, 
particularly in homes where passive or active sub-slab depressurization 
systems are installed. Because of the common use of sub-slab and 
crawlspace ducting in some areas of the United States, it is not 
considered feasible to recommend prohibition or elimination of this 
type of construction. EPA believes that the current wording of this 
section contains sufficient safeguards to ensure that installation of 
such ductwork does not result in increased radon entry into homes.
    Section 9.1.16  This section includes a recommendation that air 
handling units not be placed in crawlspaces. One commenter suggested 
that ``it is possible to place air handling units in crawlspaces if the 
joints and seams are sealed.'' As in the previous comment, EPA 
recognizes that placing air handling units in crawlspaces is a common 
construction practice in many areas of the United States. To 
accommodate this reality and, at the same time, ensure that such 
installations do not contribute to radon entry, this section has been 
revised to include a standard for designing and sealing air handling 
units in a manner that prevents air surrounding the unit from being 
drawn into the unit.
    Section 9.1.20  This section introduces the requirements for 
installing components of a passive sub-membrane depressurization (SMD) 
system in homes with crawlspace foundations. Two commenters identified 
cases where such components should not be required due to the 
installation of other effective radon control systems. EPA concurs and 
has added an ``Exception'' to this section which eliminates the 
requirement for SMD components when other effective crawlspace 
ventilation systems are installed.
    Section 9.1.20.1  This section addresses the installation 
requirements for crawlspace membranes. Several commenters recommended 
deletion of the requirement to seal the membrane to interior piers and 
foundation walls. Based on experience in mitigation of radon in 
existing crawlspace homes (and considering that the Model Standards 
recommend use of passive radon control systems in areas of high radon 
potential), EPA believes that sealing the membrane to piers and walls 
should be a standard construction technique in order to maximize the 
effectiveness of passive SMD systems. An additional sentence has been 
added to this section to further ensure that the integrity of the 
membrane is maintained after construction activity is completed.
    Sections 9.1.20.2, 9.21.1, 9.21.2, and 9.3.4.  Each of these 
sections addresses, among other things, the routing and exhaust point 
of radon vent pipes. Three commenters recommended revisions in these 
sections to clarify limitations on the exhaust point location. These 
sections have been revised to more clearly define the limitations.
    Section 9.21.1.1  Two commenters questioned the permitted use and 
effectiveness of small diameter (2 and 3-inch) radon vent pipes when 
installed as part of a passive radon control system. Small vent pipes 
down to 2 inches in diameter have been shown to be effective when 
installed in active radon control systems, but EPA agrees that there is 
insufficient evidence at this time to support a recommendation that 2-
inch pipes be permitted in passive radon vent stacks. That provision 
has been deleted from this section.
    Section 9.2.1  One commenter recommended revision of this section 
to more clearly define the types of air passages that should be closed 
or sealed to reduce the stack effect in buildings. EPA concurs and 
revised this section accordingly.
    Section 9.2.3  Three commenters recommended a more specific 
definition of the type of recessed ceiling lights that should be 
installed to reduce the loss of conditioned air through these fixtures. 
EPA concurs and has revised this section to include the recommended 
Type IC light fixture rating.
    Section 9.2.4  Four commenters recommended deletion of the 
requirement to install outside air ducts to provide combustion and 
makeup air for fireplaces and other combustion and vented appliances. 
Conflicts were cited between that proposed requirement and existing 
building, mechanical, and gas codes. EPA concurs and has revised this 
section to require installation of combustion and vented appliances in 
accordance with local codes.
    Section 9.3  Two commenters suggested the need for more detailed 
guidance on the type, location, and specifications of system failure 
warning devices to be used when radon control systems are activated. 
There are a variety of devices currently available to builders and 
homeowners that provide an acceptable level of audible or visual 
warning if the active radon control system fails. EPA believes that 
establishment of more detailed warning device specifications in the 
Model Standards could increase costs and inhibit installation of such 
devices. EPA concurs, however, with the need to require, as a minimum, 
that warning devices be prominently positioned to ensure that building 
occupants are alerted if the radon control system fails. This section 
has been revised to include that requirement.
    Section 9.3.3  One commenter suggested that establishment of a 
specific slope requirement (\1/8\ inch per foot) for horizontal runs of 
radon vent pipes is overly restrictive and that any slope would be 
effective for handling rain water and condensation flow. The \1/8\ inch 
per foot slope specification was based on the more demanding need for 
sufficient slope to handle sewage flow in plumbing waste lines. EPA 
agrees that such a specification is not applicable to radon vent pipes 
and has revised this section to require only that such pipes slope 
downward.
    Section 9.3.5  One commenter recommended adding a requirement that 
radon vent pipes be routed through attics in a location that would 
facilitate future installation and maintenance of a fan. EPA concurs 
with the recommendation and has inserted this section as an addition to 
the Model Standards.
    Section 9.3.6  (Formerly 9.3.5)  This section addresses the size 
and air movement capacity of radon vent pipe fans. One commenter 
recommended inclusion of a more definitive prescriptive size for the 
fan. EPA believes that a general specification, related to sub-slab or 
sub-membrane pressure field extension, permits needed flexibility in 
selection of fans for the wide variety of new home sizes and 
configurations that exist in the U.S.

