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Community and Q&A

Seal inside seams of Zip-R sheathing?

alan72 | Posted in General Questions on

Climate zone 5

we are working on air sealing details on our new home build that is sheathed with Zip R sheathing. 

the exterior taping/liquid flashing was done per specs.  The bottom of the sheathing was taped to the foundation wall with zip tape augmented with 3m 90 adhesive.

Would taping or caulking (or liquid flashing) the inside seams (polyiso) help with air sealing? Or would this just be a waste of time/money?

if it is worth it, what works on plain (un-faced) polyiso?

Thanks in advance. 


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  1. natesc | | #1

    All sheathing edges should typically fall on studs or blocking between studs - they should be inaccessible to tape. All sheathing edges need to be blocked solid so the wall diaphragm can do its job.

  2. CMObuilds | | #2

    1 component foam would work in the stud bays and is cheap if you either doubt some areas of quality or are really going for tight.

  3. Expert Member
    BILL WICHERS | | #3

    A foam gun such as the great stuff pro gun with the fine tip attachment works pretty well for injecting foam into small gaps and seams. I’ve done this before with XPS and EPS foam, but I’ve never tried it with Zip. The Process should be the same for Zip though.


  4. GBA Editor
    Brian Pontolilo | | #4

    Hi Allen.

    The horizontal seams, which are the only seams that would be accessible from the inside do not need to be sealed as long as everything is taped or covered with liquid flash from the exterior, as it should be.

    When sheathing is the main air barrier on walls, sometimes the perimeter of sheets may need sealant between them and the framing, but this is rare as most builders use tape as the bottom of the sheathing (sheathing to foundation), are using tape around window and door rough openings and may even be transitioning from sheathing to a ceiling air barrier at the top plate with a taped flange. But it is worth thinking about all of these locations to make sure that the sheathing is sealed one way or another.

    I'm just not sure there is any benefit in an interior redundancy if the exterior is detailed properly though. Plenty of builders are hitting ridiculously low air changes per house with doing this.

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