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Effectiveness of radon mitigation in a crawl space using spray foam insulation

DavidS2010 | Posted in General Questions on

Hello, all.  My wife and I are having an ICF home built in the Colorado mountains (climate zone 7B).  The house will soon be dried-in and has a crawl space with a floor of several inches of small stones.  We plan to use the crawlspace for storage.  A chaseway is being constructed from the crawl space to the roof of the house in case, after radon measurements are eventually taken by a radon mitigation professional, a sub-membrane depressurization system is called for.

As an alternative to the sub-membrane depressurization system, our contractor indicates that several of his clients have sealed their crawlspaces to prevent radon from gaining entry.  They used insulation spray foam (he referenced NCFI InsulStar) to seal the crawl space floor.

Theoretically, I can see how this might work for us – – – sealing out the radon and providing a hard surface that would allow us to use the space for storage.  However, I cannot find anything on-line that indicates the sole use of insulation spray foam in a crawl space is an acceptable way to mitigate radon.

There are a couple of Canadian companies that promote using spray foam to mitigate radon . . .

https://www.gni.ca/services/new-construction-residential/airtight-radon-protection-system

http://atlassprayfoam.com/wp-content/uploads/2016/03/RADON-Solution-Demilec-ENG.pdf

However, other than these sales claims, I cannot find information from an authoritative source (such as USEPA or a scientific study) that documents the long-term effectiveness of using spray foam as a stand-alone means to mitigate radon.

Any experiences, references or ideas on using insulation spray foam to seal out radon from a crawl space floor would be greatly appreciated. Thanks!

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Replies

  1. User avatar
    Brian Pontolilo | | #1

    David,

    I think it is more common to finish the crawl space to achieve a healthy and efficient home and plan to mitigate radon with a dedicated system. In other words, not to compromise on the crawl space design so that you don't have to install a radon mitigation system. Installing a passive system as part of new construction is pretty affordable and it's easy to add a fan later if you need it. Here are some articles to read about best practices for both crawl spaces and radon mitigation:

    https://www.greenbuildingadvisor.com/article/building-an-unvented-crawl-space

    https://www.greenbuildingadvisor.com/article/all-about-radon

  2. User avatar
    Jon R | | #2

    Air sealing and then only using depressurization if needed makes sense (for any design). I expect that spray foam does provide better air sealing than say taped plastic - but I don't know of data for long term proof.

    I assume you are talking about pouring concrete over the spray foam to get a smooth, flat, durable surface.

  3. User avatar
    Peter Engle | | #3

    Spray foam on the floor would not be any ore airtight than a continuous layer of poly or other membrane, taped at the seams. A sealed floor and a vent pipe running up through the house are the primary components of a "passive" radon system. These do reduce radon levels in the crawl and the house, but not by a predictable amount. Locally, I see reductions of 1 or 2 pCi/l, sometimes a bit more. Never enough if you have very high radon levels in the soils.

    For high radon levels, some sort of fan system is usually necessary. Subslab depressurization has been the standard treatment for most radon issues for years, and it works fine for all but the toughest radon problems. I would install the pipe to the roof with your initial construction - it is probably required anyhow. If you test moderately high for radon, go ahead and install a taped membrane and concrete slab to protect it. If the radon is still high, install the fan.

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