ASTM E2121-21

Standard Practice for Installing Radon Mitigation Systems in Existing Low-Rise Residential Buildings

SIGNIFICANCE AND USE
5.1 The purpose of the methods, systems, and designs described in this practice is to reduce radiation exposures for occupants of residential buildings caused by radon and its progeny. The goal of mitigation is to maintain reduced radon concentrations in occupiable areas of buildings at levels as low as reasonably achievable. This practice includes sections on reducing radiation exposure caused by radon and its progeny for workers who install and repair radon mitigation systems. The goal for workers is to reduce exposures to radon and its progeny to levels as low as reasonably achievable.  
5.2 The methods, systems, designs, and materials described here have been shown to have a high probability of success in mitigating radon in attached and detached residential buildings, three stories or less in height (see EPA, “Radon Reduction Techniques for Existing Detached Houses, Technical Guidance (Third Edition) for Active Soil Depressurization Systems”). Application of these methods does not, however, guarantee reduction of radon levels below any specific level, since performance will vary with site conditions, construction characteristics, weather, and building operation.  
5.3 When applying this practice, contractors also shall conform to all applicable local, state, and federal regulations, and laws pertaining to residential building construction, remodeling, and improvement.
SCOPE
1.1 This practice describes methods for reducing radon entry into existing attached and detached residential buildings three stories or less in height. This practice is intended for use by trained, certified or licensed, or both, or otherwise qualified individuals.  
1.2 These methods are based on radon mitigation techniques that have been effective in reducing radon levels in a wide range of residential buildings and soil conditions. These fan powered mitigation methods are listed in Appendix X1. More detailed information is contained in references cited throughout this practice.  
1.3 This practice is intended to provide radon mitigation contractors with a uniform set of practices that will ensure a high degree of safety and the likelihood of success in retrofitting low rise residential buildings with radon mitigation systems.  
1.4 The methods described in this practice apply to currently occupied or formerly occupied residential buildings, including buildings converted or being converted to residential use, as well as residential buildings changed or being changed by addition(s) or alteration(s), or both. The radon reduction activities performed on new dwellings, while under construction, before occupancy, and for up to one year after occupancy, are covered by Practice E1465.  
1.5 This practice also is intended as a model set of practices, which can be adopted or modified by state and local jurisdictions, to fulfill objectives of their specific radon contractor certification or licensure programs. Radon mitigation performed in accordance with this practice is considered ordinary repair.  
1.6 The methods addressed in this practice include the following categories of contractor activity: general practices, building investigation, systems design, systems installation, materials, monitors and labeling, post-mitigation testing, and documentation.  
1.7 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.  
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. See Section 6 for specific safety hazards.  
1.9 This international standard was developed in accordance with internationally recognized principles...

General Information

• Status: Published
• Publication Date: 30-Sep-2021
• ICS: 91.120.99 - Other standards related to protection of and in buildings
• Technical Committee: E06 - Performance of Buildings
• Drafting Committee: E06.41 - Air Leakage and Ventilation Performance

Relations

• Refers: ASTM E631-15 - Standard Terminology of Building Constructions
• Effective Date: 01-Mar-2015
• Refers: ASTM E631-14 - Standard Terminology of Building Constructions
• Effective Date: 01-Nov-2014
• Refers: ASTM E1745-11 - Standard Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs
• Effective Date: 01-Oct-2011
• Refers: ASTM E1745-09 - Standard Specification for Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs
• Effective Date: 15-Feb-2009
• Refers: ASTM E1465-08a - Standard Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings (Withdrawn 2017)
• Effective Date: 01-Dec-2008
• Refers: ASTM E1465-08 - Standard Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings
• Effective Date: 01-Mar-2008
• Refers: ASTM E1465-07a - Standard Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings
• Effective Date: 15-Jul-2007
• Refers: ASTM E1465-07 - Standard Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings
• Effective Date: 01-Jun-2007
• Refers: ASTM E1465-06 - Standard Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings
• Effective Date: 01-Oct-2006
• Refers: ASTM E631-06 - Standard Terminology of Building Constructions
• Effective Date: 01-Jun-2006
• Refers: ASTM E1745-97(2004) - Standard Specification for Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs
• Effective Date: 01-May-2004
• Refers: ASTM E631-93a(1998)e1 - Standard Terminology of Building Constructions
• Effective Date: 28-Jul-2000
• Refers: ASTM E1745-97 - Standard Specification for Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs
• Effective Date: 10-Mar-1997
• Refers: ASTM E1465-92 - Guide for Radon Control Options for the Design and Construction of New Low Rise Residential Buildings (Withdrawn 2001)
• Effective Date: 01-Jan-1992

Overview

ASTM E2121-21 is the key international standard for the installation of radon mitigation systems in existing low-rise residential buildings, specifically those that are three stories or less in height. Published by ASTM International, this standard provides comprehensive guidance for professionals tasked with reducing radon gas concentrations in both attached and detached homes. Its primary goal is to ensure that mitigation efforts effectively lower radon exposure for building occupants and for workers installing or maintaining these systems, all while maintaining safety and compliance with applicable regulations.

Radon is a naturally occurring radioactive gas known for its carcinogenic potential, making radon mitigation critical for indoor air quality and the safety of residential occupants. ASTM E2121-21 outlines best practices for designing, installing, and documenting radon mitigation systems, helping contractors achieve the highest probability of success in lowering hazardous radon levels.

Key Topics

• Scope of Practice: Covers existing attached and detached residential buildings up to three stories, including converted structures and buildings subject to remodeling or alteration.
• Qualified Installers: Recommends that only trained, certified, licensed, or otherwise qualified individuals undertake radon mitigation work.
• Mitigation System Types: Addresses a variety of methods such as active soil depressurization (ASD), sub-slab depressurization (SSD), sub-membrane depressurization (SMD), sump pit depressurization (SPD), and drain tile depressurization (DTD).
• Performance and Safety: Emphasizes the importance of system performance, ongoing safety for both occupants and workers, and the use of durable, code-compliant materials.
• Building Codes Compliance: Requires conformity to federal, state, and local building construction, remodeling, health, and safety codes.
• Documentation and Testing: Mandates clear documentation, system labeling, and post-installation testing to verify the effectiveness of the radon mitigation system.

Applications

ASTM E2121-21 is designed for broad applicability in the residential building sector:

• Retrofit Projects: Used when mitigating radon in already occupied or previously occupied homes, including those being converted to residential use.
• Renovations and Additions: Applies when existing residential buildings undergo changes such as remodeling or structural additions.
• Contractor Certification Programs: Serves as a model practice for state and local jurisdictions developing radon mitigation contractor certification or licensure standards.
• Ordinary Repair: Considers radon mitigation activities performed under this standard as ordinary building repair, streamlining compliance in maintenance contexts.

Implementing the standard helps achieve radon reduction to levels as low as reasonably achievable, prioritizing both health and regulatory requirements. Applications extend to any home where elevated indoor radon levels have been detected or where preventive action is warranted.

Related Standards

To ensure comprehensive and compliant radon mitigation, ASTM E2121-21 references related standards and official guidance, such as:

• ASTM E631: Terminology of Building Constructions
• ASTM E1465: Practice for Radon Control Options for New Low-Rise Residential Buildings
• ASTM E1745: Specification for Plastic Water Vapor Retarders
• EPA Documents: Including technical guidance for radon reduction, consumer guides, and relevant federal regulations
• OSHA Standards: Occupational safety and health regulations concerning radon exposure, hazardous materials, and respiratory protection

