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.

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.

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, 25 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.

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

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

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

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

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

Radon level population among homes is roughly log-normally distributed

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

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

95% ranges of radon concentrations among homes 3.3

Radon concentration differentials between cap-off and cap-on Cap-off improvements: Basement: 0.35/3.3 = 10.6% 1st Floor: 0.56/2.56 = 21.9% 2nd Floor: 0.37/2.23 = 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.

Cap-off improvement distributions Basement: 0.35/3.3 = 10.6% 1st Floor: 0.56/2.56 = 21.9% 2nd Floor: 0.37/2.23 = 16.6%

Ratio of radon concentrations of 1st floor to basement

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

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

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%.

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.

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