United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-94/002 March 1994
EPA Project Summary
Assessment of the Effects of
Weatherization on Residential
Radon Levels
Timothy M. Dyess
The U. S. Environmental Protection
Agency conducts research to determine
the factors that influence radon entry
into residences. Reducing air leaks in
the home has the potential for reduc-
ing the pressure-driven flow of radon
' into the home and has been suggested
as a potential radon-reduction tech-
nique. However, the reduction of air
leaks in a home also reduces the air
exchange rate and therefore the dilu-
tion rate of radon with outdoor air. Be-
cause the underlying physical
processes at work can interact in dif-
ferent ways, the relationship between
tightening the building envelope and
indoor radon levels is not well under-
stood.
Part of a project with the Maryland
Weatherization Assistance Program in-
volved weatherizing homes throughout
the state of Maryland according to two
protocols—a Retro-Tech technique ex-
pected to achieve approximately a 10
to 20% reduction in air leakage and an
advanced technique expected to reduce
air leakage by as much as 50%. For the
project that is the subject of this re-
port, time-integrated radon measure-
ments were taken for 30- to 45-day
periods both before and after Weather-
ization in 32 Retro-Tech homes, 28 ad-
vanced homes, and 16 control homes
that were not weatherized during the
study period. Air leakage rates before
and after Weatherization were measured
with a blower door, and ambient tem-
peratures and precipitation levels dur-
ing the monitoring periods for each
study home were obtained from local
weather stations.
Based on results of blower-door
tests, air leakage rates were reduced
by an average of 10 to 15% in
Retro-Tech homes and by 35 to 40% in
advanced homes. The radon concen-
tration data generally suggest that
Weatherization procedures did not ad-
versely affect indoor radon levels. How-
ever, interpretations are clouded by
weather factors that may influence ra-
don entry rates changing differentially
for the three groups of homes between
the two measurement periods.
This Project Summary was developed
by EPA's Air and Energy Engineering
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).
Introduction
The primary factors that influence ra-
don entry include (1) the radon content of
the soil gas, (2) the pressure differential
between the interior of the home and the
soil, (3) the air exchange rate for the home,
(4) the moisture content of soil surround-
ing the home, and (5) the presence and
size of entry pathways. The pressure dif-
ferential between the soil and the interior
of the home is influenced by the wind,
temperature differential between indoors
and outdoors, and the operation of venti-
lation and combustion equipment. The air
exchange rate is also influenced by the
same factors. The pressure differential is
Printed-on Recycled Paper
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the primary force driving the radon entry
into the building, and the air exchange
rate affects the dilution of the radon with
outdoor air. Both factors are influenced by
the tightness of the building envelope.
Reducing the air leaks in the home
has the potential for reducing the
pressure-driven flow of radon into the
home and has been suggested as a
potential radon-reduction technique.
However, the reduction of air leaks in a
home also reduces the air exchange
rate and therefore the dilution rate of
radon with outdoor air. Because the un-
derlying physical processes at work can
interact in different ways, the relationship
between tightening the building envelope
and indoor radon levels is not well under-
stood.
Because reducing the air exchange rate
in buildings is a very desirable energy
conservation measure, it is important to
understand how tightening the building
envelope affects the indoor radon level.
As part of a project with the Maryland
Weatherization Assistance Program for
tow-income households, 72 homes in the
state of Maryland were weatherized. Two
Weatherization protocols were applied in
this study: one expected to achieve ap-
proximately a 10 to 20% reduction in air
leakage, and the other expected to re-
duce air leakage by as much as 50%.
Eighteen homes, used as a control group,
were not weatherized.
Objective
The objective of this two-phase effort
was to measure the radon levels inside
study homes before and after Weatheriza-
tion so that the effect of Weatherization on
indoor radon could be assessed. Alpha
track detectors (ATDs) were used to mea-
sure indoor radon levels before and after
Weatherization, and blower-door tests were
used to determine the change in air leak-
age through the building shell as a result
of the applied Weatherization techniques.
The ATDs used for both phases of the
project were manufactured and analyzed
by Tech/OPs Landauer (Glenview, IL). A
single ATD was placed in the lowest level
of each home for 30 to 45 days during
both the pre- and post-weatherization pe-
riods.
Ninety-two homes were enrolled in the
program, most during the latter part of the
characteristics,
heatitjig season. Of these 92
receiv 3d pre-weatherization ra-
L nder Phase I of this ef-
remainde r of the radon monitoring
Juring Phase II. A site
to each home by a
who documented the
conducted a
t, installed a furnace
nd placed an ATD. Dur-
\|veeks following the site
ner was called to collect
furnkce run-time and indoor
Ouldoor temperatures and
leyels from the closest
were collected. The
erjergy use, building char-
blciwer-door results for each
maintained in a project data
of the radon monitoring
home, the ATDs were
forWarded to the Tech/OPs
analysis. The laboratory ra-
ich home were added to
1990-1991
homes, 28
don monitoring
fort; the
was conducted
visit was made
two-person crew
building
blower-door tes
run-time meter, £
ing the 4 to 6
visit, the homeow
data on the
temperature.
precipitation
weather statior
weather data,
acteristics and
home were
base. At the end
period for each
retrieved and
Laboratory for
don results for e
the data base.
