United States
Environmental Protection
Agency
National Risk Management
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-95/114 August 1995
4>EPA Project Summary
Evaluation of Building Design,
Construction, and
Performance for the Control of
Radon in Florida Houses:
Evaluation of Radon Resistant
Construction Techniques in Eight
New Houses
D.E. Hintenlang, A. Shanker, FT. Najafi, and C.E. Roessler
Eight houses were studied through-
out their construction in North Central
Florida. Each house was built in com-
pliance with the proposed radon resis-
tant construction standard being
developed by the Florida Department
of Community Affairs. Post-construc-
tion monitoring was performed over a
minimum 6-day period for each struc-
ture during which each house was op-
erated in three different heating,
ventilation, and air-conditioning (HVAC)
system configurations. Continuous
measurements of indoor radon concen-
trations, house ventilation rates, across-
slab differential pressures, and
interzone differential pressures pro-
vided time resolved radon entry rates
and a performance index for passive
radon barriers. Radon entry rates were
found to be relatively constant through-
out the measurement periods and for
different house operating conditions,
implying that the passive radon barrier
eliminates the majority of convective
entry. The passive barriers maintained
radon entry fluxes at less than 1.2 pCi
rrr2 s~1 for sub-slab radon concentra-
tions as high as 9,500 pCil1.
The study results also demonstrate
that the operation of well designed and
constructed HVAC systems do not sig-
nificantly affect indoor radon concen-
trations, regardless of the pressures
that may be induced between interior
air zones. House ventilation rates
should, however, be equal to or greater
than 0.25 air change per hour in order
to prevent the accumulation of elevated
radon concentrations since passive
barriers do not block 100% of the ra-
don from entering.
This Project Summary was developed
by EPA's National Risk Management
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
The State of Florida has undertaken the
development of radon resistant construc-
tion standards for newly constructed build-
ings in the state. This is a premier effort to
develop a technically based building code
for both residential and large/commercial
buildings and focuses on the specific con-
struction practices and environmental con-
ditions found in this region of the country.
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The work presented here consists of an
evaluation of the effectiveness of the ra-
don resistant construction standards for
residential construction which will enter
the rule-making process later this year
Eight houses were studied throughout
their construction in North Central
Florida. Each house was built in compli-
ance with the proposed radon resistant
construction standard being developed
by the Florida Department of Commu-
nity Affairs. Post-construction monitor-
ing was performed over a minimum
6-day period for each structure during
which each house was operated in three
different heating, ventilation, and air-con-
ditioning (HVAC) system configurations.
Continuous measurements of indoor ra-
don concentrations, house ventilation
rate, across-slab differential pressures,
and interzone differential pressures pro-
vided time resolved radon entry rates
and a performance index for passive
radon barriers. Each of the houses was
built over high radon potential soils and
was constructed implementing the ra-
don resistant construction standards be-
ing developed by the Florida Department
of Community Affairs.
Radon entry rates were calculated from
the measured parameters. The resulting
radon entry rates were relatively constant
throughout the measurement periods and
for different house operating conditions,
with variations of indoor radon concentra-
tions being driven predominantly by the
house ventilation rate. Normal cycling in
the barometric pressure produced a semi-
diurnal cycle in the across-slab differential
pressures in all of the houses studied.
These differential pressures did not, how-
ever, correlate with observed changes of
the radon entry rate, indicating that pres-
sure driven flow is not providing a major
contribution to the radon entry. These re-
sults imply that the passive radon barrier
effectively reduces a large fraction of the
convective driven entry. Similarly, aver-
aged radon entry rates and entry fluxes
were not correlated to the foundation slab
cracking present in these structures. Al-
though measures were taken to reduce
the amount of slab cracking, half of the
slabs studied exhibited some unplanned
slab cracks.
A general figure of merit, the entry rate
per unit slab area, or radon entry flux is
useful and suggests that residences built
using the radon resistant construction stan-
dard should be able to have entry fluxes
less than about 1.2 pCi nr2 s~1. It does not
appear that sub-slab radon concentrations
were high enough to overcome the effec-
tiveness of passive barriers reached in
this study. The passive barriers have dem-
onstrated their effectiveness at maintain-
ing radon entry fluxes at less than
approximately 1.2 pCi nr2 s~1 for sub-slab
radon concentrations as high as 9,500
pCi M. If passive barrier techniques be-
come ineffective at some concentration of
sub-slab soil gas radon, it is probably
greater than 10,000 pCi M. In fact, we
observed excellent performance for House
#11 at 9,500 pCi M, which had quite a low
radon entry flux. This research provides
support for and suggests some changes
to the current version of the radon resis-
tant construction standards in several ar-
eas. Overall the study demonstrates that
the implementation of passive barriers can
be practically incorporated in foundations
during new house construction and that,
when implemented as prescribed by the
standards, can successfully prevent in-
door radon concentrations from exceed-
ing the 148 Bq rrr3 guidelines in most
houses.
The study results also demonstrate that
the operation of well designed and con-
structed HVAC systems (i.e., those built
to current building code standards) does
not significantly affect indoor radon con-
centrations, regardless of the pressures
that may be induced between interior air
zones. Therefore, there should be no re-
quirement for the radon resistant construc-
tion standards to include provisions to
transfer air between different air zones
within a structure such as transfer grills,
and door undercuts. A more important sub-
ject with which HVAC systems do interact
is the overall house ventilation rate. It
appears to be prudent to ensure an aver-
age house ventilation rate equal to, or
greater than, 0.25 air change per hour in
order to prevent the accumulation of el-
evated radon concentrations, since pas-
sive barriers do not block 100% of the
radon from entering.
The radon resistant construction stan-
dards developed for residential construc-
tion by the Florida Department of
Community Affairs have been demon-
strated to be technically feasible and can
be implemented on a practical basis. Pas-
sive barrier techniques can provide houses
constructed over sandy fills and high soil
gas radon concentrations with acceptable
indoor radon concentrations as long as
house ventilation rates are not permitted
to be too low, and active soil depressur-
ization continues to be an inexpensive
and very effective backup to passive bar-
riers.
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D.E. Hintenlang, A. Shanker, F.T. Najafi, andC.E. Roesslerare with the University
of Florida, Gainesville, FL 32611.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Evaluation of Building Design, Construction, and
Performance for the Control of Radon in Florida Houses: Evaluation of Radon
Resistant Construction Techniques in Eight New Houses," (Order No. PB95-
253910; Cost: $27.00, subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
National Risk Management Research Laboratory
(formerly Air and Energy Engineering Research Laboratory)
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
National Risk Management
Research Laboratory (G-72)
Cincinnati, OH 45268
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
Official Business
Penalty for Private Use
$300
EPA/600/SR-95/114
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