C. Response to Comments on Significant Issues

    During development of the Model Standards, a number of significant 
issues were raised that warranted special consideration. Comments were 
specifically solicited on all of these issues.
    1. The first issue relates to the effectiveness of passive systems 
in achieving average annual indoor radon levels below 4 pCi/L when 
applied in areas of high radon potential. For example, passive systems 
may be affected by climatic conditions. Although data available to the 
Agency indicates that passive systems will result in reductions of 
indoor radon levels, respondents were encouraged to provide any 
information that would serve to further quantify effectiveness of 
passive systems in different house designs and in different 
geographical and climatic areas.
    Two commenters responded on this issue. One ``did not share EPA's 
confidence in effectiveness of passive systems,'' but offered no data 
to support that concern. The second commenter indicated that ``passive 
systems rarely work'' and expressed ``doubt about the 50% radon 
reduction figure given by EPA,'' citing experience in Spokane County 
(Washington) where ``new houses with EPA-style passive systems are 
testing above 4 pCi/L at a rate of 46 percent.'' EPA is currently 
conducting three studies designed to further quantify the effectiveness 
of passive radon control systems in new homes throughout the U.S. One 
of these studies has just begun in the Spokane area and will not be 
completed until the end of 1994. EPA believes that it is premature to 
draw any conclusions from any preliminary data coming out of this 
study. EPA agrees that in some local areas, where radon source strength 
is particularly high, or where climatic conditions reduce the upward 
convective flow of soil-gas in the passive radon vent stack, installing 
passive radon control systems may not always result in radon levels 
under 4 pCi/L in the new homes built in those areas. This could be the 
case even though 50 percent reductions in radon levels were achieved in 
all of these homes. These limitations are the basis for recommending in 
the Model Standards that all new homes in which passive radon control 
systems are installed should be tested to determine whether activation 
of the system is needed.
    2. The second issue relates to questions concerning ``stack 
effect'' reduction techniques, the degree to which they contribute to 
radon reduction, and their contribution to building safety and energy 
conservation. Although widely used by many builders to enhance energy 
conservation, it is acknowledged that there are different views on the 
effectiveness of these techniques in reducing indoor radon levels. Some 
research has been done to quantify the specific impact of individual 
stack effect reduction techniques on radon entry. The Agency chose to 
include these techniques as a prescriptive requirement in the 
recommended construction method because the preliminary research 
indicates they do contribute to reducing radon entry, and produce 
significant energy savings and increased fire resistance. EPA invited 
comment and information on this topic.
    Two commenters responded to this issue. Both expressed concern that 
further research is needed to validate the effectiveness of stack 
effect reduction methods in reducing radon entry, but provided no data 
to support their concern. One commenter suggested that the ``stack 
effect reduction techniques should be discussed in a non-mandatory 
appendix to the Model Standards due to continuing doubt as to their 
effectiveness.'' EPA concurs in the need for additional research to 
reduce uncertainties on this issue. However, pending receipt of 
additional data proving otherwise, EPA continues to believe that stack 
effect reduction methods contribute to reducing radon entry (and to 
energy conservation) and should be retained as an integral part of the 
Model Standards.
    3. The third issue relates to the degree that radon measurements 
made in a new home prior to occupancy will represent actual exposure of 
future occupants to radon. The Agency believes that all new homes 
should be tested, but a concern has been raised as to whether a 
measurement in a newly constructed unoccupied house can be used to 
reliably indicate the potential for elevated post-occupancy radon 
levels. For example, can the house be closed and the heating and 
cooling systems operated under normal conditions for a minimum of 12 
hours prior to and during the radon test period? The Agency 
specifically solicited any information or quantitative analyses related 
to conditions existing in a newly constructed home versus an existing 
home that would influence radon levels.
    One commenter responded on this issue by recounting the reasons why 
radon measurements should not be made prior to occupancy of a new home, 
but offered no quantitative data. In general, EPA agrees that, for a 
variety of reasons, radon measurements taken prior to occupancy may not 
reflect actual long term exposure to occupants. To begin the process of 
quantifying the accuracy of pre-occupancy radon testing, EPA is 
currently conducting a study to assess the effect on radon levels 
caused by the normal settling and drying of a house during the first 
year after occupancy. EPA supports the need for additional studies to 
address other aspects of this issue.
    4. The fourth issue concerned the need to ensure that new homes are 
tested for radon, especially homes with passive radon control systems 
in Zone 1, where, if high radon levels are found, greater risk 
reduction can be achieved by activation of the system. The Agency 
solicited information on methods that have been successful in 
increasing testing of new homes for radon.
    There were no comments specifically responding to this issue apart 
from the related comments on pre-occupancy testing addressed in the 
third issue. One commenter did recommend that ``the Standard should 
clearly identify the homeowner as the party responsible for radon 
testing.'' EPA has consistently encouraged homeowners to test for radon 
but has not found a workable method that would guarantee that a new 
home built with a passive radon control system will voluntarily be 
tested. EPA continues to solicit information on successful approaches 
to new home testing.
    5. The fifth issue relates to areas of very low radon potential 
where jurisdictions may not believe it advisable to adopt any radon-
resistant construction techniques or radon test re- quirements in their 
building codes. As a result, a small number of homes in these areas may 
have undetected elevated radon levels. EPA solicited suggestions on how 
to address this issue.
    Related to this issue, one commenter asked why the Model Standards 
``address radon only in high radon zones,'' but did not offer any 
suggestions for how to deal with isolated cases of high radon levels in 
low radon potential zones. EPA believes that use of passive radon 
control systems in areas of high radon po- tential (Zone 1), and 
activation of those systems if necessitated by follow-up testing, is 
the best approach at this time to achieving both significant radon risk 
reduction and cost-effectiveness in construction of new homes. Other 
options considered in the CBA were not judged to be cost-effective. EPA 
will continue to explore ways in which new houses with elevated radon 
levels in Zones 2 and 3 can be identified and mitigated. As indicated 
in sections 8.2.2 and 8.2.3 of the Model Standards, if jurisdictions in 
Zones 2 and 3 have reason to believe that radon ``hot spots'' exist in 
their area, the Agency recommends that appropriate radon-resistant 
features be built-in to new homes in those areas.
    6. A final issue concerned the approaches that may be taken to 
achieve early adoption of the Model Standards by Model Code 
Organizations and by local jurisdictions. It was noted that in some 
jurisdictions, adoption has been facilitated by including language in 
the codes or regulations that absolves builders and building officials 
from liability if the required new construct- ion standards and 
techniques are applied as dictated by such codes or regulations. EPA 
indicated a special interest in comments on that approach and in 
examples of other successful attempts to have model standards relating 
to environmental issues adopted by Model Code Organizations or local 
jurisdictions. One commenter reinforced the example cited above, 
suggesting that adoption of the Model Standards would be ``best 
facilitated by state laws and model codes containing provisions that 
absolve builders from liability if new construction standards are 
applied as dictated by local laws and codes.'' There were no other 
examples of approaches that might facilitate early adoption of the 
Model Standards. EPA will continue to work with state and local 
building officials and with Model Code Organizations to gain acceptance 
and early adoption of the Model Standards.
    7. While EPA requested comments on the entire document, the Agency 
was particularly interested in comments relating to the foregoing 
issues. Respondents were also encouraged to provide comments on the 
overall energy impact of applying the Model Standards. There were no 
comments specifically addressing the energy impact of the Model 
Standards. EPA continues to believe that an important by-product of 
building radon-resistance into new homes is the significant energy 
savings that also results.