By following ASTM E2121-21, contractors and building professionals can ensure radon mitigation systems are installed to the highest industry standards, maximizing the safety, effectiveness, and durability of radon mitigation in existing low-rise residential buildings.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E2121 − 21
Standard Practice for
Installing Radon Mitigation Systems in Existing Low-Rise
Residential Buildings
This standard is issued under the fixed designation E2121; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope building investigation, systems design, systems installation,
materials, monitors and labeling, post-mitigation testing, and
1.1 This practice describes methods for reducing radon
documentation.
entry into existing attached and detached residential buildings
1.7 The values stated in inch-pound units are to be regarded
three stories or less in height. This practice is intended for use
as standard. The values given in parentheses are mathematical
by trained, certified or licensed, or both, or otherwise qualified
conversions to SI units that are provided for information only
individuals.
and are not considered standard.
1.2 Thesemethodsarebasedonradonmitigationtechniques
1.8 This standard does not purport to address all of the
that have been effective in reducing radon levels in a wide
safety concerns, if any, associated with its use. It is the
range of residential buildings and soil conditions. These fan
responsibility of the user of this standard to establish appro-
powered mitigation methods are listed in Appendix X1. More
priate safety, health, and environmental practices and deter-
detailedinformationiscontainedinreferencescitedthroughout
mine the applicability of regulatory limitations prior to use.
this practice.
See Section 6 for specific safety hazards.
1.3 This practice is intended to provide radon mitigation
1.9 This international standard was developed in accor-
contractors with a uniform set of practices that will ensure a
dance with internationally recognized principles on standard-
high degree of safety and the likelihood of success in retrofit-
ization established in the Decision on Principles for the
ting low rise residential buildings with radon mitigation
Development of International Standards, Guides and Recom-
systems.
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
1.4 The methods described in this practice apply to cur-
rently occupied or formerly occupied residential buildings,
2. Referenced Documents
including buildings converted or being converted to residential
use, as well as residential buildings changed or being changed 2.1 ASTM Standards:
by addition(s) or alteration(s), or both. The radon reduction E631 Terminology of Building Constructions
activities performed on new dwellings, while under
E1465 Practice for Radon Control Options for the Design
construction, before occupancy, and for up to one year after and Construction of New Low-Rise Residential Buildings
occupancy, are covered by Practice E1465.
(Withdrawn 2017)
E1745 Specification for Plastic Water Vapor Retarders Used
1.5 Thispracticealsoisintendedasamodelsetofpractices,
in Contact with Soil or Granular Fill under Concrete Slabs
which can be adopted or modified by state and local
2.2 Government Publications:
jurisdictions, to fulfill objectives of their specific radon con-
EPA “Asbestos School Hazard Abatement Reauthorization
tractor certification or licensure programs. Radon mitigation
Act,” regulation 40 CFR Part 763, Subpart E.
performed in accordance with this practice is considered
EPA “A Citizen’s Guide to Radon (Second Edition),” EPA
ordinary repair.
402-K92-001, May 1992.
1.6 The methods addressed in this practice include the
following categories of contractor activity: general practices,
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
This practice is under the jurisdiction of ASTM Committee E06 on Perfor- the ASTM website.
mance of Buildings and is the direct responsibility of Subcommittee E06.41 on Air The last approved version of this historical standard is referenced on
Leakage and Ventilation Performance. www.astm.org.
Current edition approved Oct. 1, 2021. Published October 2021. Originally AvailablefromUnitedStatesEnvironmentalProtectionAgency(EPA),William
approved in 2001. Last previous edition approved in 2013 as E2121 – 13. DOI: Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20004,
10.1520/E2121-21. http://www.epa.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2121 − 21
EPA “Consumer’s Guide to Radon Reduction,” EPA 402- either with a micromanometer or with a heatless smoke device,
K92-003, August 1992. the extension of the vacuum field. Also called pressure-field
EPA “Handbook, Sub-Slab Depressurization for Low- extension test.
Permeability Fill Material,” EPA/625/6-91/029, July
3.2.4 contractor, n—for the purposes of this practice, a
1991.
contractor is one who contracts to performs radon reduction
EPA “Home Buyers and Sellers Guide,” EPA 402–K-
activities or is an employee of one who contracts to perform or
00–008, July 2000.
performs radon reduction activities, with the expectation that
EPA“NationalEmissionStandardforAsbestos,” 40CFR61,
payment will be received for the work performed. A person
Subpart M.
who does radon reduction activities as an employee of a
EPA “ Radon Mitigation Standards,” EPA 402-R-93-078,
building owner is also a contractor for purposes of this
April 1994.
practice. Persons whose normal activity is not radon reduction,
EPA “Radon Reduction Techniques for Existing Detached
but who do work related to radon reduction like indoor air
Houses, Technical Guidance (Second Edition),” EPA/625/
quality consultants, radon consultants, plumbers, building
5–87/019, revised January 1988.
contractors, or employees of these persons are all viewed as
EPA “Radon Reduction Techniques for Existing Detached
contractors when performing radon reduction activities cov-
Houses, Technical Guidance (Third Edition) for Active
ered by this practice.
Soil Depressurization Systems,” EPA/625/R-93-011, Oc-
3.2.5 crawlspace depressurization (CSD) (active), n—a ra-
tober 1993.
don mitigation technique designed to achieve lower air pres-
NCRP “Measurement of Radon and Radon Daughters in
sure in the crawlspace than in the rooms bordering and above
Air,” NCRP Report No. 97, 1988.
the crawlspace. A radon fan, draws air from the crawl space
NIOSH “Guide to Industrial Respiratory Protection,”
and exhausts that air outside the building. Crawlspace depres-
NIOSH Publication No. 87–116.
surization (CSD) is intended to mitigate rooms bordering and
OSHA“AsbestosStandardfortheConstructionIndustry” 29
above the crawlspace but not the crawlspace itself. All CSD
CFR 1926.1102.
systems, for purposes of this practice, are active.
OSHA “Hazard Communication Standard for the Construc-
tion Industry,” 29 CFR 1926.59.
3.2.6 depressurization, n—a negative pressure induced in
OSHA“Occupational Safety and Health Regulations, Ioniz-
one area relative to another.
ing Radiation,” 29 CFR 1910.96.
3.2.7 diagnostic tests, n—procedures used to identify or
OSHA “Respiratory Protection Standard,” 29 CFR
characterize conditions under, beside and within buildings that
1920.134, 1998.
may contribute to radon entry or elevated radon levels or that
OSHA “Safety and Health Regulations for Construction,
may provide information regarding the performance of a
Ionizing Radiation,” 29 CFR 1926.53.
mitigation system.
3. Terminology
3.2.8 drain tile depressurization (DTD) (active), n—a type
of active soil depressurization radon mitigation system where
3.1 Definitions—Definitions of terms used in this practice
the suction point piping attaches to a drain tile or is located in
are defined in accordance with Terminology E631.
gas-permeable material near the drain tile. The drain tile or
3.2 Definitions of Terms Specific to This Standard:
perimeter drain may be inside or outside the footings of the
3.2.1 active soil depressurization (ASD), n—a family of
building.
radon mitigation systems involving mechanically-driven soil
3.2.9 hollow wall depressurization (BWD) (active), n—a
depressurization, including sub-slab depressurization (SSD),
sump pit depressurization (SPD), drain tile depressurization radon mitigation technique that depressurizes the void space
within a foundation wall (usually a block wall). A radon fan
(DTD), hollow block wall depressurization (BWD), and sub-
membrane depressurization (SMD) (see Appendix X2). installed in the radon system piping draws air from within the
wall.
3.2.2 backdrafting, n—a condition where the normal move-
ment of combustion products up a flue (due to the buoyancy of
3.2.10 manifold piping, n—this piping collects the flow of
the hot flue gases), is reversed, so that the combustion products
soil-gas from two or more suction points and delivers that
enter the building (see pressure-induced spillage).
collected soil-gas to the vent stack piping. In the case of a
single suction point system, there is no manifold piping since
3.2.3 communication test, n—a diagnostic test to evaluate
the suction point piping connects directly to the vent stack
the potential effectiveness of a sub-slab depressurization sys-
piping. The manifold piping starts where it connects to the
tem by applying a vacuum beneath the slab and measuring,
suction point piping and ends where it connects to the vent
stack piping.
Available from the National Commission on Radiation Protection and Mea-
3.2.11 mechanically-ventilated crawlspace system, n—a
surement (NCRP), 7910 WoodmontAvenue, Suite 400, Bethesda, MD 20814-3095,
radon-controltechniquedesignedtoincreaseventilationwithin
http://www.ncrponline.org.
a crawlspace by use of a fan.
Available from Centers for Disease Control and Prevention (CDC), 1600
Clifton Rd., Atlanta, GA 30329-4027, http://www.cdc.gov.
3.2.12 mitigation system, n—any system or steps designed
Available from Occupational Safety and Health Administration (OSHA), 200
Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov. to reduce radon concentrations in the indoor air of a building.
E2121 − 21
3.2.13 natural draft combustion appliance, n—any fuel 3.2.25 sump pit depressurization (SPD) (active), n—a type
burning appliance that relies on natural convective flow to of active soil depressurization radon mitigation system where
exhaust combustion products through flues to outside air. the suction point piping enters the sump pit, that has a sealed
gasketed cover, through the side or through the cover.
3.2.14 occupiable spaces, n—for purposes of this practice,
3.2.26 vent stack piping, n—this piping collects the soil-gas
are areas of buildings where human beings spend or could
from the suction point pipe of single suction point systems or
spend time, on a regular or occasional basis.
fromthe manifold piping of multi-suction point systems.There
3.2.14.1 Discussion—Examples of occupiable spaces are
arenobranchesinventstackpiping;soil-gasiscollectedatone
those that are or could be used for sleeping, a work shop, a
endoftheventstackpipingandisdischargedfromthebuilding
hobby, reading, student home work, a home office, entertain-
at the other end. In active soil depressurization systems, the
ment (TV, music, computer, etc.), physical work-out, laundry,
radon fan is installed in the vent stack piping.
games, or child’s play.
3.2.27 ventilation, n—the process of introducing outdoor air
3.2.15 pressure-field extension, n—the distance that a pres-
into a building.
sure change, created by drawing soil-gas through a suction
point extends outward in a sub-slab gas permeable layer, under 3.2.28 working level (WL), n—aunitofradondecayproduct
a membrane, behind a solid wall, or in a hollow wall (see exposure. Numerically, any combination of short-lived radon
communication test). decay products in one litre of air that will result in the ultimate
emission of 130 000 MeV of potential alpha energy. This
3.2.16 pressure-induced spillage, n—the unintended flow of
number was chosen because it is approximately the total alpha
combustion gases from an appliance/venting system into a
energy released from the short lived decay products in equi-
dwelling,primarilyasaresultofbuildingdepressurization(see
librium with 100 pCi of Rn-222.
backdrafting).
3.2.29 working level month (WLM), n—a unit of exposure
3.2.17 radon system piping, n—this active or passive soil
used to express the integrated human exposure to radon decay
