AN EVALUATION OF INDOOR RADON REDUCTIONS
POSSIBLE WITH THE USE OF
DIFFUSION RESISTANT FLEXIBLE CONSTRUCTION MEMBRANES
David C. Sanchez
U.S. Environmental Protection Agency
Research Triangle Park, NC
Robin Minga and Cephas Sloan
Eastman Chemical Company
Kingsport, TN

ABSTRACT

The importance of foundation construction design and materials used is recognized as critically important to
the radon resistance of buildings. Numerous states have adopted "standards" or guidelines which prescribe methods
and materials of construction. This paper provides a modeling assessment of the indoor radon reductions possible
through the use of "improved" radon resistant membranes. The analysis focuses on quantifying the impacts on
indoor radon concentrations of using "improved radon diffusion resistant membranes" for a typical experimentally
determined range of membrane radon diffusion coefficients. The evaluation considers the application of radon
resistant membranes to slab on grade construction typical of Florida and source strengths and site conditions typical
of Florida. Guidance for the extrapolation of findings to non-Florida construction and site conditions is discussed.
ACKNOWLEDGEMENT

The inspiration for this paper is derived from a jointly sponsored research effort, CRADA No. 0 122-95 of the

U.S. EPA and Eastrnan Chemical Company of Kingsport, Tennessee, intended to develop methods and data on the
radon diffusion barrier resistance of construction membranes. The model, RAETRAD 4.1, used for assessing the
radon resistance of possible radon barrier, was provided by Rogers and Associates Engineering Corporation of Salt
Lake City, Utah. Finally, Richard Snoddy with Acurex Environmental, Research Triangle Park, is acknowledged for
his assistance in exercising the RAETRAD analysis.
INTRODUCTION

A maturation exists in government and private sector responses to dealing with the public health risk of indoor
radon. Federal and state programs of problem assessment, control technology development, and demonstration, and
the transfer of guidance reached their zenith of effort in the period 1988 to 1995 (EPA88, EPA91, EPA93, EPA94,
DCA95). Government efforts are now focussed on outreach programs and privatization of certification programs.
(RRTC95). Necessarily private sector efforts to deal with all aspects of the indoor radon problem have been
challenged.
The current state of the art of radon control technology, as indicated by formalized guidance and extensive
demonstrations (HenscheISS, Fowle~-91,Leovic94, Tyson95, Hintenlang95, Najafi95, and Fowler96 ) indicate that
an adequate technical basis exists for dealing with most indoor radon problem situations found in new construction
and existing buildings. Yet there are problem situations, e.g., buildings built over high radon potential lands where
more effective or robust control technologies are needed. An early expression of this concern, focused on one
control strategy, is found in the proceedings of a workshop on innovative radon barriers sponsored by EPA and held
at the National Association of Home Builders headquarters in Washington ,DC on July 21, 1992 (Geomet92). Some
1996 International Radon Symposium 111 - 3.1

of the above referenced control technology evaluations of new construction techniques (Tyson 95, Hintenlang 95,
Najafi 95, and Fowler 96) also support consideration of the use of passive controls such as the use of vapor barriers
employed and required in Florida new construction. This paper addresses this technical issue, in the context of
Florida construction (DCA95), by using (1) a computer model (Nielson94) developed and enhanced in support of
the Florida Radon Research Program(Sanchez91) and (2) existing data on the expected radon diffusion resistance
performance of classes of flexible membranes.
ASSESSMENT APPROACH