    Dated: March 9, 1994.
Carol M. Browner,
Administrator.

Model Standards and Techniques for Control of Radon in New Residential 
Buildings

1.0  Scope

    1.0.1  This document contains model building standards and 
techniques applicable to controlling radon levels in new construction 
of one- and two-family dwellings and other residential buildings three 
stories or less in height as defined in model codes promulgated by the 
respective Model Code Organizations.
    1.0.2  The model building standards and techniques are also 
applicable when additions are made to the foundations of existing one- 
and two-family dwellings that result in extension of the building 
footprint.
    1.0.3  This document is not intended to be a building code nor is 
it required that it be adopted verbatim as a referenced standard.
    1.0.4  It is intended that the building standards and techniques 
contained in section 9.0 of this document, the construction method in 
section 7.0, and the recommended procedures for applying the standards 
and construction method in section 8.0, serve as a model for use by the 
Model Code Organizations and authorities within states or other 
jurisdictions that are responsible for regulating building construction 
as they develop and adopt building codes, appendixes to codes, or 
standards and implementing regulations specifically applicable to their 
unique local or regional radon control requirements.
    1.0.5  The preferential grant assistance authorized in section 
306(d) of the Indoor Radon Abatement Act of 1988 (title III of the 
Toxic Substances Control Act, TSCA, 15 U.S.C. 2666) will be applied for 
states where appropriate authorities who regulate building construction 
are taking action to adopt radon-resistant standards in their building 
codes.
    1.0.6  Model building standards and techniques contained in this 
document are not intended to supersede any radon-resistant construction 
standards, codes or regulations previously adopted by local 
jurisdictions and authorities. However, jurisdictions and authorities 
are encouraged to review their current building standards, codes, or 
regulations and their unique local or regional radon control 
requirements, and consider modifications, if necessary.
    1.0.7  This document will be updated and revised as ongoing and 
future research programs suggest revisions of standards, identify ways 
to improve the model construction techniques, or when newly tested 
products or techniques prove to be equivalent to or more effective in 
radon control. Updates and revisions to the model building standards 
and techniques contained in section 9.0 will undergo appropriate peer 
review.
    1.0.8  EPA is committed to continuing evaluation of the 
effectiveness of the standards and techniques contained in section 9.0 
and to research programs that may identify other more effective and 
efficient methods.

2.0  Limitations

    2.0.1  The Indoor Radon Abatement Act of 1988 (title III of TSCA) 
establishes a long-term national goal of achieving radon levels inside 
buildings that are no higher than those found in ambient air outside of 
buildings. While technological, physical, and financial limitations 
currently preclude attaining this goal, the underlying objective of 
this document is to move toward achieving the lowest technologically 
achievable and most cost effective levels of indoor radon in new 
residential buildings.
    2.0.2  Preliminary research indicates that the building standards 
and techniques contained in section 9.0 can be applied successfully in 
mitigating radon problems in some existing nonresidential buildings. 
However, their effectiveness when applied during construction of new 
nonresidential buildings has not yet been fully demonstrated. 
Therefore, it is recommended that, pending further research, these 
building standards and techniques not be used at this time as a basis 
for changing the specific sections of building codes that cover 
nonresidential construction.
    2.0.3  Although radon levels below 4 pCi/L have been achieved in 
all types of residential buildings by using these model building 
standards and techniques, specific indoor radon levels for any given 
building cannot be predicted due to different site and environmental 
conditions, building design, construction practices, and variations in 
the operation of buildings.
    2.0.4  These model building standards and techniques are not to be 
construed as the only acceptable methods for controlling radon levels, 
and are not intended to preempt, preclude, or restrict the application 
of alternative materials, systems, and construction practices approved 
by building officials under procedures prescribed in existing building 
codes.
    2.0.5  Elevated indoor radon levels caused by emanation of radon 
from water is of potential concern, particularly in areas where there 
is a history of groundwater with high radon content. This document does 
not include model construction standards or techniques for reducing 
elevated levels of indoor radon that may be caused by the presence of 
high levels of radon in water supplies. EPA has developed a suggested 
approach (see paragraph 8.3.2) that state or local jurisdictions should 
consider as they develop regulations concerning private wells. EPA is 
continuing to evaluate the issue of radon occurrence in private wells 
and the economic impacts of testing and remediation of wells with 
elevated radon levels.
    2.0.6  While it is not currently possible to make a precise 
prediction of indoor radon potential for a specific building site, a 
general assessment, on a statewide, county, or grouping of counties 
basis, can be made by referring to EPA's Map of Radon Zones and other 
locally available data. It should be noted that some radon potential 
exists in all areas. However, EPA recognizes that based on available 
data, there is a lower potential for elevated indoor radon levels in 
some states and portions of some states, and that adoption of building 
codes for the prevention of radon in new construction may not be 
justified in these areas at this time. There is language in paragraph 
8.2.3 of this document recommending that jurisdictions in these areas 
review all available data on local indoor radon measurements, geology, 
soil parameters, and housing characteristics as they consider whether 
adoption of new codes is appropriate.

