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Crawl Space Vapor barrier

Alexio | Posted in General Questions on

Where can I buy 40 mil crawl space vapor barrier in Canada?  Even tough to find in the states.

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Replies

  1. Expert Member
    Michael Maines | | #1

    Do you really need 40 mil? That's extremely thick. The only times I've used that thickness in crawlspaces was when they had very rough surfaces that would have been too hard to smooth out with fill. In those cases, I used 0.040" or 0.060" EPDM roofing membrane, available at roofing suppliers, and often lumberyards, usually by special order. It's not an ideal material for indoor use as it does have a rubber odor, meaning it's offgassing VOCs.

  2. Expert Member
    BILL WICHERS | | #2

    Code minimum is 6 mil. Recommended minimum is 10 mil (on the floor). I like to use 20 mil if I expect the floor might see some traffic, such as servicing any equipment that might be in the crawlspace. I used a 20 mil reinforced poly material on the floor of my own crawlspace, and I used 6 mil on the walls to save some money.

    Why do you need 40 mil? I've never even seen anything made that thick for this purpose. If that's really what you want, I think Michael's suggesting of roofing membranes is the only way to go. At my plastics supplies, 30+ mil isn't a rolled sheet anymore, it's a rigid panel (although still called a "sheet"). You buy that in 4x8 foot panels instead of on a roll.

    Keep in mind that 20 mil is pretty hefty material and unlikely to easily tear or puncture. Unless you really need more than that, I'd just stick with one of the crawlspace liners that are made in thicknesses up to 20 mil.

    Bill

    1. Expert Member
      Michael Maines | | #3

      The 2021 IRC now requires 10-mil under concrete slabs: https://codes.iccsafe.org/content/IRC2021P1/chapter-5-floors#IRC2021P1_Pt03_Ch05_SecR506.2.3. Otherwise it requires a Class 1 vapor retarder but doesn't specify a thickness. The exception is wood foundations, where they do specify 6-mil. FYI.

      1. Expert Member
        BILL WICHERS | | #4

        Thanks for bringing that to my attention! I'm glad that was changed -- I never thought 6 mil was thick enough to avoid tears/punctures even just during installation.

        Bill

  3. Expert Member
    MALCOLM TAYLOR | | #5

    Alexio,

    If you need more than 10 mil poly I suspect you are asking it to do a task it isn't really designed for. 10 mil will work well as both a vapour and air-barrier, and if it is in a situation where it risks being damaged, it's probably better to protect it than rely on the material itself to stay intact.

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