Aouroach
This paper is an applications paper, i.e., it uses tools and information developed within the Florida Radon
Research Program and research findings specific to the radon diffusion characteristics of selected flexible
membranes as input for a computer model simulation and estimation of resultant indoor radon impacts. The
following discussion presents a description of the main technical aspects and data input needed for background and
understanding the context in which the computer simulations are undertaken.
Radon Diffusion Throueh Flexible Films
The study of gas diffusion as a mass transport process has been well defined since 1855 (Fickl855) and its
application to contemporary problems is evidenced by the development of ASTM standards (ASTM82, ASTM84,
ASTM95a, ASTM95b) and research specific to the radon transmission through plastic films (Jha82,
Hafez86,Nielson96) including ongoing research (Perry96, Mosley96). Table 1 presents the diffusion coefficients
determined by this research and some of the characteristics of these research tests. Of special note is the variability
of test results, for nominally the same materials, between researchers. This variable result is largely explained by the
uncertainty introduced by the quality of test materials and use of different test methods.
Florida Standard for Passive Radon Resistant New Residential Building Construction
The Florida Standard for Radon Resistant New Residential Construction was the result of a concentrated
research effort, undertaken by the Florida Radon Research Program (FRRP) (1989-1995). The FRRP's initial effort
was directed at indoor radon problem assessment and the development of diagnostic measurement and assessment
tools. This effort was followed by an extensive effort directed at developing a quantitative basis for rank ordering
the efficacy of selected radon-resistant construction techniques and control approaches. The results are individually
reported in "new house evaluation studies"( Najafi95, Hintenlang95, Tyson95, and Fowler96) and presented in
summary in Nielson96 and Nielson 95. Tables 2,3, and 4 present house parameters and site conditions encountered
at the study houses.

1996 International Radon Symposium 111 - 3.2

Comparison of Test Results and Conditions
for Radon Diffusion Coefficient Measurements

Table 1.

Publication :

Jha 82

Hafez 86

Nielson 96

Units :

m2 s-'

m2 8

m2 s-'

Material

u

Natural Rubber
Cellulose Nitrate

-

6 . 3 6 ~10-lo
1.24~10'"

Cellulose Acetate
Polwinylchloride
-

7.5~10-l3
500x10'"

58x10-l3

Polyethylene

7.8~1
0'12

Polyethylene
terephthalate

3 .OX 10'"

3.36xl0-"

-

Polyester
Polycarbonate

1 . 9 510-l3
~
3.82~10"~

2 . 4 ~0'112
5.5~1
0'l3

Mylar
Test Conditions U
Exposure Time

NR

Radon Source

Ore, Ra @
1730 pCi/g

Monitor

alpha

alpha-track

alpha

Steady State

Yes

Yes

NR

Thickness

NR

0.5, 1,3 mil

6 mil

NR = Not Reported

30 d

NR
Mill
Tailings

No CRADA prototype data is reported.

-

1996 International Radon Symposium 111 3.3

Table 2. House Parameters by Study Cohort

Base
Area

Ref.

(m2)

683
*I98

2.9
i0.3

10.0
h2.9

1.4
M.5

212
iS.D.
±3
Mean
268
±S.D i108

645
±I4
908
a64

3.0
i0.2
3.6
±1.

13.3
h1.5
17.6
i5.0

1.1
*0.2
1.7
*0.4

Nielson Mean
iS.D.
95

'
11

Nielson
94b

233
i59

Mean

Mean

217

S.D.

*43

623
*181

2.8
M.3

10.7
*1.0

Mean

199
i81

602
±28

3.1
il.O

10.0
k2.1

258
±5

750
i170

2.9
*0.3

11.6
k1.1

S.D.

'

Occup. Inside Equiv.
V O ~ . ~Height widb No.
House
(m3)
(m)
(m) Stories Constc

Mean
iS.D.

Floor Slab
Detail

Slump
(cmle

19
±

"Volume of the occupied space in the house.
*widthof the equivalent rectangular area of the house footprint
cConstruction: block (BL), frame (FR), or brick (BR).
^slab edge detail: slab poured into stem wall (SSW)or monolithic slab (Mono).
'Concrete slump.
/super plasticizer used in slab concrete (Yes or No).
^Slab reinforcement: wire mesh (W), glass fiber (F), or post-tensioned (PT).
^sub-slab ventilation system: well point (WP), suction pit (SP), or ventilation mat (VM).

1996 International Radon Symposium 111 - 3.4

17
i4

plastf

Reinforced

SSV
systh

Table 3. House, Soil, and Ventilation Measurements by Study Cohort

Nielson
95

Mean
~s.D.

2 . 3 ~ v7
1
±l.lxl0

7.2
k5.4

5.7
*3.1

35
±1

5.2
i1.2

0.29
k0.07

Mean
~s.D.

l . l x l ~ - ~ 8.6
*l.2xl0'~
k3.6

5.6
*2.1

33
±1

5.8
k1.2

0.3 1
i0.08

92.
±200

1 .60e

Mean
±s.D

7 . 4 ~ 1 0 ' ~ 7.3
 ± 7 . 8 ~ 1 0 ' *2.5

7.2
±2.

