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Radon Resistant Construction
Building radon resistance
into a new house is far less costly than radon mitigation after
construction. The passive system outlined below costs only about $300
for a modest house and has no operating costs.
In contrast, an effective radon mitigation retrofit with sub-slab
depressurization costs about $1,200 to install and can have significant
operating costs.
Radon enters basements by pressure driven flow through cracks and
openings to the soil. It enters because basement air tends to be at lower
pressure than the soil gasses with radon under the slab.
This slightly lower pressure is due to winds and the buoyancy of
warm indoor air in cold weather. To control radon effectively, sealing
cracks and openings to soil and production of a greater depressurization
under the basement floor are needed.
The following five features from the EPA
(exit DHS) are to be installed as new construction is
built, to constitute a proper system for controlling radon. To meet the new NAHB
National Green Building Standard for areas
with high radon potential,
(exit DHS) the features of Appendix F in
the ICC
International Residential Code for One and Two-Family Dwellings (exit DHS)
are required, as summarized below. Appendix
F is derivative of EPA’s "Model
Standards and Techniques for Control of Radon in New Residential
Buildings",
(exit DHS) in which these key features are detailed in Section
9.
Methods
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Where the gravel and plastic sheeting are standard, the only
additional elements are the passive stack through a heated partition and
the sealing of joints and other openings to soil.
Before the basement slab is poured, a three-
or four inch diameter PVC stack is placed vertically from under slab, to
run up through an interior, heated partition of the house and through the
roof. If the sub-slab region
is well sealed from the basement, winds and (when outdoor air is cold)
warmer air in the stack rising then create a slight depressurization under
the slab. With the gravel, the
depressurized region can extend completely under the slab. The
bottom of the passive stack connects to a PVC tee with about ten feet of
perforated pipe on both ends in the gravel. Dirt-floor crawl
spaces are treated similarly with depressurization under a membrane
adhered to the walls.
Studies across the country and in Wisconsin show
that such passive stacks in properly built and sealed new construction
typically reduce the radon in indoor air by 50%, compared to the radon
measured with the stacks capped.
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Since the radon in a home may still be elevated
despite these precautions (though it is significantly less likely,) a
radon measurement is needed after the home is finished. If
the radon is elevated, installing a fan in the stack, in space originally
provided for it in the attic, ensures adequate control at a low additional
cost. The fan must not be located in conditioned air, i.e.
not in the basement.
The trades persons doing this work must understand
that the stack goes through a heated, interior partition, that space for
installing a fan must be left in the attic, and that sealing of the
floor-wall joints must be done before any basement finish walls are
installed.
Costs
If the indoor radon is elevated, a fan-powered mitigation system (the
only thing that will work as a retrofit) can cause withdrawal of
conditioned air via cracks and openings through the slab behind finish
walls. The energy for the fan,
plus heating of the cold outdoor air infiltrating to replace air withdrawn
from the home, can cost
$200 per year in northern climates.
(exit DHS)
Back to Radon Home Page
Last Revised: December 27, 2011
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