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Foam OSB seams instead of taping

NormanWB | Posted in Energy Efficiency and Durability on

My insulation contractor has recommended using closed cell spray foam on the OSB sheathing seams instead of taping the seams. Any thoughts on this approach?

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  1. GBA Editor
    Martin Holladay | | #1

    I can't quite visualize this.

    Is he talking about the flash-and-batt approach -- which requires about 2 inches of closed-cell spray foam to cover the interior side of the sheathing?

    Or is he only planning to address the OSB seams?

    I can understand sealing the horizontal seams from the interior (sort of). But the vertical seams land in the middle of a stud, so you can't address them from the interior. Does the contractor intend to run a vertical stripe of closed-cell spray foam at the intersection between the stud and the interior face of the sheathing?

    Taping is simpler, in my opinion, unless this is a flash-and-batt job. Of course, if your siding is already installed, and you forgot to tape the sheathing before the siding went up, it may be too late for tape.

  2. user-1072251 | | #2

    I assume you are asking about the exterior of the sheathing. We've used urethane caulk in the past, but have changed to a good peel & stick building tape which will last far longer. Foam in a thin bead between two surfaces, unlike urethane caulk or tape, can easily crack and leave the seam open to infiltration.

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