PB96-153473
Information b our business
RESIDENTIAL RADON RESISTANT CONSTRUCTION
FEATURE SELECTION SYSTEM
ROGERS AND ASSOCIATES ENGINEERING CORP., SALT LAKE CITY, UT
FEB 96
U.S. DEPARTMENT OF COMMERCE
National Technical Information Service
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EFA-6Q0/R-96-Q05
February 1996
Residential Radon Resistant Construction Feature
Selection System
Final Report
by
Kirk K. Nielson, Rodger B. Holt, and Vein C. Rogers
Rogers and Associates Engineering Corporation
P. O. Box 330, Salt Lake City, Utah 84110-0330
Florida DCA Contract 94RB-30-13-00-22-003
University of Florida Subcontract (Acct 1506481-12)
" U.S. EPA IAG RWFL 933783
Project Officers:
Mohammad Madani
Florida Department of Community Affairs
2740 Cenierview Drive
Tallahassee, FL 32399
David C. Sanchez
National Risk Management Research Laboratory
Research Triangle Park, NC 27711
Stanley Latimer
Department of Urban and Regional Planning
431 ARCH, University of Florida
Gainesville, FL 32611
Prepared for:
State of Florida
Florida Department of Community Affairs
2740 Centerview Drive
Tallahassee, FL 32399
U. S. Environmental Protection Agency
Office of Research and Development
Washington, DC 20460
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TECHNICAL REPORT DATA
(Flesst rvcd Ixzaitctioni cm Che merit before compu
I. REPORT NO. 2.
EPA-600/R-96-005
3.
f
4. TITLE AND SUBTITLE
Residential Radon Resistant Construction Feature
Selection System
S. REPORT DATE
February 1996
6. PERFORMING ORGANIZATION CODE
7. AUTHORIS)
Kirk K. Nielson, Rodger B. Holt, and Vern C. Rogers
S. PERFORMING ORGANIZATION REPORT NO.
RAE-9226/2-1R1
0. PERFORMING ORGANIZATION NAME AND ADDRESS
Rogers and Associates Engineering Corporation
P. C. Box 330
Salt Lake City, Utah 84110
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
EPA IAG RWFL 933783
DCA 94RD-30-13-00-22-003
12. SPONSORING AGENCY NAME AND ADORESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final; 2-7/94
14. SPONSORING AGENCY CODE
EPA/600/13
15.supplementary notes APPCD project officer is David C. Sanchez. Mail Drop 54. 919/
541-2979. DCA project officer is Mohammad Madani, 2740 Centerview Dr., Talla-
hassee. FL 32399.
is.abstract rep0r£ describes a proposed residential radon resistant construction
feature selection system. The features consist of engineered barriers to reduce ra-
don entry and accumulation indoors. The proposed Florida standards require radon
resistant features in proportion to regional soil radon potentials, defined from a
statewide radon potential map. The effectiveness of different radon control features
was estimated from new laboratory measurements, analyses of new and previous
house studies, and mathematical model simulations. The laboratory measurements
characterized five brands of polyethylene sub-slab membranes. The analyses showed
that both monolithic-slab (mono) and slab-in-stem-wall (SSW) foundation designs can
passively control indoor/sub-slab radon ratios to average levels that are slightly lo-
wer than measurements in other houses the previous year, and two to four times lo-
wer than ratios from earlier studies. The Southern Research Institute ratios are 1.4
to 3. 7 times lower than values from a lumped-parameter model, primarily due to
improved sealing of slab penetrations. The University of Florida ratios are within a
factor of 1. 74 of calculated ratios. The mono design offers about twice as much pas-
sive radon resistance as SSW designs. A Florida radon protection map was developed
to show where the active and passive features were needed.
17. KEY WORDS AND DOCUMENT ANALYSIS
X. DESCRIPTORS
b.lOENTIFIERS/OPEN ENOEDTERMS
c. COSATl Field/Group
Pollution
Radon
Residential Buildings
Construction
Soils
Mathematical Models
Pollution Control
Stationary Sources
Indoor Air
13 B
07B
13 M
08G.08M
12A
IB. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
21. NO. OF PAGES
56
20. SECURITY CLASS (ThU page)
Unclassified
22. PRICE
CPA Form 2220-1 (9*73)
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FOREWORD
The U. S. Environmental Protection Agency is charged by Congress with pro-
tecting the Nation's land, air, and water resources. Under a mandate of national
environmental laws, the Agency strives to formulate and implement actions lead-
ing to a compatible balance between human activities and the ability of natural
systems to support and nurture life. To meet this mandate, EPA's research
program is providing data and technical support for solving environmental pro-
blems today and building a science knowledge base necessary to manage our eco-
logical resources wisely, understand how pollutants affect our health, and pre-
vent or reduce environmental risks in the future.
The National Risk Management Research Laboratory is the Agency's center for
investigation of technological and management approaches for reducing risks
from threats to human health and the environment. The focus of the Laboratory's
research program is on methods for the prevention and control of pollution to air,
land, water, and subsurface resources; protection of water quality in public water
systems; remediation of contaminated sites and groundwater; and prevention and
control of indoor air pollution. The goal of this research effort is to catalyze
development and implementation of innovative, cost-effective environmental
technologies; develop scientific and engineering information needed by EPA to
support regulatory and policy decisions; and provide technical support and infor-
mation transfer to ensure effective implementation of environmental regulations
and strategies.
This publication has been produced as part of the Laboratory's strategic long-
term research plan. It is published and made available by EPA's Office of Re-
search and Development to assist the user community and to link researchers
with their clients.
E. Timothy Oppelt, Director
National Risk Management Research Laboratory
EPA REVIEW NOTICE
This report has been peer and administratively reviewed by the U.S. Environmental
Protection Agency, and approved for publication. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
This document is available to the public through the National Technical Information
Service, Springfield, Virginia 22161.
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ABSTRACT
Radon gas generated from radium decay in soils can enter houses through foundation
openings and accumulate to levels that pose significant risks of lung cancer with chronic
exposure. The Florida Department of Community Affairs (DCA) has proposed construction
standards to protect public health by requiring radon-resistant building features in areas of
elevated soil radon potential. State-wide maps of soil radon potential have been developed
to implement the proposed standards regionally, and the system for selecting specific radon-
resistant building features from the mapped soil radon potentials is described in this report.
This report summarizes all work under Task C of the subcontract to Rogers &
Associates Engineering Corp. under DCA contract 94RD-30-13-00-22-003 to Uni\*ersity of
Florida. One task element is to characterize the radon resistance of polyethylene membranes
used under concrete slabs. Triplicate measurements were made on five different brands of
0.015 cm (6 mil < polyethylene plastic sheeting purchased at building supply outlets in Florida.
Radon diffusion coefficients averaged 3.4x10" cm2 s*1 with a standard deviation of 6.3xl0'8
cm2 s"1 among 15 measurements. There were no significant differences between brands. Air
permeability measurements averaged 6.5xl0'15 cm2 with a geometric standard deviation of
8.4 among 15 measurements. One brand exhibited significantly lower air permeability than
the others.
A second task element summarizes additional lumped-parameter analyses of 1993
New House Evaluation Program data. Fourteen houses characterized by Southern Research
Institute (SRI) and ten houses characterized by University of Florida (UF) suggested that
both monolithic-slab (Mono) and slab-in-stem-wall (SSW) designs can achieve passive radon
control to keep the ratios of net indoor radon to sub-slab radon at C^C^ = 3.3xl0*4 to
4.2x10"*. These ratios are slightly better (lower) than measured ratios from the previous
year, and two to four times lower than measured ratios from two years earlier.
The SRI measured ratios are 1.4 to 3.7 times lower than values calculated from an
earlier lumped-parameter equation, primarily due to improved sealing of slab penetrations.
The UF measured ratios are within a factor of 1.74 of calculated ratios. The geometric mean
ii
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of all measured Cnct/Cjub ratios representative of Mono houses is 5.5X10"4 (GSD=3.14, n=43),
and the geometric mean of the ratios representative of SSW houses is l.lxlO'3
(GSD=3.02, n=52). The monolithic-slab design therefore offers approximately twice as much
passive radon resistance as SSW designs. Houses with active sub-slab ventilation (SSV)
systems had only slightly lower Crcs/Cf„i, ratios (approximately 3.3x10"*) because many of the
SSV systems were activated in houses with only marginally-elevated radon.
Another task element analyzed different residential building construction features by
computer simulations of radon resistance effectiveness. The RAdon Emanation and
TRAnsport into Dwellings (RAETRAD) model was used for numerous analyses of reference
buildings with three slab edge details: floating slab, SSW, and Mono. The model analyses
identified steady-state indoor radon concentrations for the reference houses under different
construction conditions to identify the radon resistance of the following features: fill soil
compaction, vapor barrier placement, concrete slump (10,15, and 20-cm categories), concrete
slab reinforcement with wire mesh, reinforcement of re-entrant corners of the slab, sealing
of large slab openings, and sealing of slab penetrations.
The radon resistance effectiveness of the different building construction features was
used to rank the features according to their usefulness for radon control. A summary ranking
was estimated for cases where the features depended inseparably on the slab edge detail.
The ranking indicated the following ordering (descending effectiveness) of building features:
Active sub-slab ventilation system, vapor barrier placement, enhanced ventilation, avoidance
of floating slab construction (use of SSW or Mono), use of 4-inch slump concrete, use of 6-inch
slump concrete, sealing of slab openings and all cracks, sealing of slab penetrations, sealing
of openings and large cracks, use of a passive sub-slab ventilation system, compaction of fill
soil, elimination of slab reinforcement, and reinforcement of re-entrant corners. From these
rankings, active radon control features were recommended to be active sub-slab ventilation
with either a pit-based or mat-based system. Passive controls were recommended to be a
group of four features, including elimination of floating slab construction, use of 15-cm slump
concrete, sealing of slab penetrations, and sealing of large openings and large cracks. The
minimum overall effectiveness of the passive group is a factor of 2.1, and the combined
minimum effectiveness of the active and passive groups is a factor of 9.3.
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The Florida Radon Protection Map was developed to show where the proposed Florida
Standard for Radon Resistant Residential Building Construction requires only passive radon
controls and where it also requires active radon controls. The map is based on a state-wide
data base and map of soil radon potential, on the radon resistance determined for passive
radon controls, and on a cost-benefit analysis to determine the appropriate margin of safety
for the map.
The radon protection map was developed by assigning all regions of the state to one
of three radon protection categories. The green category designated regions in which less
than 5Tc of the area was estimated to exceed 4 pCi L"1 in a reference house. Regions where
the top 5Tc of the computed indoor radon levels were between 4 pCi L"1 and 8.3 pCi L'1 were
assigned to the yellow category, indicating a need for passive radon controls in new
residential construction. Regions where the top 5Tc of the computed indoor radon levels
exceeded 8.3 pCi L"1 were assigned to the red category, indicating a need for active radon
controls in addition to passive controls. The S.3 pCi L*1 cut point was based on both
theoretical simulations and empirical measurements of the radon resistance effectiveness of
passive radon control features.
iv
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TABLE OF CONTENTS
Chapter Page No.
Abstract ii
List of Figures vi
List of Tables vii
1 INTRODUCTION 1-1
1.1 Background 1-1
1.2 Objective and Scope 1-2
2 RADON RESISTANCE OF POLYETHYLENE 2-1
VAPOR BARRIERS
3 LUMPED-PARAMETER MODEL ESTIMATES 3-1
OF FEATURE EFFECTIVENESS
3.1 Summary of Previous Analyses 3-1
3.2 Analyses of New Data 3-2
3.3 Comparisons with the Lumped-Parameter Model 3-10
3.4 Comparisons with Prior NHEP Measurements 3-14
4 RAETRAD MODEL ESTIMATES OF FEATURE 4-1
EFFECTIVENESS
5 RANKING AND GROUPING OF CONSTRUCTION FEATURES 5-1
6 DEVELOPMENT AND USE OF THE FLORIDA RADON 6-1
PROTECTION MAP
6.1 Basis of the Radon Protection Map 6-1
6.2 Development of the Radon Protection Map 6-2
6.3 Use of the Radon Protection Map 6-7
7 LITERATURE REFERENCES 7-1
v
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LIST OF FIGURES
Figure No. Page No.
