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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:

  1. duck tape the drain board
  2. spray foam
  3. polyurethane spray
  4. cement

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.

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No answer yet... If you can post a pic I might be able to understand better the relationship of the plastic board to the drain and the concrete. Perhaps you can get an answer that way? –  allindal Apr 12 '11 at 1:10
Are you working with a licensed radon mitigation contractor? If not, that's who you should be going to first. –  DA01 Nov 17 '11 at 5:25

1 Answer 1

If the French drain is between your basement slab and the exterior walls, it may be the source of most of your radon. Sounds like a small suction from the drain sump to the outside is a good plan. A small fan with its own exhaust pipe shouldn't be a problem for the water heater or furnace but a CO detector is never bad for closed rooms with gas appliances.

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