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Mr. Tight-Watt: Crawl Space Sealing  Smart Choices Archive

Mr. Tight-Watt: Crawl Space Sealing

A well-insulated crawl space makes your home more comfortable.

Ask Mr. Tight-Watt

Q: I have a dirt crawl space under my modular home. And I am having a local basement waterproofing and sealing company give me an estimate to put down plastic (that they sell). Will this solution work? Or is there another option I should consider?  —Tom

Mr. Tight-Watt asked Bill McAnally, energy efficient building expert, to answer this question.

A: There are reputable basement contractors who should be able to do this job, including the one you mentioned in your initial request.

Here’s what a reputable contractor should do: The crawlspace should have a consistent 6 mill poly vapor retarder put on top of the soil. All of the joints and perforations need to be sealed with tape. Use either 3-M or Tyvek tape, not duct tape!

The walls should have 2 inches of extruded polystyrene foam such as Dow Styrofoam placed from the soil to top of the wall. Cut sections of foam to fit between the floor joists and place them in and caulk the edges to prevent warm air from reaching the band joist.

Treat the crawlspace like a basement. Do not vent it. For added comfort, place a 1-inch layer of foam on top of the poly.

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