1 Sample configuration for measuring the air permeability 2-4
of plastic sheeting.
2 Comparison of air permeability and radon diffusion coefficients 2-5
among the five brands of polyethylene sheeting.
3 Comparison of measured Cnct/Cwb ratios with estimates 3-13
from eqn. (2).
4 Comparison of the present C^/C^ measurements with 3-14
corresponding measurements from previous studies.
5 - Illustration of the chronological trend in Cnel/Ciub 3-16
measurements from Mono and SSW houses.
6 Soil profiles for radon entry simulations. 4-3
7 Development of the Florida radon protection map. 6-3
8 The Florida radon protection map. 6-5
vi
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LIST OF TABLES
Table No. Page No.
1 Sources and properties of the five vapor barrier plastic samples. 2-2
2 Results of radon diffusion and air permeability measurements. 2-2
3 SRI house parameters. 3-3
4 UF house parameters. 3-4
5 SRI house ventilation and soil measurements. 3-6
6 ' UF house ventilation and soil measurements. 3-7
7 Sub-slab and indoor radon measurements in SRI houses. 3-8
8 Sub-slab and indoor radon measurements in UF houses. 3-9
9 Soil profile properties for the radon entry simulations. 4-3
10 Radon transport properties of building materials used to define 4-5 ,
the reference houses.
11 Results of RAETRAD model simulations. 4-8 /
12 Ranking of residential construction features by average 5-2
radon resistance effectiveness.
vii
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1. INTRODUCTION
1.1 BACKGROUND
Radon (^^Rn) gas generated by naturally occurring radium (-Ra) in soils can enter buildings
through their foundations. With elevated entry rates and inadequate ventilation, radon can
accumulate indoors to levels that pose significant risks of lung cancer with chronic exposure. The
U.S. Environmental Protection Agency (EPA) attributes 7,000 to 30,000 lung cancer fatalities
annually to radon exposure, and recommends remedial action if indoor radon levels average four
picocuries per liter (4 pCi L"1) or higher (EPA92a,b). The EPA recommends reducing indoor radon
levels below 4 pCi L*' where possible to approach outdoor ambient levels and further reduce health
risks. Indoor radon levels average about 1.25 pCi L'1 in the United States, and exceed 8 pCi L"1 in
about 1% of all U.S. homes (EPA92c).
Although outdoor air, building materials, and water supplies can also contribute to indoor
radon, radon from soil is usually the dominant source that leads to elevated indoor radon levels. The
Florida Department of Community Affairs (DCA) has developed radon-resistant building standards
to help reduce health risks by reducing radon entry from soils (San91). The standards utilize
improved designs and understructure sealing, altered air pressures, and other engineered features
developed under the DCA's Florida Radon Research Program (FRRP) for radon control. If all of the
features were integrated into state-wide building codes, the standards could add excessively to the
cost of new residential construction. The potential cost impact is being minimized by requiring
radon resistance features only in proportion to the soil radon potential of different geographic areas.
State-wide soil radon potential maps are being developed to provide a basis for this targeted
application of engineered radon-resistance features (Nie95a).
The radon resistance effectiveness of some construction features has been estimated
previously in the Florida Radon Research Program (FRRP), EPA research, or other studies reported
in the scientific literature. The effectiveness of other features and their interactions have not been
1-1
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previously characterized. To estimate the individual contributions of different proposed features and
their interactions, mathematical models are used with measured data to help obtain a consistent
comparison of the effectiveness of each feature. Two types of models were used, including an
empirically-based lumped-parameter model, and a detailed theoretically-based numerical model
called RAETRAD (RAdon Emanation and TRAnsport into Dwellings).
1.2 OBJECTIVE AND SCOPE
This report describes a system for selecting which construction features or groups of features
are appropriate for residential construction on soils with different levels of radon potential. The
work in this report was performed by Rogers & Associates Engineering Corp. (RAE) under Task C
of a subcontract to the University of Florida GeoPlan Center under DCA contract 94RD-30-13-00-
22-003. The task includes seven technical elements, which are summarized in the following sections
of this report. Section 2 presents new measurements from Task Element 1, characterizing the radon
resistance of polyethylene vapor barriers. Section 3 summarizes the status of lumped-parameter
model estimates of construction feature effectiveness from Task Element 2. Section 4 presents
RAETTIAD model analyses of construction feature effectiveness from Task Element 3. Section 5
ranks the various construction features according to their radon resistance, and groups them
according to common practices under Task Elements 3 and 6. Section 6 identifies the radon
resistance required to achieve a 4 pCi L*1 indoor radon average, and compares the requirements with
the construction practice groups to assign minimum construction practices to each map polygon
(Task Elements 4 and 5). Section 7 describes the radon standard reference map prepared from data
from Section 6, and explains its intended uses and limitations (Task Element 7).
1-2
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2. RADON RESISTANCE OF POLYETHYLENE VAPOR BARRIERS
The radon transport properties of polyethylene vapor barriers are important to
correctly model radon entry through floor slabs. Although polyethylene membranes are
required by building codes (SBC86) and are commonly used under Florida floor slabs, their
radon transport properties have not been reported previously. Therefore, model analyses of
radon entry through floor siabs have relied only on concrete slab properties (Rog93b, Rog94a).
These analyses show that radon moves by diffusion (concentration-driven) and advection
{with pressure-driven air flow) through slab cracks and openings, and also by diffusion
through intact slab regions. Advective radon movement through intact areas is negligible for
typical pressure gradients and concrete permeability (Rog94a). Although the vapor barrier
was expected to restrict radon transport, its numerical effectiveness was unknown.
The radon transport properties of polyethylene vapor barriers were measured as part
of this task to fill the data gap and permit more accurate and detailed modeling of radon
entry. Five rolls of different commercial brands of polyethylene plastic sheet were purchased
from building supply stores in Orange and Seminole Counties in September of 1993.
Although all of the plastics were listed as "6-mil" (0.015 cm) thick, their actual thicknesses
and densities were measured in the laboratory. The sources, measured thicknesses, and
densities of each plastic are listed in Table 1. Three pieces were cut from each roll for
triplicate laboratory measurements of the radon diffusion coefficients and air permeabilities
of the plastic.
For radon diffusion measurements, 10-cm diameter circles of the plastic sheets were
mounted at the top of each of three standard radon diffusion test columns with epoxy cement.
The radon diffusion tests utilized the standard time-dependent method documented
previously for soils and concrete samples (XieS2, Rog94a). The test columns were exposed
on one side to a high, constant concentration of radon gas, while the air in a 2.5-cm gap on
the other side was monitored for alpha particle activity. The increase in alpha activity with
time from the start of exposure to the radon source was fitted to a time-dependent radon
diffusion equation to determine the radon diffusion coefficient. The results of these radon
diffusion measurements are presented in Table 2.
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Table 1. Sources and properties of the five vapor barrier plastic samples.
Measured Thickness Measured Density
Brand & Description (cm: mean =s.d., n ) (g cm*3)
1.
Film Gard: All purpose construction
grade clear plastic sheeting
0.012 =0.002,
15
2.10
2.
Frost King: No. P1016 clear plastic
sheeting
0.010 =0.001,
26
2.20
3.
Husky: Contractors choice plastic
sheeting, Poly-America, Grand Prairie, TX
0.012 =0.001,
30
2.23
4.
Sunbelt: clear plastic sheeting,
Sunbelt Mfg., Monroe, LA
0.012 =0.001,
30
2.16
5.
Sunbelt: black plastic sheeting.
Sunbelt Mfg., Monroe, LA
0.012 =0.001,
15
2.20
Table 2. Results of radon diffusion and air permeability measurements.
Plastic Brand
Measurement
Radon Diffusion Coefficient
(cm2 s*1)
Air Permeability
(cm2)
1.
Film Gard
1
3.17x10"'
l.lxlO*13
2
3.54x10*"
2.8xl0*15
3
3.94x10*'
9.6xl0'16
Mean0
3.55x10*"
6.7xl0"15
2.
Frost King
1
4,38x10*'
2.0xl0"13
2
3.54x10*"
8.7xl0*14
3
2.84x10*;
8.4xl0"15
Mean2
3.59x10"
5.3xl0*u
3.
Husky
1
3.94x10*"
1.2xl0"16
2
2,26x10*"
6.4xl0'16
3
3.94x10*"
o.lxlO46
Mean0
3.38x10"'
3.3xl0*16
4.
Sunbelt Clear
1
3.17x10*'
1.2xl0*14
2
3.54x10*'
3.9xl0*15
3
3.17x10*'
4.8xl0*14
Mean"
3.29x10*"
1.3xl0"14
5.
Sunbelt Black
1
3.94x10*'
5.4xl0*15
2
2.54x10'"
l.OxlO*14
3
2.48x10*"
7.7xl0"15
Mean0
2.99x10'"
7.4xl0*15
"Arithmetic mean of diffusion coefficients and geometric mean of air permeabilities
2-2
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An analysis of variance among the radon diffusion coefficients in Table 2 indicates
that there are no significant differences (p < 0.25) among the five different brands of plastic
sheeting. The 15 measured radon diffusion coefficients therefore can be grouped together and
represented by their overall mean value of 3.36x10"' cm2 s"1 and their standard deviation of
-6.28X10*8 cm2 s*1.
The air permeability of each of the five brands of plastic sheeting similarly was
measured in triplicate. Three large pieces of plastic (1.5 x 3.0 m) were cut from each roll, and
each was folded to form a square measuring 1.5 m on each side. The three open edges were
laminated together by heat-sealing with mylar laminating film {Figure 1). The clear
laminating film provided visual verification of a complete seal over a 2-3 cm wide border.
After sealing, a plastic tube was inserted into the face of one of the laminated sheets and
sealed with moldable sealant tape (RS-200, Richmond Aircraft Products, Richmond, VA). The
tube was connected to a permeameter for air pressure and flow measurements (MK-II, Rogers
& Associates Engineering Corp., Salt Lake City, UT). The entire assembly was then placed
on a carpeted floor surface to permit air flow even from the plastic sheet on the bottom side.
A permeability measurement was performed by filling the plastic envelope with a
known volume of air using the MK-II permeameter pump. The air volume was determined
from the measured air flow rate and the air pumping time. The valve in the tube then was
closed, and a 12 kg mass was placed on the inflated envelope to provide a sustained higher
inside air pressure. The starting time was recorded, and the mass was left on the envelope
for approximately S - 16 hours. The volume of air remaining inside the envelope was then
determined by removing the 12 kg mass, opening the tube valve, and timing the air removal
while pumping the remaining air from the bag. The air permeability of the plastic sheeting
was then calculated as
K = V p Ax / (t A AP) (1)
where K = Air permeability of the plastic sheet (cm2)
V = Air volume lost during the test (cm3)
p = Air viscosity (1.83X10"3 Pa s)
2-3
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Ax - Thickness of the plastic sheet (cm)
t = Time of pressurized air flow through the plastic (s)
A = Area of plastic sheet exposed to the air pressure (cm2)
AP = Air pressure difference across the plastic (Pa).
FcMec Side
Laminating
film
Sealed'
Sides
Plastic .
Sheeting'
Heat
Seal
12 kg weight
Carpeted
Floor
Surface
Plastic Sheets _
Being Tested
Figure 1. Sample configuration for measuring the air permeability
of plastic sheeting.