depressurization piping is composed of three parts: suction
products. It is calculated by multiplying the average working
point piping, manifold piping, and vent stack piping.
level to which a person has been exposed by the number of
3.2.18 re-entrainment, n—the unintended re-entry of radon
hours exposed and dividing the product by 170.
into a building from leaks in the radon system piping, from
leaksinthefanhousing,orfromthedischargeoftheventstack
4. Summary of Practice
piping.
4.1 This practice describes methods for mitigating elevated
3.2.19 soil-gas, n—the gas mixture present in soil, which
levels of radon in existing attached and detached residential
may contain radon.
buildings three stories or less in height.
3.2.20 soil-gas-retarder, n—a continuous membrane or
4.2 The mitigation process is described in terms of the
other comparable material used to retard the flow of soil gases
categories of activity associated with radon mitigation and
into a building. See Specification E1745 for permeance and
includes: general practices, building investigation, systems
durability of water vapor retarders that may be used as
design, systems installation, materials, monitors and labeling,
soil-gas-retarders.
post-mitigation testing, and contracts and documentation.
3.2.21 submembrane depressurization (SMD) (active), n—a
4.3 The systems installation category contains subsections
radon mitigation technique designed to achieve lower air
describing the specific requirements applicable to each of the
pressure under a soil-gas-retarder membrane than above it. For
components of radon mitigation systems, for example, radon
example, a soil-gas-retarder membrane could be used to cover
system piping, radon fans, sealing, electrical, etc.
thesoilfoundonacrawlspacefloor.Aradonfaninstalledinthe
radon system piping draws air from below the soil-gas-retarder
5. Significance and Use
membrane.
5.1 The purpose of the methods, systems, and designs
3.2.22 sub-slab depressurization (SSD) (active), n—a radon
described in this practice is to reduce radiation exposures for
mitigation technique designed to achieve lower air pressure
occupants of residential buildings caused by radon and its
under a floor slab than above it. A radon fan installed in the
progeny. The goal of mitigation is to maintain reduced radon
radon system piping draws soil-gas from below the floor slab.
concentrations in occupiable areas of buildings at levels as low
3.2.23 sub-slab depressurization (passive), n—a radon miti- as reasonably achievable. This practice includes sections on
gation technique designed to achieve lower air pressure under reducing radiation exposure caused by radon and its progeny
a floor slab than above it. The radon system piping is routed for workers who install and repair radon mitigation systems.
through the conditioned (heated and cooled) space of a The goal for workers is to reduce exposures to radon and its
building. progeny to levels as low as reasonably achievable.
3.2.24 suction point piping, n—one end of this piping 5.2 The methods, systems, designs, and materials described
penetrates the slab, the solid wall, the hollow wall, the here have been shown to have a high probability of success in
membrane, the sump cover, or the drain tile. The other end mitigatingradoninattachedanddetachedresidentialbuildings,
extends outward to the first accessible pipe connection beyond three stories or less in height (see EPA, “Radon Reduction
the penetration of the soil-gas barrier. Techniques for Existing Detached Houses,Technical Guidance
E2121 − 21
(Third Edition) for Active Soil Depressurization Systems”). certified person that such work will be undertaken in a manner
Application of these methods does not, however, guarantee which complies with applicable asbestos regulations, including
reduction of radon levels below any specific level, since those of EPA and OSHA (see 2.2).
performance will vary with site conditions, construction 6.2.8 Contractors shall advise employees of the potential
characteristics, weather, and building operation. hazards, of the materials and supplies used, and provide
applicable Safety Data Sheets (SDS).
5.3 When applying this practice, contractors also shall
conform to all applicable local, state, and federal regulations,
7. Standard Practices for Radon Mitigation
and laws pertaining to residential building construction,
7.1 General Practices:
remodeling, and improvement.
7.1.1 Radon mitigation systems shall be designed and in-
stalled to conform to applicable building codes, and maintain
6. Safety Hazards
the function and operation of all existing equipment and
6.1 Contractors shall comply with all OSHA, state and local
buildingfeatures,includingdoors,windows,accesspanels,etc.
standards or regulations relating to worker safety and occupa-
Where discrepancies exist between provisions of this practice
tional radon exposure. Applicable references in the Code of
and local or state codes that prevent compliance with this
Federal Regulations include those in 2.2. Contractors also shall
practice, the local or state codes shall take precedence.
follow occupational radon guidance in 2.2.
7.1.2 Prior to starting work, the contractor shall inform the
client of the nature of work to be done, the anticipated use of
6.2 In addition to OSHA standards and NIOSH
any potentially hazardous solvents or other materials, and the
recommendations, the following requirements specifically ap-
need to ventilate work areas during and after the use of such
plicable to the safety and protection of radon mitigation
materialsasrecommendedbythemanufacturerofthematerial.
workers shall be met:
Applicable Safety Data Sheets (SDS) shall be made available
6.2.1 The contractor shall advise workers of the hazards of
to the client on request.
exposure to radon and the importance of protective measures
7.1.3 Prior to installing a radon mitigation system, a visual
when working in areas of elevated radon concentrations. In
inspection of the building should be conducted to evaluate
addition, the contractor shall advise employees of other poten-
characteristics of the building which might affect radon miti-
tial hazards according to the hazard communication standard
gation system performance.
for the construction industry (see OSHA, “Hazard Communi-
7.1.4 If a contractor has concerns about backdrafting poten-
cation Standard for the Construction Industry”).
tial at a particular site, the contractor shall recommend that a
6.2.2 The contractor shall ensure that appropriate safety
qualified person inspect the natural draft combustion appli-
equipment, such as ventilators, respirators, hard hats, face
ancesandventingsystemsforcompliancewithlocalcodesand
shields, and ear plugs, are available on the job site during
regulations. The contractor should recommend that the build-
mitigation activities.
ing owner bring any combustion appliance or venting system,
6.2.3 Work areas shall be ventilated to reduce worker
found to be noncomplying, into compliance.
exposure to radon, dust, or other airborne pollutants.
7.1.5 System components, which are added, or existing
6.2.4 Consistent with OSHA permissible exposure limits,
system components, which are replaced, repaired, or altered,
contractorsshallensurethatemployeesareexposedtonomore
shall be in compliance with this practice. Existing system
than four working level months (WLM) over a 12-month
components, which are not repaired, replaced, or altered but
period(ortheequivalent68 000pCi/L-h,whenconvertedatan
are observed to be noncompliant with this practice, shall be
equilibrium ratio of 100 %.AWLM is calculated by multiply-
reportedtotheclientinwriting.Thereportshouldreferencethe
ing the average working level to which a person has been
relevant sections of this practice.
exposed by the number of hours exposed and dividing the
product by 170 h.
7.2 Systems Design:
6.2.5 Contractors shall maintain records of employee expo- 7.2.1 All radon mitigation systems shall be designed and
sure to radon sufficient to verify that field employees are
installed as permanent, integral additions to the building.
exposed to less than 4 WLM in any 12-month period. 7.2.2 All radon mitigation systems shall be designed and
6.2.6 Where ventilation cannot reduce radon levels to less
installed to avoid the creation of other health, safety, or
than 0.3 WL, contractors shall provide the respiratory protec- environmental hazards to building occupants, such as
tion that is required to comply with 6.2.4. When unable to backdrafting/spillage from natural draft combustion
makeworkinglevelmeasurements,aradonconcentrationof30 appliances, constricting or blocking building exits with pipe
pCi/1 (1100 Bq/m ) shall be used in lieu of 0.3 WL. The runs, or degradation of fire rated assemblies with pipe, or
contractor should provide respiratory protection that conforms cabling penetrations, or both.
with NIOSH “Guide to Industrial Respiratory Protection,” and 7.2.3 Radon mitigation system design is not limited to
the OSHA“Respiratory Protection Standard,” which covers fit safety, radon reduction effectiveness, and compliance with
tests for employees and other items related to respirators. building codes and regulations. Radon reduction systemdesign
6.2.7 Radon mitigation work shall not be conducted in any also is concerned with installation costs, operating costs,
work area suspected of containing friable asbestos material, or energy usage, durability, reliability, maintainability, physical
where work would render non-friable asbestos material friable, comfort for occupants, quietness for occupants and neighbors,
until a determination has been made by a properly trained or as well as impact on interior and exterior building appearance.
E2121 − 21
7.3 System Installation: be secured either above or below the points of penetration
7.3.1 General Requirements: through floors, ceilings, and roofs, or at least every 8 ft (2.5 m)
7.3.1.1 All components of radon mitigation systems de- on runs that do not penetrate floors, ceilings, or roofs.
signed and installed in compliance with provisions of this 7.3.2.6 To prevent blockage of air flow into the bottom of
practice also shall be in compliance with the applicable suction point pipes, they shall be supported and secured in a
mechanical, electrical, building, plumbing, energy and fire permanent manner that prevents their downward movement to
prevention codes, standards, and regulations of the local the bottom of suction pits or sump pits, or into the soil beneath
jurisdiction. a soil-gas-retarder membrane. For guidance on submembrane
7.3.1.2 When portions of structural framing members must piping, see 7.3.8.3.
be removed to accommodate radon system components, the 7.3.2.7 Horizontal runs in radon system piping shall be
amount of the member removed shall be no greater than that sloped to ensure that water from rain or condensation drains
permitted for plumbing installations by applicable building or downward into the ground beneath the slab or soil-gas-retarder
plumbing codes. membrane.
7.3.2 Radon System Piping Installation Requirements: 7.3.2.8 If suction point pipes are installed to draw soil gas
7.3.2.1 Radon System Pipe Size—Also see Appendix X3.
from sump pits, the system shall be designed to facilitate
Allventstackpipingshallbesolid,rigidpipenotlessthan3 in.
removal of the sump pit cover for sump pump maintenance.
(75 mm) inside diameter (ID). The vent stack piping’s ID shall
7.3.2.9 To reduce the risk of vent stack blockage due to
be at least as large as the largest used in the manifold piping.
heavy snow fall, to reduce the potential for re-entrainment of
All manifold piping shall be rigid pipe not less than 3 in.
radon into the living spaces of a building, and to prevent direct
(75 mm) ID.The manifold piping’s ID shall be at least as large
exposure of individuals outside of buildings to high levels of
asthatusedinanysuctionpoint.Manifoldpipingtowhichtwo
radon, the discharge from vent stack pipes of active soil
or more suction points are connected shall be at least 4 in.
depressurization systems shall meet the following minimum
(100 mm)ID.Wheninstallingmanifoldpipestowhichthreeor
requirements. The discharge from vent stack pipes shall be:
more suction points need to be installed, the contractor may
(1) Vertical and upward, outside the structure, at least 10 ft
benefit from guidance in an industrial ventilation manual. All
