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Community and Q&A

Waterproofing a Foundation Stem Wall

mjezzi | Posted in General Questions on

I’m struggling to get a clear answer on this:

Is it necessary to waterproof the downhill side of a foundation stem wall? We’re building on a hillside, and of course we have drainage and waterproofing on the uphill side of the foundation, but I’m not clear if it’s necessary on the downhill side. The slab will be at least 3′ above grade on the downhill side and the downhill side of the home will have a 8′ concrete deck sloped towards the downhill side, so in theory, little to no water should get to the downhill side in the first place. Of course I could just play it safe and waterproof it anyway, but I try to avoid waste if it’s a safe bet.


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  1. Expert Member
    Michael Maines | | #1

    The wall may not see much liquid water but soil is typically cool and damp, compared to indoor space, and concrete is porous so it wicks moisture. Damp-proofing helps minimize how much moisture makes its way to the concrete. Water-proofing and a capillary break would ensure that next to no moisture makes its way to the interior or the framing, where it can eventually cause problems. I'd say that asphalt emulsion damp-proofing is cheap insurance, and a capillary break is a good idea, but you probably don't need to go to the trouble and expense of full waterproofing.

  2. user-2310254 | | #2

    I had some similar foundation walls in a previous house. The builder decided not to waterproof a short section of stem wall because it was being used to create an outdoor closet. That turned out to be a mistake since the space stayed much to humid, which led to an ongoing battle with mold and mildew.

    Waterproofing is cheap insurance against this type of issue.

  3. gozags | | #3

    5gal of Henry 795 is $45. Seems cheap insurance.

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