2-4
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The results of the air permeability measurements are presented in Table 2. The large
range and distribution of values for each brand suggested that the measurements were log-
normally distributed. They were therefore summarized by geometric means for each of the
brands, as shown in Table 2. An analysis of variance among the air permeability
measurements indicates that there are significant differences among the different brands
(p < 0.025). A plot of the measurements (Figure 2) suggests that the Husky brand has
significantly lower air permeability than the other brands. However for modeling purposes,
brand-specific information is seldom available, and the overall geometric mean {6.5xl0'15 cm2)
and geometric standard deviation (8.4) of the 15 measurements are recommended for general
use.
10
-6
-7
10
M <„-8
"E 10
o
S 10"9
*5
O io-10
tr
O , A-11
Q. 10
w
2 io*12
c
o
T5
ttJ
c 10
10 13
.14
-15
10
10
•16
Radon Diffusion Coefficients (cm2s*1;
Air Permeability Coefficients (cm 2)
f
Rim
Guard
Frost
King
Husky
Sunbelt
Sunbelt
Black
Figure 2. Comparison of air permeability and radon diffusion coefficients
among the five brands of polyethylene sheeting.
2-5
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3. LUMPED-PARAMETER MODEL ESTIMATES OF FEATURE EFFECTIVENESS
The effectiveness of different residential construction features in resisting radon entry has been
studied in several different building construction demonstration projects under the FRRP. These have
included two test cells and 20 houses studied by Geomet Technologies, Inc. (Geo90, Geo92), 28 houses
studied by Florida Solar Energy Center (Cum92, Tys95), 30 houses studied by Southern Research Institute
(Nie94b), and 14 houses studied by University of Florida (Naj93). Fourteen additional houses have been
studied more recently by Southern Research Institute (SRI), and twelve additional houses were studied by
the University of Florida (UF). Data from these recent studies are analyzed here for evaluating the
effectiveness of radon control features using the same net/sub-slab radon ratio and lumped-parameter model
as was used with the previous studies (Nie94b, Nie95c), in addition to the empirical interpretations provided
by the authors (Fow94).
3.1 SUMMARY OF PREVIOUS ANALYSES
The results of the first semi-empirical study (Nie94b) suggest a nominal 0.25 air change per hour
(ach) passive infiltration rate for Florida houses, associated with a passive, ventilating indoor air pressure
of -0.7 Pa relative to outdoors. Sub-slab ventilation system (SSV) effectiveness was approximated by an
80% estimate for active SSV systems and approximately 6% effectiveness for passive SSV systems. Floor
crack areas were recognized as difficult to characterize by visual inspection, but to consist of an approximate
0.2% leakage area plus an additional 0.29% that could result from a hollow foundation wall. The
effectiveness of different house construction features was compared by changes in the net indoor/subslab
radon concentration ratios
Measured CnJC^ ratios for both slab in stem wall (SSW) houses and monolithic slab houses were
highest for houses with no SSV system, were slightly lower for houses with a passive SSV system, and were
significantly lower for houses with active SSV systems. Houses with capped SSV systems were erratic,
being higher than those without SSV systems for SSW houses and lower than those without SSV systems
3-1
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for SSW houses and lower than those without SSV systems for monolithic slab houses.
Measured Cnct/C„b ratios for SSW houses averaged 2.7X10"3 for houses without SSV systems,
4.9xl0'3 for houses with capped SSV systems, 1.7xl0"3 for houses with passive SSV systems,
and 4.3X10"1 for houses with fan-activated SSV systems. Measured Cnct/Csub ratios for
monolithic-slab houses averaged 2.3xl0'3 for houses without SSV systems, 6.2X10"4 for houses
with capped SSV systems, 2.2xl0"3 for houses with passive SSV systems, and 4.4X10"1 for
houses with fan-activated SSV systems.
The results of the second semi-empirical' study (Nie95c) suggested that SSW
construction, when completed in accordance with the FRRP standard, reduces indoor radon
to about 9xl0"4 of the sub-slab concentration (with an uncertainty factor of 2.2). Capping the
SSV system does not significantly alter its radon-resistance effectiveness compared to leaving
it in a passive mode. Monolithic slab construction may improve radon resistance by
approximately 33?c, reducing indoor radon levels by a factor of 0.67 compared to SSW
construction. Activation of SSV systems with exhaust fans reduces the Cnct/CJub ratio by
approximately 70Cc, reducing indoor radon levels to about 0.3 times the levels that occur
when the SSV system is in the passive or capped mode. The measurements on active SSV
systems are sparse and uncertain, however, due to the small number of houses where the
SSV systems were activated.
3.2 ANALYSES OF NEW DATA
Data from the 1993 FRRP New House Evaluation Program CNHEP) were compiled in
terms of the parameters used in the lumped-parameter model or their surrogates. The data
were measured by SRI (Fow94) and UP (Hin94). The basic parameters for the SRI and UF
houses are summarized in Tables 3 and 4, respectively. The SRI set contained fourteen
houses, eight of which were monolithic slab-stem wall houses (Mono) and six of which had
slabs poured into stem walls (SSW). The UF set contained twelve houses, ten of which were
Mono and two of which were SSW designs. The SRI set continued the trend noted previously
for a slightly larger size for SSW houses than for Mono houses. The UF set had
approximately equivalent sizes among the two groups. Concrete slump generally averaged
3-2
-------
in the 15 to 18 cm range except for the UF SSW houses, where slabs had a 10-cm concrete
slump. Superplastirizer was used in all houses except three of the UF houses, where a low
concrete slump was maintained. All slabs were cured with either water spray or curing
compound, and all were reinforced with either wire mesh or glass fiber.
Table 3. SRI house parameters.
Base Occup. Inside Equiv.
Floor Slab
House
Area
Vol.°
Height Wid.6
No.
House
Edgec
Slump Super-
Rein- Cure
SSV
ID
(m2)
(m3)
(m)
(m)
Levels Const.
Detail
(cm)
plast/
fore.' Type^ Syst*
F-01
285
957
3.4
12.2
1
Block
Mono
20
Yes
Fiber Water
VM
F-04
182
500
2.7
9.8
1
Block
Mono
13
Yes
Wire Comp.
VM
F-05
215
591
2.7
10.
1
Block
Mono
18
Yes
Wire Comp.
VM
F-06
170
414
2.4
9.5
1
Block
Mono
18
Yes
Wire Comp.
VM
F-07
339
1135
3.3
13.4
1
Block
Mono
13
Yes
Fiber1 Water
VM
F-09
81
445
5.2
6.5
2
Frame Mono
20
Yes
Wire Water
VM
F-12
151
368
2.4
8.9
1
Block
Mono
13
Yes
Fiber Comp.
VM
F-13
167
408
2.4
9.4
1
Block
Mono
13
Yes
Fiber Comp.
VM
Mean
199
602
3.1
10.0
16
=S.D,
=81
=286
=1.0
=2.1
=4
F-02
240
659
2.7
11.2
1
Block
SSW
18
Yes
Wire Water
VM
F-03
281
856
3.0
12.2
1
Block
SSW
13
Yes
Fiber Water
VM
F-OS
343
941
2.7
13.4
1
Block
SSW
13
Yes
Wire Comp.
VM
F-10
220
603
2.7
10.8
1
Block
SSW
20
Yes
Wire Comp.
VM
F-ll
268
899
3.4
11.9
1
Block
SSW
20
Yes
Wire Comp.
VM
F-14
196
539
2.8
10.2
1
Block
SSW
20
Yes
Wire Comp.
VM
Mean
258
750
2.9
11.6
17
=S.D.
=52
=170
=0.3
= 1.1
=4
Overall
Mean
224
665
3.0
10.7
17
=S.D.
=74
=247
=0.7
=1.9
=4
"Volume of the occupied space in the house.
HVidth of the equivalent rectangular area of the house footprint.
eSlab edge detail: slab poured into stem wall (SSW) or monolithic slab (Mono).
^Superplastirizer used in the slab concrete (Yes or No).
'Slab reinforcement: wire mesh (Wire) or glass fiber (Fiber).
'Slab cured by water spray (Water) or liquid membrane curing compound (Comp.).
^Sub-slab ventilation system: ventilation mat (VM).
*Post-tensioned slab.
3-3
-------
Table 4. UF house parameters.
Base Occup. Inside Equiv. Floor Slab
House
Area
Vol."
Height Wid.6
No.
House Edgec
Slump Super-
Rein-
Cure
SSV
ID
(m2)
(m3)
(m)
(m)
Levels Const Detail
(cm)
plast.d
fore*
Typef Syst-
1
1S7
518
2.8
9.9
1
Frame Mono
10
Yes
Wire
Comp.
SP
2
216
624
2.9
10.7
1
Frame Mono
18
Yes
Wire
Comp.
SP
3
233
685
2.9
11.1
1
Frame Mono
15
Yes
Wire
Comp.
SP
4
220
641
2.9
10.8
1
Frame Mono
18
Yes
Wire
Comp.
SP
5
216
645
3.0
10.7
1
Frame Mono
18
Yes
Wire
Comp.
SP
7
321
1085
3.4
13.0
1
Frame Mono
15
Yes
Wire
Comp.
SP
9
237
590
2.5
11.2
1
Frame Mono
17
Yes
Wire
Comp.
SP
10
190
525
2.8
10.0
1
Frame Mono
15
Yes
Wire
Comp.
SP
11
195
476
2.4
10.1
1
Frame Mono
18
Yes
Wire
Comp.
SP
12
160
444
2.8
9.2
1
Frame Mono
10
No
Wire
Comp.
SP
Mean
217
623
2.8
10.7
15
=S.D.
=43
=181
=0.3
=1.0
=3
6
186
513
2.8
9.9
1
Frame SSW
10
No
Wire Comp.
SP
8
216
645
3.0
10.7
1
Frame SSW
10
No
Wire Comp.
SP
Mean
201
579
2.9
10.3
10
=S.D.
=21
=93
=0.2
=0.6
=0.0
Overall
Mean
215
616
2.8
10.6
14
=S.D.
=40
=167
=0.2
=1.0
=3
"Volume of the occupied space in the house.
HVidth of the equivalent rectangular area of the house footprint.
eSlab edge detail: monolithic slab (Mono) or slab poured into stem wall (SSW).
dSuperplasticizer used in the slab concrete (Yes or No).
'Slab reinforcement: wire mesh (Wire).
'Slab cured by liquid membrane curing compound (Comp.K
^Sub-slab ventilation system: suction pit (SP).
The major differences between the SRI and UF data sets were in the building shell
and the types of sub-slab ventilation systems. The SRI houses utilized hollow-block concrete
walls for all but one of the houses, while all twelve of the UF houses were built with frame
walls. All of the SRI houses utilized ventilation mats for the sub-slab ventilation systems,
while all of the UF houses utilized suction pits in their sub-slab ventilation systems. With
the exceptions of UF houses 6 and 10, none of the SSV systems were activated in either
3-4
-------
group. The SSV exhaust pipes were capped in both sets of houses throughout the testing
period except for SRI house F-10. The caps thus precluded passive sub-slab venting, which
was suggested previously to only reduce indoor radon levels by about 6% (Nie95c).
Measurements of house ventilation and soil parameters are summarized in Tables 5
and 6 for the SRI and UF houses, respectively. Soil air permeability data were unavailable
for the UF houses. The SRI air permeability averages were nearly identical for the Mono and
SSW houses, as were the moisture contents of the soil and fill materials. Soil moisture for
the UF houses v/as much more variable, and fill materials were not characterized for the
1993 UF houses. Measurements of soil density were only reported for the UF houses, they
averaged 1.62 g cm"3, approximately equivalent to the value of 1.6 g cm'3 that was assumed
for the SRI houses.