(3 m) above the ground level, above the edge of the roof, and
suction point piping shall be rigid pipe not less than 3 in.
shall also meet the separation requirements of 7.3.2.9 (2) and
(75 mm)insidediameter.Notwithstandingtheminimumradon
(3). Whenever practicable, they shall be above the highest roof
system piping diameters specified herein, alternate pipe sizes
of the building and above the highest ridge.
may be used when sufficiently justified by field diagnostic
(2) Ten ft (3 m) or more away from any window, door, or
measurements, including static pressure, air velocity, and rate
other opening into conditioned or otherwise occupiable spaces
of air flow measurements, and documented using the method- of the structure, if the radon discharge point is not at least 2 ft
ologies found in “Industrial Ventilation:AManual of Standard
(0.6 m) above the top of such openings.
Practice, 23rd Edition,” or its equivalent. When alternate pipe (3) Ten ft (3 m) or more away from any opening into the
sizesandshapesareused,astatementofjustification,including
conditioned or other occupiable spaces of an adjacent building.
justification methodology, calculations employed, and all site
Chimneyfluesshallbeconsideredopeningsintoconditionedor
specific field data collected shall be prepared. A copy of the
otherwise occupiable space.
justification shall become part of the system documentation
(4) For vent stack pipes that penetrate the roof, the point of
and shall be provided to the building owner.
discharge shall be at least 12 in. (0.3 m) above the surface of
7.3.2.2 All pipe joints and connections in radon mitigation
the roof. For vent stack pipes attached to or penetrating the
systems,bothinteriorandexterior,shallbesealedpermanently.
sides of buildings, the point of discharge shall be vertical and
Exceptions include installation of radon fans (see 7.3.3.6) and
a minimum of 6 in. (150 mm) above the edge of the roof and
sump covers (see 7.3.2.8).
in such a position that it can neither be covered with snow, or
7.3.2.3 Radon system piping installed in the interior or on
other materials nor be filled with water from the roof or an
the exterior of a building, should be insulated where conden-
overflowing gutter. In areas where it snows the point of
sationonthepipe’sexteriormaydripontoanddamageceilings
discharge shall be 12 in. (0.3 m) above the surface of the roof.
and floors, etc., and where water vapor, from the soil, may
(5) When a horizontal run of vent stack pipe penetrates the
condense inside the pipe, and then freeze partially or fully
gable end walls, the piping outside the structure shall be routed
blocking the soil-gas exhaust.
to a vertical position so that the discharge point meets the
7.3.2.4 Radon system piping shall be fastened to the struc-
requirements of 7.3.2.9 (1), (2), (3), and (4).
ture of the building with hangers, strapping, or other supports (6) Points of discharge that are not in a direct line of sight
that will secure it adequately. Radon system piping shall not be
from openings into conditioned or otherwise occupiable space
attached to or supported by existing pipes, ducts, conduits, or because of intervening objects, such as dormers, chimneys,
any kind of equipment. Radon system piping shall not block
windows around the corner, etc. shall meet the separation
window and doors or access to installed equipment.
requirements of 7.3.2.9 (1), (2), (3), (4), and (5).
7.3.2.5 Supportsforradonsystempipingshouldbeinstalled
NOTE 1—Measurements from the point of discharge to openings into
at least every 6 ft (2 m) on horizontal runs. Vertical runs shall
the conditioned or otherwise occupiable spaces of the structure shall be
made from the point of discharge to the closest part of any opening into
Available from American Conference of Governmental Industrial Hygienists, such space. For example, to determine compliance with 7.3.2.9, when the
Inc. (ACGIH), 3640 Park 42 Drive, Cincinnati, OH 45241, http://www.acgih.org. location of a planned vent stack discharge can not be seen from a dormer
E2121 − 21
window, the contractor would determine whether the required separation
should be inserted into the joint before the application of the
existed by routing a flexible measuring tape between the planned
sealant. For guidance on channel and French drain sealing, see
discharge point location and the part of the dormer window that is the
7.3.13.3.
shortest distance away. The measuring tape must follow the shortest
possible path, and be allowed to bend where it passes intervening part(s)
NOTE 2—Field experience has shown that sealing the floor-wall joint
of the dormer.
and small cracks in the slab of poured concrete foundation systems of
SSD, sump pit depressurization (DPD), and DTD systems usually is not
7.3.3 Radon Fan Installation Requirements:
necessary when an active soil depressurization is employed. Sealing is
7.3.3.1 Radon fans shall be sized to provide the pressure
desirable when significant below grade air leakage is occurring, or when
difference and air flow characteristics necessary to achieve the
the air flow into the gas permeable layer below the slab is creating
objectionable noise. Failure to limit air flow into the depressurized soil of
radon reduction goals established for the specific mitigation
an active soil depressurization system may be a contributing factor to a
project. Guidelines for sizing radon fans and piping can be
backdraft condition. SMD and BWD systems, active or passive, and any
found in “Industrial Ventilation: A Manual of Standard
passive radon reduction system require more thorough sealing.
Practice, 23rd Edition,” and in Appendix X3.
7.3.4.3 When installing baseboard-type suction systems, all
7.3.3.2 Radon fans used in ASD radon mitigation systems
seams and joints in the baseboard material shall be joined and
shall be installed either outside the building or inside the
sealed using materials recommended by the manufacturer of
building, outside of occupiable space, and above the condi-
the baseboard system. Baseboards shall be sealed to walls and
tioned(heated/cooled)spacesofabuilding.Radonfanlocation
floors with adhesives also designed and recommended for such
is chosen to minimize the risk of radon entry into living spaces
installations.
which could result from leaks in radon fan housings or in the
7.3.4.4 Utility and other penetrations through a soil-gas-
vent stack piping above the radon fan. Preferred locations
retarder membrane shall be sealed.
include places on the exterior of the building, unconditioned
house and garage attics not suitable for occupancy, and other 7.3.5 Active Sub-Slab Depressurization (SSD) Require-
unconditioned house and garage locations not suitable for ments:
occupancy, which have no occupiable or conditioned spaces
7.3.5.1 To enhance pressure field extension, when the sub-
above them.
slab material exhibits poor gas-permeability, it is helpful to
7.3.3.3 Radon fans shall be installed in a configuration that excavateasmuchas1ft (28L)ofsub-slabmaterialbelowand
avoids condensation or other water accumulation in the radon around each suction point pipe. Even when the sub-slab
fan housing. material is highly permeable, like crushed stone, the end of the
suction point pipe should have an excavated hole, at least one
7.3.3.4 Radon fans mounted on the exterior of buildings
pipe diameter deep, directly below it.
shall be rated for outdoor use or installed in a weather proof
protective housing. 7.3.6 Sump Pit Requirements:
7.3.3.5 Radon fans shall be mounted and secured in a 7.3.6.1 Sump pits or other large openings in slabs or
manner that minimizes transfer of vibration to the structural basement walls that allow a significant amount of soil gas
framing of the building. leakageintothebasementorairleakageintothesub-floorareas
should be covered and sealed (see 7.4.7 and 7.4.8 for details on
7.3.3.6 To facilitate maintenance and future replacement,
sump covers and sealing materials).
radon fans shall be installed in the vent pipe using removable
couplings or flexible connections that can be tightly secured to 7.3.6.2 When a radon mitigation system is designed to draw
both the radon fan and the vent pipe. soil-gas from a sump pit, a sump cover shall be installed as
described in 7.3.13.4, 7.4.7, and 7.4.8.
7.3.3.7 Outside air intake vents of fan powered systems
shall be screened to prevent the intake of debris. Screens shall 7.3.7 Drain Tile Depressurization (DTD) Requirements:
be removable to permit cleaning or replacement and building
7.3.7.1 Whenever a DTD radon mitigation system that is
owners shall be informed of the need to periodically replace or
intended to depressurize a sub-slab area by drawing soil-gas
clean such screens.
from a perimeter drain tile loop (internal or external) is
7.3.4 General Sealing Requirements: installed, all drain lines extending from the drain tile loop to
daylight shall have a one-way flow valve, a water trap, or other
7.3.4.1 Openings around the suction point piping penetra-
controldeviceinstalledtopreventoutdoorairfromenteringthe
tions of the slab, accessible openings around utility penetra-
sub-slab area. The control device is intended to prevent air
tions of the foundation walls and slab, and other openings in
from entering the drain line but not prevent water from flowing
slabs cast over gas permeable soils or aggregates, that reduce
out of the drain line.
the pressure field extension, and the effectiveness of soil
depressurization systems, shall be sealed, using methods and 7.3.8 SubmembraneDepressurization(SMD)Requirements:
materials that are permanent and durable. For guidance on
7.3.8.1 Any seams in soil-gas-retarder membranes (not
sump pits and sump pit covers see 7.3.6.1 and 7.3.6.2.
covered by concrete slabs) used for submembrane depressur-
7.3.4.2 Sealing the Floor-Wall Joint—Sealing openings and izationsystems,passiveoractive,shallbelappedatleast12in.
cracks where the slab meets the foundation wall is sometimes (300 mm). The membrane’s seams shall be sealed. The
appropriate. When urethane caulk or equivalent material is to membrane shall be sealed around posts and other penetrations.
be used, and when the joint is greater than ⁄2 in. (13 mm) in The edges of the membrane shall be sealed to the walls to the
width, a foam backer rod or other comparable filler material extent practical. When there are indications that water is likely
E2121 − 21
to collect on the membrane, it shall be fitted with trapped the crawlspace, or when work in the crawlspace would render
drains at the lowest part of the locations that are likely to be nonfriable asbestos material friable. If asbestos is to be
wet. removed from the crawlspace, to allow the installation of a
7.3.8.2 Passive submembrane depressurization systems, CSD system, the contractor shall employ trained and certified
which are installed while anticipating possible activation, shall asbestos removers whose work will be undertaken in a manner
meet all the requirements for an active SMD systems, but which complies with applicable asbestos regulations, including
without the radon fan and monitor. those of EPA and OSHA (see 2.2).
7.3.8.3 ActiveSMDsystemsmaybenoisy,butthenoisecan 7.3.11 Combination Foundations:
be reduced by sealing the membrane (see 7.3.8.1), which 7.3.11.1 Buildings with elevated radon levels may have
reduces the amount of air leakage and its associated noise and more than one foundation type. Mitigation may be required in
also improves the pressure field extension under the mem- parts of the building involving one or more foundation types.
brane. Utilizing a special suction point design can also signifi- Foundation types include slab-on-grade, basement, and crawl-
cantly reduce the noise caused by air flowing into the suction space. Isolation of foundation spaces using barriers intended to
point.Thedesigncallsforeightormoreslotsbeingcutintothe keep radon from passing, for example, from the crawlspace to
lowest foot (0.3 m) of the suction point pipe, with the slots the basement or vise versa are not recommended, because
1 1
being ⁄2 in. (13 mm) wide and ⁄2 in (13 mm) apart. The slots walls built using available building trade techniques, usually
may be parallel or perpendicular to the axis of the pipe. Slots do not accomplish their isolation objective. In addition, if the
that are perpendicular to the axis of the pipe shall be cut half purpose of the isolation is to seal off the crawlspace to enable
