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Advice on air sealing locations

HartiganWill | Posted in General Questions on

I’m reading a lot about air sealing and the various locations it can be done but it’s not clear yet what the best locations are to use?

1.) For the exterior, is it best to put maximum effort into taping/sealing at the OSB/Plywood sheathing or at the next layer of rigid foam? I’ll be using ADA for the interior dry-wall as well but I’d like to get as close as possible on the exterior layer so the house’s nooks and crannies are exposed for easy remediation with the blower door.

2.) For the interior ceiling air barrier is drywall sufficient or should that be sheathed with Plywood/OSB or even another air barrier product?

3.) For the attic what’s generally easier and or more successful; taping the sheathing and adding rigid foam on top or doing spray foam from below? The attic will be a desert-style sealed flat roof so once it’s insulated I don’t expect there will be much room opportunity to crawl it… I’m leaning toward spray foam in this instance.


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  1. Expert Member
    PETER Engle | | #1

    1) Most builders find that taping the seams on the exterior sheathing is the easiest way to achieve the air barrier as there are far fewer penetrations and interruptions than trying to make the interior airtight. That said, ADA inside also helps.

    2) If you are diligent about the air sealing, the drywall can be your air barrier. But you need to really consider what you are going to do about the junctions with walls, wall top plate penetrations, etc. Cobbling together a continuous air barrier can be a challenge. You also need to consider your vapor retarder in cold climates. One approach that works especially well with truss roof construction is to install a plastic membrane (semi-permeable or not depending on climate) over the entire underside of the roof framing before installing walls.
    3) Not sure what you mean by "desert style sealed flat roof" along with attic. Some additional details would help us answer this one.

    1. HartiganWill | | #2

      Thanks Pete!

      For #3, the roof will be flat (low slope) trusses. It’s a modern style house in a suburb of Phoenix AZ. So just think modern flat roof.

      I mean to say I planned for an unvented design sealed either by spray foam from below or rigid foam from above.

    2. HartiganWill | | #3

      I’ll also add in, when sealing exterior sheathing have folks found a difference in air tightness comparing products like ZIP vs. bare OSB/CDX?

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