The permeability or leakage of the house superstructures was measured for at least
some houses in both data sets under passive pressure conditions. The SRI houses had an
average natural ventilation rate of only 0.19 air changes per hour (ach), while the UF houses
averaged 0.29 ach. The difference in these average rates may be due in part to construction
differences for the superstructures (concrete block versus frame). The difference also could
be related to different measurement methods, occupancy differences during the measurement
periods, weather conditions, or air handler locations. For example, the SRI data are
estimated from 50-Pa blower door leakage measurements (as in Nie95c), and the UF data are
measured from tracer gas data.
The average of the observed floor crack areas for the SRI houses was nore than twice
as high as the average for the UF houses. However these averages come from highly variable
data, and additional effective crack areas may be concealed (Nie95b). The SRI mean is
dominated by the SSW houses, which averaged three to five times higher than the other
groups.
3-5
-------
Table 5. SRI house ventilation and soil measurements.
Soil Air
Soil"
Fill0
Fill
Reported6
Air
Slab*
Soil**
House
Permeability
Moist.
Moist.
Depth
Nat. Vent
Handler Crk. Area Density
ID
(cm2)
{% dry) (% dry)
(cm)
(ach)
Location
(cm2)
(g cm*3)
F-01
1.1x10""
4.5
5.7
15
e
Attic
250
1.6
F-04
2.2xl0's
7.3
4.0
30
e
Attic
90
1.6
F-05
3.0xl0'9
9.5
6.0
30
0.17
Attic
43
1.6
F-06
6.4x10 s
5.4
5.0
30
0.17
Attic
0
1.6
F-07
2.4x10""
9.9
6.0
30
e
Attic
240
1.6
F-09
3.1xl0'9
11.1
13.0
30
e
Garage
0
1.6
F-12
5.0x10"*
5.5
9.0
28
0.16
Laundry
0
1.6
F-13
9.8xl0'8
5.3
9.0
30
0.30
Laundry
130
1.6
Mean
7.4X10"5
7.3
7.2
28
0.20
94
=S.D.
=7.8x10'6
=2.5
=2.9
=5
±0.07
=104
F-02
8.8xl0'5
5.3
5.3
15
0,17
Attic
610
1.6
F-03
S.4xl0"6
3.8
5.0
30
0,17
Attic
300
1.6
F-08
1.1x10'"
8.3
9.0
30
e
Attic
600
1.6
F-10
3.4x10'"
12.0
9.0
33
0.20
Garage
350
1.6
F-ll
5.7xl0's
8.3
7.0
28
e
Garage
140
1.6
F-14
3.5xlO'10
11.8
9.0
30
e
Garage
0
1.6
Mean
1,1x10'"
8.3
7.4
28
0.18
330
=S.D.
2:1.2x10*"
=3.3
=1.9
=6
=0.02
=240
Overall
Mean
9.1xl0"8
7.7
7.3
28
0.19
200
=S.D.
=9.5xl0-8
=2.8
=2.5
=6
=0.05
=210
"Moisture percentage, dry-weight basis.
Passive-condition air infiltration rate.
Total area of observed slab cracks.
^Assumed typical soil densities, since none were reported.
*Not reported.
3-6
-------
Table 6. UF house ventilation and soil measurements.
Soil Air
Soil0 Fill
Fill
Reported*
Air
Slabc
Soil
House
Permeability
Moist. Moist.
Depth
Nat. Vent
Handler Crk. Area Density
ID
(cm2)
(% dry) (9r dry)
(cm)
(ach)
Location
(cnr)
(g cm-^)
1
€
6.0 e
e
0.49
Garage
0
1.66
2
e
7.0 e
e
0.33
Garage
7.1
1.76
3
e
7.3 e
t
0.34
Garage
130
1.64
4
€
8.3 c
t
0.27
Garage
0
1.63
5
e
5.0 e
€
0.31
Garage
0
1.48
7
e
e e
e
e
Garage
410
1.62*
9
e
8.7 c
e
e
Garage
18
1.54
10
e
C C
e
e
Garage
0
1.45
11
e
9.8 *
e
0.21
Garage
0
1.62*
12
e
22.0 c
e
e
Garage
0
1.62*
Mean
9.3
0.33
57
1.59
=S.D.
=5.4
=0.10
=130
=0.11
6
t
20.0 c
e
0.26
Garage
16
1.62*
8
e
C €
e
0.38
Garage
47
1.79
Mean
20.0
0.27
32
=S.D.
=0.12
=22
i, i y
Overall
Mean
10.5
0.29
52
1.62
=S.D.
=6.2
=0.11
=120
=0.12
"Moisture percentage, dry-weight basis.
^Passive-condition air infiltration rate.
Total area of observed slab cracks.
Where density was not reported, the overall average was used.
'Not reported.
Radon measurements in the SRI soils, houses, sub-slab, and outdoor regions are
summarized in Table 7. The sub-slab ventilation systems were not activated for these
houses; therefore the measurements represent passive radon control conditions. The
measurements in Table 7 were made with interior doors open, both while the air handler was
miming and while it was turned off. Radon levels were generally similar with or without air
handler operation. The soil radon levels for some houses varied markedly from sub-slab
radon levels, but no clear trend is apparent.
3-7
-------
Table 7. Sub-slab and indoor radon measurements in SRI houses.
Air Handler Off Air Handler On AH Off AH On
TT Indoor Outdoor Subslab Indoor Outdoor Subslab
House Radon ' , „ " . , „ j _ , Ratio6 Ratio6
m t p* t -i\ Radon Radon Radon Radon Radon Radon r /n n
iu tput Li j(pC. L.i)(pCi L-i)(pCi L'1) (pCi L-'XpCi L4)(pCi L'1)
F-01
5,510
1.6
0.4
4,310
0.9
0.4
4,890
2.8x10"*
1.0x10"*
F-04
5,180
4.1
1.3
12,100
4.6
0.9
12,000
2.3x10"*
3.1x10"*
F-05
19,900
1.5
0.1
4,490
1.5
0.4
4,420
3.3x10"*
2.5X10-4
F-06
3,050
1.6
0.5
4,520
2.7
0.6
4,710
2.4x10"*
4.5x10"*
F-07
2,690
1.4
0.3
4,240
1.0
0.3
4,280
2.6X10*4
1.6x10"*
F-09
14,300
1.0
0.7
7,670
4.0x10 s
F-12
5,700
2.7
0.6
6,480
2.6
0.2
7,820
3.2x10"*
3.1x10"*
F-13
5,990
2.5
0.7
6,210
2.5
0.1
5,640
2.9x10"*
4.3x10"*
G.M.,
6,230
2.0
0.4
5,640
2.1
0.4
6,040
2.8x10"*
2.0x10"*
GSD
1.99
1.49
2.23
1.46
1.96
2.04
1.44
1.15
2.29
F-02
1,480
1.6
0.6
886
1.6
0.2
946
l.lxlO'3
l.SxlO"3
F-03
2,630
3.8
0.3
5,990
2.2
0.7
5,900
5.8x10"*
2.5x10"*
F-08
1,310
3.3
0.3
4,000
3.0
0.5
4,440
7.5x10"*
5.6x10"*
F-10
11,500
8.0
1.3
5,580
5.5
0.8
4,580
1.2xl0"3
l.OxlO"3
F-ll
2,760
1.9
0.4
4,180
1.3
0.4
4,150
3.6xl0"4
2.2x10"*
F-14
2,510
3.1
1.3
8,270
2.4
1.1
4,680
2.2x10-*
2.9x10"4
G.M.,
2,720
3.1
0.6
4,000
2.4
0.5
3,610
6.0x10"*
4.9X10"4
GSD
2.17
1.77
1.97
2.19
1.66
1.83
1.95
1.93
2.21
Overall
G.M.,
4,370
2.5
0.5
4.810
2.2
0.4
4,840
3.9xl0"4
3.0x10"*
GSD
2.27
1.67
2.07
1.82
1.80
1.96
1.75
1.81
2.46
°From SRI screening measurements (Fow94).
6Based on semi-continuous estimates, excluding non-equilibrium conditions (Fow94).
Radon measurements in the UF soils, houses, sub-slab, and outdoor regions are
summarized in Table 8, The sub-slab ventilation systems were only activated for one SSW
house and one Mono house, as shown. Outdoor radon levels were apparently defined
generically for all of the houses to obtain the 0.5 pCi L"1 outdoor concentration. Sub-slab
concentrations were consistently lower than soil radon concentrations, except for the two
cases where the SSV system was operating. This suggests that the sub-slab values were
measured in the suction pits, giving the apparent negative bias. Therefore the Cncl/Csub ratios
3-8
-------
for passive conditions were computed using the larger of either the soil radon concentration
or the sub-slab radon concentration to avoid possible bias due to radon dilution by the air in
the suction pits. The resulting ratios are tabulated in the next-to-last column of Table 8 for
passive SSV conditions and in the last column for active SSV operation.
Table 8. Sub-slab and indoor radon measurements in UF bouses.
Passive SSV
Active SSV
Passive
Active
Soil
Indoor
Outdoor
Subslab
Indoor
Radon
Radon
House
Radon
Radon
Radon
Radon
Radon
Ratio
Ratio
ID
(pCi L"1)
(pCi L*1)
(pCi L'1)
(pCi L'1)
(pCi L*1)
Cn«.t/G«ib
1
1,680
2.3
0.5
730
l.lxlO"3
2
2,940
3.0
0.5
970
8.5X10"4
3
1,190
2.2
0.5
488
1.4xl0'3
4
911
2.7
0.5
809
2.4xl0'3
5
2,900
2.5
0.5
1,220
6.9X10"4
7
921
1.2
0.5
722
8.7xl0"4
9
1,300
0.5
10
1,060
10.9
0.5
3,870
2.9
2.7xl0"3
e.ixio'4
11
10,700
2.8
0.5
8,480
2.2X10"4
12
6,980
0.5
G.M.,
2,070
2.8
0.5
5,840
l.OxlO*3
e.ixio-4
GSD
2.38
1.86
1.00
1.46
2.9
2.20
6
1,110
4.2
0.5
7,490
1.8
4.9xl0'4
1.7X10*4
8
6,610
2.7
0.5
289
3.3xl04
G.M.,
2,710
3.4
0.5
3,590
4.1xl0"4
1.7xl0"4
GSD
3.53
1.37
1.00
1.94
1.8
1.32
Overall
G.M.,
2,170
2.9
0.5
4,660
2.2
8.4x10"*
3.2X10"4
GSD
2.40
1.75
2.09
1.76
1.42
2.23
2.51
3-9
-------
For consistency with the Cnet/Csub calculations in Table 8, the corresponding Cr ^CSVlb
ratios for Table 7 were also computed using the maximum of either the soil radon
concentration or the sub-slab radon concentration. The resulting geometric mean and GSD,
combining air handler operation conditions, were 1.6X10*4 (GSD=2.68) for the Mono houses
and 4.2X10"4 (GSD=1.70) for the SSW houses. These values are up to about 507c lower than
the corresponding averages of the data in Table 7.
3.3 COMPARISONS WITH THE LUMPED PARAMETER MODEL
The measured Cnet/Csub ratios reported in Tables 7 and 8 for the SRI and UF houses
were compared with corresponding Cnet/C,.ub ratios that were calculated using the lumped
parameter model as reported previously (Nie94b, Nie95c):
Cnec/Csab = (3.6 f#sv/luh) {fc[l/70 + APexp(-3-0.045e6S)]
+ 2.9x10"" e114W + 4.6xl0"5/xh + 3.5xl0-5(xcrk/xh)}, (2)
where Cnet = net indoor radon concentration (indoor-outdoor, pCi L"1)
Csub = sub-slab radon concentration (pCi L'1)
3.6 = unit conversion (pCi L"1 h'1 per pCi m'3 s*1) .
fssv = sub-slab ventilation factor (dimensionless)
h = mean height of house interior (m)
Xh = rate of house ventilation by outdoor air (h*1)
fc = crack area fraction (dimensionless)
1/70 = diffusive component of effective radon entry velocity (mm s'1)
AP = indoor-outdoor air pressure difference (Pa)
S = soil water saturation fraction (dimensionless)
W = slab concrete water/cement ratio (dimensionless)
xh = house minor dimension (m), from equivalent rectangular footprint
xcrk = location of the dominant floor openings from the house perimeter (m).
