1. Effectiveness Evaluation of Passive Radon Mitigation Systems in a Townhome Community in Illinois
Yigang Sun, Paul Francisco, & Stacy Gloss
Indoor Climate Research & Training, University of Illinois
David & Sue Smith
David Smith Radon Remedies, Inc.
Lin Marie Carey
Healthy Homes, Inc.

2. Background and Motivation
Passive radon mitigation systems are more economical than active systems for less installation cost and electrical and heat energy savings. Many states, municipalities, contractors and architects are adopting these kind of systems.
Passive radon systems have been claimed to reduce radon levels by 50%.
Illinois radon professionals and researchers at the University of Illinois came together to evaluate this claim.

3. Radon tests were conducted at Spring Ridge in Bloomington, IL
Constructed 1998 – 2006 by the same builder
50 single or 2 story buildings: 13 duplex, triplex, 12 quads
Total 149 units
All homes have footing
tile and
sump
pits
Homes have basement construction. High percentage of finished basements. Some units have a small crawlspace addition. 42% had open earth crawlspaces of less than 200 square feet each.

4. Passive mitigation systems All the systems were installed by David Smith Radon Remedies, Inc.
14 units had active mitigation systems installed prior to the study
5” core drilled suction points
Removal of approximate ½ of 5 gallon bucket of river gravel
3” PVC radon vent shared with hot water exhaust chase.
Wall floor joints caulked with polyurethane concrete caulk

5. 106 of 149 homes in Spring Ridge participated in this Radon Resistant Construction Study
Testing conducted from July to September 2013
The average outside air temperatures during the tests were 76.5 F for cap-off, and 79.6 for cap-on

6. Charcoal canister test kits were used to test Radon in air for 72 – 120 hours
Each home tested:
2 test kits in basement level
1 test kit on first level
1 test kit on second level when applicable
Test sequence
Test with cap off
Cap on, wait for three days
Test with cap on
Over 800 charcoal canisters were used

7. Only one unit WITHOUT an active system had radon > 2 pCi/L if there was a unit in the building that had an active system
75 homes for evaluating cap on/off effects

8. Radon level population among homes is roughly log-normally distributed
Logarithm

9. Radon level population among homes
is roughly log-normally distributed

10. Radon concentration differential between cap-on and cap-off among homes is more irregularly distributed

11. Radon concentration differential between cap-on and cap-off among buildings is more like normally distributed

12. 95% ranges of radon concentrations among homes
3.3

13. Radon concentration differentials between cap-off and cap-on
Cap-off improvements:
Basement: 0.35/3.3 = 10.6%
1st Floor: /2.56 = 21.9%
2nd Floor: /2.23 = 16.6%
0.35
0.37
At the 0.05 level, the Radon concentration differential between Cap-on and Cap-off on 1st floors is significantly greater than 0; while the differentials in basements and on 2nd floors are not significantly greater than 0.

14. Cap-off improvement distributions
Basement: 0.35/3.3 = 10.6%
1st Floor: /2.56 = 21.9%
2nd Floor: /2.23 = 16.6%

15. Ratio of radon concentrations of 1st floor to basement

16. Ratio of radon concentrations of 2nd floor to basement and 1st floor

17. Comparison of radon concentrations between interior and end units in townhouse buildings

18. Conclusions (1)
Passive systems can mitigate the radon level, statistically, by 10.6% in basements, 21.9% on 1st floor, and 16.6% on 2nd floor. However, statistically at the 0.05 level, only the radon concentration differential on 1st floors is significant.
Some improvement on average, but not 50%.

19. Conclusions (2)
Radon concentrations among homes is roughly log-normally distributed.
Compared with no radon mitigation measures, passive systems can decrease the ratio of radon concentration of 1st floor to basement, and 2nd floor to basement as well; but have little effect on the ratio of 2nd floor to 1st floor.
The radon concentration average in interior homes is slightly higher than that in end homes in triplexes and quads.

20. Acknowledgment
Thanks to Patrick Daniels and Illinois Emergency Management Agency for supporting this project.