For radon reduction work, you should always consider hiring a contractor who is certified (and trained) in a Radon Proficiency Program.
We keep a list of contractors who are certified for radon mitigation by the National Environmental Health Association.
Sealing: Nearly all radon in Wisconsin comes from the soil beneath houses. Radon in the soil under basement floors is often at levels of 300 to 1,000 pCi/L or more. Gaps and openings to soil through basement floors and walls should be sealed with gas-tight materials. Polyurethane, not silicone, is best for use with concrete. However, research shows that sealing cracks and openings in basements only reduces radon by more than 50% in about 20% of houses. This is worth a try since it can be inexpensive and is part of the next method, but it may not have a major effect. Sealing likely has a greater effect when sealing large areas or a great number of cracks and openings. Very small cracks are not worth sealing.
Soil Depressurization usually works well, reducing radon to below 2 pCi/L. Air is brought up from beneath the basement floor and let out at roof level. A continuously-running fan in a pipe that is 3 or 4 inches wide pulls the air up and out of the house, so that it does not move into the house and get stuck there. This process also reduces the air pressure below the floor, so that small unsealed cracks and openings allow basement air to flow down into the soil instead of allowing radon gas to flow up into the basement.
All public libraries in Wisconsin have an eleven-minute videotape Radon Reduction: Sub-Slab Depressurization, provided by the State of Wisconsin. This video explains how a system works and shows one being put in. This video from US Radon Management also explains how this system works. Some radon mitigation supply sources have pictures at their sites.
The cost for a proficiency-listed contractor to install a system can range from $800 to $2,000, and is usually around $1,200. Sub-slab depressurization is not a do-it-yourself project unless you have considerable contractor skills.
