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Caulking gaps in exterior rigid foam

quantumgirl | Posted in General Questions on

I have a detail question that may or may not even be important. 

my windows were installed on top of the OSB and integrated/ flashed with the Tyvek according to Tyvek instructions. I then added two layers of 3/4” poly Iso on top of the Tyvek. I taped the seams. My plan is to add a rainscreen, then Hardie siding.
Now what should I do with the gaps between the foam and the window jamb extensions? Just leave them since my windows are technically flashed underneath the foam layer? Or do I caulk them to offer extra protection for water penetration? If so, what caulk? Does osi quad agree with poly Iso?

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Quantumgirl.

    If your water management and air sealing are taken care of at the sheathing level, I would leave this gap open so that you are not inadvertently trapping water near the window.

    I'll be curious to see what others do here.

    1. Expert Member
      MALCOLM TAYLOR | | #2

      I'm with Brian. Leave that layer alone and concentrate on sealing the cladding, which is your primary protection against bulk water intrusion.

    2. quantumgirl | | #3

      What about gaps around penetrations like pipes or exterior outlets? Some of those gaps are 3/4” wide due to my apparent inability to cut the foam snug enough.

      1. GBA Editor
        Brian Pontolilo | | #4

        Again, if your water and air management is taken care of at the sheathing level, you don't need to do anything with the gaps in the foam. At an electrical or plumbing penetration, though, you could squirt some canned spray foam in the gap if you wanted, but mostly think about detailing the siding and trim well.

      2. Expert Member
        BILL WICHERS | | #5

        I would definitely seal up any cable or pipe penetrations with some canned foam. Even if you have air seal handled elsewhere, you have a risk of critters coming in around pipes and the like.


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