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Community and Q&A

Air-Sealing Beneath Hardwood Floors

finePNW | Posted in General Questions on

We will be installing hardwood flooring with nails and I’m hoping to find an underlayment that will help maintain a good (if not perfect) air seal between the topside of the floor and the crawlspace underneath. Are there any good products or techniques for this? Unfortunately, floating is currently off the table.

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  1. walta100 | | #1

    Your crawlspace should be inside your thermal envelope and conditioned to about the same temp and humidity as the rest of your home.


    1. finePNW | | #7

      Yes, we've had this conversation before. If I could with my budget, I would. Thanks.

  2. Expert Member
    Michael Maines | | #2

    I generally agree with Walta's advice above but in case that's not possible in the short term:

    If your floor sheathing is 3/4" sheet goods you can use short cleats (flooring nails) that won't puncture the sheathing. Tape the sheathing joints before installation. There may be short flooring staples available but if so, I haven't used them.

    If your floor sheathing is boards, you could run 1/4" or 3/8" sheet goods over them before installing flooring, taping the joints.

    1. finePNW | | #6

      Ah, very interesting idea re: short cleats. Do they have less reliability in terms of longterm floor squeaks becoming an issue or anything like that?

      1. finePNW | | #8

        The sub flooring is 3/4" tounge-and-grove that has been glued to the joists. I will tape seams where they cut through the subfloor during construction as well as penetration, but I'm curious of taping is usually considered useful along the tongue-and-groove seams?

  3. Expert Member
    BILL WICHERS | | #3

    It's probably worth pointing out that a nail in a typical plywood subfloor won't be an air leak. Remember that nails fit *very* tightly in wood, so the wood self-seals around the nail and won't be an air leak. I wouldn't worry about the nails.

    What I would be concerned about is the gaps between the plywood/OSB panels that make up the subfloor. You'll probably want to tape those, and then try to avoid nailing through the tape right at the seams, where you could potentially tear the tape and then you would have a leak.


    1. Expert Member
      MALCOLM TAYLOR | | #4


      I agree. If nails had enough space around them for air to move through, they wouldn't have any holding power.

    2. finePNW | | #5

      Right. Very good point. Thanks!

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