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Community and Q&A

Waterproofing on the outside or inside of foundation wall?

Michael Schonlau | Posted in Green Building Techniques on

A colleague of mine here in Omaha, NE has an unfinished basement and is planning to finish it. The North wall of this basement is 8″ poured concrete. It is about 50-60%% below grade, going from 100% in the NW corner down to about 20% in the NE corner (East wall is a walkout). He has noticed some frost on the inside of this concrete wall a few times during very cold weather. He has also seen some moisture on the wall after heavy rains. He asked me if he can waterproof the interior instead of the exterior (he is afraid that waterproofing the exterior will create an unsightly finish on the exposed concrete) before he adds rigid foam insulation, studs, and drywall. What should I tell him?


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  1. GBA Editor
    Martin Holladay | | #1

    The best way to waterproof a below-grade concrete wall is from the exterior. The waterproofing details don't have to extend above grade, though, so the details don't have to be unsightly. The best waterproofing details include a dimple mat. Needless to say, a functioning footing drain (draining to daylight, ideally) is essential.

  2. Michael Schonlau | | #2

    They did waterproof the exterior below grade section with a spray-on material. He is concerned now that he will get moisture behind the foam unless he seals the concrete on the inside.

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