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Polyethylene sheeting on exterior foundation wall

hotrod796 | Posted in Energy Efficiency and Durability on

I am building a new home in NW Denver, CO. The home sits on a walkout basement where half of the basement is sub-grade. The plans from the foundation engineer call for a perimeter drain with poly sheeting under the drain tile and extending 2′ up the foundation wall. It also calls for damp proofing (no particular method specified) for the remainder of the foundation that is sub-grade. 3″ of eps insulation will be exterior of the damp proofing/sheeting with house wrap between insulation and dirt or siding.

What would happen if I were to continue the poly sheeting up the foundation wall as a means of damp proofing? Asphaltic coatings seem to be out of favor because of degradation due to exposure to earth. Will the layer of poly and insulation over the asphalt stop the degradation?

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  1. GBA Editor
    Martin Holladay | | #1

    You can install polyethylene on the exterior of a foundation wall if you want, but it will be less effective than asphaltic dampproofing (because the integrity of the polyethylene will be compromised by a single hole or tear, and because the exterior of a foundation is a rough environment for protecting poly from tears).

    If you want to invest in a dampproofing layer that is more robust than asphaltic dampproofing, you can install a dimple mat. Google "dimple mat for foundations" and you'll get lots of results.

    For information on ways to protect the above-grade portion of your exterior EPS from abuse and sunlight, see this article: How to Insulate a Basement Wall.

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