3.0  Reference Documents

    References are made to the following publications throughout this 
document. Some of the references do not specifically address radon. 
They are listed here only as relevant sources of additional information 
on building design, construction techniques, and good building 
practices that should be considered as part of a general radon 
reduction strategy.
    ``Building Foundation Design Handbook,'' ORNL/SUB/86-72143/1, May 
1988.
    ``Building Radon Resistant Foundations--A Design Handbook,'' NCMA, 
1989.
    ``Council of American Building Officials (CABO) Model Energy Code, 
1992.
    ``Design and Construction of Post-Tensioned Slabs on Ground,'' Post 
Tensioning Institute Manual.
    ``Energy Efficient Design of New Buildings Except Low-Rise 
Residential Buildings,'' ASHRAE Standard 90.1-1989.
    ``Energy Efficient Design of New Low-Rise Residential Buildings,'' 
Draft ASHRAE Standard 90.2 (Under public review).
    ``Homebuyer's and Seller's Guide to Radon,'' EPA 402-R-93-003, 
March 1993.
    ``Guide to Residential Cast-in-Place Concrete Construction,'' ACI 
332R.
    ``Indoor Radon and Radon Decay Product Measurement Device 
Protocols.'' EPA 402-R-92-004, July, 1992.
    ``Protocols For Radon and Radon Decay Product Measurements in 
Homes.'' EPA 402-R-92-003, June, 1993.
    ``Permanent Wood Foundation System--Basic Requirements, NFPA 
Technical Report No. 7.''
    ``Radon Control Options for the Design and Construction of New Low-
Rise Residential Buildings,'' ASTM Standard Guide, E1465-92.
    ``Radon Handbook for the Building Industry,'' NAHB-NRC, 1989.
    ``USEPA Map of Radon Zones,'' Dec. 1993.
    ``Radon Reduction in New Construction, An Interim Guide.'' OPA-87-
009, August 1987.
    ``Radon Reduction in Wood Floor and Wood Foundation Systems.'' 
NFPA, 1988.
    ``Radon Resistant Construction Techniques for New Residential 
Construction. Technical Guidance.'' EPA/625/2-91/032, February 1991.
    ``Radon-Resistant Residential New Construction.'' EPA/600/8-88/087, 
July 1988.
    ``Guide for Concrete Floor and Slab Construction,'' ACI 302.1R-89.
    ``Ventilation for Acceptable Indoor Air Quality,'' ASHRAE 62-1989.

4.0  Description of Terms

    For this document, certain terms are defined in this section. Terms 
not defined herein should have their ordinary meaning within the 
context of their use. Ordinary meaning is as defined in ``Webster's 
Ninth New Collegiate Dictionary.''
    Action Level: A term used to identify the level of indoor radon at 
which remedial action is recommended. (EPA's current action level is 4 
pCi/L.)
    Air Passages: Openings through or within walls, through floors and 
ceilings, and around chimney flues and plumbing chases, that permit air 
to move out of the conditioned spaces of the building.
    Combination Foundations: Buildings constructed with more than one 
foundation type; e.g., basement/crawlspace or basement/slab-on-grade.
    Drain Tile Loop: A continuous length of drain tile or perforated 
pipe extending around all or part of the internal or external perimeter 
of a basement or crawlspace footing.
    Governmental: State or local organizations/agencies responsible for 
building code enforcement.
    Map of Radon Zones: A USEPA publication depicting areas of 
differing radon potential in both map form and in state specific 
booklets.
    Mechanically Ventilated Crawlspace System: A system designed to 
increase ventilation within a crawlspace, achieve higher air pressure 
in the crawlspace relative to air pressure in the soil beneath the 
crawlspace, or achieve lower air pressure in the crawlspace relative to 
air pressure in the living spaces, by use of a fan.
    Model Building Codes: The building codes published by the 4 Model 
Code Organizations and commonly adopted by state or other jurisdictions 
to control local construction activity.
    Model Code Organizations: Includes the following agencies and the 
model building codes they promulgate: Building Officials and Code 
Administrators International, Inc. (BOCA National Building Code/1993 
and BOCA National Mechanical Code/1993); International Conference of 
Building Officials (Uniform Building Code/1991 and Uniform Mechanical 
Code/1991); Southern Building Code Congress, International, Inc. 
(Standard Building Code/1991 and Standard Mechanical Code/1991); 
Council of American Building Officials (CABO One- and Two-Family 
Dwelling Code/1992 and CABO Model Energy Code/1993).
    pCi/L: The abbreviation for ``picocuries per liter'' which is used 
as a radiation unit of measure for radon. The prefix ``pico'' means a 
multiplication factor of l trillionth. A Curie is a commonly used 
measurement of radioactivity.
    Soil Gas: The gas present in soil which may contain radon.
    Soil-Gas-Retarder: A continuous membrane or other comparable 
material used to retard the flow of soil gases into a building.
    Stack Effect: The overall upward movement of air inside a building 
that results from heated air rising and escaping through openings in 
the building super-structure, thus causing an indoor pressure level 
lower than that in the soil gas beneath or surrounding the building 
foundation.
    Sub-Slab Depressurization System (Active): A system designed to 
achieve lower sub-slab air pressure relative to indoor air pressure by 
use of a fan-powered vent drawing air from beneath the slab.
    Sub-Slab Depressurization System (Passive): A system designed to 
achieve lower sub-slab air pressure relative to indoor air pressure by 
use of a vent pipe routed through the conditioned space of a building 
and connecting the sub-slab area with outdoor air, thereby relying 
solely on the convective flow of air upward in the vent to draw air 
from beneath the slab.
    Sub-Membrane Depressurization System: A system designed to achieve 
lower sub-membrane air pressure relative to crawlspace air pressure by 
use of a fan-powered vent drawing air from under the soil-gas-retarder 
membrane.