3-10
-------
The parameters used in equation (2) were defined primarily from site-specific
measurements or surrogates. For the SRI houses, the sub-slab ventilation systems were not
active, so the ventilation factor was defined as fuv = 1. The heights of the houses were
defined from the measurements listed in Table 3. The passive-condition ventilation rates
were defined from the measured values in Table 5. Where measured values were
unavailable, \ = 0.25 h"1 was assumed, corresponding to typical FRRP ventilation rates
observed previously (Nie95c). The slab crack area fraction, fc, was defined by dividing the
slab crack areas reported in Table 5 by the slab areas in Table 3. The indoor-outdoor air
pressure difference was defined genericallv as AP = -0.52 Pa, corresponding to previous
estimates (equation [20] in Nie9oc). The soil water saturation fraction was defined from
moisture measurements in Table 5 using the relation:
S = 0.01 p pg M / (pg - p) (3)
where p = soil density (bulk dry basis, g cm*3)
pg = soil specific gravity (g cm"3)
M = soil water content (Tr, dry %veight basis).
The water/cement ratio, W, was defined as in the previous study (Nie95c) from the
concrete slump (listed here in Table 3) as:
W = (0.0144 Sc + 0.48) V (4)
where Sc = slump of poured concrete (inches)
V = 0.9 if superplasticizer was used, or 1.0 otherwise.
The house width, xh, was also defined from Table 3, and the dominant crack position, x„k,
was defined as zero (dominated by perimeter cracks for SSW houses, and unknown but of
small consequence for Mono houses).
3-11
-------
For similar calculations of C^/C^g, for the UF houses, the sub-slab ventilation factor
was again defined as fMV = 1 for the passive-house conditions. Since no changes in sub-slab
radon levels were reported for active-SSV conditions, there was no basis to define f^, for the
active SSV system. Therefore, equation (2) was not applied for the active-SSV conditions.
The heights of the houses were defined from measurements listed in Trble 4, and passive-
condition ventilation rates were defined from the measured values in Table 6. Where
measured ventilation rates were not reported, Xh = 0.25 h*1 was assumed, corresponding to
typical FRRP ventilation rates observed previously (Nie95c). The slab crack area fraction,
fc, was defined by dividing the slab crack areas in Table 6 by the slab areas in Table 4. The
indoor-outdoor air pressure difference, AP, was defined as in the previous study (equation [20]
in Nie95c) from blower-door pressure exponents that averaged approximately -1.0 ± 0.5 Pa
for the UF houses. The soil water saturation fraction was defined from equation (3) using
soil moisture measurements from Table 6. The water/cement ratio was defined from equation
(4) using concrete slump estimates from Table 4. The house width, xh, was defined from
Table 4, and the dominant crack position, xCTk, was again defined as zero, corresponding to
a perimeter position for any measured crack openings.
The results of the lumped-parameter calculations of Cnet/Csub are summarized in
Figure 3. The measured ratios for the SRI houses are lower than the calculated values by
factors of 3.7 for the eight Mono houses and 1.4 for the six SSW houses. The primary cause
of the lower measured ratios is estimated to be the greatly improved sealing of slab
penetrations by SRI in the present study (Fow94). Since the Mono houses have virtually no
advective radon entry routes other than slab penetrations, the greatest difference was noted
for the SRI Mono houses. The SSW houses, despite improved sealing of penetrations, still
have permeable channels at the stem walls where advective radon entry can occur.
3-12
-------
10 *2
n
3
d°
0)
c
O
10
-3
10
-4
Passive Controls
JUL
(n = 10)
SRI
(n = 8)
Active
SSV
he
(n = 1)
o
• Measured
o Calculated
Monolithic Slab & Footing
Passive Controls
SRI
(n = 6)
UF
(n = 2)
I
Active 3
SSV i
HE
(n = 1)
Slab Poured Into Stem Wall
Figure 3. Comparison of measured Cnet/Club ratios with estimates from eqn. (2).
The ten UF Mono houses show closer agreement between measured and calculated
radon ratios, differing by an average factor of 1.74 (with la error bars of more than a factor
of two on both the measured and calculated averages). The closer agreement suggests better
consistency with the previous radon resistance effectiveness on which equation (2) is based.
The two UF SSW houses have significantly lower measured radon ratios than the calculated
values (by an average factor of nearly 2.7). This lower ratio may reflect better construction
technique; however it is more uncertain because only two houses are being compared.
The active-SSV systems represented in Figure 3 are difficult to evaluate, since only
one house was studied in each of these categories. Furthermore, the measured data were
inadequate to compare the measured ratios with equation (2). Therefore no conclusions are
drawn solely from these two points.
3-13
-------
3.4
COMPARISONS WITH PRIOR NHEP MEASUREMENTS
The present NHEP measurements of CMt/Cmh ratios can be interpreted better with
the perspective of the two prior sets of NHEP house studies by the present contractors and
others. For consistent comparisons with the prior studies, houses where sub-slab radon
concentrations were below 1,000 pCi L"1 were excluded, since houses built on a low-radon lot
provide an insensitive measure of radon-resistance effectiveness. The prior studies,
summarized in Nie94b and Nie95c, primarily covered the FY-91 and FY-92 budget periods
when the earlier work was performed. The present measured ratios are compared
with corresponding ratios from the individual former studies in Figure 4. The two FSEC sets
of Mono houses show excellent consistency, and are intermediate between the Geomet *91 and
SRI '91 sets and the UF *92 set and the present SRI data set. The geometric mean of all of
the passive Mono houses in Figure 4 is o.oxlO"4 (GSD = 3.14).
3
W
o
o
o
*o
2
3
in
CO
&
-2
10
-3
10
10
10
Passive Controls
GEOMET
S1
FSEC
SI
SRI
91
UF
92
SRI
S3
FSEC
92
UF
52
Active SSV
UF
93
FSEC
92
SRI
91
Monolithic Slab & Footing
Passive Controls
Active SSV
GEOMET
91
FSEC
81
UF
92
SRI
91
FSEC
92
SRI
93
UF
S3
FSEC
91
SRI
91
FSEC
92
UF
93
L"F
92
Slab Poured Into Stem Wall
Figure 4. Comparison of the present Cnet/Ctub measurements with corresponding
measurements from previous studies.
3-14
-------
The present C^/C^ ratios for passive SSW houses are in the same range as the
FSEC "92 and UF '92 data, but the present data average slightly lower. The present data are
well below the range of the FSEC *91, the Geomet '91, and the SRI "91 studies. The
geometric mean of all of the passive SSW houses in Figure 4 is l.lxlO'3 (GSD = 3.02). The
52 SSW houses comprising this estimate therefore are approximately half as resistant to
radon entry as the 43 Mono houses (averaged from Figure 4).
Since passive radon controls generally provided adequate radon protection, the SSV
systems were not activated for study in many of the NHEP houses. The data for estimating
the effectiveness of active SSV systems is therefore much more limited. The geometric mean
of the seven Mono houses represented in Figure 4 with active SSV systems is 3.3xl0'4
(GSD = 1.51). The geometric mean of the 17 SSW houses represented in Figure 4 with active
SSV systems is nearly identical at 3.4xl0"4 (GSD = 2.58).
The Cncl/Csub ratios summarized in Figure 4 suggest a chronological improvement in
radon control. If all of the studies are averaged by the approximate period when they were
performed, the data in Figure 4 can be presented as shown in Figure 5. The systematic
improvement in radon control suggested by Figure 5 may potentially be attributed to
increasing experience in building the passive radon control features. At least some of the
1991 studies included older houses (built before the radon standard) or allowed builders to
build Mono and SSW houses according to their own selection of passive control features from
the then-current Florida residential radon standard. In some of the later studies, closer
surveillance and training by FRRP researchers assured that most or all of the desired radon-
resistant features were actually incorporated. As shown by comparison with the
ratio calculated for the radon map reference house, the NHEP measurements in the 1951
period averaged about equivalent to the reference house, and the SSW houses had somewhat
less radon resistance.
3-15
-------
O Slab in Stem Wall
® Monolithic Slab
A
3
CO
Reference House
(n = 27)
(n = 18)
(n = 8)
(n = 17)
(n = 14)
FY-91
FY-92
FY-93
Figure 5. Illustration of the chronological trend in C ,/C b measurements for
Mono and SSW houses.
3-16
-------
4. RAETRAD MODEL ESTIMATES OF FEATURE EFFECTIVENESS
The effectiveness of different residential construction features in resisting radon entry
was evaluated by numerical simulations with the RAETRAD computer model in addition to
the empirical evaluations presented in Chapter 3. The simulations utilized reference houses
and soil profiles to compare indoor radon levels with and without the building feature being
evaluated. The effectiveness of each feature was defined as the ratio of the reference indoor
radon concentration (without the feature) to the indoor radon concentration with the feature
(C^c/Cf,,,^). This chapter describes how the simulations were conducted and presents the
simulation results.
Although building features and soil characteristics are interactive and cannot always
be separated to estimate a unique effectiveness factor, many features are relatively
independent. This independence permits direct estimation of the individual contribution of
a particular feature to radon resistance. For features that are interactive, several different
reference houses are defined so that the feature effectiveness can be evaluated with the
different interactions. The features evaluated were chosen from those recommended in the
1991 version of the Florida Standard for Radon-Resistant Building Construction (DCA91).
These features include the effects of fill soil compaction, sub-slab vapor barriers, slab
reinforcement, reinforcement of re-entrant slab corners, sealing of slab penetrations, closure
and sealing of large slab openings, reduction of water/cement ratio (as estimated by reduced
concrete slump), and use of different slab edge details.
The RAETRAD model has been used and compared previously with Florida residential
housing and FRRP research structures (Nie94c, Nie94a). This model provides a numerical-
analytical calculation of radon entry into houses of different size, shape, and construction
design. The model houses are analyzed on user-defined soil profiles. The soil properties
include density, porosity, textural classification, water content, radium concentration, radon
emanation coefficient, radon diffusion coefficient, and air permeability. RAETRAD features
complete multiphase calculations of radon generation and transport to properly include
moisture effects on the radon entry simulations (Rog91a, Rog93a).
4-1
-------
The houses were modeled on a 4.3-m soil profile that was divided into ten layers for
calculation purposes. The top layer consisted of 30 cm of fill soil, and the others were
comprised of native materials, as illustrated in Figure 6 and as defined parametrically in
Table 9. The soil density in layers three through ten was defined from an average of the soils
listed in the Alachua County Soil Survey (Tho85). The top two layers were considered
disturbed, and their density was defined as 879c compaction for uncompacted soils and 92%
compaction for compacted soils. The maximum dry density for sandy soils also was defined
from Alachua County Soil Survey data (ThoS5) as 1.80 g cm*3 for estimating the compacted
and uncompacted soil densities. Soil porosity was calculated as
p = 1 - p/pg (5)
where p = porosity (cm3 pore space per cm3 total space).
The porosity calculations assumed a specific gravity of 2,7 g cm"3. The depth of the water
table was defined as 2.5 m, and soil water contents were defined from the position of the
center of the soil layer above the water table (Nie92). Water saturation fractions were
calculated as in equation (3). Radon diffusion and air permeability coefficients were defined
from soil moisture, porosity, and particle size (Rog91b), assuming a sandy soil textural
classification (SCS75). All soil radium concentrations and radon emanation coefficients were
defined as 4 pCi g'1 and 0.55.