28
±

Mean

l.lxlO"
8.3
*1.2~10-~ i3.3

7.4
k1.9

28
±

0.27
*O. 12

32
±2

1.79

0.3 1
±O13

0.0 15
A0.005

1.60
±0.1

50.
±67
-

I#

I$

1.60e
~p

-

It

~s.D.
Nielson
94b

Mean
kS.D.

- -

Mean
±S.D

If

Nielson
95
!I

20.0

Mean
±S.D

9.1 x 10''
±\.9xl0

5.2
*3.5

Mean
kS.D.

9 . 0 ~ 1 0 ' ~ 3.6
 ±.7xlo4
±I 1

0
±

--

5.6
±.3

"Moisture percentage, dry-weight basis.
hfiltration air changes per hour at 50 Pa pressure, from blower-door test.
"Passive-condition air infiltration rate.
'^Total area of observed slab cracks.
^Assummed typical soil densities, since none were reported.

1996 International Radon Symposium III - 3.5

-

Table 4. Sub-slab and Indoor Radon Measurements in Study Houses (Nielson 94b)

,
House
ID

Soil
Indoor
Radon
Radon
(pCiL ~ ) (pCi L-~)

Outdoor
Radon
(pCi p)

Subslab
Radon
( p ~p)
i

5,510
5,180
19,900
3,050
2,690
14.300
5.700
5.990

1.6
4.1
1.5
1.6
I .4

0.4
1.3
0.1
0.5
0.3

4.3 10
12,100
4,490
4,520
4.240

2.7
2.5

0.6
0.7

6.480
6.2 10

F-02
F-03
F-08
F-10
F-l l
F-14

1,480
2,630
1.310
I 1,500
2,760
2.5 10

1.6
3.8
3.3
8.0
1.9
3.1

0.6
0.3
0.3
1.3
0.4
1.3

886
5,990
4.000
5,580
4,180
8,270

1
2
3
4
5
7
9
10
11
12

I ,680
2.940
,190
91 1
2,900
92 1
1,300
1.060
10,700
6.980

2.3
3.0
2.2
2.7
2.5
1.2

0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5

730
970
488
809
1,220
722

10.9
2.8

3,870
8,480

Statistical Summary
Soil
Radon
(pCi L')

Indoor
Radon (pCi
L-I)

Outdoor
Radon
(pCi L')

Subslab
Radon
(pCi L-I)

6,230
1.99

2.0
1.49

0.4
2.23

5,640
1.46

GSD

2.720
2.17

3.1
1.77

0.6
1.97

4,000
2.19

G.M..
GSD

2,070
2.38

2.8
1.86

0.5
1.00

5,840
1.46

Statistic

G.M..

GSD

G.M.,

The Florida Standard for Radon Resistant Construction (DCA95) is a performance based standard requiring
the installation of passive construction features. It contains quantitative requirements to ensure a standard quality of
construction, e.g., requirements specifying slump of concrete, and the use of ASTM rated sealants, and vapor
barriers. Figures 1 and 2 show examples of how the Florida Standard addresses certain important radon-resistant
construction features (Shanker93).
The RAETRAD Model
The RAETRAD (Radon Emanation and Transport into Dwellings model) (Nielson94, Rogers96) is a
public-domain computer simulation model developed and refined within the FRRP.It has been used extensively in
support of the Florida Standard development, especially in evaluations of (1) radon contributions of foundation soils
and fill materials,(2) advective and diffusive radon transport, (3) geographic distributions of radon potential in
Florida, and (4) the development of simplified models for the assessment of the radon resistance of building features.
This paper uses the RAETRAD model to evaluate the indoor radon reduction potential of two distinct vapor
membranes on the diffusive entry of radon into a typical Florida Standard house built over three distinct radon
potential sites. Table 5 presents the scenarios evaluated using the RAETRAD model.