5.0  Principles for Construction of Radon-Resistant Residential 
Buildings

    5.1  The following principles for construction of radon-resistant 
residential buildings underlie the specific model standards and 
techniques set forth in section 9.0.
    5.1.1  Residential buildings should be designed and constructed to 
minimize the entrance of soil gas into the living space.
    5.1.2  Residential buildings should be designed and constructed 
with features that will facilitate post-construction radon removal or 
further reduction of radon entry if installed prevention techniques 
fail to reduce radon levels below the locally prescribed action level.
    5.2  As noted in the limitations section (paragraph 2.0.2), 
construction standards and techniques specifically applicable to new 
nonresidential buildings (including high-rise residential buildings), 
have not yet been fully demonstrated. Accordingly, the specific 
standards and techniques set forth in section 9.0 should not, at this 
time, be considered applicable to such buildings. There are, however, 
several general conclusions that may be drawn from the limited 
mitigation experience available on large nonresidential construction. 
These conclusions are summarized below to provide some initial factors 
for consideration by builders of nonresidential buildings.
    5.2.1  HVAC systems should be carefully designed, installed and 
operated to avoid depressurization of basements and other areas in 
contact with the soil.
    5.2.2  As a minimum, use of a coarse gravel or other permeable base 
material beneath slabs, and effective sealing of expansion joints and 
penetrations in foundations below the ground surface will facilitate 
post-construction installation of a sub-slab depressurization system, 
if necessary.
    5.2.3  Limited mitigation experience has shown that some of the 
same radon reduction systems and techniques used in residential 
buildings can be scaled up in size, number, or performance to 
effectively reduce radon in larger buildings.

6.0  Summary of the Model Building Standards and Techniques

    The model building standards and techniques listed in section 9.0 
are designed primarily for control of radon in new one- and two-family 
dwellings and other residential buildings three stories or less in 
height.

6.1  Basement and Slab-on-Grade Foundations

    The model building standards and techniques for radon control in 
new residential buildings constructed on basement and slab-on-grade 
foundations include a layer of permeable sub-slab material, the sealing 
of joints, cracks, and other penetrations of slabs, floor assemblies, 
and foundation walls below or in contact with the ground surface, 
providing a soil-gas-retarder under floors and installing either an 
active or passive sub-slab depressurization system (SSD). Additional 
radon reduction techniques are prescribed to reduce radon entry caused 
by the heat induced ``stack effect.'' These include the closing of air 
passages (also called thermal by-passes), providing adequate makeup air 
for combustion and exhaust devices, and installing energy conservation 
features that reduce nonrequired airflow out of the building 
superstructure.

6.2  Crawlspace Foundations

    The model building standards and techniques for radon control in 
new residential buildings constructed on crawlspace foundations include 
those systems that actively or passively vent the crawlspace to outside 
air, that divert radon before entry into the crawlspace, and that 
reduce radon entry into normally occupied spaces of the building 
through floor openings and ductwork.

6.3  Combination Foundations

    Radon control in new residential buildings constructed on a 
combination of basement, slab-on-grade or crawlspace foundations is 
achieved by applying the appropriate construction techniques to the 
different foundation segments of the building. While each foundation 
type should be constructed using the relevant portions of these model 
building standards and techniques, special consideration must be given 
to the points at which different foundation types join, since 
additional soil-gas entry routes exist in such locations.

7.0  Construction Methods

    The model construction standards and techniques described in 
section 9.0 have proved to be effective in reducing indoor radon levels 
when used to mitigate radon problems in existing homes and when applied 
in construction of new homes. In most cases, combinations of two or 
more of these standards and techniques have been applied to achieve 
desired reductions in radon levels. Because of success achieved in 
reducing radon levels by applying these multiple, interdependent 
techniques, limited data have been collected on the singular 
contribution to radon reduction made by any one of the construction 
standards or techniques. Accordingly, there has been no attempt to 
classify or prioritize the individual standards and techniques as to 
their specific contribution to radon reduction. It is believed that use 
of all the standards and techniques (both passive and active) will 
produce the lowest achievable levels of indoor radon in new homes 
(levels below 2 pCi/L have been achieved in over 90 percent of new 
homes). It is also believed that use of only selected (passive) 
standards and techniques will produce indoor radon levels below the 
current EPA action level of 4 pCi/L in most new homes, even in areas of 
high radon potential.
    7.1  It is recommended that all the passive standards and 
techniques listed in section 9.0 (including a roughed-in passive radon 
control system) be used in areas of high radon potential, as defined by 
local jurisdictions or in EPA's Map of Radon Zones. Based on more 
detailed analysis of locally available data, jurisdictions may choose 
to apply more or less restrictive construction requirements within 
designated portions of their areas of responsibility. To ensure that 
new homes are below the locally prescribed action level, in those cases 
where only passive radon control systems have been installed, occupants 
should have their homes tested to determine if passive radon control 
systems need to be activated. In addition, it is recommended that 
periodic retests be conducted to confirm continued effectiveness of the 
radon control system.
    7.2  Any radon testing referenced in this document should be 
conducted in accordance with EPA Radon Testing Protocols or current EPA 
guidance for radon testing in real estate transactions as referenced in 
paragraph 3.0. It is recommended that all testing be conducted by 
companies listed in EPA's Radon Measurement Proficiency Program (RMP) 
or comparable State certification programs.
    7.3  The design and installation of radon control systems should be 
performed or supervised by individuals (i.e., builders, their 
representatives, or registered design professionals such as architects 
or engineers) who have attended an EPA-approved radon training course, 
or by an individual listed in the EPA Radon Contractor Proficiency 
Program.