way through the pipe. The intake end of the special suction crawlspace depressurization, it is not recommended. Crawl-
point should be buried deep in a bed of clean 1 in. (25 mm) space depressurization usually is not the first choice radon
aggregate. mitigation method for crawlspaces because of its greater
7.3.9 Hollow Block-Wall Depressurization (BWD) Require- potential for hazardous failure, that is, backdrafting, and the
ments: probability of a high energy loss associated with its operation
7.3.9.1 When a hollow BWD system is used to mitigate during the colder and hotter months. Sub-slab and submem-
radon, openings in the tops of such walls and all accessible brane depressurization are the crawlspace mitigation methods
openings or cracks in the interior surfaces of the walls should that should be used whenever possible.
be closed and sealed with polyurethane or equivalent caulks, 7.3.12 Electrical Requirements:
expandable foams, or other fillers and sealants. Large, inacces-
NOTE 3—For purposes of this section, electrical power is assumed to be
sible openings or cracks that have not been sealed should be
providedby120V,15 ampere,20 ampere,or30amperecircuits;however,
disclosed to the client and included in the documentation.
for all cases and all situations see 7.3.12.1 for guidance.
7.3.10 Crawlspace Depressurization (CSD)—Crawlspace
7.3.12.1 Wiring for all active radon mitigation systems shall
depressurization is usually not the first choice radon mitigation
conform to provisions of the “1999 National Electrical Code
method for crawlspaces because of its greater potential for
Handbook, Eighth Edition” and any additional local regula-
hazardous failure, that is, backdrafting, and the probability of a
tions.
high energy loss associated with its operation during the colder
7.3.12.2 Wiring shall not be located inside the radon system
and hotter months. Sub-slab and submembrane depressuriza-
piping or within any other heating or cooling ductwork.
tion are the crawlspace mitigation methods that should be used
7.3.12.3 Any plugged cord used to supply power to a radon
whenever possible.
fan shall be no more than 6 ft (2 m) in length.
7.3.10.1 WhenCSDisusedforradonmitigation,cracksand
7.3.12.4 No plugged cord may penetrate a wall or be
openings in floors above the crawlspace, which would permit
concealed within a wall.
conditionedairtopassfromthelivingspacestothecrawlspace
7.3.12.5 Adisconnecting means is a switch, a plugged cord,
shall be sealed to the extent practicable. Openings or cracks
or a branch circuit overcurrent device. A disconnecting means
that are determined to be inaccessible or beyond the ability of
shall be present in the electric circuit powering radon fans.The
the contractor to seal shall be disclosed to the client and
disconnecting means shall be located within sight of the radon
included in the documentation.
fan,exceptwhenthefanmotordevelops ⁄8horsepowerorless.
7.3.10.2 CSD shall not be used as a radon control system
The branch circuit overcurrent device is permitted to be the
when combustion appliances are installed within the
disconnecting means when the fan motor develops ⁄8 horse-
crawlspace, or within an abutting crawlspace or basement, or
power or less. The primary purpose of the fan’s disconnecting
whereadequateisolation(fromdepressurization)doesnotexist
means is to temporarily disconnect the fan’s electric power
or cannot be created in a practical manner, between interior
when maintenance is performed. Operation of the radon fan’s
spaces containing one or more combustion appliances and the
disconnecting means should not interrupt the power to other
crawlspace.
electrical devices in the dwelling. See “1999 National Electri-
7.3.10.3 CSD shall not be used as a radon control system 10
calCodeHandbook,EighthEdition” Articles430-102(b)and
when evidence suggests that friable asbestos material exists in
430-109(b), (c), and (f). Also see Appendix X4, Determining
Radon Fan Motor Horsepower.
Henschel, D. B., “Indoor Radon Reduction in Crawl Space Houses: A Review
ofAlternativeApproaches,” Indoor Air, Vol 2, No. 2, 1994, pp. 272–278, available
from International Society of Indoor Air Quality and Climate; ISIAO Secretariat, Available from National Fire Protection Association (NFPA), 1 Batterymarch
Via Magenta 25, 20020 Busto Garolfo (Milan), Italy. Park, Quincy, MA 02169-7471, http://www.nfpa.org.
E2121 − 21
air exchange rate is low enough to indicate a high probability of success.
7.3.12.6 Flexiblepluggedcords,properlyratedforelectrical
capacity and weather, may be used on radon fans inside or
7.3.15.1 Heat recovery ventilation (HRV) systems shall not
outside the building. These flexible plugged cords may also
beinstalledinareasofthebuildingthatcontainfriableasbestos
serve as a disconnecting means inside or outside the building.
material or where the work would render nonfriable asbestos
Radon fans, cords, plugs, receptacles, receptacle enclosures,
material friable, until a determination has been made by a
switches, switch enclosures, etc., intended for outside use must
properly trained or certified person that such work will be
have a weatherproof and unattended use rating, and are
undertaken in a manner which complies with applicable
different than what is generally used inside the building. See
asbestos regulations, including those of EPA and OSHA. See
“1999 National Electrical Code Handbook, Eight Edition.”
2.2.
(Warning—Ahard-wired electrical connection (with a discon-
7.3.15.2 In HRV installations, interior supply and exhaust
nect switch) may be a preferable alternative to a flexible
ports shall be a minimum of 12 ft (3.8 m) apart, horizontally.
plugged cord connection for radon fans installed outdoors.
Exterior supply and exhaust ports shall be positioned a
There are safety issues and other disadvantages to flexible
minimum of 12 in. (30 cm) above the ground or higher if
plugged cords being installed outdoors. Children may play
necessary to avoid blockage by snow, leaves, or other things
with the outdoor cord or receptacle. Because the protection of
and be a minimum of 10 ft (3 m) apart, horizontally. Exterior
wires in an outdoor plugged flexible cord radon fan installation
supply and exhaust ports shall be located away from areas
may not equal that of a hard wired outdoor installation, the
where stored material or equipment could block airflow.
wiring may be subjected to greater risk of accidental damage.
Exterior supply/intake ports shall be kept away from where car
Theoutsideflexiblepluggedcord,whichmaybelocatedwhere
and truck exhaust or other air pollutants may be present.
access to it is n
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E2121 − 13 E2121 − 21
Standard Practice for
Installing Radon Mitigation Systems in Existing Low-Rise
Residential Buildings
This standard is issued under the fixed designation E2121; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This practice describes methods for reducing radon entry into existing attached and detached residential buildings three stories
or less in height. This practice is intended for use by trained, certified or licensed, or both, or otherwise qualified individuals.
1.2 These methods are based on radon mitigation techniques that have been effective in reducing radon levels in a wide range of
residential buildings and soil conditions. These fan powered mitigation methods are listed in Appendix X1. More detailed
information is contained in references cited throughout this practice.
1.3 This practice is intended to provide radon mitigation contractors with a uniform set of practices that will ensure a high degree
of safety and the likelihood of success in retrofitting low rise residential buildings with radon mitigation systems.
1.4 The methods described in this practice apply to currently occupied or formerly occupied residential buildings, including
buildings converted or being converted to residential use, as well as residential buildings changed or being changed by addition(s)
or alteration(s), or both. The radon reduction activities performed on new dwellings, while under construction, before occupancy,
and for up to one year after occupancy, are covered by GuidePractice E1465.
1.5 This practice also is intended as a model set of practices, which can be adopted or modified by state and local jurisdictions,
to fulfill objectives of their specific radon contractor certification or licensure programs. Radon mitigation performed in accordance
with this practice is considered ordinary repair.
1.6 The methods addressed in this practice include the following categories of contractor activity: general practices, building
investigation, systems design, systems installation, materials, monitors and labeling, post-mitigation testing, and documentation.
1.7 The values stated in inch-pound units are to be regarded as standard. The values given in parentheses are mathematical
conversions to SI units that are provided for information only and are not considered standard.
1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. See Section 6 for specific safety hazards.
1.9 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
This practice is under the jurisdiction of ASTM Committee E06 on Performance of Buildings and is the direct responsibility of Subcommittee E06.41 on Air Leakage
and Ventilation Performance.
Current edition approved March 1, 2013Oct. 1, 2021. Published March 2013October 2021. Originally approved in 2001. Last previous edition approved in 20122013 as
E2121 – 12.E2121 – 13. DOI: 10.1520/E2121-13.10.1520/E2121-21.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E2121 − 21
2. Referenced Documents
2.1 ASTM Standards:
E631 Terminology of Building Constructions
E1465 Practice for Radon Control Options for the Design and Construction of New Low-Rise Residential Buildings (Withdrawn
2017)
E1745 Specification for Plastic Water Vapor Retarders Used in Contact with Soil or Granular Fill under Concrete Slabs
2.2 Government Publications:
EPA “Asbestos School Hazard Abatement Reauthorization Act,” regulation 40 CFR Part 763, Subpart E.
EPA “A Citizen’s Guide to Radon (Second Edition),” EPA 402-K92-001, May 1992.
EPA “Consumer’s Guide to Radon Reduction,” EPA 402-K92-003, August 1992.
EPA “Handbook, Sub-Slab Depressurization for Low-Permeability Fill Material,” EPA/625/6-91/029, July 1991.
EPA “Home Buyers and Sellers Guide,” EPA 402–K-00–008, July 2000.
EPA “National Emission Standard for Asbestos,” 40 CFR 61, Subpart M.
EPA “ Radon Mitigation Standards,” EPA 402-R-93-078, April 1994.
EPA “Radon Reduction Techniques for Existing Detached Houses, Technical Guidance (Second Edition),” EPA/625/5–87/019,
revised January 1988.
EPA “Radon Reduction Techniques for Existing Detached Houses, Technical Guidance (Third Edition) for Active Soil
Depressurization Systems,” EPA/625/R-93-011, October 1993.
NCRP “Measurement of Radon and Radon Daughters in Air,” NCRP Report No. 97, 1988.
NIOSH “Guide to Industrial Respiratory Protection,” NIOSH Publication No. 87–116.
OSHA “Asbestos Standard for the Construction Industry” 29 CFR 1926.1102.
OSHA “Hazard Communication Standard for the Construction Industry,” 29 CFR 1926.59.
OSHA “Occupational Safety and Health Regulations, Ionizing Radiation,” 29 CFR 1910.96.
OSHA “Respiratory Protection Standard,” 29 CFR 1920.134, 1998.
OSHA “Safety and Health Regulations for Construction, Ionizing Radiation,” 29 CFR 1926.53.
3. Terminology
3.1 Definitions—Definitions of terms used in this practice are defined in accordance with Terminology E631.
3.2 Definitions of Terms Specific to This Standard:
3.2.1 active soil depressurization (ASD), n—a family of radon mitigation systems involving mechanically-driven soil
depressurization, including sub-slab depressurization (SSD), sump pit depressurization (SPD), drain tile depressurization (DTD),
hollow block wall depressurization (BWD), and sub-membrane depressurization (SMD) (see Appendix X2).
3.2.2 backdrafting, n—a condition where the normal movement of combustion products up a flue (due to the buoyancy of the hot
flue gases), is reversed, so that the combustion products enter the building (see pressure-induced spillage).
3.2.3 communication test, n—a diagnostic test to evaluate the potential effectiveness of a sub-slab depressurization system by
applying a vacuum beneath the slab and measuring, either with a micromanometer or with a heatless smoke device, the extension
