oEPA
NAHB
RESEARCH »
FOUNDATION, INC.
United States
Environmental Protection
Agency
Offices of
Air and Radiation and
Research and Development
Washington DC 20460
August 1987
OPA-87-009
Radon
Reduction in
New Construction
An Interim Guide
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Introduction
The U.S. Environmental Protection
Agency (EPA) is concerned about the
increased risk of developing lung
cancer faced by persons exposed to
radon in their homes. Because many
families already face the problem,
early emphasis was placed on
identifying the danger in existing
homes and developing cost-effective
methods to make such housing safer.
Based on this early research, EPA
published three documents in 1986: A
Citizen's Guide to Radon: What It Is
and What To Do About It, Radon
Reduction Methods: A Homeowner's
Guide, and a more detailed manual,
Radon Reduction Techniques for
Detached Houses: Technical
Guidance. These documents were
designed to help homeowners
determine if they have a radon
problem and to present information
on how to reduce elevated radon
levels in their homes.
This pamphlet is the next step in
> attempting to reduce the radon hazard
1 in homes. It is designed to provide
radon information for those involved
^ in new construction and to introduce
methods that can be used during
construction to minimize radon entry
and facilitate its removal after
construction is complete. If there is
concern about the potential for
elevated indoor radon levels, it may
be prudent to use these construction
techniques in new homes. The
"Techniques for Site Evaluation"
section of this pamphlet outlines
several methods for assessing the
potential for elevated indoor radon
levels. The decision to incorporate
these construction techniques rests
solely with the builder or homeowner.
In addition to extensive internal
EPA review, this pamphlet has been
developed in coordination with the
National Association of Home
Builders Research Foundation, Inc.
(NAHB-RF),a,not for profit organization,
and other federal agencies including
the Department of Energy (DOE),
Housing and Urban Development
(HUD), United States Geological
Survey (USGS), and the National
Bureau of Standards (NBS). It also
reflects comments solicited from a
broad spectrum of individual experts
in home construction and related
industries.
It is potentially more cost-effective
to build a home that resists radon
entry than to remedy a radon problem
after construction. The construction
methods suggested in this pamphlet
represent current knowledge and
experience gained primarily from
radon reduction tests and
demonstrations on existing homes.
Field tests are underway to develop
and refine the most cost-effective
new-home construction techniques.
After completion of these field tests, a
more detailed "Technical Guidance"
manual will be published to expand
and revise, as necessary, the interim
guidance presented in this pamphlet.
Accordingly, this Interim Guide
should not be referenced in codes and
standards documents.
Radon Facts
Radon is a colorless, odorless,
tasteless, radioactive gas that occurs
naturally in soil gas, underground
water, and outdoor air. It exists at
various levels throughout the United
States. Prolonged exposure to elevated
concentrations of radon decay
products has been associated with
increases in the risk of lung cancer.
An elevated concentration is defined
as being at or above the EPA
suggested guidelines of 4|pCi/l or 0.02
WL average annual exposure.*
Although exposures below this level
do present some risk of lung cancer,
reductions to lower levels may be
difficult, and sometimes impossible to
achieve.
Soil gas entering homes through
exposed soil in crawl spaces, through
cracks and openings in slab-on-grade
floors, and through below-grade walls
and floors is the primary source of
elevated radon levels (Figure 1).
Radon in outside air is diluted to such
low concentrations that it does not
present a health hazard. In some small
public and private well-water
supplies, radon is a hazard primarily
to the extent that it contributes to
indoor radon gas concentrations.
When water is heated and agitated
(aerated), as in a shower or washing
machine, it will give off small**
quantities of radon.
Radon moves through the small
spaces that exist in all soils. The
speed of movement depends on the
permeability of the soil and the
presence of a driving force caused
when the pressure inside a home is
lower than the pressure outside or in
the surrounding and underlying soil.
A lower pressure inside a home may
result from:
• Heated air rising, which causes a
stack effect.
• Wind blowing past a home, which
causes a down-wind draft or Venturi
effect.
• Air being used by fireplaces and
wood stoves, which causes a vacuum
effect.
• Air being vented to the outside by
clothes dryers and exhaust fans in
bathrooms, kitchens, or attics, which
also causes a vacuum effect.
In homes, where a partial vacuum
exists, outdoor air and soil gas are
driven into the home.
New Construction Principles
The facts just discussed form the
basis for the following
new-construction principles:
• Homes should be designed and
constructed to minimize pathways for
soil gas to enter.
• Homes should be designed and
built to maintain a neutral pressure
differential between indoors and
outdoors.