4-2
-------
Natural
Grade
Slab^^
Footing
Layer 1 (re-compacted fill)
Layer 2 (re-compacted)
Layer 3 (undisturbed)
Layer 4 (undisturbed)
Layer 5 (undisturbed)
Layer 6 (undisturbed)
Layer 7 (undisturbed)
Layer 8 (undisturbed)
®«^250 cm depth
N/yys..-. -
Layer 9 (undisturbed)
Water Table kkk
Layer 10 (undisturbed)
Figure 6. Soil profiles for radon entry simulations.
Table 9. Soil profile properties for the radon entry simulations.
Depth to
Radon
Water
Layer
Soil
Soil
Water
Diffusion
Air
Layer
Table
Height
Density
Soil
Water
Saturation
Coeff.
Permeability
No.
-------
A significant interaction between radon transport through the slab and the construction detail
at the slab edge was noted in preliminary simulations. Therefore three separate reference houses
were defined to evaluate feature effectiveness for houses with three different slab-edge details:
floating slab, slab poured into stem wall (SSW), and monolithic slab. Other features of the houses
were analyzed for each of these reference cases. The reference houses were defined to have a
footprint area measuring 8.6 x 16.5 m (28.4 x 54.3 ft.), and an interior height of 2.4 m (8 ft.) for the
occupied space. The indoor air pressure and air exchange rate with outside air were defined
respectively as -2.4 Pa and 0.25 h"\ consistent with previous model analyses to represent Florida
housing (Nie94b). A 30 cm layer of fill soil was placed above grade beneath the floor slab of the
slab on grade houses.
The foundation footing extended to 61 cm below grade for the floating-slab and SSW houses,
and to 30 cm below grade for the monolithic-slab house. The foundation concretes were defined to
have a radon source term (product of radium concentration and radon emanation coefficient) of 0.07
pCi g*!, consistent with previous measurements on Florida residential concretes (Rog94a). The
radon transport properties of the slab and foundation details are presented in Table 10. The poured
concrete physical and transport properties are based on laboratory measurements on samples cored
from Florida residential floor slabs. The samples measured are estimated to have a slump of
approximately 20 cm (8 inches). The permeability coefficients for concrete block are based on
estimates from unpublished measurements of advective radon transport through concrete blocks by
the Air and Energy Engineering Research Laboratory* of the U.S. Environmental Protection
Agency (Research Triangle Park, NC). Estimates of radon diffusion in concrete blocks are based
on block geometry and density, and correlations of concrete diffusion coefficients with density
(Rog94a).
* Now the National Risk Management Research Laboratory.
4-4
-------
Table 10. Radon transport properties of building materials
used to define the reference houses.
Radon Air
Water Diffusion Permeability
Material Density Porosity Saturation Coefficient Coefficient
(g cm"3) (cm3 cm*3) (fraction) (cm2 s"1) (cm2)
Poured Concrete
2.1
0.22
0.40
lJxlO"3
l.lxlO*12
Concrete Block (hollow)
1.2
0.56
0.40
2.2xl0"2 Q
9.4x10*® 0
Concrete Block (solid)
2.0
0.26
0.40
2.9X10"3
1.3x10-*
Polyethylene Vapor
2.1S
1.00
0.00
3.4x10"
4.3xl013
Barrier"
"Horizontal coefficient; vertical coefficient is 4.1 times higher.
^Nominal 0,015 cm (6 mil) thick.
The floating slab house was defined to have a 0.5 cm perimeter shrinkage crack
between the slab and the stem wall. The crack volume was estimated to contain soil with
a porosity of 0.60, a radon diffusion coefficient of 0.06 cm2 s"\ and an air permeability of
4x10'° cm2. The bottom 30 cm of the footing was defined as poured concrete, and the next
two 30-cm layers were defined as hollow concrete block. The top 10 cm of the footing was
defined to be capped with a solid concrete block. The properties of these components are
listed in Table 10. The vapor barrier, when used, extended beneath all of the slab, but not
into the stem wall or beneath the perimeter crack.
The SSW house similarly was modeled to have a perimeter crack at the outer edge of
the slab, where it is poured into the chair block. Although this crack ideally does not exist,
it is included for two reasons. First, observations of typical construction practice suggest that
the SSW slabs often have small cracks and openings at their interface with the chair blocks.
Second, the porosity of the chair block walls is sufficient to correspond to a significant
opening at this location (Nie95b). The crack was represented by the same width and
properties as the perimeter crack for the floating slab case. The footing for the SSW house
was identical to that for the floating slab house except on the top layer, where the solid block
cap was replaced by poured concrete properties. The vapor barrier, when used, extended
beneath all of the slab, but not into the stem wall.
4-5
-------
The monolithic slab and stem wall house was modeled with no perimeter cracks or openings,
and consisted of a continuum of poured concrete (as defined in Table 10). Its footing extended only
30 cm below the fill soil into the native terrain, instead of the 61 cm used for the SSW and floating
slab houses. The vapor barrier, when used, extended beneath both the slab and the footing.
The effect of varying concrete slump was expressed by varying the radon diffusion
coefficient of the concrete. As reported previously (Rog94a), the diffusion coefficient of concrete
varies with its density, which in turn varies with the slump of the poured concrete. The diffusion
coefficient of concrete with a 10-cm (4-inch) slump was estimated to be 6.7x10"4 cm2 s"\ compared
to a diffusion coefficient of 1.3xl0*3 cnr S? for concrete with a 20-cm (8-inch) slump. An
intermediate value was estimated for the 15-cm (6-inch) slump concrete using the same trend.
Analyses characterizing slab reinforcement were performed to represent three possible
conditions: cracking due to non-reinforced slabs, reduced cracking due to reinforced slabs, and the
absence of any cracking related to slab shrinkage or settlement. The non-reinforced case was
represented by modeling the equivalent of a single crack through the midpoint of the slab. Its area
was defined to represent a conservative shrinkage fraction of 6x10""1, which has been estimated to
produce a crack approximately every 8.5 m (Ytt87). Reinforced slabs were considered to utilize
15x15cm 10-gauge wire mesh reinforcement (specification of 6x6x10), which produces smaller
cracks spaced at approximately 3 m (Acr90). Although this would cause approximately four cracks
in the reference house slab, the cracks were combined into a single crack of equal total area for
model calculation purposes. For all of the crack simulations, the sub-slab vapor barrier was
considered to remain intact because of the relatively small size of the shrinkage cracks. Separate
analyses also were performed without shrinkage cracks as a reference for analyzing other
construction features.
Further analyses estimated the effects of cracks from re-entrant slab corners that have no
additional reinforcement beyond the wire mesh in the slab. These analyses assumed either no
cracking if the comer is further reinforced, or a single crack of approximately 2.1m length and 0.019
4-6
-------
cm width if the comer is not further reinforced. The crack length is based on an average measured
crack length and a width that is typical of cracks in mesh-reinforced slabs. The sub-slab vapor
barrier was also considered to remain intact in this case because of the relatively small size of the
comer-induced cracks.
Slab penetrations by pipes and other utilities were modeled to compare radon entry for cases
where the penetration joint was not sealed to cases where it was effectively sealed. The penetration
openings were estimated to have a total area corresponding to all of the plumbing, gas, and electrical
penetrations through a slab. They were grouped for calculation purposes to occur in three separate
locations in the slab, and their total area was equally distributed among the three equivalent locations
in the interior area of the slab. The sub-slab vapor barrier was assumed to be open beneath the
penetration cracks for cases where they were unsealed, and closed for cases where they were sealed.
The analyses utilized compacted fill soil, and assumed that any penetration cracks or openings that
were sealed did not permit radon entry.
Similar analyses were conducted to compare the effects of larger slab openings with analyses
where the openings were sealed. The larger openings were represented by a single 30 cm by 30 cm
opening, which is typical of plumbing access openings beneath bath tubs or showers (Hen93). The
sub-slab vapor barrier was assumed to be open beneath this opening for cases where the opening was
not closed and sealed. The analyses utilized compacted fill soil, and assumed that if the opening
were sealed, it did not permit radon entry beyond that which would occur for a corresponding area
of intact concrete over a continuous vapor barrier membrane.
Indoor radon concentrations were computed from all of the model simulations based on the
calculated radon entry rates and an indoor air ventilation rate of 0.25 air changes per hour. The
results of these calculations are presented in Table 11.
4-7
-------
Table 11. Results of RAETRAD model simulations.
Slab"
Concr/
Concrete*
Sea/
Indoor*
Edge
Compact4 Vaporc
Slump
Reinforcement
SSW
Radon
Detail
Fill Barrier
(cm)
Slab
Corners Opening Penetr.
System
(pCi L"1)
Floating
X Y
20
—
Y
Y
Y
N
5.229
Floating
Y Y
20
—
Y
Y
Y
N
5.264
Floating
X N
20
—
Y
Y
Y
N
8.985
Floating
Y N
20
—
Y
Y
Y
X
9.350
Floating
Y Y
20
Y
Y
Y
Y
X
5.316
Floating
Y Y
15
Y
Y
Y
Y
X
4.917
Floating
Y Y
10
Y
Y
Y
Y
N
4.546
Floating
Y Y
20
—
Y
Y
X
X
5.702
Floating
Y Y
20
X
Y
Y
Y
X
5.285
Floating
Y Y
20
Y
X
Y
Y
X
5.318
Floating
Y Y
20
X
Y
X
Y
X
5.780
SSW
X Y
20
Y
Y
Y
X
3.563
SSW
Y Y
20
...
Y
Y
Y
X
3.637
SSW
X X
20
...
Y
Y
Y
X
7.380
SSW
Y X
20
...
Y
Y
Y
X
7.790
SSW
Y Y
20
Y
Y
Y
Y
X
3.701
SSW
Y Y
15
Y
Y
Y
Y
X
3.313
SSW
Y Y
10
Y
Y
Y
Y
X
2.943
SSW
Y Y
20
...
Y
Y
X
X
4.081
SSW
Y Y
20
X
Y
Y
Y
X
3.660
SSW
Y Y
20
Y
X
Y
Y
X
3.704
SSW
Y Y
20
X
Y
X
Y
X
4.159
Mono
X Y
20
...
Y
Y
Y
X
2.967
Mono
Y Y
20
...
Y
Y
Y
X
3.029
Mono
X X
20
...
Y
Y
Y
N
7.365
Mono
Y X
20
...
Y
Y
Y
X
7.808
Mono
Y Y
20
Y
Y
Y
Y
X
3.108
Mono
Y Y
15
Y
Y
Y
Y
X
2.652
Mono
Y Y
10
Y
Y
Y
Y
X
2.213
Mono
Y Y
20
—
Y
Y
X
X
3.497
Mono
Y Y
20
X
Y
Y
Y
N
3.057
Mono
Y Y
20
Y
N
Y
Y
X
3.112
Mono
Y Y
20
X
Y
N
Y
X
3.568
"Floating slab, slab poured into stem wall, or monolithic poured slab and stem wall.
6Fill soil compacted to 92?c (Y), or left at ST^ of maximum dry density (N).
c0.015 cm (6 mil) polyethylene vapor barrier under slab (Y>» or absent (X).
rfSlump of concrete as poured (cm).
'Reinforcement with wire mesh in slab or bars in re-entrant corners (Y or N), or no slab crack (—).
'Sealed large openings in slab or small openings around utility pipe penetrations (Y or N).
'Sub-slab soil ventilation system (Y or X).
*Indoor radon concentration reported with excess digits for comparison purposes only.
4-8
-------
The effects on radon entry and indoor radon concentrations of compacting the fill soil
are relatively small and nearly independent of slab edge detail. Soil compaction increases
the indoor radon levels by factors of 1.04 for the floating-slab house, 1.04 for the SSW house,
and 1.03 for the monolithic-slab house. Vapor barrier effectiveness exhibited a much larger
effect, which varied for the different slab edge detail cases. The sub-slab vapor barrier
reduced indoor radon levels by factors of 0.58 in floating-slab houses, 0.61 in SSW houses,
and 0.44 in monolithic-slab houses. Improved concrete in the floor slabs similarly had a
significant effect that varied with the slab edge detail of the houses. Reducing the concrete
slump from 8 inches to 4 inches lowered indoor radon levels by a factor of 0.86 for floating-
slab houses, 0.80 for SSW houses, and 0.71 for monolithic-slab houses. The intermediate
slump case gave an intermediate benefit of 0.92 for floating slab houses, 0.90 for SSW houses,
and 0.85 for monolithic-slab houses.
