How do I lay plastic on a rocky crawl space floor?

kitaseiOctober 1, 2013

The plan to control moisture from the dirt crawl space under my cottage calls for laying heavy plastic on the floor. But when we actually got down in there to do it,we realized that the floor (like the walls) is very uneven and rocky, and now wonder if this is really the best way to do it. Whatever we do, it will have to be able to withstand some walking on it as we occasionally have to access pipes down there. And should we drape the plastic on the rubble walls as well? How should all of the seams and overlaps be sealed? Thanks for any advice. I'm stalled til then.

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Controlling the ground moisture is step one in an unvented crawlspace. Ideally, you could add gravel with venting for radon gas, then pour a slab on top of the plastic Even with punctures it will work fine.

Instead of using 6 mil plastic, you could upgrade to 20 mil plastic. Seal all seams with building tape and mechanically attach to the walls, which are best insulated.

For further details on an unvented crawl, see link below.

In some climates, such as the Pacific Northwest, a traditional vented crawl is more efficient.

Here is a link that might be useful: USDoE: Unvented Crawlspaces

    Bookmark   October 1, 2013 at 8:19PM
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Thank you Worthy. But I am still left wondering how one lays or attaches plastic to very uneven stone surfaces..

    Bookmark   October 1, 2013 at 10:09PM
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Just unroll it to cover the ground, then stake it down with landscape fabric stakes as needed. It's not like you're laying carpet; creases and wrinkles are allowed.

    Bookmark   October 2, 2013 at 12:24AM
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Thank you - I didn't know it was acceptable to put holes in the plastic.

    Bookmark   October 2, 2013 at 11:57AM
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Worthy, i just realized you said "unvented crawl space." I wouldn't describe ours as that. I'm sure it is quite porous even if it isn't well ventilated. so much of it inaccessible.. That said, do you still recommend insulating the walls? My head spins with so much information. Somewhere I read that insulation and vapor barriers that go up to the sill will cause it to rot. Oy..

    Bookmark   October 5, 2013 at 12:46AM
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