8.0  Recommended Implementation Procedures

    The following procedures are recommended as guidelines for applying 
the model building standards and techniques and construction methods 
contained in this document. These procedures are based on the rationale 
that a passive radon control system and features to facilitate any 
necessary post-construction radon reduction should be routinely built-
in to new residential buildings in areas having a high radon potential.
    8.1  State, county, or local jurisdictions that use these model 
building standards and techniques as a basis for developing building 
codes for radon resistant construction should classify their area by 
reference to the Zones in EPA's Map of Radon Zones or by considering 
other locally available data. While EPA believes that the Map of Radon 
Zones and accompanying state-specific booklets are useful in setting 
general boundaries of areas of concern, EPA recommends that state and 
local jurisdictions collect and analyze local indoor radon 
measurements, and assess geology, soil parameters and housing 
characteristics--in conjunction with referring to the EPA radon maps--
to determine the specific areas within their jurisdictions that should 
be classified as Zone 1.
    8.2  State, county, or local jurisdictions that use these model 
building standards and techniques as a basis for developing building 
codes for radon-resistant construction should specify the construction 
methods applicable to their jurisdictional area.
    8.2.1  In areas classified as Zone 1 in the Map of Radon Zones, or 
by local jurisdiction, application of the construction method in 
paragraph 7.1 is recommended.
    8.2.2  In areas classified as Zone 2, home builders may apply any 
of the radon-resistant construction standards and techniques that 
contribute to reducing the incidence of elevated radon levels in new 
homes and that are appropriate to the unique radon potential that may 
exist in their local building area.
    8.2.3  In those areas where state and local jurisdictions have 
analyzed local indoor radon measurements, geology, soil parameters, and 
housing characteristics and determined that there is a low potential 
for indoor radon, application of radon-resistant construction 
techniques may not be appropriate. In these areas, radon-resistant 
construction techniques may not be needed, or limited use of selected 
techniques may be sufficient.
    8.3  It is recognized that specific rules, regulations, or 
ordinances covering implementation of construction standards or codes 
are developed and enforced by state or local jurisdictions. While 
developing the model construction standards and techniques contained in 
this document, EPA also developed several approaches to regulation that 
states or local jurisdictions may find useful and appropriate as they 
develop rules and regulations that meet their unique requirements. For 
example:
    8.3.1  In areas where the recommended construction method or 
comparable prescriptive methods are mandated by state or local 
jurisdictions, regulations would need to include, as part of the 
inspection process, a review of the radon-resistant construction 
features by inspectors who have received additional training, to ensure 
that the radon-resistant construction features are properly installed 
during construction. It would also be necessary to establish 
requirements for those building officials who review and approve 
construction plans and specifications to become proficient in 
identifying and approving planned radon-resistant construction 
features.
    8.3.2  In any area where surveys have shown the existence of high 
levels of radon in groundwater, or in areas where elevated levels of 
indoor radon have been found in homes already equipped with active 
radon control systems, well water may be the source. In such areas, 
authorities responsible for water regulation should consider 
establishing well water testing requirements that include tests for 
radon.

