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Community and Q&A

Walkout basement waterproofing detail

user-7183380 | Posted in GBA Pro Help on

Hi all,
I’m working on a house that has foundation walls up and is prepped for the slab, but there is a detail that got overlooked. I am wondering how crucial it is to waterproof the interior face of the below slab portion of a walkout. The entire perimeter of the building is well waterproofed with proper drainage and insulated to the exterior. On the interior, there is good drainage, but that portion of the wall is not waterproofed.

How crucial of a detail is that for a high performance building where moisture levels are a concern? My assumption is that moisture below grade can/will travel up the portion of the wall that extends both above and below the slab and into the interior space if it is not waterproofed.

Obviously, it would have been better to be safe than sorry (which was the original plan/intention), but it got passed over and now the basement is filled and prepped for the slab. This seems like the last shot at fixing it (i.e. digging everything out along that wall to waterproof). Is that the best way to go?Are there other ways of adequately mitigating moisture in that spot down the road, short of perpetually running a dehumidifier (e.g. painting the interior of basement wall with waterproofer or paint to encourage drying to the exterior)? How big of a concern should this be?

Thanks for any help, it’s greatly appreciated.

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  1. GBA Editor
    Martin Holladay | | #1

    Below the walkout side of a walkout basement, I don't think waterproofing is critical. But every foundation needs drainage (crushed stone around a perforated drainage pipe leading to daylight) and insulation (in your case, vertical rigid foam on the exterior side of the foundation wall on the walkout side, below the door).

    If the drainage details and insulation are missing, then by all means remedy the omission.

    1. user-7183380 | | #2

      Glad to hear it. Drainage and insulation are both where they need to be.

      Thanks, Martin

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