1996 International Radon Symposium I11 - 3.6

Table 5. Model Simulation Matrix

Scenario

House Parameters
(see Table 6)

Soil Parameters
Soil Ra Content
(p~i~-l)

Site Parameters
Vapor Barrier Diffusion
Coefficient (m2s"l)

Set to Default
t'
7'

'I
!I
'1

I8
I1

I#

none
none
none
1.00x10-11
1.00x10-11
1.00x10-11
i.oo~io-13
I .ooxio-13
i.oo~io-13

MODELING SCENARIOS RESULTS
Introduction
The purpose of the RAETRAD evaluation presented below is to identify the significance of improvements
in moisture barrier radon diffusion resistances to the resultant indoor radon. The belief before this evaluation was
that technically feasible enhancements to the diffusive resistance of vapor barriers should produce cost effective
reductions in indoor radon, especially (1) in those instances where small reductions, though hard to come by
reductions, in indoor radon are needed or (2) where radon source variability is such that more robust passive
controls are a prudent addition to the Florida Standard. For example, the results of the "new house evaluation
projects" identified exceptions to the adequacy of the Florida Standard's passive controls, on high radon potential
sites, to always produce indoor radon concentrations below EPA's 4 p ~ i ~ action
" 1 level (Tyson 95, Hintenlang 95,
Najafi 95, and Fowler 96).
Baseline Conditions
Table 6 presents the baseline or reference house input parameters used in the RAETRAD model. These
conditions are common to all scenarios listed in Table 5. Tables 7 and 8 present the foundation and soils (1)
physical characteristics and (2) radiological characteristics input into the baseline (no barrier) and vapor barrier
analysis runs. Vapor barrier thicknesses of 6 mils (150 \an) are used for all vapor barrier runs with the only
parameter changing among runs being the radial and vertical diffusion coefficients. The diffusion coefficient values
used, though hypothetical, are representative of the values shown in Table 1.

1996 International Radon Symposium 111 - 3.7

Table 6. House Parameter Values Used in Model Runs
Dimensions:

28.4 x 54.3 ft.

Area:

1542 ft2

Fill Thickness:

I unit (0.9 ft.)

Footing Depth:

3 units (2.9 ft.)

Indoor Pressure:

-2.4 Pa

Outdoor Pressure:

0 Pa

Outdoor Radon Cone.:

0 PC~L-'

Floor Openings:

Eliptical Crack at Slab Edges, 1 cm width
Utility Penetrations, 2 at 13 ft. from edge

Table 7. Foundation and Soil Characteristics
Materials:

Sand, Concrete, Membranes

Layers:

Soil, Floor, Footing

Parameters:

Density, Porosity, Saturation Fraction, Panicle Diameter

-

Table 8. Foundation and Soils Radiological Characteristics
Materials:

Sand. Concrete. Membranes

Layers:

Soil, Floor, Footing

Parameters:

Radium Content, Emanation Fraction, Diffusion
Coefficient, Permeability Coefficient, Adsorption
Coefficient

Results
Table 9 presents the indoor radon concentrations predicted by RAETRAD for the selected soil radon potential and
radon barrier diffusion coefficient test conditions. Those are compared with the baseline no barrier case.

-

1996 International Radon Symposium 111 3.8

Table 9. Comparison of Baseline (No Barrier) and Flexible Membrane
Barrier Effects on Indoor Radon Concentration

Indoor Radon Concentration (PC&')
for Selected Barrier Conditions
Soil Radon Potential:
Soil "'Ra Content (pCig-')

Diffusion Coefficient (m2s"')
No Barrier

I x l0-I1

I x lo-"

Figure 3 presents the above results on a semilog plot to show the overall relationship of indoor radon
concentrations to building site radon potentials (soil radium content). This figure shows clearly the non linear nature
of the radon entry process with respect to diffision limiting processes and the proportionality of indoor radon
concentrations to source strength for advective and high diffusion coefficient conditions.
CONCLUSION
Placement of an integral impermeable flexible membrane (vapor barrier) under slab on grade construction can
produce significant (100 x) reductions in indoor radon concentration from the no barrier case.

