United States
               Environmental Protection
               Agency	
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
               Research and Development
EPA/600/SR-95/159    December 1995
EPA      Project  Summary
               Demonstration of Radon
               Resistant  Construction
               Techniques - Phase  II
               James L. Tyson and Charles R. Withers
                 The Florida Radon Research Program
               (FRRP), sponsored by the Environmen-
               tal Protection Agency and the Florida
               Department of Community  Affairs
               (DCA), is developing the technical ba-
               sis for a radon-control construction
               standard. The full report summarizes a
               project that examined indoor radon in
               houses that  were constructed accord-
               ing to the draft residential construction
               code.
                 This Project Summary was developed
               by EPA's Air and Energy Engineering
               Research Laboratory, Research Tri-
               angle Park, NC,  to announce key find-
               ings of the research project that is fully
               documented in a separate report of the
               same title (see Project Report ordering
               information at back).

               Introduction
                 The data presented here are from work
               performed  by the Florida Solar Energy
               Center designed to demonstrate radon re-
               sistant construction  techniques in new
               Florida houses.  Fifteen  houses are  in-
               cluded in the  Phase II study. Some analy-
               sis, however, includes the 13 houses in
               the 1991 study, to expand the data pool
               from which conclusions can be drawn.
                 Three types of  data were collected:
                 1)  Soils were tested to determine type,
                    permeability, radon and radium con-
                    tent, radium emanation coefficient,
                    and moisture.

                 2)  The house slab was examined to
                    characterize  the  crack  size and
                    number, and the pressure field ex-
                    tension under the slab created by
                    the sub-slab depressurization sys-
                    tem was measured.
  3)  The house itself underwent exten-
      sive testing, including blower door,
      tracer gas, and duct leak measure-
      ments.
  The full report discusses and provides
 a compliance checklist of the  adherence
 of the subject houses to the radon codes
 and standards. It then explains the objec-
 tives, methods used, results expected, and
 problems encountered in  each part of the
 project. Then the results of testing are
 presented, followed by an analysis of the
 data for correlations to radon intrusion.

 Soil
  Fill soil with high radium content contin-
 ues to be used in the area of this study. A
 total of 70% (16 of 23) of the  houses for
 which both  radium measurements are
 available had higher radium values in the
 fill soil than in the native soil.  Native soil
 radium seems to have a greater effect on
 final indoor radon levels,  probably due to
 the thin fill soil layer under most  houses.
 Neither native  nor fill soil radium levels
 directly correlate with indoor radon, how-
 ever. High levels of radium in fill soils can
 still import a radon problem onto a site
 that otherwise would not have one, based
 on native soil gas readings.
  Sub-slab measurements of soil-gas ra-
 don taken at the same point on different
 days can vary by as much as  100%, and
 measurements taken at  different points
 on a slab  on the same day can also vary
 by 100% or more. This variability matches
 that of measurements taken in different
 seasons on the same slab, and leads to
 the conclusion that a number of measure-
 ments taken on the same day  at different
 locations on a  site are necessary to ad-
 equately characterize radon potential.

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Slab
  All sub-slab mitigation systems had ad-
equate pressure field extension, although
pressure fields for both monolithic  and
stem-wall  slabs dropped to zero just in-
side or at  the slab edge.  The pressure
field can be short-circuited if the ventila-
tion mat or suction pit  is located  closer
than 6 ft (1.8 m) from the slab edge.  The
6 ft distance mentioned in the code should
be taken as a minimum, as distances up
to 40  ft (12.2 m),  measured  from the end
of a ventilation mat to the slab edge, have
been depressurized.
  Post-tensioned  slabs performed best at
preventing  cracks, containing an average
crack length of 13 ft (4 m) in four slabs.
Stem-wall systems had  an average of 36
ft (11  m) of crack in 10  slabs, and  mono-
lithic slabs  an average of 100 ft (30.5 m)
in 14 slabs. Average crack length in slabs
using plasticizer in the concrete was 63 ft
(19.2  m) compared with 76  ft (23.2 m) in
slabs  without  plasticizer. Plasticizer  use
seems to  have the desired effect of re-
ducing total crack length when all slabs
are lumped together, but  conflicting  re-
sults appear when slabs are separated by
type. Average crack length in two  mono-
lithic slabs  with plasticizer was 35 ft (10.7
m), and was  114  ft (34.7 m) in 10  mono-
lithic slabs without plasticizer. Stem-wall
slabs,  however, had  an average of 75 ft
(22.9  m)  of  cracks  in  three slabs with
plasticizer and an average of only  16.5 ft
(5 m)  of  cracks  in  eight  slabs without
plasticizer.  Also, all three slabs  in these
groups with no cracks were  among those
without plasticizer. Clearly, more data are
required before a definitive conclusion can
be reached.
  Placing   reinforcement in  the top  por-
tions of slab  inside corners  helps to  pre-
vent cracks from starting in these corners.
Houses with corner reinforcement had 50%
less total cracking than those without cor-
ner reinforcement. In at least one instance,
however, the corner reinforcement merely
forced the  crack to start beyond the ex-
tent of the  reinforcing bars.
  Total crack length  does  not correlate
with indoor radon  levels.  In some  in-
stances, high levels of radon were  drawn
through cracks during testing, but these
tests used  much higher levels of depres-
surization  than those found  in the  house
environment,  and  most cracks are  pro-
tected  by the  intact vapor barriers under
new homes. No data are available, how-
ever,  on how long these vapor barriers
will remain intact,  and it is  possible  that
radon  levels  in these houses will  rise if
vapor barriers deteriorate over time.
  Pipe penetrations through slabs are an-
other avenue for radon intrusion; testing
would help determine the extent to which
this occurs. Radon levels in houses with-
out tar protecting pipes in slab penetra-
tions had  an  average indoor radon level
33% higher than those with tar on the
pipes.  Monitoring  in  house 7  has  also
shown that slab penetrations for plumbing
pipes not built to code standards can con-
tribute to indoor radon levels.
  High ambient radon levels found on the
house 7 site were not duplicated on other
reclaimed mine  sites tested during the
project. This site does present the oppor-
tunity,  however,  to study the  effects  of
weather and  atmospheric conditions on
the exhalation rate of radon from the  soil.
  The  best measure of slab leakiness is
the amount of conditioned air being pulled
through the slab during mitigation fan op-
eration. Dividing  by the  house  volume
gives slab air changes per  hour (ach),
which takes into account all slab openings
including cracks and pipe penetrations.