of the vacuum field. Also called pressure-field extension test.
3.2.4 contractor, n—for the purposes of this practice, a contractor is one who contracts to performs radon reduction activities or
is an employee of one who contracts to perform or performs radon reduction activities, with the expectation that payment will be
received for the work performed. A person who does radon reduction activities as an employee of a building owner is also a
contractor for purposes of this practice. Persons whose normal activity is not radon reduction, but who do work related to radon
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Available from United States Environmental Protection Agency (EPA), Ariel Rios William Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC
20460,20004, http://www.epa.gov.
Available from the National Commission on Radiation Protection and Measurement, Measurement (NCRP), 7910 Woodmont Avenue, Suite 400, Bethesda, MD
20814,20814-3095, http://www.ncrponline.org.
Available from Centers for Disease Control &and Prevention (CDC), 1600 Clifton Rd., Atlanta, GA 30333,30329-4027, http://www.cdc.gov.
Available from Occupational Safety and Health Administration (OSHA), 200 Constitution Ave., NW, Washington, DC 20210, http://www.osha.gov.
E2121 − 21
reduction like indoor air quality consultants, radon consultants, plumbers, building contractors, or employees of these persons are
all viewed as contractors when performing radon reduction activities covered by this practice.
3.2.5 crawlspace depressurization (CSD) (active), n—a radon mitigation technique designed to achieve lower air pressure in the
crawlspace than in the rooms bordering and above the crawlspace. A radon fan, draws air from the crawl space and exhausts that
air outside the building. Crawlspace depressurization (CSD) is intended to mitigate rooms bordering and above the crawlspace but
not the crawlspace itself. All CSD systems, for purposes of this practice, are active.
3.2.6 depressurization, n—a negative pressure induced in one area relative to another.
3.2.7 diagnostic tests, n—procedures used to identify or characterize conditions under, beside and within buildings that may
contribute to radon entry or elevated radon levels or that may provide information regarding the performance of a mitigation
system.
3.2.8 drain tile depressurization (DTD) (active), n—a type of active soil depressurization radon mitigation system where the
suction point piping attaches to a drain tile or is located in gas-permeable material near the drain tile. The drain tile or perimeter
drain may be inside or outside the footings of the building.
3.2.9 hollow wall depressurization (BWD) (active), n—a radon mitigation technique that depressurizes the void space within a
foundation wall (usually a block wall). A radon fan installed in the radon system piping draws air from within the wall.
3.2.10 manifold piping, n—this piping collects the flow of soil-gas from two or more suction points and delivers that collected
soil-gas to the vent stack piping. In the case of a single suction point system, there is no manifold piping since the suction point
piping connects directly to the vent stack piping. The manifold piping starts where it connects to the suction point piping and ends
where it connects to the vent stack piping.
3.2.11 mechanically-ventilated crawlspace system, n—a radon-control technique designed to increase ventilation within a
crawlspace by use of a fan.
3.2.12 mitigation system, n—any system or steps designed to reduce radon concentrations in the indoor air of a building.
3.2.13 natural draft combustion appliance, n—any fuel burning appliance that relies on natural convective flow to exhaust
combustion products through flues to outside air.
3.2.14 occupiable spaces, n—for purposes of this practice, are areas of buildings where human beings spend or could spend time,
on a regular or occasional basis.
3.2.14.1 Discussion—
Examples of occupiable spaces are those that are or could be used for sleeping, a work shop, a hobby, reading, student home work,
a home office, entertainment (TV, music, computer, etc.), physical work-out, laundry, games, or child’s play.
3.2.15 pressure-field extension, n—the distance that a pressure change, created by drawing soil-gas through a suction point extends
outward in a sub-slab gas permeable layer, under a membrane, behind a solid wall, or in a hollow wall (see communication test).
3.2.16 pressure-induced spillage, n—the unintended flow of combustion gases from an appliance/venting system into a dwelling,
primarily as a result of building depressurization (see backdrafting).
3.2.17 radon system piping, n—this active or passive soil depressurization piping is composed of three parts: suction point piping,
manifold piping, and vent stack piping.
3.2.18 re-entrainment, n—the unintended re-entry of radon into a building from leaks in the radon system piping, from leaks in
the fan housing, or from the discharge of the vent stack piping.
3.2.19 soil-gas, n—the gas mixture present in soil, which may contain radon.
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3.2.20 soil-gas-retarder, n—a continuous membrane or other comparable material used to retard the flow of soil gases into a
building. See Specification E1745 for permeance and durability of water vapor retarders that may be used as soil-gas-retarders.
3.2.21 submembrane depressurization (SMD) (active), n—a radon mitigation technique designed to achieve lower air pressure
under a soil-gas-retarder membrane than above it. For example, a soil-gas-retarder membrane could be used to cover the soil found
on a crawlspace floor. A radon fan installed in the radon system piping draws air from below the soil-gas-retarder membrane.
3.2.22 sub-slab depressurization (SSD) (active), n—a radon mitigation technique designed to achieve lower air pressure under a
floor slab than above it. A radon fan installed in the radon system piping draws soil-gas from below the floor slab.
3.2.23 sub-slab depressurization (passive), n—a radon mitigation technique designed to achieve lower air pressure under a floor
slab than above it. The radon system piping is routed through the conditioned (heated and cooled) space of a building.
3.2.24 suction point piping, n—one end of this piping penetrates the slab, the solid wall, the hollow wall, the membrane, the sump
cover, or the drain tile. The other end extends outward to the first accessible pipe connection beyond the penetration of the soil-gas
barrier.
3.2.25 sump pit depressurization (SPD) (active), n—a type of active soil depressurization radon mitigation system where the
suction point piping enters the sump pit, that has a sealed gasketed cover, through the side or through the cover.
3.2.26 vent stack piping, n—this piping collects the soil-gas from the suction point pipe of single suction point systems or from
the manifold piping of multi-suction point systems. There are no branches in vent stack piping; soil-gas is collected at one end of
the vent stack piping and is discharged from the building at the other end. In active soil depressurization systems, the radon fan
is installed in the vent stack piping.
3.2.27 ventilation, n—the process of introducing outdoor air into a building.
3.2.28 working level (WL), n—a unit of radon decay product exposure. Numerically, any combination of short-lived radon decay
products in one litre of air that will result in the ultimate emission of 130 000 MeV of potential alpha energy. This number was
chosen because it is approximately the total alpha energy released from the short lived decay products in equilibrium with 100 pCi
of Rn-222.
3.2.29 working level month (WLM), n—a unit of exposure used to express the integrated human exposure to radon decay products.
It is calculated by multiplying the average working level to which a person has been exposed by the number of hours exposed and
dividing the product by 170.
4. Summary of Practice
4.1 This practice describes methods for mitigating elevated levels of radon in existing attached and detached residential buildings
three stories or less in height.
4.2 The mitigation process is described in terms of the categories of activity associated with radon mitigation and includes: general
practices, building investigation, systems design, systems installation, materials, monitors and labeling, post-mitigation testing, and
contracts and documentation.
4.3 The systems installation category contains subsections describing the specific requirements applicable to each of the
components of radon mitigation systems, for example, radon system piping, radon fans, sealing, electrical, etc.
5. Significance and Use
5.1 The purpose of the methods, systems, and designs described in this practice is to reduce radiation exposures for occupants of
residential buildings caused by radon and its progeny. The goal of mitigation is to maintain reduced radon concentrations in
occupiable areas of buildings at levels as low as reasonably achievable. This practice includes sections on reducing radiation
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exposure caused by radon and its progeny for workers who install and repair radon mitigation systems. The goal for workers is
to reduce exposures to radon and its progeny to levels as low as reasonably achievable.
5.2 The methods, systems, designs, and materials described here have been shown to have a high probability of success in
mitigating radon in attached and detached residential buildings, three stories or less in height (see EPA, “Radon Reduction
Techniques for Existing Detached Houses, Technical Guidance (Third Edition) for Active Soil Depressurization Systems”).
Application of these methods does not, however, guarantee reduction of radon levels below any specific level, since performance
will vary with site conditions, construction characteristics, weather, and building operation.
5.3 When applying this practice, contractors also shall conform to all applicable local, state, and federal regulations, and laws
pertaining to residential building construction, remodeling, and improvement.
6. Safety Hazards
6.1 Contractors shall comply with all OSHA, state and local standards or regulations relating to worker safety and occupational
radon exposure. Applicable references in the Code of Federal Regulations include those in 2.2. Contractors also shall follow
occupational radon guidance in 2.2.
6.2 In addition to OSHA standards and NIOSH recommendations, the following requirements specifically applicable to the safety
and protection of radon mitigation workers shall be met:
6.2.1 The contractor shall advise workers of the hazards of exposure to radon and the importance of protective measures when
working in areas of elevated radon concentrations. In addition, the contractor shall advise employees of other potential hazards
according to the hazard communication standard for the construction industry (see OSHA, “Hazard Communication Standard for
the Construction Industry”).
6.2.2 The contractor shall ensure that appropriate safety equipment, such as ventilators, respirators, hard hats, face shields, and
ear plugs, are available on the job site during mitigation activities.
6.2.3 Work areas shall be ventilated to reduce worker exposure to radon, dust, or other airborne pollutants.
6.2.4 Consistent with OSHA permissible exposure limits, contractors shall ensure that employees are exposed to no more than four
working level months (WLM) over a 12-month period (or the equivalent 68 000 pCi/L-h, when converted at an equilibrium ratio
of 100 %. A WLM is calculated by multiplying the average working level to which a person has been exposed by the number of
hours exposed and dividing the product by 170 h.
6.2.5 Contractors shall maintain records of employee exposure to radon sufficient to verify that field employees are exposed to less
than 4 WLM in any 12-month period.
6.2.6 Where ventilation cannot reduce radon levels to less than 0.3 WL, contractors shall provide the respiratory protection that
is required to comply with 6.2.4. When unable to make working level measurements, a radon concentration of 30 pCi/1 (1100
Bq/m ) shall be used in lieu of 0.3 WL. The contractor should provide respiratory protection that conforms with NIOSH “Guide
to Industrial Respiratory Protection,” and the OSHA “Respiratory Protection Standard,” which covers fit tests for employees and
