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Community and Q&A

Can the air barrier be in the middle of a double stud wall?

user-5374846 | Posted in Energy Efficiency and Durability on

I am building a pretty good house in NJ, climate zone 4. I have considered many wall options and in the interest of controlling both material and labor or costs, I have arrived at the following:
2×6 wall filled with Roxul Batts R23
Air and Smart Vapor barrier, (Pro Clima Intello or similar) on the interior of the 2X6 wall.
3 inches of Roxul comfort board installed on the interior…covering the studs and Air Barrier, held in place with 2×4 strapping, creating a service cavity and nailing for Sheetrock. Total R35.
Sheet rock with latex paint on the interior.
Plywood sheathing, covered with a rain screen house wrap such as Hydo Gap and clad in Cedar Shingles.
I like this idea because it provides traditional window installation, siding and trim details and will not require a cross hatch of 1×2’s to create a rain screen for the shingles that exterior insulation would require. Additionally, having the air barrier in the center of the wall allows for an effective service cavity with minimum penetrations.
Please provide feedback as to reasons I shouldn’t like tis design.
Bill S.

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  1. Reid Baldwin | | #1

    I suggest that you draw up cross-sections that include the interfaces to floors, foundation, roof/ceiling, windows, and interior walls. That exercise tends to highlight issues that are not apparent in a middle-of-wall stackup.

  2. GBA Editor
    Martin Holladay | | #2

    Q. "Can the air barrier be in the middle of a double stud wall?"

    A. Yes.

    Reid's point is a good one. Make sure that you can keep your air barrier continuous at intersection points like wall-to-ceiling transitions (rim joist areas) and wall-to-roof transitions.

    To me, the trickiest part of your plan is keeping the interior horizontal 2x4s, which rest (apparently) on a cushion of continuous mineral wool insulation, co-planar and firm (not squishy). I think it's possible to achieve, but it will take some practice and experimentation -- and your builder may not like it.

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