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Transitioning an Air Barrier From Wall to Roof

sabotcat | Posted in Green Building Techniques on

Hey all,
Just a quick question…I was browsing the Detail Library and couldn’t find what I was looking for…which is more a comment on me than on the incredible sections that are saved there.

I’m doing a Pretty Good House in the desert, I’ve posted here before.  But along with providing the structural guy with all are materials…I want to give him a general idea of how we want the joists to terminate at the wall so we can run the sheathing up to the roof line.  Then I’d like to build out the overhang with a short beams that run along the roof.

I intend to cover the walls and room with external insulation after everything sealing the air/water barrier.

is there a detail for on the site…and if not, can someone point me toward a detail elsewhere.


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  1. sabotcat | | #2

    Thanks for this. It's really helpful...and I'm totally sold on the ripped strip of advantech on the top plate in this application. The trick here I see it, the air barrier transitions from the outside to the inside at the top plate. I'm thinking more a shed-style roof ... in which the joists terminate at the top plate. I'm hoping I can either use zip on the outside or a self-adhered membrane that will go from the sill right along the roof. Then lay the external insulation over that, and fill the cavity with dense pack.

    I know it's done...and it's pretty much what Matt Risinger did on his house in recent posts over there...but to explain it, I'm hoping someone's made a CAD drawing. I went to Matt's site, but it's the build show network now...and while I know there must be a forum somewhere, I can't for the life of me find it!

  2. BirchwoodBill | | #3

    Here is some details from a personal house that I am designing for Zone 6. (These have not been approved by a structural engineer).

    16-inch I-Joists terminate at the wall and are covered with ZIP sheathing - that forms a continuous layer. On top of the I-Joist I have a Cor-A-Vent purlin strip and a 2x4 forming a ventilation chute. With the 3:12 roof pitch I need a 2 1/2 inch air gap. Underneath the joists - there are 2x4 attached to the ceiling to form a service channel for running electrical - without damaging the membrane.

    For the out-riggers - I am looking to cantilever a 2x4- and have them connected to at least 3 I-Joists. Then have a hurricane strap under-neath to deal with up-lift.

    Where the shed-roof meets up at the clerestory, there is another detail - that I used from Fine Home-Building issue 99. That requires cutting a 1-inch gap through the over-roof and then using a Cor-A-Vent strip to block any incoming air/water.

    The basic concept comes from the PERSIST design pattern - I am looking through whatever I can find online as well.

  3. sabotcat | | #4

    thanks! These are super helpful. I really appreciate the time. And I'm going to go back to the PERSIST site and read up on their strategies. Our climate is much for forgiving when it comes to drying...but these rules all still apply, especially if we're trying to keep our off grid solar as reasonable as possible.

    thanks again for this...this forum and the folks on it are an incredible, and a very charitable resource. You're all a lot nicer than those guys over on the wristwatch forum...they can be ruthless!

  4. BirchwoodBill | | #5

    Your welcome, I need to rewatch Steve Bazcek’s build show on you tube. I think he and big red discussed some of the details. I just listen and then draw, it helps me to relax.

    1. sabotcat | | #6

      I've become a huge fan of big red.

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