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Insulating the floor of a house on piers

Roger Steinbrink | Posted in Energy Efficiency and Durability on

Here in south Louisiana & Mississippi we have a lot of homes that are raised on piers, typically 1-3 ft. It would be nice to insulate the floor from underneath, but there seems to be no good way of doing it.

I am working on a project now where we’ve taken up the floor, and I would like to install some kind of 4’x8′ sheathing underneath the floor joists so that i could then spray closed -cell from above. Is there a product out there that isn’t flammable or doesn’t cost too much that would work? A well meaning friend suggested stapling Tyvek under the joists, but I don’t think that would hold it.

Any ideas?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Roger,
    Lots of products are flammable, including plywood, floor joists, and spray foam. But at long as your spray foam is protected by 1/2-in. plywood, your building inspector should be happy.

    In your climate, you should choose an insulation that isn't vapor permeable. The two best options are closed-cell spray polyurethane foam -- I think it makes more sense to spray it from below, aiming for the subfloor -- or foil-faced rigid polyisocyanurate foam, attached across the underside of the floor joists in an airtight manner and protected from abuse by a layer of plywood.

  2. Roger Steinbrink | | #2

    Thanks for your input, but wrestling plywood on my back in a 2' crawlspace doesn't appeal to my sense of cosmology or sciatia. Seeing how the joists are16 o.c. & solid bridging at every 4',making the "bays" approx15 1/2' x 46 1/2', maybe I could attach metal stud guards at each end from underneath, about 2' in from the bridging and lay in some 1" rigid foam, caulk it & then spray. I tried spaying from underneath once & I almost became a mummy.

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