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Wall construction – hot humid climate

quantumgirl | Posted in General Questions on

I’m trying to figure out how to build the wall of a home addition. I am in Houston, hot and humid, climate zone 2. 2×6 framed wall with open cell spray foam insulation. OSB sheathing on the outside, Tyvek and Hardie siding. I was thinking of using seam tape on the OSB, to get it as air tight as possible, then creating a second air tight barrier by caulking top and bottom of the Tyvek to the sheathing and taping all the joints. Tyvek website says not to cover the sheathing seams though. What am I missing? Why not? Is it wrong to create 2 (hopefully) air tight barriers right on top of each other

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Quantumgirl.

    I am not sure why Dupont does not want the sheathing seams taped, perhaps a GBA user will be able to speak to that. With spray foam insulation, you are off to a good start with your air sealing. So, whether you also tape the sheathing seams and/or detail the housewrap for as much airselaing as possible, you should have a fairly tight addition.

    One thing to think about is that in your climate inward vapor drive is common. Since your wall will be able to dry in both directions, this shouldn't cause problems in the wall assembly, but you do want to avoid excess moisture getting inside and raising indoor humidity levels. Installing your siding with a rainscreen gap will minimize this potential. Here's some info on rainscreens:

  2. GBA Editor
    Martin Holladay | | #2

    Here are the installation instructions for Tyvek.

    I can't find any statements forbidding you to tape sheathing seams.

  3. Jon R | | #3

    > Tyvek website says not to cover the sheathing seams though.

    Do you have a link to this specific statement?

    Also consider spending the same time/money on more blower door directed air sealing.

  4. quantumgirl | | #5

    So it seams like they are concerned about creating a vapor barrier. But even if u can really consider plywood or OSB a vapor barrier, would that be an issue with me being in Houston? My brain is hurting from all the research but I thought vapor barriers, if installed at all, should be on the outside in my local climate zone.

  5. Jon R | | #6

    "Can sheathing board seams be taped? Taping sheathing board or fan-fold seams creates a continuous vapor barrier..."

    This is usually wrong and even when not (say taped foil faced), it doesn't matter. Avoid Tyvek and use something with lower perms - like Typar. Or something fully adhered (like Blueskin VP100).

  6. GBA Editor
    Martin Holladay | | #7

    The DuPont Tyvek web site is flat-out wrong. Taping sheathing seams to create an air barrier is standard practice in a high-performance home.

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