Home>Discussions>INTERIORS>Molding & Carpentry>sealing an interior basement perimeter drain, maybe a french drain that is 2/8" wide
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sealing an interior basement perimeter drain, maybe a french drain that is 2/8" wide

Have a basement floor built with a perimeter drain, maybe called a French drain that is 2/8" wide. Have a minimal radon problem and need to seal this perimeter drain and a 6" diameter round floor drain that goes to a sump pump. Any suggestions?

Re: sealing an interior basement perimeter drain, maybe a french drain that is 2/8" w

Why is there a perimeter drain inside the basement- aren't you stopping the water before it enters the structure? If not, then that's where you need to start at. The floor drain shouldn't be leaking air around it and it should not be leaking air with radon into the pipe so that should not be an issue. The open slab at the perimeter drain is a totally different thing.

If the slab doesn't already have a centrally located radon vent pipe, installing one may reduce the levels to acceptable with no other work. There are powered vent systems which may give enough draw to reduce the infiltration at the perimeter even more. If this is not enough, then you're going to have to eliminate the perimeter drain and seal it closed. If it was necessary to handle water ingression then you're either going to have to live with that water problem or handle it properly- from the outside. The only other option is to ventilate the entire basement with a powered exhaust which will create a negative pressure inside away from the living space and draw the radon-laden air out safely. Radon is rarely an issue with traditionally built homes that weren't so well-sealed. In solving one problem we've created another. Since we're sealing the conditioned space above the basement, it will pay to make sure that it is truly well-sealed while you're at it. All pipe, wire, and ductwork openings should be fire-caulked. And doors leading to the basement from inside should be weather-stripped and sealed as if they were an exterior door. If there is any return-air ductwork exposed to the basement it needs to have every joint sealed with mastic so that it is not drawing in any air from the basement area through leaks.

Unless you spend a lot of time in the basement, a marginal amount of radon should not be a worry so long as the levels in the house itself are OK. If it can be easily done, during milder weather opening to basement to outside air will keep the levels down during those times. Hopefully a central vent will be enough.


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