• Features can also be incorporated
during construction that will facilitate
radon removal after completion of the
home if prevention techniques prove
to be inadequate.
The following techniques for site
evaluation and construction are based
on these principles.
Techniques for Site Evaluation
The first step in building new
radon-resistant homes is to determine,
to the degree possible, the potential
for radon problems at the building
site. At this time, there are no
standard soil tests or specific
* pCi/1, the abbreviation for pica Curies per
liter, is used as a radiation unit of measure for
radon. The prefix "pica" means a
multiplication /actor of l trillionth. A Curie is a
commonly used measurement of radioactivity.
WL, the abbreviation for Working Level, is used
as a radiation unit of measure for the decay
products of radon. The relationship between
the two terms is generally 200 pCtfl = 1 WL.
" The generally accepted rule of thumb for
emanation of radon gas from water is: 10,000
pCi/1 of radon in water will normally produce a
concentration of about 1 pCi/1 of radon in
indoor air.
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'E
MAJOR RADON ENTRY ROUTES
A. Cracks in concrete slabs
B. Spaces behind brick veneer walls
that rest on uncapped hollow-block foundation
C. Pores and cracks in concrete blocks
D. Floor-wall joints
E. Exposed soil, as in a sump
F. Weeping (drain) tile, if drained to open sump
G. Mortar joints
H. Loose fitting pipe penetrations
I. Open tops of block walls
J. Building materials such as some rock
K. Water (from some wells)
Figure 1
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standards for correlating the results of
soil tests at a building site with
subsequent indoor radon levels. The
variety of geological conditions in the
United States will probably continue
to preclude establishment of any
all-inclusive, nationwide standards for
such correlation. We can, however,
estimate the radon potential at a
building site based on factors other
than soil tests. If the answer to any of
the following questions is yes, radon
problems might be anticipated and
radon reduction features should be
considered for inclusion in
construction plans.
• Have existing homes in the same
geologic area experienced elevated
radon levels? ("Same geologic area" is
defined as an area having similar rock
and soil composition characteristics.)
State or regional EPA offices may be
able to assist in obtaining this
information.
• What are the general characteristics
of the soil? State and local geological
or agricultural offices can normally
help in providing answers to the
following questions on soil:
—Is the soil derived from underlying
rock that normally contains
above-average concentrations of
uranium or radium, e.g., some
granites, black shales, phosphates or
phosphate limestones?
—Is the permeability of the soil and
underlying rock conducive to the flow
of radon gas? Note that soil
permeability (influenced by grain size,
porosity, and moisture content) and
the degree to which underlying and
adjacent rock structures are stable or
fractured can significantly affect the
amount of radon that can flow toward
and into a home.
• If the source of water to the site is
going to be a local or onsite well, have
excessive levels of radon been
detected in other wells within the
same geologic area? (Levels measured
above 40,000 pCi/lof water could
alone produce indoor radon
concentrations of about 4 pCi/1 or
above. Such levels are considered
excessive.) State or local health
agencies, departments of natural
resources, or environmental protection
offices may be able to assist in
providing this information. Testing
well water for radon before the home
is built could provide an additional
indication of a potential radon
problem. If excessive radon levels are
confirmed, a granular activated-carbon
filtration system or an aeration system
might be designed into the plumbing
plan.
Construction Techniques
Some of the radon prevention
techniques discussed below are
common building practices in many
areas and, in any case, are less costly
if accomplished during construction.
Costs to retrofit existing homes with
the same features would be signifi-
cantly higher. Although these
construction techniques do not
require any fundamental changes in
building design, there is a continuing
need for quality control, supervision,
and more careful attention to certain
construction details. Construction
techniques for minimizing radon entry
can be grouped into two basic
categories:
• Methods to reduce pathways for
radon entry.
• Methods to reduce the vacuum
effect of a home on surrounding and
underlying soil.
Typically, the techniques in both
categories are used in conjunction
with each other.
Methods to Reduce Pathways for
Radon Entry (Figure 2)
In Basement and Slab-on-Grade
Construction:
• Place a 6-mil polyethylene vapor
barrier under the slab. Overlap joints
in the barrier 12 inches. Penetrations
of the barrier by plumbing should be
sealed or taped, and care should be
taken to avoid puncturing the barrier
when pouring the slab.
• To minimize shrinkage and cracks
in slabs, use recommended water
content in concrete mix and keep the
slab covered and damp for several
days after the pour.
