http://www.fixradon.com/techniques.html

Sealing openings -” Years ago, the EPA experimented with various radon mitigation techniques.  To assess the effect of sealing, they sealed basement walls, floors and ceilings with epoxy, made the return air ductwork airtight, put an airtight door at the top of the stairs, installed sealed combustion furnaces and water heaters and more.  After spending $4,000 to $5,000 per home, they got radon reductions ranging form 0 to 50%.  For this reason, the EPA does not consider sealing to be a primary mitigation technique.  Our experience has been similar.  We have sealed 1,500 square foot crawl spaces and seen no change in the radon level.  In 50% of the homes we have sealed, the radon level went up slightly, in 50% it went down slightly.  A small number of homes will have a significant decrease or increase in the radon level after sealing.  To maximize the performance of a SSD system, sump holes and large cracks near the suction point will generally be sealed.”

http://www.waterproofmag.com/back_issues/201104/enclosed_crawlspaces.php

An unexpected finding was an increased level of radon in homes with closed crawl spaces in Flagstaff. The elevated level was above the EPA action level so the Flagstaff study was actually discontinued early, says Dastur. “The EPA action level is 4 PPL,” Dastur explains. “The houses with closed crawl spaces were measuring 11, 17, and 22 PPL. That was a situation we wanted to eliminate.”
The soil type in Flagstaff already has a high level of radon. “Gas is hard to block,” Dastur says. “It was just a good warning for everyone to test for radon.”  If your customer wants the energy savings, include a radon mitigation system with the closed crawl space installation.

Tennesee Study of Radon Gas

 

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