-

In most cases, even for floating slab on grade construction, on moderately high radon potential ( I O ~ C ~ ~ " ~ ,
2 2 6 ~ a )soil, currently available and diffision resistant membranes can keep indoor radon concentrations
below 4 p ~ i ~ * 1 .
Enhanced radon diffusion limiting membranes (e.g., going from 1 x 10-I to 1 x lo'^ m2s'l diffusion
coefficients) may become cost effective on high radon potential sites, i.e., sites greater than 20 p ~ i g ' ^ ^ ^ ~ a .
The placement of a completely intact vapor barrier is critical to limiting radon entry into new and existing
structures even at the well-balanced indoortoutdoor pressure differential condition (-2.4 Pa) used in this
analysis.
Comparison of the performance of new house evaluation study results with RAETRAD model predictions
indicate the potential for enhanced radon entry limiting performance of vapor barriers, perhaps through
enhanced placement practices.
REFERENCES
"The National Radon Measurement Proficiency Program." EPA 52011-88-024, U.S. Environmental
rotection Agency, Washington, DC 20460. September 1988.
"The National Radon Contractor Proficiency Program." € 52011-91-016, U.S. Environmental
Protection Agency, Washington, D.C.20460. June 1991.

I996 International Radon Symposium III - 3.9

"Radon Mitigation Standards." EPA 402-R-93-078, U.S. Environmental Protection Agency,
Washington, D.C. 20460. October 1993.
"Model Standards and Techniques for Control of Radon in New Residential Buildings." EPA402-R94-009, U. S. Environmental Protection Agency, Washington, D.C. 20460. March 1994.
Florida
'Florida Standard for Passive Radon-Resistant New Residential Building Construction!'
Department of Community Affairs, State of Florida, Talahassee, FL 32399-2100. July 1, 1995.
"Emanations." Newsletter of the Regional Radon Training Centers, Vol.5, No.4, Kansas State
University, Manhattan, KS 66506-2508. September 1995.
Henschel, D.B. "Radon Reduction Techniques for Detached Houses." EPN62515-871019, U.S.
Environmental Protection Agency, Research Triangle Park, NC 277 1 1. January 1988.
Fowler, C.S., Williamson, A.D., Pyle, B. E., Belzer, F.E., Coker, R.N. "Hankbook, Design and
Installation of a Home Radon Radiation System- Sub slab Depressurization Systems in Low
Permeability Soils." USEPA/625/6-911029, U. S. Envuonbmental Protection Agency, Research
Triangle Park, NC 277 1 1. July 1991.
Leovic, K.W. and Craig, A.B. "Radon Prevention in the Design and Construction of Schools and
Other Large Buildings." EPA/625/R-921016, US. Environmental Protection Agency, Research
1994.
Triangle Park, NC 277 11. June
Tyson, J.L. and Withers, C.R. "Demonstration of Radon Resistant Construction Techniques- Phase
I1 Final Report." EPA-600iR-95-159, U.S. Environmental Protection Agency, Research Triangle
Park, NC 277 1 1. November 1995.
Hintenlang95 Hintenlang, D. E., Shanker, A., Najafi, F.T., and C.E. Roessler. "Evaluation of Building Design,
Construction, and Performance for the Control of Radon in Florida Houses Evaluation of Radon
Resistant Construction Techniques in Eight New Houses. EPA-600/R-95-114, U.S. Environmental
Protection Agency, Research Triangle Park, NC 2771 1. July 1995.

-

Najafi, F.T., Shanker, A.J., Roessler, C.E., Hintenlang, D.E., and Tyson, J. "New House Evaluation
of Potential Building Design and Construction for the Control of Radon in Marion and Alachua
Counties, Florida." EPA-600/R-95-170, U.S. Environmental Protection Agency, Research Triangle
Park, NC 277 11. December 1995.
Fowler, C.S., McDonough, S.E., Williamson, A.D. "Effectiveness of Radon Control Features in
New House Construction South Central Florida." EPA-600lR-96-044, U.S. Environmental Protection
Agency, Research Triangle Park, NC 277 11. April 1996.
"Radon Barrier Systems." EPA Contract No. 68-D9-0166, Task No. 3-24 Geomet Report No. IE2605. Geomet Technologies, Inc. Gennantown, MD 20874. September 30, 1992
Sanchez, D.C., Dixon, R., and Madani, M. "The Florida Radon Research Program: Technical
Support for the Development of Radon Resistant Construction Standards" Presented at the Fifth
Annual AARST National Radon Conference, October 9-12, 1991 Rockville, MD
Fick, A. "Ueber Diffusion." Amal. Physik 17059-86: 1855 (In German)