After the 4-toe
data collection
homes received
ment. The
pre-determined
the main concebt
according to (1)
fuel used for hee
location of the
of occupants.
was assigned
Retro-Tech
used in the
was assigned
vanced technique
tive to Retro-T
similar characte
the control group
cedures are des
tye
Results
The following
Weatherization
marize pre- and
suits for this
concentrations,
tures, average
blower-door test
results were
leakage rates,
(CFM) at 50 pa
to house volume!
i-week pre-weatherization
period had ended, 74
a Weatherization treat-
of treatment was
the project staff, with
being to pair homes
:he type of home, (2) the
ting, (3) the geographical
home, and (4) the number
Within a pair, one home
Weatherization with the
tech lique (existing technique
and the other home
wkatherization with the ad-
(contemplated alterna-
;h). Other homes with
istics were assigned to
. The Weatherization pro-
;ribed in the report.
(sen
., measurements from the
project were used to sum-
post-weatherization re-
project: indoor radon
average outdoor tempera-
precipitation levels, and
results. The blower-door
e> pressed as absolute air
n cubic feet per minute
icals (Pa), and in relation
in air changes per hour
(ACH) at 50 Pa. The Weatherization cases
were grouped by type of Weatherization
and analyzed to determine whether any of
the changes were statistically significant.
The pre- and post-weatherization values,
as well as their differences, are summa-
rized in Table 1 and are discussed in the
report.
Between the pre- and post-weatherization
measurement periods, average indoor ra-
don concentrations decreased with statis-
tical significance for two subgroups of
homes—the control group, which received
no Weatherization, and the Retro-Tech
group, for which Weatherization reduced
air leakage rates by 10 to 15%. For the
advanced group of homes, Weatherization
reduced air leakage rates by 35 to 40%
and radon levels rose slightly, but the
increase in radon is not statistically signifi-
cant while air leakage reductions are.
Thus, the data generally suggest that
Weatherization procedures did not ad-
versely affect indoor radon levels. These
interpretations related to changes in in-
door levels are clouded by weather fac-
tors that may influence radon entry rates
changing differentially for the three groups
of homes between the two measurement
periods. More specifically, both outdoor
temperature and precipitation levels
changed significantly for the control group,
only outdoor temperature changed signifi-
cantly for the advanced group, and nei-
ther changed significantly for the
Retro-Tech group.
Within the Retro-Tech group, the corre-
lation coefficient between changes in air-
tightness (CFM at 50 Pa) and changes in
indoor radon concentration are statistically
significant: the sign of the coefficient (r =
0.33) indicates that reduced air leakage
was statistically associated with reduced
radon concentrations. However, within the
advanced group that had greater changes
in airtightness, no significant relationship
was evident between changes in airtight-
ness and radon.
Based on analysis for the control group,
precipitation was the most influential
weather factor. The sine of the coefficient
(r = -0.66) indicated that radon concentra-
tions generally decreased as precipitation
levels increased. Such a finding broadly
supports the theory that moisture-laden
soil suppresses radon migration in all di-
rections.
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Table 1. • Summary of Monitoring Results
Measurement
Parameter"
Advanced Weatherization
Indoor Radon, pCi/L
Precipitation, in.
Outdoor Temperature, "F
Airtightness, CFM @ SO Pa
Airtightness, ACH @ 50 Pa
Retro-Tech Weatherization
Indoor Radon, pCi/L
Precipitation, in.
Outdoor Temperature, °F - • .
Airtightness, CFM @ 50 Pa
Airtightness, ACH @ 50 Pa
No Weatherization (Controls)
Indoor Radon, pd/L
Precipitation, in.
Outdoor Temperature, °F
Airtightness, CFM @ 50 Pa
Airtightness, ACH @ 50 Pa ,
by Type of Weatherization Procedure
No. of Pre-Weatherization
Cases Value, Avg. ± Std. Dev.
28
28
28
25
25
32
32
32
29
29
16
16
16
15
15
2.1 ±3.0
6.5 ±4.9
48.1 ±4.5
3897 + 2732
23.9 + 12.4
1.1 ±0.7
6.2 ±5.2
46.2 ±4.5
3422 ±1464
24.5 ±12.5
2.5 ±4.1
4.4 ±3.8
44.5 ±5.4
3949±3435
23.0 ±14.2
Post Weatherization
Value, Avg. ± Std. Dev.
2.5 ±4.5
5.7 ±2.1
41.4+9.1
2351 ± 938
14.8+4.2
0.8 ± 0.6
5.8 ±1.2
42.4 + 13.7
2984 ±1248
21.7 ± 12.2
2.2 ±3.8
7.3+2.7
38.9 ±9.1
3697 ±2522
22.5 ±14.6
Difference (Post-Pre),
Avg. ± Std. Dev.
0.4 ± 2.4
-0.8 ±4.9
-6.7 » + 9.8
-1546 "±2001
-9.1" ±10.0
-0.3" ±0.5
-0.4 + 5.6
-3.8 + 14.7
-438 "±550
2.8 "+3.9
-0.3 b ± 0.5
2.9 "±4.7
-5.6 b ±9.9
-252+2320
-0.5 ±9.6
' 1 in. = 2.54cm, "F = 9/5°C + 32, and 1 cfm = 0.000472 cms.
* Significantly different from zero (p < 0.05).
•&U.S. GOVERNMENT PRINTING OFFICE: 1994 - 550467/8020*
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Timothy M. Dyess Is the EPA Project Officer (see below).
The complete report, entitled "Assessment of the Effects of
Residential Radon Levels," (Order No. PB94-141181; Cost:
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
\ifeatherization on
1,'19.50; subject to
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penally for Private Use
$300
EPA/600/SR-94/002
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
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