House
  Houses needing mitigation system acti-
vation  in  the project were  on average
smaller and tighter, with a higher value for
slab ach. Activated houses also had higher
levels of depressurization than unactivated
houses.
  The radon stress test did not give mean-
ingful results and  was  discarded during
the project. No calculated values based
on  its data showed  any correlation  with
indoor radon levels. The stress test should
be  relegated  to  research  houses, where
much longer  time periods for testing are
possible.
  No direct correlations with indoor radon
were found in this set of houses, due to
the complex  nature of the  house as a
system, it is usually  impossible  to isolate
one building component from another dur-
ing testing, and each component is likely
to have an opposite effect on the results
of a test. The factors seeming to have the
closest relationship with indoor  radon are
the sub-slab  radon  level  as  the source
term, the differential pressure across the
slab as the driving force, and the slab ach
as the medium of radon intrusion. House
leakiness affects the dilution of  the radon
level once  it  has entered  the house  and
may be the deciding factor as to whether
or not a house's  mitigation system should
be activated.
  There continue to  be problems relating
to energy efficiency,  especially  relating to
house  shell design and heating, ventila-
tion, and air-conditioning (HVAC) system
installation  procedures. The  lack of test-
ing of these systems and the house enve-
lope itself have  led  many builders to ig-
nore certain building components and in-
stallation procedures that are causing en-
ergy  inefficiency to  be built  into new
homes.

Recommendations
  Recommendations for the continuation
of the new house  evaluation  project in-
clude shifting testing emphasis from slab
cracks to slab pipe penetrations. The test-
ing apparatus is available to use the same
protocol on pipe penetrations as has been
used  on  slab cracks. Number and types
of slab penetrations should be catalogued
as slab cracks have been. Sealing of sub-
slab vapor barriers to the  pipe  penetra-
tions  and the use of tar on pipes where
they contact the concrete should be con-
sidered as mandatory additions to the ra-
don code.
  Different types  of pipe penetration  pro-
tection should be tested in a laboratory
setting to isolate the pipe penetration and
determine the best way to protect against
radon intrusion.  Obtaining direct correla-
tions between different types of protection
for pipe penetrations and radon  intrusion
through the slab will be much easier when
all other conditions can be controlled. Mul-
tiple penetrations can  also be poured  in
the same test bed to allow more accurate
results to be achieved through averaging.
  Older homes should be investigated  to
determine if vapor  barriers remain intact
over  long  periods  of time.  Ignoring the
repair of slab cracks while emphasis shifts
to the testing  of  other slab penetrations
could create a  radon problem  if vapor
barriers  do  not  last long. Older  houses
could be surveyed  for cracks while new
carpet is being installed. Vapor barrier in-
tegrity could easily  be  determined by us-
ing the same testing protocol now in place.
Slab cores could  also  be cut to examine
firsthand  the condition of older vapor bar-
riers.
  Requirements for concrete slump should
be relaxed from 4 to 5 in. (10 to 12.7 cm).
Requiring a 4-in. slump would be unen-
forceable: it would require an inspector to
be on hand for every concrete truck deliv-
ery on every slab built in the code area. It
would also be an economic hardship  to
builders:  4-in.  slump concrete cannot be
pulled across a slab by hand  and would
require a pump truck  to place the con-
crete  on  any slab with access problems.
  Requirements  for specific spacing  of
slab control joints should be dropped from
the code. Average  total crack length  for
the 28 houses over the 2-year project was
71 ft (21.6 m), with an average drop to 42

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ft  (12.8  m) after  subtracting the three
houses  with  the most  cracks.  Contrast
this with an average control joint length
requirement of 442 ft (134.7 m) based on
the average project  house footprint.  The
control joint spacing requirement clearly
requires more work from the builder than
can be  justified, since slab cracks have
not been shown to be directly correlated
to indoor radon levels.
  Testing of new houses should continue,
to collect data  on how sub-slab depres-
surization (SSD) works in  real houses,
and how the  houses themselves perform
as barriers to radon. Determining correla-
tions between indoor radon levels and in-
dividual parts  of the radon  code will be
difficult, however, due to the complex na-
ture  of real-world  houses.  Investigations
of code sections that can be isolated in a
laboratory setting will yield better results
due to an enhanced ability to  control the
experiment.

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 James L Tyson and Charles R. Withers are with the Florida Solar Energy Center, Cape
   Canaveral, FL 32920.
 David C. Sanchez is the EPA Project Officer (see below).
 The complete report,  entitled "Demonstration of Radon Resistant Construction Tech-
   niques - Phase II," (Order No. PB96-121512; Cost: $44.00, subject to change) will be
   available only from:
         National Technical Information Service
         5285 Port Royal Road
         Springfield, VA 22161
         Telephone: 703-487-4650
 The EPA Project Officer can be contacted at:
         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

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EPA/600/SR-95/159

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