• To help reduce major floor cracks,
ensure that steel reinforcing mesh, if
used, is imbedded in (and not under)
the slab. Reducing major cracks in
footings, block foundation, and
poured-concrete walls will reduce the
rate of radon entry. Radon can,
however, enter homes through even
the smallest of cracks in concrete
slabs and walls if a driving pressure is
applied to those surfaces.
• The most common radon-entry
pathways are inside perimeter
floor/wall joints and any control joints
between separately poured slab
sections. To reduce radon entry
through these joints, install a
common flexible expansion joint
material around the perimeter of the
slab and between any slab sections.
After the slab has cured for several
days, remove or depress the top 1/2
inch or so of this material and fill the
gap with a good quality, non-cracking
polyurethane or similar caulk. Similar
techniques for sealing these joints
may also be used.
» In some areas, basement slabs are
poured with a French Drain channel
around the slab perimeter. To be
effective, this moisture control
technique requires that the floor/wall
joint be open to permit water to seep
out into the sub-slab area. To reduce
radon entry through such open joints,
it may be necessary to install a
perforated drain pipe loop under the
slab, adjacent to the footing and
imbedded in aggregate, and to tie this
pipe into a sub-slab ventilation system
to draw radon gas away from the
French Drain joint (Figure 4). For
additional information on water
control techniques, refer to National
Association of Home Builders (NAHB)
publication Basement Water Leakage:
Causes, Prevention, and Correction.
• When building slab-on-grade homes
in warm climates, pour the foundation
and slab as a single (monolithic) unit.
If properly insulated below
grade-level, shallow foundations and
slabs can also be poured as a single
unit in cold climates.
• Remove all grade stakes and screed
boards and fill the holes as the slab is
being finished. This will prevent
future radon pathways through the
slab, which might otherwise be
created as imbedded wood eventually
deteriorates.
• Carefully seal around all pipes and
wires penetrating the slab, paying
particular attention to bathtub,
shower, and toilet openings around
traps.
• Floor drains, if installed, should
drain to daylight, a sewer, or to a
sump with pump discharge. Floor
drains should not be drained into a
sump if such a pit will be used as part
of a sub-slab ventilation system.
Suction on the sump could be
defeated by an open line to the floor
drain.
• Sumps should be sealed at the top.
In closed sumps used for sub-slab
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ventilation systems, the continuous
flow of moist air through the sump
can cause rapid corrosion of exposed
sump pump motors. For this reason,
submersible-type sump pumps are
recommended for closed-sump
applications.
In Basement and Crawl space
Construction:
• Seal or cap the tops of hollow-block
foundation walls using one of the
techniques shown in Figure 2.
• Carefully seal around any pipe or
wire penetrations of below-grade
walls.
• Exterior block walls should be
parged and coated with high-quality
vapor/water sealants or polyethelene
films. For additional information on
wall sealing, refer to NAHB
publication Basement Water Leakage:
Causes, Prevention, and Correction.
Several new products for use on
exterior walls are designed to provide
an airway for soil gas to reach the
surface outside the wall rather than
being drawn through the wall. Similar
materials may also be used in sub-slab
ventilation applications.
• Interior surfaces of masonry
foundations may be covered with a
high-quality, water-resistant coating.
• Heating or air-conditioning
ductwork that must be routed through
a crawl space or beneath a slab should
be properly taped or sealed. This is
particularly important for return air
ducting, which is under negative
pressure. Due to difficulty in
achieving permanent sealing of such
ductwork, it may be advisable to
redesign heating and ventilating
systems to avoid ducting through
sub-slab or crawl space areas,
particularly in areas where elevated
soil radon levels have been confirmed.
• Install air-tight seals on any doors
or other openings between basements
and adjoining crawl spaces.
• Seal around any ducting, pipe, or
wire penetrations of walls between
basements and adjoining crawl spaces,
and close any openings between floor
joists over the dividing wall.
• Place a 6-mil polyethelene vapor
barrier on the soil in the crawl space.
Use a 12-inch overlap and seal the
seams between barrier sections. Seal
edges to foundation walls.
GRADE
n
PARGED
OR SEALED-*
WALLS
TO SEWER
OR DAYLIGHT
• 4" OR 8" SOLID BLOCKS
2" CAP BLOCKS-
WATER
•RESISTANT
COATING
SEAL ALL PLUMBING
PENETRATIONS
D
GRADE
SUBMERSIBLE
SUMP PUMP
TO DAYLIGHT,
SEWER OR
SUMP
METHODS TO REDUCE PATHWAYS FOR RADON ENTRY
Figure 2
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Methods to Reduce the Vacuum
Effect (Figure 3)
• Ensure that vents are installed in
crawl space walls and are sized and
located in accordance with local
building practices. Adequate
ventilation of crawl spaces is the best
defense against radon entry in
crawl space-type homes.