Slab reinforcement by wire mesh reduced the overall crack areas, but increased their
total length. As a result, slab reinforcement increased indoor radon by the following very
small factors: 1.003 for floating slab houses, 1.004 for SSW houses, and 1.017 for monolithic
slab houses. Reinforcement of re-entrant corners of the slab with reinforcing bars had even
smaller effects because of the smaller crack areas involved. These effects were therefore
considered negligible.
Sealing of slab penetration joints reduced indoor radon levels by factors of 1.23 for the
floating slab house. 1.08 for the SSW house, and 1.04 for the monolithic slab house. Similar
sealing of the large opening reduced indoor radon by factors of 1.24 for the floating slab
house, 1.09 for the SSW house, and 1.06 for the monolithic slab house.
4-9
-------
5. RANKING AND GROUPING OF CONSTRUCTION FEATURES
The relative effectiveness of the various house construction features in reducing radon
entry was used to rank the features in order of their importance to radon resistance. The
effectiveness factor for each feature was defined as the ratio of the indoor radon concentration
for the reference case divided the radon concentration with the feature. The resulting
features then were ranked in descending order of effectiveness. The reference case was
defined similar to existing practice (without the proposed radon standard) to be a floating
slab house with no SSV system. The reference house had a relatively low air ventilation rate
(0.25 air changes per hour), and had a sub-slab vapor barrier, since this is generally used,
and is required by some building codes. The house floor slab was made from 20-cm (8-inch)
slump concrete, and slab openings and penetrations were left unsealed. The slab was
reinforced with wire mesh, but re-entrant corners were not reinforced. The fill soil was not
compacted.
The resulting rank-ordered list of radon resistance effectiveness factors is presented
in Table 12. As indicated, several of the effectiveness factors were grouped because of their
dependence on slab edge details, and their values were averaged to obtain an average
effectiveness. The average factor used to represent the feature is listed in the last column
in Table 12. For cases where the most radon-resistant approach was already the standard
building practice, the factors were less than unity. In these cases, the feature ranking was
listed as the reciprocal of the factor, but the factor was not considered for inclusion in the
proposed standard because it is already being utilized.
A further grouping of features was performed to distinguish active radon control
features from passive features. The distinction between active and passive included both the
use of mechanical control and the association of a continuing cost with operation of the
feature. Thus, all of the features in Table 12 are considered passive except for the SSV
system (because it is fan-driven) and the enhanced ventilation option (because it either
requires a heat exchanger or will incur heating/cooling costs from the air handler). The
passive features may have an initial cost, but no continuing costs except for those associated
with normal house maintenance.
5-1
-------
Table 12. Ranking of residential construction features
by average radon resistance effectiveness.
Effectiveness Summary Ranked
Construction Feature Crf/Cfgatur< Relative to Effectiveness
1.
Active SSV system
4.45
No SSV
4.45
2a.
No vapor barrier - floating slab
0.57
6 mil v. barrier
0.48 (2.1)
2b.
No vapor barrier - SSW
0.47
6 mil v. barrier
2c.
No vapor barrier - monolithic
0.40
6 mil v. barrier
**
3.
Enhanced ventilation
2
0.25 ach
2
4 a.
Monolithic slab & stem wall
1.76
Floating Slab
1.62
4b.
Slab poured into stem wall
1.47
Floating Slab
"
5a.
10-cm concr. slump - floating slab
1.17
20-em slump
1.33
5b.
10-cm concr. slump - SSW
1.26
20-cm slump
«v
5c.
10-cm concr. slump - monolithic
1.40
20-cm slump
9*
6a.
15-cm concr. slump - floating slab
1.06
20-cm slump
1.15
6b.
15-cm concr. slump - SSW
1.12
20-cm slump
"
6c.
15-cm concr. slump - monolithic
1.17
20-cm slump
**
7.
Seal slab openings & cracks
1.15 "
Unsealed
1.15
8.
Seal slab penetrations
1.13
Unsealed
1.13
9.
Seal openings & large cracks
1.10
Unsealed
1.10
10.
Passive SSV system
1.07
No SSV
1.07
11.
Compacted fill soil
0.98
Uncompacted
0.98 (1.02)
12.
Non-reinforced slab
1.01
Reinforced
1.01
13.
Reinforced re-entrant corners
1.001
Non-reinforced
1.001
Passive Group 4, 6, S, 9 Average (Minimum)
2.3 (2.1)
Active plus Passive Group Average (Minimum)
10.3 (9.3)
Selection of building features for inclusion in the radon building standard was made
to exclude those already required by existing building codes. Features with negligible
effectiveness Mess than ten percent) also were eliminated. The remaining features were then
considered on the basis of their associated costs and effectiveness.
For the passive features, slab-edge detail was dominant, and is recommended as the
prime radon control feature for new construction. The second most effective feature, lower
slump concrete, is also recommended because of its minimal cost and significant radon
reduction. Sealing of slab penetrations also has significant benefit despite some initial costs
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and the possibility of subsequent maintenance requirements. Sealing of large floor openings
and cracks also is recommended, since these can be readily identified, are likely to be
completed successfully, and have significant radon reduction benefit. Together these four
features, identified at the bottom of Table 12, give an average passive radon resistance
effectiveness of a factor of 2.3. However, since SSW houses may have significantly lower
radon resistance effectiveness, a more conservative (passive-group) value of 2.1 was
determined for use in radon map development, based on the 1.47 factor for SSW construction
(item 4b in Table 12). The remaining radon resistance features contribute little to further
radon reduction, and in some cases (such as passive SSV systems) are associated with
significant initial construction costs.
For the active features, the SSV systems (either suction pit type or ventilation mat
type) are most effective when costs are considered, and are recommended as the only active
feature for inclusion in the standard. The effectiveness listed in Table 12 may be a
minimum, since active SSV systems nationwide are usually considered to have an
effectiveness of at least a factor of ten or more (sometimes approaching a factor of 100)
(Hen93). The number in Table 12 represents an average of the few cases where an FRRP
study house had the SSV fan activated, however, and is used conservatively until additional
data become available for Florida houses. Enhanced ventilation, while potentially effective,
incurs a continuing cost that generally is unacceptable except in temporary situations.
Therefore the active radon control system, when used alone, is estimated to reduce indoor
radon by at least a factor of 4.45. When used with the average passive features, the house
radon resistance is increased to a factor of 10.3. From cost/benefit considerations, the set of
passive features should always be incorporated with the active SSV system wherever active
radon control is needed.
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6. DEVELOPMENT AND USE OP THE FLORIDA RADON PROTECTION MAP
A Florida Radon Protection Map was developed for use by the DCA with the 1994
proposed Florida Standard for Radon Resistant Residential Building Construction (the
proposed Standard) (DCA94). This map is designed to show where the proposed Standard
requires active radon controls, where it requires passive radon controls, and where it requires
no controls beyond existing building codes and construction practices. The map supports the
proposed Standard's protection of public health in proportion to risk and helps avoid the costs
of radon controls where they are not justified. The radon protection map is based on the
proposed Standard's goal to keep indoor radon as low as reasonably achievable, not to exceed
4 pCi L"1. This section describes the basis and development of the radon protection map and
its intended use and interpretation.
6-1 BASIS OF THE RADON PROTECTION MAT
The radon protection map is based on a state-wide data base and map of soil radon
potential (Nie95a), the radon resistance effectiveness of the group of passive radon control
features identified in Section 5 of this report, and a cost-benefit analysis performed to
determine the appropriate margin of safety for the radon protection map (Rog94b).
The state-wide soil radon potential map was developed from state surface geology
maps provided by the Florida Geological Survey and from the state-wide STATSGO soil maps
provided by the University of Florida Soil and Water Science Department. These maps were
digitally intersected with a geographic information system (University of Florida GeoPlan
Center) to define 3,919 different polygons (regions) with different soil and geology
combinations. The radon potential of each polygon was estimated from computer simulations
of radon entry into a reference house from the different soil profiles found in each polygon.
The radon produced in each soil profile was defined from (a) nearly 0.3 million soil
radium determinations extracted from the National Uranium Resource Evaluation (NURE)
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data base by the University of Florida, (b) geologic radium levels estimated by the U.S.
Geological Survey for the 60 geologic units identified by the Florida Geological Survey, and
(c) radon emanation trends from several hundred soil analyses by Rogers & Associates
Engineering Corporation. Radon movement out of the soil profiles was estimated from soil
and water table properties obtained from the State Soil Geographic Data Base by the
University of Florida. The simulations of radon production and movement into the reference
house were based on the RAETRAD model (Nie94a), and considered variations within each
polygon that resulted from local NURE variations and soil variations.
The soil radon potential maps show the annual average rats of radon entry into the
reference house in each map region, independent of house and occupant variations. The
radon entry rate for each polygon is plotted in one of seven tiers, each of which is color-coded
to provide visual distinction of radon potential ranges. The seven tiers of radon potential are
defined as: 0-0.4, 0.4-1, 1-2, 2-3, 3-6, 6-12, and greater than 12 mCi y"1.
6.2 DEVELOPMENT OF THE RADON PROTECTION MAP
The radon protection map was developed as illustrated in Figure 7, The soil and
geology maps defined the polygons for the radon protection map. The NURE, geologic radium
values, radon emanation measurements, soil physical and hydrological properties, and water
table data all were used in the model simulations of radon entry, which determined the
distribution of soil radon potentials for each map polygon. From the state-wide distribution
of soil radon potentials, indoor radon distributions were computed for the reference house for
use in a cost-benefit analysis to determine the appropriate margin of safety for the radon
protection map.
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Soil Maps
Geology Maps
NURE Measurements
Geologic Radium
Emanation Measurements
Soil Properties
Water Table
Model Simulations
Radon Control
Feature
Effectiveness
Soil Radon
Potential
Maps &
Data Base
Cost/Benefit
Analysis
Radon
Protection
Map
Protm»a
Figure 7. Development of the Florida radon protection map.
Indoor radon levels for the reference house were based on its ventilation rate (0.25 air changes per
hour), volume (350 mJ), and the calculated soil radon potential. The numerical relation between indoor
radon and radon potential for the reference house was:
0^ = 0^+1.3(3 (6)
where = annual average radon in the reference house (pCi L*1)
Q»do« = annual average outdoor radon (pCi L"')
1.3 = reference house unit conversion (pCi L"1 per mCi y1)
Q = median soil radon potential (mCi y*1).
6-3
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The use of a safety margin for the radon protection map stems from the goal of keeping indoor radon
as low as reasonably achievable (ALARA), not to exceed 4 pCi L"'. The ALARA portion of the Standard
was addressed by applying the safety margin to the indoor radon levels that require passive, and possibly
active radon controls. Based on the cost-benefit analysis (Rog94b), a 95% confidence limit was found to
be cost-effective for the radon protection map. This means that if more than 5% of a polygon area is
predicted to have indoor radon concentrations above 4 pCi L'1 (in the reference house), then radon controls
are required for the entire polygon. The soil radon potentials at the 95% confidence limit, tabulated in the
radon potential map report (Nie95a), were used for Q in equation (6) to define the indoor radon level that
was above 95% of the reference-house values in a polygon, but that was below the top 5% of the reference-
house radon levels in the polygon. Outdoor levels for use in equation (6) were approximated with the value
of 0.1 pCi L1.
