Radon system design with drain tile to daylight
We are in the process of remodeling our basement and will be pouring a new concrete slab. The house was built in the 1940’s and sits on very dense clay soil. The old concrete has just been removed and we’ve dug down 4” below the top of the footings so that 2” of stone can be placed followed by 2” of EPS, a poly vapor barrier and new concrete. A one year radon test was completed two weeks ago and the average value was 6.6 pCi/l (test completed with all old concrete in place); we will be installing a radon vent prior to pouring the new slab. We have both exterior and interior drain tile that connect to a sump pump. With the exterior drain tile system there are vertical vent stacks that extend up to the into the bottom of the window wells for the basement windows. The tops of the vents are covered with a grate and about 1” of clean rock. The radon vent pipe in our slab will be located approximately 7-8’ away from the perimeter wall of the foundation. Being that the entire drain tile system is effectively open to the exterior air through the vertical vent stacks at each window, will a powered radon mitigation system be effective? It seems like I would just be pulling in exterior air through the drain tile and doing little to create negative pressure under the slab. It was suggested by a radon mitigation company that a PVC swing check valve be installed on the horizontal inlet pipe where the exterior drain tile enters the sump pit. I’m not sure how effective this would be in sealing the system as the valve could potential swing open when the radon system fan turns on. This may not be a concern, but I am not sure how much vacuum the fan is capable of creating. I also don’t want to introduce an unnecessary valve that may fail/clog and be impossible to access at a later date. Any advice would be appreciated.
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