9.0  Model Building Standards and Techniques

    9.1  Foundation and Floor Assemblies:
    The following construction techniques are intended to resist radon 
entry and prepare the building for post-construction radon mitigation, 
if necessary. These techniques, when combined with those listed in 
paragraph 9.2, meet the requirements of the construction method 
outlined in paragraph 7.1. (See also the construction methods listed in 
ASTM Standard Guide, E-1465-92.)
    9.1.1  A layer of gas permeable material shall be placed under all 
concrete slabs and other floor systems that directly contact the ground 
and are within the walls of the living spaces of the building, to 
facilitate installation of a sub-slab depressurization system, if 
needed. Alternatives for creating the gas permeable layer include:
    a. A uniform layer of clean aggregate, a minimum of 4 inches thick. 
The aggregate shall consist of material that will pass through a 2-inch 
sieve and be retained by a \1/4\-inch sieve.
    b. A uniform layer of sand, a minimum of 4 inches thick, overlain 
by a layer or strips of geotextile drainage matting designed to allow 
the lateral flow of soil gases.
    c. Other materials, systems, or floor designs with demonstrated 
capability to permit depressurization across the entire subfloor area.
    9.1.2  A minimum 6-mil (or 3-mil cross laminated) polyethylene or 
equivalent flexible sheeting material shall be placed on top of the gas 
permeable layer prior to pouring the slab or placing the floor assembly 
to serve as a soil-gas-retarder by bridging any cracks that develop in 
the slab or floor assembly and to prevent concrete from entering the 
void spaces in aggre- gate base material. The sheeting should cover the 
entire floor area, and separate sections of sheeting should be 
overlapped at least 12 inches. The sheeting shall fit closely around 
any pipe, wire or other penetrations of the material. All punctures or 
tears in the material shall be sealed or covered with additional 
sheeting.
    9.1.3  To minimize the formation of cracks, all concrete floor 
slabs shall be designed, mixed, placed, reinforced, consolidated, 
finished, and cured in accordance with standards set forth in the Model 
Building Codes. The American Concrete Institute publications, ``Guide 
for Concrete Floor and Slab Construction,'' ACI 302.1R, ``Guide to 
Residential Cast-in-Place Concrete Construction,'' ACI 332R, or the 
Post Tensioning Institute Manual, ``Design and Construction of Post-
Tensioned Slabs on Ground'' are references that provide additional 
information on construction of concrete floor slabs.
    9.1.4  Floor assemblies in contact with the soil and constructed of 
materials other than concrete shall be sealed to minimize soil gas 
transport into the conditioned spaces of the building. A soil-gas-
retarder shall be installed beneath the entire floor assembly in 
accordance with paragraph 9.1.2.
    9.1.5  To retard soil gas entry, large openings through concrete 
slabs, wood, and other floor assemblies in contact with the soil, such 
as spaces around bathtub, shower, or toilet drains, shall be filled or 
closed with materials that provide a permanent air-tight seal such as 
non-shrink mortar, grouts, ex- panding foam, or similar materials 
designed for such application.
    9.1.6  To retard soil gas entry, smaller gaps around all pipe, 
wire, or other objects that penetrate concrete slabs or other floor 
assemblies shall be made air tight with an elastomeric joint sealant, 
as defined in ASTM C920-87, and applied in accordance with the 
manufacturer's recommendations.
    9.1.7  To retard soil gas entry, all control joints, isolation 
joints, construction joints, and any other joints in concrete slabs or 
between slabs and foundation walls shall be sealed. A continuous formed 
gap (for example, a ``tooled edge'') which allows the application of a 
sealant that will provide a continuous, air-tight seal shall be created 
along all joints. When the slab has cured, the gap shall be cleared of 
loose material and filled with an elastomeric joint sealant, as defined 
in ASTM C920-97, and applied in accordance with the manufacturer's 
recommendations.
    9.1.8  Channel type (French) drains are not recommended. However, 
if used, such drains shall be sealed with backer rods and an 
elastomeric joint sealant in a manner that retains the channel feature 
and does not interfere with the effectiveness of the drain as a water 
control system.
    9.1.9  Floor drains and air conditioning condensate drains that 
discharge directly into the soil below the slab or into crawlspaces 
should be avoided. If installed, these drains shall be routed through 
solid pipe to daylight or through a trap approved for use in floor 
drains by local plumbing codes.
    9.1.10  Sumps open to soil or serving as the termination point for 
sub-slab or exterior drain tile loops shall be covered with a gasketed 
or otherwise sealed lid to retard soil gas entry. (Note: If the sump is 
to be used as the suction point in an active sub-slab depressurization 
system, the lid should be designed to accommodate the vent pipe. If 
also intended as a floor drain, the lid shall also be equipped with a 
trapped inlet to handle any surface water on the slab.)
    9.1.11  Concrete masonry foundation walls below the ground surface 
shall be constructed to minimize the transport of soil gas from the 
soil into the building. Hollow block masonry walls shall be sealed at 
the top to prevent passage of air from the interior of the wall into 
the living space. At least one continuous course of solid masonry, one 
course of masonry grouted solid, or a poured concrete beam at or above 
finished ground surface level shall be used for this purpose. Where a 
brick veneer or other masonry ledge is installed, the course 
immediately below that ledge shall also be sealed.
    9.1.12  Pressure treated wood foundations shall be constructed and 
installed as described in the National Forest Products Association 
(NFPA) Manual, ``Permanent Wood Foundation System--Basic Requirements, 
Technical Report No. 7.'' In addition, NFPA publication, ``Radon 
Reduction in Wood Floor and Wood Foundation Systems'' provides more 
detailed information on construction of radon-resistant wood floors and 
foundations.
    9.1.13  Joints, cracks, or other openings around all penetrations 
of both exterior and interior surfaces of masonry block or wood 
foundation walls below the ground surface shall be sealed with an 
elastomeric sealant that provides an air-tight seal. Penetrations of 
poured concrete walls should also be sealed on the exterior surface. 
This includes sealing of wall tie penetrations.
    9.1.14  To resist soil gas entry, the exterior surfaces of portions 
of poured concrete and masonry block walls below the ground surface 
shall be constructed in accordance with water proofing procedures 
outlined in the Model Building Codes.
    9.1.15  Placing air handling ducts in or beneath a concrete slab 
floor or in other areas below grade and exposed to earth is not 
recommended unless the air handling system is designed to maintain 
continuous positive pressure within such ducting. If ductwork does pass 
through a crawlspace or beneath a slab, it should be of seamless 
material. Where joints in such ductwork are unavoidable, they shall be 
sealed with materials that prevent air leakage.
    9.1.16  Placing air handling units in crawlspaces, or in other 
areas below grade and exposed to soil-gas, is not recommended. However, 
if such units are installed in crawlspaces or in other areas below 
grade and exposed to soil gas, they shall be designed or otherwise 
sealed in a durable manner that prevents air surrounding the unit from 
being drawn into the unit.
    9.1.17  To retard soil gas entry, openings around all penetrations 
through floors above crawlspaces shall be sealed with materials that 
prevent air leakage.
    9.1.18  To retard soil gas entry, access doors and other openings 
or penetrations between basements and adjoining crawlspaces shall be 
closed, gasketed or otherwise sealed with materials that prevent air 
leakage.
    9.1.19  Crawlspaces should be ventilated in conformance with 
locally adopted codes. In addition, vents in passively ventilated 
crawlspaces shall be open to the exterior and be of noncloseable 
design.
    9.1.20  In buildings with crawlspace foundations, the following 
components of a passive sub-membrane depressurization system shall be 
installed during construction: (Exception: Where local codes permit 
mechanical crawlspace ventilation or other effective ventilation 
systems, and such systems are operated or proven to be effective year 
round, the sub- membrane depressurization system components are not 
required.)
    9.1.20.1  The soil in both vented and nonvented crawlspaces shall 
be covered with a continuous layer of minimum 6-mil thick polyethylene 
sheeting or equivalent membrane material. The sheeting shall be sealed 
at seams and penetrations, around the perimeter of interior piers, and 
to the foundation walls. Following installation of underlayment, 
flooring, plumbing, wiring, or other construction activity in or over 
the crawlspace, the membrane material shall be inspected for holes, 
tears, or other damage, and for continued adhesion to walls and piers. 
Repairs shall be made as necessary.
    9.1.20.2 A  length of 3- or 4-inch diameter perforated pipe or a 
strip of geotextile drainage matting should be inserted horizontally 
beneath the sheeting and connected to a 3- or 4-inch diameter ``T'' 
fitting with a vertical standpipe installed through the sheeting. The 
standpipe shall be extended vertically through the building floors, 
terminate at least 12 inches above the surface of the roof, in a 
location at least 10 feet away from any window or other opening into 
the conditioned spaces of the building that is less than 2 feet below 
the exhaust point, and 10 feet from any adjoining or adjacent 
buildings.
    9.1.20.3  All exposed and visible interior radon vent pipes shall 
be identified with at least one label on each floor level. The label 
shall read: ``Radon Reduction System.''
    9.1.20.4  To facilitate installation of an active sub-membrane 
depressurization system, electrical junction boxes shall be installed 
during construction in proximity to the anticipated locations of vent 
pipe fans and system failure alarms.
    9.1.21  In basement or slab-on-grade buildings the following 
components of a passive sub-slab depressurization system shall be 
installed during construction:
    9.1.21.1  A mimimum 3-inch diameter PVC or other gas-tight pipe 
shall be embedded vertically into the sub-slab aggregate or other 
permeable material before the slab is poured. A ``T'' fitting or other 
support on the bottom of the pipe shall be used to ensure that the pipe 
opening remains within the sub-slab permeable material. This gas tight 
pipe shall be extended vertically through the building floors, 
terminate at least 12 inches above the surface of the roof, in a 
location at least 10 feet away from any window or other opening into 
the conditioned spaces of the building that is less than 2 feet below 
the exhaust point, and 10 feet from any adjoining or adjacent 
buildings.

