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Sealing sheathing seams

Mtech | Posted in General Questions on

Hi, good morning to all. I was just wondering: if I use flash-n-batt insulation system in a new house, do I need to tape the 1/8 sheathing joints on the outside or would the 2 inches of closed cell spray foam seal this joint? I’m in zone 5 northern New Jersey. Thanks

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  1. GBA Editor
    Martin Holladay | | #1

    M. Tech.,
    Most builders and homeowners would say that 2 inches of closed-cell spray foam creates such a good air barrier that you don't have to tape the sheathing joints. That said, you still need to pay attention to all of the usual air leaks that spray foam doesn't address: These include double studs (which need caulk on the interior at the seam between the studs), double top plates (ditto), and the crack between the subfloor and the bottom plates of your wall (which need gaskets or interior caulk).

    If this is your builder's first attempt at a tight house, it would be a good idea to get a blower-door test before drywall is installed, and to address any leaks that the blower door reveals.

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