crawl space insulation


crawl space insulation

Asked by Neil Miller

Spray on foam or solid styrofoam. low clearance crawlspace. Only 12 years old. Heard foam can allow wood to rot. Every contractor seems to have a different system or opinion. 19 X 25 foot crawl space.

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Doug Garrett's picture

I see that you live in Michigan and yes, that makes a big difference in what the right answer is to your question. First, you must use only a Closed Cell foam product, no open cell foams. Why? In your very cold climate, you need an insulation that is a vapor barrier. Closed cell foam is a vapor barrier (0.1 Perms.) while open cell foams are highly vapor permeable and would result in warm water vapor reaching the cold crawl space wall and condensing into water. The result would be mold and rot. You can use either spray on or rigid board closed cell (Styrofoam, equivalent) products but you must achieve an air tight seal to control condensation. Often the spray in place product makes this easier. Also, if you are sealing the crawlspace, you must cover the ground/floor with a vapor barrier like 6 mil polyethylene.