Replies

1. Expert Member
   Dana Dorsett | Feb 21, 2018 06:16pm | #1

   The first order of business is to make the sub-grade surfaces in contact with the soil as air tight as possible. Air seal any cracks in the slab with a self-leveling type of polyurethane caulk, as well as at the slab edges. Use a heavier bodied polyurethane caulk formulated for concrete Seal up any plumbing penetrations, sumps, drains etc. The more air-tight the slab and below-grade foundation walls are, the less soil gas gets in.

   The second step is ventilation from known clean air sources. Installing a reasonably sized heat recovery ventilator in a space will typically cuts the radon levels by about half, sometimes more, which may be good enough for the rest of the house on it's own, especially after sealing up the foundation. At 5 pCi/l you're already at the remediation level requirements of most of the more stringent European countries, and almost at the 4 pCi/l remediation level recommended by the EPA.

   If all else fails, a slab depressurization fan in the most egregious area (probably the garage-slab) will likely get you there.

   If the crawlspace doesn't currently have a slab or vapor barrier, a heavy vapor barrier air-sealed to the foundation walls would be in order.

2. GBA Editor
   Martin Holladay | Feb 22, 2018 05:24am | #2

   Jimmie,
   Dana gave you good advice. If you don't feel competent to do the sealing work, just call up a radon mitigation contractor. Radon mitigation contractors are familiar with the steps required to install a retrofit system to depressurize the soil under a slab (if indeed that proves necessary).

   To learn more, see this article: All About Radon.

3. 
   seabornman | Feb 22, 2018 12:17pm | #3

   I hired a radon remediator who designed and installed the system (depressurized under slab with power vent to exterior) and gave me a guarantee for less than $1100. It wasn't worth entertaining a DIY approach, in my mind.