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Wall assembly

Matt_Ohio | Posted in General Questions on

I need advice/confirmation of residential wall assembly.

Wood framed home, from inside to out: ½” drywall, 2×6 studs w/fiberglass or roxul, R-5 Thermo-Brace SIB (think ZIP System), either a mesh (Tyvek DrainVent) or dimple board (Delta-Dry), LP Smart siding.
I’m confused on what rainscreen to use (DrinVent or Delta-Dry). Not sure if I need a permeable or impermeable. Since the insulation board has an integrated WRB I don’t want to trap any moisture.

Thanks in advance for the advice!

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  1. Expert Member
    Dana Dorsett | | #1

    And your IECC/DOE climate zone is...??

    1. Matt_Ohio | | #3

      Would this wall assembly need a Poly vapor barrier on the inside prior to the drywall? I'm a bit confused on the CI, I believe I read that in Zone 5 you should have a minimum of R7 exterior, but due to multiple reasons that is not an option for this project.

  2. Matt_Ohio | | #2

    Zone 5

  3. GBA Editor
    Brian Pontolilo | | #4

    Hi Matt.

    The international Residential Code calls for a class I (poly sheeting) or class II (kraft-faced insulation) interior vapor retarder in your area unless you meet one of two conditions. Those conditions are R-7.5 continuous insulation or a vented siding installation. You'll be meeting the second requirement, so you can choose to use a class III interior vapor retarder, which is essentially painted drywall.

    However, since you will not be meeting the R-value requirement with your continuous insulation, which is meant to keep water vapor from condensing on the inside face of the sheathing, I'd consider a smart vapor retarder on the inside, like the Intello membrane.

    I couldn't find the perm rating of the Thermo-Brace sheathing, but I don't think it matters, you'll want the most vapor open rainscreen assembly possible. Is there a reason why you are not considering a built system with furring strips?

  4. Jon_R | | #5

    Sounds like Thermo-Brace SIB is reversible - if so, put the foam to the exterior and then use below to verify the design.

    IMO, not being forthcoming with perm values is a negative. Huber (Zip) also engages in this.

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