1996 International Radon Symposium 111 - 3.10

'Standard Test Method for Determining Gas Permeability Characteristics of Plastic Film and
Sheeting." ASTM D 1434-82, American Society for Testing and Materials. West Conshohocken,
PA 19428. May 1995
"Standard Specification for Polyethylene Sheeting for Construction, Industrial, and Agricultural
Applications." ASTM D4397-84, American Society for Testing and Materials. West Conshohocken,
PA 19428. September 1984.
"Standard Test Methods for Water Vapor Transmission of Materials." ASTM E96-95, American
Society for Testing and Materials. West Conshohocken, PA 19428. May 1995.
"Standard Test Method for Oxygen Gas Transmission Rate Through Plastic Film and Sheeting
Using a Coulometric Sensor." ASTM E96-95, American Society for Testing and Materials. West
Conshohocken, PA 19428. November 1995.
Jha, G., Raghavayya, M., and Padmanabhan, H. "Radon Permeability of Some Membranes."
Health Physics, V42, No 5, pp732-725. 1982
Hafez, A. And Somogyi, G. "Determination of Radon and Thoron Permeability through some
Plastics by Track Technique." Nuclear Tracks, V12, Nos 1-6, pp 697-700. 1986
Nielson, K.K., Holt, R.B., and Rogers, V.C. "Residential Radon Resistant Construction Feature
Selection System." EPA-600R-96-005, U.S. Environmental Protection Agency, Research Triangle
Park, NC 277 11. February 1996.
Perry, R. and Snoddy, R. , "A Method for Testing the Diffusion Coefficient of Polymer Films!'
Prepared for Presentation at the 1996 AARST International Radon Symposium, September 29October 2, 1996. Haines City, FL
Mosley, R. "Description of a Method for Measuring the Diffusion Coefficient of Thin Films to ^ ~ n
Using a Total Alpha Detector." Prepared for Presentation at the 1996 AARST International Radon
Symposium, September 29- October 2, 1996. Haines City, FL
Nielson, K.K., Holt, R.B., Rogers, V.C. "Lumped-Parameter Model Analysis of Data from the 1992
New House Evaluation Project Florida Radon Research Program." EPA-600R-95-090, U.S.
Environmental Protection Agency, Research Triangle Park, NC 2771 I .July 1995.
Shanker, A. "Guidelines for Radon-ResistantResidentialConstruction in the State of Florida." Final
Report to the State of Florida. Department of Community Affairs. University of Florida.
Gainesville, FL August 1993.
Nie1son.K.K.. Rogers,V.C., Rogers, V., and Holt, R.B. "The 'RAETRAD Model of Radon
Generation and Transport from Soils into Slab-onOGrade Houses." Health Physics, V67, No4.
October 1994.
Rogers, V., Nielson, K.K., and Rogers, V.C. "RAETRAD Version 4.1 User Manual." RAEG 1W33-2, Rogers and Associates Engineering Corporation. Salt Lake City, UT 841 10-0330. June
1996.

1996 International Radon Symposium 111 - 3.1 1

Fig. 1 Monolithic Slab,
Vapor Barrier Installation

In monothic slab construction-slab edges are thickened around the
perimeter to form a monolithic concrete beam. The soil cover membrane
should extend beyond the outer edge of the monolithic slab (see Figure
16). Monolithic slab is recommended for radon resistant construction.

A. 4" thick concrete slab with monolithic
edge.
B. 6 mil soil cover membrane continues
beyond outside edge of slab.

Fig. 2 Slab Poured Into
Stem Wall Vapor Barrier
Installation
When a slab is poured into a stem wall. concrete header blocks
(see Figure 17 part A) serve as forms for the concrete slab. The soil cover
membrane should extend at least 1" into the header block. The slab
extends to the inside surface of header blocks. The cores of header blocks
should be completely filled with concrete.
A. Concrete header blocks.
6. Fill header block cores along perimeter to
form 8" thick cap.
C. 4" nominal concrete slab.
0.6 mil vapor barrier at least 1" into the
header block.
E. Compacted fill soil.
F. Undisturbed soil.
G. Grade.

-

1996 International Radon Symposium 111 3.12

-.---. --

-

1996 International Radon Symposium 111 3.13