XPS under floor insulation/vented crawlspace?

attofaradOctober 20, 2011

I live in a moderate climate, in a house built over a vented crawlspace. Presently there is no floor insulation. I'm considering doing some spot insulation, in particular under a bathroom. I could put fiberglass batts between the floor joist, but I'm also considering using 2" XPS, which would also be between the floor joists. Small area, so the slightly increased installation time wouldn't be much.

Okay, or bad idea?

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I doubt insulating one area will make any difference. But if you're doing it, use the XPS as it won't be affected by moisture.

To make a real difference consider converting your vented crawl into an unvented conditioned space.

Here is a link that might be useful: Crawl Space Insulation

    Bookmark   October 20, 2011 at 10:09PM
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I would be doing the XPS under a tile bathroom floor, to make the floor a bit less cold in winter. Tile plus backer plus 3/4" plywood only comes to maybe R=1.5, so an increase to R-10 should make a difference.

Pretty rough crawlspace (rock, rebar) which would need quite a bit of work to make it where plastic could be put on the "dirt". Much of it is well under 24" of clearance, and as it was added on there are 3 separate zones (think of as "peripheral" foundation right through the middle of the house. I also draw combustion air from the crawlspace, so that would need some changes also.

    Bookmark   October 21, 2011 at 3:00AM
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Expect the tile to still be cold, despite insulation. For a small area such as a bathroom, electric radiant heat under tile is terrific.( Unless floor is installed already??).

    Bookmark   November 10, 2011 at 8:42PM
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