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Air sealing a vented crawl space

joenorm | Posted in General Questions on

Yes, you read it correctly, I am building a vented crawl space. I know everyone here believes they should be outlawed but here in the Pac NorthWest I’m not too worried about it.

My question is how to properly air seal the crawl from the living space. The subfloor will be glued to the joists, if I use the right glue will this be an air seal?

Any other problem spots to pay close attention to?


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  1. Jon_R | | #1

    I'd also add tape. But without a blower door test, anything you do is suspect.

  2. Peter Yost | | #2

    Definitely need to tape the seams and use a high-quality acrylic pressure-sensitive adhesive (PSA) tape. The tape will be seeing quite a bit of moisture over time. And make sure you gap the plywood at all joints because that plywood will also being seeing quite a bit of moisture with resulting contraction and expansion.

    The biggest challenge for vented crawlspaces are all the penetrations; you will need to seal them well.

    Totally agree with Jon R; if there was ever a place for performance testing with a blower door, it would be the air sealing of a vented crawlspace.


    1. joenorm | | #3

      Penetrations meaning nail holes or holes for plumbing, electrical, anchors, etc?

      1. Expert Member
        MALCOLM TAYLOR | | #4

        Holes for plumbing, electrical etc. The other weak spot is the t&g between sheets, which doesn't fall over a joist or get construction adhesive applied. And just like an attic, the access is potentially a big air-leak. If possible, relocating it to an exterior wall helps.

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