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Community and Q&A

Basement damp-proofing

Jay Johnson | Posted in General Questions on

I’ve been doing a lot of reading about basement, both on this site and through the BSC articles. I am still a little unclear on basement damp-proofing.

I have a 1960s rambler, below-grade basement made out of cinder block walls. No major cracks. I’ve had no problem with the basement being wet after rain, but I do run a dehumidifier in the summer and I have heavy clay soil. I don’t have any mold issues.

I am in the middle of building a workshop room in an unfinished section. I have already insulated and sealed the rim joists with XPS and spray foam. What I was planning on doing for the walls was to use 2” of XPS, then build my 2×4 in front of it. No plans to use batt insulation. But I was unsure of was whether I need to damp-proof the cider block before I insulate it with XPS. Is that necessary, if I don’t have major water problems? Or is damp-proofing always a good idea?


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  1. GBA Editor
    Martin Holladay | | #1

    The term "dampproofing" is usually used for asphaltic compounds applied to the exterior side of a foundation wall during new construction.

    In your case, if your basement has no signs of water entry, and if your wall has never been damp, you can go ahead and insulate the interior of the wall with rigid foam. For more information on this work, see How to Insulate a Basement Wall.

    If you want to provide a little insurance against future water entry problems, you can install an interior coating like Thoroseal, UGL Drylok, or Xypex before installing the rigid foam. For more information on the uses and limitations of these products, see Fixing a Wet Basement.

  2. Jay Johnson | | #2

    Martin, that was exactly the answer I was looking for. Just wanted to be sure that I could forego the interior coatings since my basement is dry. Thank you.

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