    Note: Because of the uniform permeability of the sub-slab layer 
prescribed in paragraph 9.1.1, the precise positioning of the vent 
pipe through the slab is not critical to system performance in most 
cases. However, a central location shall be used where feasible.

    In buildings designed with interior footings (that is, footings 
located inside the overall perimeter footprint of the building) or 
other barriers to lateral flow of sub-slab soil gas, radon vent pipes 
shall be installed in each isolated, nonconnected floor area. If 
multiple suction points are used in nonconnected floor areas, vent 
pipes are permitted to be manifolded in the basement or attic into a 
single vent that could be activated using a single fan.
    9.1.21.2  Internal sub-slab or external footing drain tile loops 
that terminate in a covered and sealed sump, or internal drain tile 
loops that are stubbed up through the slab are also permitted to 
provide a roughed-in passive sub-slab depressurization capability. The 
sump or stubbed up pipe shall be connected to a vent pipe that extends 
vertically through the building floors, terminates at least 12 inches 
above the surface of the roof, in a location at least 10 feet away from 
any window or other opening into the conditioned spaces of the building 
that is less than 2 feet below the exhaust point, and 10 feet from any 
adjoining or adjacent buildings.
    9.1.21.3  All exposed and visible interior radon vent pipes shall 
be identified with at least one label on each floor level. The label 
shall read: ``Radon Reduction System.''
    9.1.21.4  To facilitate installation of an active sub-slab 
depressurization system, electrical junction boxes shall be installed 
during construction in proximity to the anticipated locations of vent 
pipe fans and system failure alarms.
    9.1.21.5  In combination basement/crawlspace or slab-on-grade/
crawlspace buildings, the sub-membrane vent described in paragraph 
9.1.20.2 may be tied into the sub-slab depressurization vent to permit 
use of a single fan for suction if activation of the system is 
necessary.
    9.2  Stack Effect Reduction Techniques.
    The following construction techniques are intended to reduce the 
stack effect in buildings and thus the driving force that contributes 
to radon entry and migration through buildings. As a basic principle, 
the driving force decreases as the number and size of air leaks in the 
upper surface of the building decrease. It should also be noted that in 
most cases, exhaust fans contribute to stack effect.
    9.2.1  Openings around chimney flues, plumbing chases, pipes, and 
fixtures, ductwork, electrical wires and fixtures, elevator shafts, or 
other air passages that penetrate the conditioned envelope of the 
building shall be closed or sealed using sealant or fire resistant 
materials approved in local codes for such application.
    9.2.2  If located in conditioned spaces, attic access stairs and 
other openings to the attic from the building shall be closed, 
gasketed, or otherwise sealed with materials that prevent air leakage.
    9.2.3  Recessed ceiling lights that are designed to be sealed and 
that are Type IC rated shall be used when installed on top-floor 
ceilings or in other ceilings that connect to air passages.
    9.2.4  Fireplaces, wood stoves, and other combustion or vented 
appliances, such as furnaces, clothes dryers, and water heaters shall 
be installed in compliance with locally adopted codes, or other 
provisions made to ensure an adequate supply of combustion and makeup 
air.
    9.2.5  Windows and exterior doors in the building superstructure 
shall be weather stripped or otherwise designed in conformance with the 
air leakage criteria of the CABO Model Energy Code.
    9.2.6  HVAC systems shall be designed and installed to avoid 
depressurization of the building relative to underlying and surrounding 
soil. Specifically, joints in air ducts and plenums passing through 
unconditioned spaces such as attics, crawlspaces, or garages shall be 
sealed.
    9.3  Active Sub-Slab/Sub-Membrane Depressurization System. When 
necessary, activation of the roughed-in passive sub-membrane or sub-
slab depressurization systems described in paragraphs 9.1.20 and 9.1.21 
shall be completed by adding an exhaust fan in the vent pipe and a 
prominently positioned visible or audible warning system to alert the 
building occupant if there is loss of pressure or air flow in the vent 
pipe.
    9.3.1  The fan in the vent pipe and all positively pressurized 
portions of the vent pipe shall be located outside the habitable space 
of the building.
    9.3.2  The fan in the vent pipe shall be installed in a vertical 
run of the vent pipe.
    9.3.3  Radon vent pipes shall be installed in a configuration and 
supported in a manner that ensures that any rain water or condensation 
accumulating within the pipes drains downward into the ground beneath 
the slab or soil-gas-retarder.
    9.3.4  To avoid reentry of soil gas into the building, the vent 
pipe shall exhaust at least 12 inches above the surface of the roof, in 
a location at least 10 feet away from any window or other opening into 
the conditioned spaces of the building that is less than 2 feet below 
the exhaust point, and 10 feet from any adjoining or adjacent 
buildings.
    9.3.5  To facilitate future installation of a vent fan, if needed, 
the radon vent pipe shall be routed through attics in a location that 
will allow sufficient room to install and maintain the fan.
    9.3.6  The size and air movement capacity of the vent pipe fan 
shall be sufficient to create and maintain a pressure field beneath the 
slab or crawlspace membrane that is lower than the ambient pressure 
above the slab or membrane.
    9.3.7  Under conditions where soil is highly permeable, reversing 
the air flow in an active sub-slab depressurization system and forcing 
air beneath the slab may be effective in reducing indoor radon levels.

    (Note: The long-term effect of active sub-slab depressurization 
or pressurization on the soil beneath building foundations has not 
been determined. Until ongoing research produces definitive data, in 
areas where expansive soils or other unusual soil conditions exist, 
the local soils engineer shall be consulted during the design and 
installation of sub-slab depressurization or pressurization 
systems.)

[FR Doc. 94-6551 Filed 3-18-94; 8:45 am]
BILLING CODE 6560-50-P