• Reduce air flow from the
crawl space into living areas by
closing and sealing any openings and
penetrations of the floor over the
crawlspace.
• To reduce the stack effect, close
thermal bypasses such as spaces
around chimney flues and plumbing
chases. Attic access stairs should also
be closed and sealed. (Note: Because
of potential heat buildup, most codes
prohibit insulating around recessed
ceiling lights. Such lights should
therefore be avoided in top-floor
ceilings. As an alternative, use
recessed ceiling lights designed to
permit insulation or "hi-hat" covers
and seal to minimize air leakage.)
• Install ducting to provide an
external air supply for fireplace
combustion.
• In areas frequently exposed to
above-average winds, install extra
weather sealing above the soil line to
reduce depressurization caused by the
Venturi effect. Such sealing will also
save energy and reduce the stack
effect.
• Air-to-air heat exchange systems are
designed to increase ventilation and
improve indoor air quality. They may
also be adjusted to help neutralize any
imbalance between indoor and
outdoor air pressure and thus reduce
the stack effect of the home. They
should not, however, be relied upon
as a stand-alone solution to radon
reduction in new construction. (A
slightly positive pressure, in the
basement, may contribute to reducing
radon flow into a home.)
Construction Methods That Will
Facilitate Post-Construction
Radon Removal (Figure 4)
Recognizing that radon prevention
techniques may not always result in
radon levels below the suggested
guideline of 4 pCi/1 average annual
exposure, there are several additional
construction techniques that can be
used to facilitate any post-
construction radon removal that may
be required.
• Before pouring a slab, fill the entire
sub-floor area with a layer (4 inches
thick) of pea gravel or larger, clean
aggregate to facilitate installation of a
sub-slab ventilation system.
• Lay a continuous loop of perforated
4-inch diameter drain pipe around the
inside perimeter of the foundation
footing. Run the vent from this loop
into the side of a closed sump that
can, if necessary, be equipped with a
fan-driven vent to the outside. In this
configuration, the drain pipe loop can
aid in water seepage control as well as
radon reduction.
• As an alternative to the vented
interior drain pipe loop, a similarly
vented exterior loop can be laid
outside the foundation footing.
• In areas where water seepage into
below-grade spaces is not a problem
and sump pumps are not installed,
exterior or interior drain pipe loops
can be stubbed-up outside the home
or through the slab and can be
available for use as sub-slab
ventilation points if needed.
• The soil beneath a slab can also be
ventilated using the following
technique: Prior to pouring the slab,
insert (in a vertical position) one or
more short (12-inch) lengths of 4-inch
minimum diameter PVC pipe into the
sub-slab aggregate and cap the top
end. After construction is complete,
these standpipes can, if necessary, be
uncapped and connected to one or
more convection stacks or fan-driven
vent pipes. When positioning these
standpipes, choose locations
permitting venting to the roof through
already planned flue or plumbing
chases, interior walls, or closets. In
homes where flue or other chases are
restricted in size or not easily
accessible, it may be less expensive to
go ahead—during the framing and
rough-in plumbing/electric phase of
construction—and complete the vent
pipe hookup, temporarily terminating
the vent in the attic along with an
electric outlet for future fan
installation. Experience has shown
that in homes with higher radon
levels—above 20 pCi/1—convection
(passive) venting may not produce
acceptable radon reductions. If lower
radon levels are expected and passive
venting is attempted, performance is
improved by using a 6-inch diameter
vent routed straight from the floor
through the roof, with minimum
bends.
Drilling 4-inch holes through
finished slabs for insertion of vent
pipes is an alternative to this
technique.
• To create the necessary convection
flow, radon prevention techniques
that involve passive venting normally
require stacks that pass through the
floors and roof. When active
(fan-driven) systems are installed,
venting through to the roof is still
preferred. Recognizing, however, that
active systems can be vented through
the band joist or below-grade walls to
the outside, it is considered advisable
in such active systems to position the
exit point of the vent pipe at or above
the eave line of the roof and away
from any doors or windows. This will
preclude any possible recirculation of
air containing concentrated radon gas
back into the house.
• In homes where an active
(fan-driven) sub-slab ventilation
system has been installed, it may be
necessary to provide make-up air to
avoid back drafting.
