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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