Best practices for controling radon in existing buildings include air sealing openings and cracks in below-grade walls and floors to reduce radon infiltration, and installing an active mitigation system that re-routes radon gas away from the home. However, we initially hoped that by taking the air sealing measures up a notch and foaming the entirety of the basement, an active mitigation system would be unecessary.
We started by installing two inches of closed cell foam (R-11.5) on the basement floor and the walls, creating a "boat hull" effect to block soil gases, moisture and outdoor air from penetrating the space. We then retested radon levels and discovered that while these measures cut radon levels in half, they weren't sufficient to eliminate the problem. So in the end we had to install an active mitigation system.
Radon levels in the home are now well within EPA's recommended limits. The basement, which had been dank and damp, is now pleasantly warm and dry—so dry that the owner, a musician, has considered storing guitars down there. The clients also report that their home is much more comfortable: the floors on the main level aren't as cold in the winter and indoor temperatures are more stable and consistent from room to room.
In addition, the energy used for heating has dropped by 18%—due in part to the basement insulation but also to the clients' decision to replace their oil boiler with a high-efficiency condensing gas boiler shortly before hiring us. The clients have since installed an 8 kw solar photovoltaic system, proving that even very old homes can be transformed into high energy performers.
You can learn more about radon
on the EPA's radon website.