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Air sealing between rafters

benjwadsworth | Posted in Energy Efficiency and Durability on

I am getting ready to side a “backyard cottage” with a shed roof in Seattle.  The wall and roof assemblies consist of the following…

Unvented Roof – 2×10 rafters filled with fiberglass or cellulose, 5/8″ OSB with taped seams, 2 layers of 2″ polyiso insulation, 1/2″ OSB nail base, ice and water shield, metal roof

Walls – OSB, 1 1/2 ” polyiso with taped seams that will serve as air barrier and WRB, 1/2″ rain screen battens, Hardiboard siding (mostly).  I opted not to tape the OSB seams as the polyiso seams are taped to serve as the WRB, and taping both seemed redundant.

I feel good about the air barrier in general, but my question is what is the most efficient and effective way to seal the space between the roof rafters?  Cut and cobble polyiso?  Spray foam on the inside?  Photos attached.  Thanks.

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  1. the74impala | | #1

    Why not use plywood on the soffit and tape/caulk the joints. Whole lot less cobbling to that, and easier to tape.

    1. benjwadsworth | | #2

      That's a possibility but I'm not sure how that would seal the edge of the foam at the top of the walls? It also seems like it might be fairly expensive given the size of the overhangs/soffits (3' and 2') and the cost of plywood these days.

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