The Radon level in my crawl space is above the threshold (~5.5) and the level in my basement is around 4. I'd like to install a radon mitigation fan that sucks air from the sump pump of a French drain system.
The problem is that the French drain has a black plastic drain board at the edge between the new concrete and the cinder block wall. It's a few inches tall. I was told I should seal that because the radon mitigation system's fan would basically just suck air through those gaps and wouldn't do much sucking from the soil. Furthermore, a powerful fan would create some backdraft and I may get a CO problem.
It's a pity to have to seal that thing, but looks like I'd have to do it. What is the best thing to do?
I have some ideas but they are probably not great:
- duck tape the drain board
- spray foam
- polyurethane spray
By the way, I'm finishing the basement and putting some rigid foam insulation (1 or 2 inch) on the wall so I'd have to take that into consideration too.