other items related to respirators.
6.2.7 Radon mitigation work shall not be conducted in any work area suspected of containing friable asbestos material, or where
work would render non-friable asbestos material friable, until a determination has been made by a properly trained or certified
person that such work will be undertaken in a manner which complies with applicable asbestos regulations, including those of EPA
and OSHA (see 2.2).
6.2.8 Contractors shall advise employees of the potential hazards, of the materials and supplies used, and provide applicable
material safety data sheets (MSDS).Safety Data Sheets (SDS).
7. Standard Practices for Radon Mitigation
7.1 General Practices:
7.1.1 Radon mitigation systems shall be designed and installed to conform to applicable building codes, and maintain the function
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and operation of all existing equipment and building features, including doors, windows, access panels, etc. Where discrepancies
exist between provisions of this practice and local or state codes that prevent compliance with this practice, the local or state codes
shall take precedence.
7.1.2 Prior to starting work, the contractor shall inform the client of the nature of work to be done, the anticipated use of any
potentially hazardous solvents or other materials, and the need to ventilate work areas during and after the use of such materials
as recommended by the manufacturer of the material. Applicable Material Safety Data Sheets (MSDS)(SDS) shall be made
available to the client on request.
7.1.3 Prior to installing a radon mitigation system, a visual inspection of the building should be conducted to evaluate
characteristics of the building which might affect radon mitigation system performance.
7.1.4 If a contractor has concerns about backdrafting potential at a particular site, the contractor shall recommend that a qualified
person inspect the natural draft combustion appliances and venting systems for compliance with local codes and regulations. The
contractor should recommend that the building owner bring any combustion appliance or venting system, found to be
noncomplying, into compliance.
7.1.5 System components, which are added, or existing system components, which are replaced, repaired, or altered, shall be in
compliance with this practice. Existing system components, which are not repaired, replaced, or altered but are observed to be
noncompliant with this practice, shall be reported to the client in writing. The report should reference the relevant sections of this
practice.
7.2 Systems Design:
7.2.1 All radon mitigation systems shall be designed and installed as permanent, integral additions to the building.
7.2.2 All radon mitigation systems shall be designed and installed to avoid the creation of other health, safety, or environmental
hazards to building occupants, such as backdrafting/spillage from natural draft combustion appliances, constricting or blocking
building exits with pipe runs, or degradation of fire rated assemblies with pipe, or cabling penetrations, or both.
7.2.3 Radon mitigation system design is not limited to safety, radon reduction effectiveness, and compliance with building codes
and regulations. Radon reduction system design also is concerned with installation costs, operating costs, energy usage, durability,
reliability, maintainability, physical comfort for occupants, quietness for occupants and neighbors, as well as impact on interior and
exterior building appearance.
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7.3 System Installation:
7.3.1 General Requirements:
7.3.1.1 All components of radon mitigation systems designed and installed in compliance with provisions of this practice also shall
be in compliance with the applicable mechanical, electrical, building, plumbing, energy and fire prevention codes, standards, and
regulations of the local jurisdiction.
7.3.1.2 When portions of structural framing members must be removed to accommodate radon system components, the amount
of the member removed shall be no greater than that permitted for plumbing installations by applicable building or plumbing codes.
7.3.2 Radon System Piping Installation Requirements:
7.3.2.1 Radon System Pipe Size—Also see Appendix X3. All vent stack piping shall be solid, rigid pipe not less than 3-in.
(75-mm)3 in. (75 mm) inside diameter (ID). The vent stack piping’s ID shall be at least as large as the largest used in the manifold
piping. All manifold piping shall be rigid pipe not less than 3-in. (75-mm)3 in. (75 mm) ID. The manifold piping’spiping’s ID shall
be at least as large as that used in any suction point. Manifold piping to which two or more suction points are connected shall be
at least 4 in. (100 mm) (100 mm) ID. When installing manifold pipes to which three or more suction points need to be installed,
the contractor may benefit from guidance in an industrial ventilation manual. All suction point piping shall be rigid pipe not less
than 3-in. (75-mm)3 in. (75 mm) inside diameter. Not withstanding the minimum radon system piping diameters specified herein,
alternate pipe sizes may be used when sufficiently justified by field diagnostic measurements, including static pressure, air velocity,
and rate of air flow measurements, and documented using the methodologies found in “Industrial Ventilation: A Manual of
Standard Practice, 23rd Edition,” or its equivalent. When alternate pipe sizes and shapes are used, a statement of justification,
including justification methodology, calculations employed, and all site specific field data collected shall be prepared. A copy of
the justification shall become part of the system documentation and shall be provided to the building owner.
7.3.2.2 All pipe joints and connections in radon mitigation systems, both interior and exterior, shall be sealed permanently.
Exceptions include installation of radon fans (see 7.3.3.6) and sump covers (see 7.3.2.8).
7.3.2.3 Radon system piping installed in the interior or on the exterior of a building, should be insulated where condensation on
the pipe’s exterior may drip onto and damage ceilings and floors, etc., and where water vapor, from the soil, may condense inside
the pipe, and then freeze partially or fully blocking the soil-gas exhaust.
7.3.2.4 Radon system piping shall be fastened to the structure of the building with hangers, strapping, or other supports that will
secure it adequately. Radon system piping shall not be attached to or supported by existing pipes, ducts, conduits, or any kind of
equipment. Radon system piping shall not block window and doors or access to installed equipment.
7.3.2.5 Supports for radon system piping should be installed at least every 6 ft (2 m) on horizontal runs. Vertical runs shall be
secured either above or below the points of penetration through floors, ceilings, and roofs, or at least every 8 ft (2.5 m) on runs
that do not penetrate floors, ceilings, or roofs.
7.3.2.6 To prevent blockage of air flow into the bottom of suction point pipes, they shall be supported and secured in a permanent
manner that prevents their downward movement to the bottom of suction pits or sump pits, or into the soil beneath a
soil-gas-retarder membrane. For guidance on submembrane piping, see 7.3.8.3.
7.3.2.7 Horizontal runs in radon system piping shall be sloped to ensure that water from rain or condensation drains downward
into the ground beneath the slab or soil-gas-retarder membrane.
7.3.2.8 If suction point pipes are installed to draw soil gas from sump pits, the system shall be designed to facilitate removal of
the sump pit cover for sump pump maintenance.
7.3.2.9 To reduce the risk of vent stack blockage due to heavy snow fall, to reduce the potential for re-entrainment of radon into
Available from American Conference of Governmental Industrial Hygienists, Inc. (ACGIH), 1330 Kemper Meadow Dr.,3640 Park 42 Drive, Cincinnati, OH
45240,45241, http://www.acgih.org.
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the living spaces of a building, and to prevent direct exposure of individuals outside of buildings to high levels of radon, the
discharge from vent stack pipes of active soil depressurization systems shall meet the following minimum requirements. The
discharge from vent stack pipes shall be:
(1) Vertical and upward, outside the structure, at least 10 ft (3 m) above the ground level, above the edge of the roof, and shall
also meet the separation requirements of 7.3.2.9 (2) and (3). Whenever practicable, they shall be above the highest roof of the
building and above the highest ridge.
(2) Ten ft (3 m) or more away from any window, door, or other opening into conditioned or otherwise occupiable spaces of
the structure, if the radon discharge point is not at least 2 ft (0.6 m) above the top of such openings.
(3) Ten ft (3 m) or more away from any opening into the conditioned or other occupiable spaces of an adjacent building.
Chimney flues shall be considered openings into conditioned or otherwise occupiable space.
(4) For vent stack pipes that penetrate the roof, the point of discharge shall be at least 12 in. (0.3 m) above the surface of the
roof. For vent stack pipes attached to or penetrating the sides of buildings, the point of discharge shall be vertical and a minimum
of 6 in. (150 mm) above the edge of the roof and in such a position that it can neither be covered with snow, or other materials
nor be filled with water from the roof or an overflowing gutter. In areas where it snows the point of discharge shall be 12 in. (0.3
m) above the surface of the roof.
(5) When a horizontal run of vent stack pipe penetrates the gable end walls, the piping outside the structure shall be routed to
a vertical position so that the discharge point meets the requirements of 7.3.2.9 (1), (2), (3), and (4).
(6) Points of discharge that are not in a direct line of sight from openings into conditioned or otherwise occupiable space
because of intervening objects, such as dormers, chimneys, windows around the corner, etc. shall meet the separation requirements
of 7.3.2.9 (1), (2), (3), (4), and (5).
NOTE 1—Measurements from the point of discharge to openings into the conditioned or otherwise occupiable spaces of the structure shall be made from
the point of discharge to the closest part of any opening into such space. For example, to determine compliance with 7.3.2.9, when the location of a
planned vent stack discharge can not be seen from a dormer window, the contractor would determine whether the required separation existed by routing
a flexible measuring tape between the planned discharge point location and the part of the dormer window that is the shortest distance away. The
measuring tape must follow the shortest possible path, and be allowed to bend where it passes intervening part(s) of the dormer.
7.3.3 Radon Fan Installation Requirements:
7.3.3.1 Radon fans shall be sized to provide the pressure difference and air flow characteristics necessary to achieve the radon
reduction goals established for the specific mitigation project. Guidelines for sizing radon fans and piping can be found in
“Industrial Ventilation: A Manual of Standard Practice, 23rd Edition,” and in Appendix X3.
7.3.3.2 Radon fans used in ASD radon mitigation systems shall be installed either outside the building or inside the building,
outside of occupiable space, and above the conditioned (heated/cooled) spaces of a building. Radon fan location is chosen to
minimize the risk of radon entry into living spaces which could result from leaks in radon fan housings or in the vent stack piping
above the radon fan. Preferred locations include places on the exterior of the building, unconditioned house and garage attics not
suitable for occupancy, and other unconditioned house and garage locations not suitable for occupancy, which have no occupiable
or conditioned spaces above them.
7.3.3.3 Radon fans shall be installed in a configuration that avoids condensation or other water accumulation in the radon fan
housing.
7.3.3.4 Radon fans mounted on the exterior of buildings shall be rated for outdoor use or installed in a weather proof protective
housing.
7.3.3.5 Radon fans shall be mounted and secured in a manner that minimizes transfer of vibration to the structural framing of the
building.
7.3.3.6 To facilitate maintenance and future replacement, radon fans shall be installed in the vent pipe using removable couplings