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SEAL SPACES AROUND
FLUES AND
CHIMNEYS
AVOID RECESSED
CEILING LIGHTS IN
UPPER FLOORS
EXTERNAL AIR
SUPPLY FOR
FIREPLACE
SEAL AROUND
DUCT AND FLUE
CHASE OPENINGS
BETWEEN FLOORS
SEAL OPENINGS
AROUND PLUMBING
PENETRATIONS
SEAL AROUND
DUCT PENETRATION
BETWEEN BASEMENT
AND CRAWL SPACE
VENTS TO
MEET CODE
REQUIREMENTS
SEAL AROUND
ACCESS DOOR—
TO CRAWL SPACE
CRAWL SPACE
TIGHT
FITTING
WINDOWS
AND WEATHER
STRIPPING
TO REDUCE
VENTURI
EFFECT
METHODS TO REDUCE THE VACUUM EFFECT
Figure 3
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SEAL ALL JOINT*
ON PRESSURE SIDE
OF FANS
EXTERIOR
VENT
ROUTING
SEAL ALL JOINTS
ON PRESSURE SIDE
OF FANS
PREFERRED
FAN LOCATIONS
INTERIOR
VENT
ROUTING
SOLID
BLOCK
COURSE
SEAL AROUND ALL
PENETRATIONS OF
SUMP COVER
CAP DURING
CONSTRUCTION
SUMP DISCHAROE
CAULK UNDER
SUMP COVER
SUB-SLAB
VENT
STANDPIPE\
AGGREGATE
VAPOR BARRIER
EXTERIOR
DRAIN PIPE
LOOP
INTERIOR
DRAIN PIPE
LOOP
(USE WITH
FRENCH DRAIN)
SUMP CASINO
METHODS TO FACILITATE POST-CONSTRUCTION RADON REMOVAL
Figure 4
The U.S. EPA and the NAHB-RF strive to provide accurate, complete, and useful information. However, neither EPA, nor
NAHB-HF nor any other person contributing to or assisting in the preparation of this booklet—nor any person acting on behalf
-/ any of these parties—makes any warranty, guarantee, or representation (express or implied} with respect to the usefulness or
ffectiveness of any information, method, or process disclosed in this material or assumes any liability /or the use of—or for
lamages arising from the use of—any information, methods, or process disclosed in this material.
-------
Source of Information
If you would like further information or explanation
on any of the points mentioned in this booklet, you
should contact your State radiation protection office or
home builders association.
If you have difficulty locating these offices, you may
call your EPA regional office listed below. They will be
happy to provide you with the name, address, and
telephone number of these contacts.
STATE-ERA REGION
Alabama-4
Alaska-10
Arizona-9
Arkansas-6
California-9
Colorado-8
Connecticut-1
Delaware-3
District of
Columbia-3
Florida-4
Georgia-4
Hawaii-9
ldaho-10
lllinois-5
lndiana-5
Maryland-3
Massachusetts-1
Michigan-5
Minnesota-5
Mississippi-4
Missouri-7
Montana-8
Maine-1
New York-2
North Dakota-8
Oklahoma-6
Oregon-10
Ohio-5
Pensylvania-3
Rhode lsland'1
Nebraska-7
South Carolina-4
lowa-7
Nevada-9
South Dakota-8
Kansas-7
New Hampshire-1
Tennessee-4
Kentucky-4
New Jersey-2
Texas-6
Louisiana-6
New Mexico-6
Utah-8
North Carolina-4
Virginia-3
West Virginia-3
Washington-10
Wisconsin-5
Wyoming-8
Vermont-1
EPA REGIONAL OFFICES
EPA Region 1
Room 2203
JFK Federal Building
Boston, MA 02203
(617) 565-3234
EPA Region 2
26 Federal Plaza
New York, NY 10278
(212) 264-4418
EPA Region 3
841 Chestnut Street
Philadelphia, PA 19107
(215) 597-4084
EPA Region 4
345 Courtland Street, NE
Atlanta, GA 30365
(404) 347-2904
EPA Region 5
230 South Dearborne Street
Chicago, IL 60604
(312) 886-6175
EPA Region 6
1201 Elm Street
Dallas, TX 75270
(214) 655-7208
EPA Region 7
726 Minnesota Avenue
Kansas City, KS 66101
(913) 236-2893
EPA Region 8
Suite 1300
One Denver Place
999 18th Street
Denver, CO 80202
(303) 293-1648
EPA Region 9
215 Fremont Street
San Francisco, CA 94105
(415) 974-8378
EPA Region 10
1200 Sixth Avenue
Seattle, WA 98101
(206) 442-7660
U. S. ENVIRONMENTAL PROTECTION AGENCY
REGIONAL ORGANIZATION
"O
* U. S. GOVERNMENT PRINTING OFFICE: 1987 716-002/60673
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