Polygons with less than 5% of their area exceeding 4 pCi L"' were colored green on the protection
map to show where the Standard requires no special radon controls beyond those provided by present
building codes and practices. Polygons where the upper 5% of the computed indoor radon levels exceed 4
pCi L"' but are less than 8.3 pCi L*1 were colored yellow to show where the Standard requires passive radon
controls in new houses. The 8.3 pCi L"1 cut point was determined by multiplying the minimum passive-
feature effectiveness factor of 2.1 (from Section 5 of this report) by the 3.9 pCi L"1 soil-related radon limit
(Qafaot-Coaieo,), and then adding [2.1 x (4.0-0.1) + 0.1 = 8.3 pCi L'1]. Polygons where the upper 5%
of the computed indoor radon levels exceed 8.3 pCi L'1 were colored red to show where the proposed
Standard requires active radon controls in addition to passive controls. The resulting radon protection map
is illustrated in Figure 8.
6-4
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Legend
Low Radon Potential:
No supplementary radon
controls required
Intermediate Radon
Potential: Passive radon
controls required
Elevated Radon Potential:
Active and passive radon
controls required
Water
nA=-105=21
Figure 8. The Florida radon protection map for residential construction.
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The 2.1 effectiveness factor for passive radon controls is supported by the empirical
measurements in Section 3 in addition to the theoretical analyses in Section 5. If the
reference-house Cnct/CTOb ratio shown in Figure 5 is divided by the geometric mean of all 94
measurements represented in Figure 5, the average effectiveness of the passive controls is
found to be 2.16. This number is still considered conservative, however, since the time trend
in Figure 5 suggests that it is possible to build more effective passive controls than were
achieved in the first year of the evaluation program.
The additional radon resistance factor of 4.45 estimated in Section 5 for active radon
controls gives an upper limit to the red (active control) range of over 36 pCi L'1. This
theoretical estimate appears to be conservative when compared with the empirical data from
houses where SSV systems were required to be activated (from houses summarized in Section
3). Fifteen of the NHEP bouses had radon levels exceeding the 8.3 pCi L"1 cut point before
activating their SSV systems. Dividing the passive-system indoor radon measurements in
each of these houses by the values measured after the SSV systems were activated gave a
geometric mean effectiveness factor for the active systems of 7.7 (GSD=1.9). When combined
with the passive factor of 2.1, the upper limit to the red map range is estimated to be
approximately 63 pCi L"1. This level, based on the average performance of the NHEP active
radon controls, exceeds nearly all of the mapped B5% confidence limits for indoor radon in
Florida. Since the more extensive national experience with active radon controls suggests
even greater effectiveness, active and passive controls together are adequate to control radon
to the 4 pCi L*1 level in even the areas of Florida with the highest radon potential.
Since only three colors are required to show the radon protection categories, the radon
protection map does not show the more detailed variations in each category that are shown
by the seven tiers of the soil radon potential map. For example, the first four tiers of the soil
radon potential map (colored blue, green, yellow, and orange) all fall within the green
category of the radon protection map in Figure 8.
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63 USE OF THE RADON PROTECTION MAP
The intended use of the radon protection map is described in the proposed Standard (DCA94). The
use of the radon protection map is intended solely for compliance with the proposed Standard, which applies
to the construction of new residential buildings. As indicated in Section 302 of the proposed Standard, the
three color designations on the map (green, yellow, and red) distinguish the radon potential ranges of
different regions, and designate the radon control procedures required by the proposed standard for each
region.
Green areas on the radon protection map are regions with sufficiently low radon potential that
existing building standards (identified in Section 101.3 of the proposed Standard) control radon to the levels
identified in Section 101.2 of the proposed Standard in a dominant percentage of the green land area. The
green areas comprise most of the state of Florida. For residential construction in green map areas, the
proposed Standard requires no special radon controls beyond strict adherence to the provisions of existing
local building codes and the "Energy Efficiency Code for Building Construction 1993" (Fla93).
Yellow areas on the radon protection map are regions calculated to have intermediate radon
potential. Sufficient radon protection is provided in a dominant percentage of these areas using the passive
radon controls given in Chapter 4 of the proposed Standard (and identified in Section 5 of this report). New
residential buildings in yellow areas are required by the proposed Standard to incorporate the passive radon
controls specified by Chapter 4 of the proposed Standard.
Red areas on the radon protection map are regions calculated to have elevated radon potential.
Sufficient radon protection is provided in a dominant percentage of these areas using active radon controls
(described in Chapter 5 of the proposed Standard) in conjunction with passive controls (described in Chapter
4 of the proposed Standard). Both active and passive radon controls are required in new residential
construction in a red map area.
The numerical content of the radon protection map has been compared with 9,038 indoor radon
measurements from three different data sets (Nie95a). The Geomet land-based data set (Nag87) best
represents all regions of Florida and agrees very well with the map predictions. The middle 95% of the map
range included 95.4% of the 2,952 measurements, with 1.9% below and 2.7% above the mid-range,
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compared to 2.5% expected for each. He Florida Health and Rehabilitative Services (HRS) data from Form
1750 and the Geomet population data set (Nag87) do not represent all regions in Florida, but they were
compared with the map predictions anyway. The 2,095 measurements in the Geomet population-based data
set averaged slightly lower, with 4.0% below and 1.5% above the 95% mid-range, compared to 2.5%
expected for each. The 3,938 measurements in the HRS residential data set were slightly high, with 0.7%
below and 4.7% above the 95% mid-range, compared to 2.5% expected for each.
Over 250 houses with the greatest differences between measured and predicted indoor radon
concentrations were investigated and found to show trends that offer further explanations. Houses above
the 95% mid-range were about 25 times more likely to use slab-on-grade construction than to have crawl
spaces, while the opposite trend was seen for houses below the mid-range. Similarly, houses above the 95%
mid range were about 50% more likely to use hollow-block construction than frame construction, and the
opposite trend was also seen for houses below the mid-range. These trends are consistent with model
predictions. Considering the variations in both measurements and map calculations, the measurements give
excellent overall state wide validation of the radon protection map.
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7. LITERATURE REFERENCES
Acr90 Acres International Corp. Causes and Control of Cracking in Concrete Slabs-on-grade. Vol. I of
Radon Entry Through Cracks in Slabs-on-Grade, Acres International Corp., report P09314,1990.
Cum92 Cummings, J.B., Tooley, J.J., Jr., and Moyer, N., Radon Pressure Differential Project, Phase I,
FRRP, U.S. Environmental Protection Agency report EPA-600-R-92-008 (NTIS PB92-148519),
January 1992.
DCA91 Department of Community Affairs, Florida Standard for Radon-Resistant Building Construction,
Tallahassee: State of Florida, Department of Community Affairs, Draft Standard, October 1991.
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Construction, Tallahassee, FL: Florida Department of Community Affairs draft final report RAE-
9226/4-4, July 1994.
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Radon. Washington D.C.: U.S. Environmental Protection Agency report EPA-400-R-92-0J1
(NT1SPB92-218395), May 1992.
EPA92b Environmental Protection Agency, A Citizen's Guide to Radon (Second Edition). Washington
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EPA92c Environmental Protection Agency, National Residential Radon Survey Summary Report,
Washington D.C.: U.S. Environmental Protection Agency report EPA-402-R-92-011 (NTIS
unassigned), October 1992.
F!a93 Slate of Florida, Energy Efficiency Code for Building Construction 1993. Tallahassee, FL;
Florida Department of Community Affairs, 1993.
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Fow94 Fowler, C.S., McDonough, S.E., Williamson, A.D., and Sanchez, D.C., Passive Radon Control
Feature Effectiveness in New House Construction in South Central Florida, 1994 International
Radon Symposium Pre-Prints, V-3.l-V-3.10, AARST, Atlantic City, NJ, Sept. 25-28, 1994.
Geo90 Geomet, Test Module for Radon Entry Modeling, Germantown, MD: Geomet Technologies, Inc.,
report IE-2334, 1990.
Geo92 Geomet, New House Evaluation Program, Germantown, MD: Geomet Technologies, Inc., report
JE-2588,1992.
Hen93 Henschel, D.B., Radon Reduction Techniques for Existing Detached Houses. Technical
Guidance (Third Edition) for Active Soil Depressurization Systems, Research Triangle Park, NC:
U.S. Environmental Protection Agency report EPAJ625/R-93-Q11, 1993.
Hin94 Hintenlang, D.E., University of Florida, Gainesville, FL, unpublished data communication to K.
Nielson, Rogers & Associates Engineering Corp., Salt Lake City, UT 84110-0330, Mar. 21,
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Nag87 Nagda, N.L., Koontz, M.D., Fortmann, R.C., Schoenbom, W.A., and Mehegan, L.L., Florida
Statewide Radiation Study, Germantown, MD: Geomet Technologies Inc. report IE-1808,1987.
Naj93 Najafi, F.T., Shanker, A .J., Roesslcr, C.E., and Hintenlang, D.E., New House Evaluation of
Potential Building Design and Construction for the Control of Radon in Marion and Alachua
Counties, Florida, U. S. Environmental Protection Agency report EPA-6Q0/R-95-170, December
1995.
Nie82 Nielson, K.K., Rich, D.C., and Rogers, V.C., Comparison of Radon Diffusion Coefficients
Measured by Transient-Diffusion and Steady-State Laboratory Methods, Washington DC: U.S.
Nuclear Regulatory Commission report NUREG/CR-2875,1982.
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Nic92 Nielson, K.K. and Rogers, V.C., Radon Transport Properties of Soil Classes for Estimating
Indoor Radon Entry, in: Indoor Radon and Lung Cancer: Reality or Myth?, F.T. Cross, ed.,
Richland, NVA: Battelle Press, p. 357-372, 1992.
Nie94a Nielson, K.K., Rogers, V.C., Rogers, V., and Holt, R.B., The RAETRAD Model of Radon
Generation and Transport from Soils into Slab-on-grade Houses, Health Physics, 67,363-377,
1994.
Nie94b Nielson, K.K., Rogers, V.C., and Holt, R.B., Development of a Lumped-Parameter Model of
Indoor Radon Concentrations, Research Triangle Park, NC: U.S. Environmental Protection
Agency report EPA-600/R-94-20I (NTIS PB95-142048), November 1994.
Nie94c Nielson, K.K., Rogers, V.C., Rogers, V., and Holt, R.B., The RAETRAD Model of Radon Gas
Generation, Transport, and Indoor Entry, Research Triangle Park, NC: U.S. Environmental
Protection Agency report EPA-600/R-94-198 (NTIS PB95-I42030), November 1994.
Nie95a Nielson, K.K., Holt, R.B., and Rogers, V.C., Statewide Mapping of Florida Soil Radon Potentials,
Research Triangle Pari;, NC: U.S. Environmental Protection Agency report EPA-6QQ/R-95-142a
(NTIS PB96-10435J). (Vol. 1. Technical Report) and EPA-600/R-95-J42b (NTIS PB96-I04369)
(Vol. 2. Appendices A-P), September 1995.
Nie95b Nielson, K.K. and Rogers, V.C., Feasibility of Characterizing Concealed Openings in the House-
Soil Interface for Modeling Radon Gas Entry, Research Triangle Park, NC: U.S. Environmental
Protection Agency report EPA-600/R-95-020 (NTIS PB95-178414), February 1995.
Nie95c Nielson, K.K., Holt, R.B., and Rogers, V.C., Lumped-Parameter Model Analyses of Data from
the 1992 New House Evaluation Project — Florida Radon Research Program, Research Triangle
Park, NC: U.S. Environmental Protection Agency report EPA-600/R-95-090 (NTIS PB9S-
243077), July 1995.
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Rog91b Rogers, V.C. and Nielson, K.K., Correlations for Predicting Air Permeabilities and — Rn
Diffusion Coefficients of Soils, Health Physics 61,225-230,1991.
Rog93a Rogers, V.C. and Nielson, K.K., Generalized Source Term for the Multiphase Radon Transport
Equation. Health Physics 64,324-326, 1993.
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