or flexible connections that can be tightly secured to both the radon fan and the vent pipe.
7.3.3.7 Outside air intake vents of fan powered systems shall be screened to prevent the intake of debris. Screens shall be
removable to permit cleaning or replacement and building owners shall be informed of the need to periodically replace or clean
such screens.
7.3.4 General Sealing Requirements:
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7.3.4.1 Openings around the suction point piping penetrations of the slab, accessible openings around utility penetrations of the
foundation walls and slab, and other openings in slabs cast over gas permeable soils or aggregates, that reduce the pressure field
extension, and the effectiveness of soil depressurization systems, shall be sealed, using methods and materials that are permanent
and durable. For guidance on sump pits and sump pit covers see 7.3.6.1 and 7.3.6.2.
7.3.4.2 Sealing the Floor-Wall Joint—Sealing openings and cracks where the slab meets the foundation wall is sometimes
appropriate. When urethane caulk or equivalent material is to be used, and when the joint is greater than ⁄2 in. (13 mm) in width,
a foam backer rod or other comparable filler material should be inserted into the joint before the application of the sealant. For
guidance on channel and French drain sealing, see 7.3.13.3.
NOTE 2—Field experience has shown that sealing the floor-wall joint and small cracks in the slab of poured concrete foundation systems of SSD, sump
pit depressurization (DPD), and DTD systems usually is not necessary when an active soil depressurization is employed. Sealing is desirable when
significant below grade air leakage is occurring, or when the air flow into the gas permeable layer below the slab is creating objectionable noise. Failure
to limit air flow into the depressurized soil of an active soil depressurization system may be a contributing factor to a backdraft condition. SMD and BWD
systems, active or passive, and any passive radon reduction system require more thorough sealing.
7.3.4.3 When installing baseboard-type suction systems, all seams and joints in the baseboard material shall be joined and sealed
using materials recommended by the manufacturer of the baseboard system. Baseboards shall be sealed to walls and floors with
adhesives also designed and recommended for such installations.
7.3.4.4 Utility and other penetrations through a soil-gas-retarder membrane shall be sealed.
7.3.5 Active Sub-Slab Depressurization (SSD) Requirements:
7.3.5.1 To enhance pressure field extension, when the sub-slab material exhibits poor gas-permeability, it is helpful to excavate
as much as 1 ft (28 L) of sub-slab material below and around each suction point pipe. Even when the sub-slab material is highly
permeable, like crushed stone, the end of the suction point pipe should have an excavated hole, at least one pipe diameter deep,
directly below it.
7.3.6 Sump Pit Requirements:
7.3.6.1 Sump pits or other large openings in slabs or basement walls that allow a significant amount of soil gas leakage into the
basement or air leakage into the sub-floor areas should be covered and sealed (see 7.4.7 and 7.4.8 for details on sump covers and
sealing materials).
7.3.6.2 When a radon mitigation system is designed to draw soil-gas from a sump pit, a sump cover shall be installed as described
in 7.3.13.4, 7.4.7, and 7.4.8.
7.3.7 Drain Tile Depressurization (DTD) Requirements:
7.3.7.1 Whenever a DTD radon mitigation system that is intended to depressurize a sub-slab area by drawing soil-gas from a
perimeter drain tile loop (internal or external) is installed, all drain lines extending from the drain tile loop to daylight shall have
a one-way flow valve, a water trap, or other control device installed to prevent outdoor air from entering the sub-slab area. The
control device is intended to prevent air from entering the drain line but not prevent water from flowing out of the drain line.
7.3.8 Submembrane Depressurization (SMD) Requirements:
7.3.8.1 Any seams in soil-gas-retarder membranes (not covered by concrete slabs) used for submembrane depressurization
systems, passive or active, shall be lapped at least 12 in. (300 mm). The membrane’s seams shall be sealed. The membrane shall
be sealed around posts and other penetrations. The edges of the membrane shall be sealed to the walls to the extent practical. When
there are indications that water is likely to collect on the membrane, it shall be fitted with trapped drains at the lowest part of the
locations that are likely to be wet.
7.3.8.2 Passive submembrane depressurization systems, which are installed while anticipating possible activation, shall meet all
the requirements for an active SMD systems, but without the radon fan and monitor.
7.3.8.3 Active SMD systems may be noisy, but the noise can be reduced by sealing the membrane (see 7.3.8.1), which reduces
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the amount of air leakage and its associated noise and also improves the pressure field extension under the membrane. Utilizing
a special suction point design can also significantly reduce the noise caused by air flowing into the suction point. The design calls
for eight or more slots being cut into the lowest foot (0.3 m) of the suction point pipe, with the slots being ⁄2 in. (13 mm) wide
and ⁄2 in (13 mm) apart. The slots may be parallel or perpendicular to the axis of the pipe. Slots that are perpendicular to the axis
of the pipe shall be cut half way through the pipe. The intake end of the special suction point should be buried deep in a bed of
clean 1 in. (25 mm) aggregate.
7.3.9 Hollow Block-Wall Depressurization (BWD) Requirements:
7.3.9.1 When a hollow BWD system is used to mitigate radon, openings in the tops of such walls and all accessible openings or
cracks in the interior surfaces of the walls should be closed and sealed with polyurethane or equivalent caulks, expandable foams,
or other fillers and sealants. Large, inaccessible openings or cracks that have not been sealed should be disclosed to the client and
included in the documentation.
7.3.10 Crawlspace Depressurization (CSD)—Crawlspace depressurization is usually not the first choice radon mitigation method
for crawlspaces because of its greater potential for hazardous failure, that is, backdrafting, and the probability of a high energy loss
associated with its operation during the colder and hotter months. Sub-slab and submembrane depressurization are the crawlspace
mitigation methods that should be used whenever possible.
7.3.10.1 When CSD is used for radon mitigation, cracks and openings in floors above the crawlspace, which would permit
conditioned air to pass from the living spaces to the crawlspace shall be sealed to the extent practicable. Openings or cracks that
are determined to be inaccessible or beyond the ability of the contractor to seal shall be disclosed to the client and included in the
documentation.
7.3.10.2 CSD shall not be used as a radon control system when combustion appliances are installed within the crawlspace, or
within an abutting crawlspace or basement, or where adequate isolation (from depressurization) does not exist or cannot be created
in a practical manner, between interior spaces containing one or more combustion appliances and the crawlspace.
7.3.10.3 CSD shall not be used as a radon control system when evidence suggests that friable asbestos material exists in the
crawlspace, or when work in the crawlspace would render nonfriable asbestos material friable. If asbestos is to be removed from
the crawlspace, to allow the installation of a CSD system, the contractor shall employ trained and certified asbestos removers
whose work will be undertaken in a manner which complies with applicable asbestos regulations, including those of EPA and
OSHA (see 2.2).
7.3.11 Combination Foundations:
7.3.11.1 Buildings with elevated radon levels may have more than one foundation type. Mitigation may be required in parts of
the building involving one or more foundation types. Foundation types include slab-on-grade, basement, and crawlspace. Isolation
of foundation spaces using barriers intended to keep radon from passing, for example, from the crawlspace to the basement or vise
versa are not recommended, because walls built using available building trade techniques, usually do not accomplish their isolation
objective. In addition, if the purpose of the isolation is to seal off the crawlspace to enable crawlspace depressurization, it is not
recommended. Crawlspace depressurization usually is not the first choice radon mitigation method for crawlspaces because of its
greater potential for hazardous failure, that is, backdrafting, and the probability of a high energy loss associated with its operation
during the colder and hotter months. Sub-slab and submembrane depressurization are the crawlspace mitigation methods that
should be used whenever possible.
7.3.12 Electrical Requirements:
NOTE 3—For purposes of this section, electrical power is assumed to be provided by 120 V, 15, 20,15 ampere, 20 ampere, or 30 ampere circuits; however,
for all cases and all situations see 7.3.12.1 for guidance.
7.3.12.1 Wiring for all active radon mitigation systems shall conform to provisions of the “1999 National Electrical Code
Handbook, Eighth Edition” and any additional local regulations.
Henschel, D.B., D. B., “Indoor Radon Reduction in Crawl Space Houses: A Review of Alternative Approaches,” Indoor Air, Vol 2, No. 2, 1994, pp. 272–278, available
from International Society of Indoor Air Quality and Climate; ISIAO Secretariat, Via Magenta 25, 20020 Busto Garolfo (Milan), Italy.
Available from National Fire Protection Association (NFPA), 1 Batterymarch Park, Quincy, MA 02169-7471, http://www.nfpa.org.
E2121 − 21
7.3.12.2 Wiring shall not be located inside the radon system piping or within any other heating or cooling ductwork.
7.3.12.3 Any plugged cord used to supply power to a radon fan shall be no more than 6 ft (2 m) in length.
7.3.12.4 No plugged cord may penetrate a wall or be concealed within a wall.
7.3.12.5 A disconnecting means is a switch, a plugged cord, or a branch circuit overcurrent device. A disconnecting means shall
be present in the electric circuit powering radon fans. The disconnecting means shall be located within sight of the radon fan,
except when the fan motor develops ⁄8 th horsepower or less. The branch circuit overcurrent device is permitted to be the
disconnecting means when the fan motor develops ⁄8 th horsepower or less. The primary purpose of the fan’sfan’s disconnecting
means is to termporarilytemporarily disconnect the fan’sfan’s electric power when maintenance is performed. Operation of the
radon fan’sfan’s disconnecting means should not interrupt the power to other electrical devices in the dwelling. See “1999 National
Electrical Code Handbook, Eighth Edition” Articles 430-102(b) and 430-109(b), (c), and (f). Also see Appendix X4, Determining
Radon Fan Motor Horsepower.
7.3.12.6 Flexible plugged cords, properly rated for electrical capacity and weather, may be used on radon fans inside or outside
the building. These flexible plugged cords may also serve as a disconnecting means inside or outside the building. Radon fans,
cords, plugs, receptacles, receptacle enclosures, switches, switch enclosures, etc., intended for outside use must have a
weatherproof and unattended use rating, and are different than what is generally used inside the building. See “1999 National
Electrical Code Handbook, Eight Edition.” (Warning—A hard-wired electrical connection (with a disconnect switch) may be
a preferable alternative to a flexible plugged cord connection for radon fans installed outdoors. There are safety issues and other
disadvantages to flexible plugged cords being installed outdoors. Children may play with the outdoor cord or receptacle. Because
the protection of wires in an outdoor plugged flexible cord radon fan installation may not equal that of a hard wired outdoor
installation, the wiring may be subjected to greater risk of accidental damage. The outside flexible plugged cord, which may be
located where access to it is not easily controlled, can be unplugged to free the receptacle for other purposes, and the radon fan
may not be plugged in again.)
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