Rigid foam over WRB
I am finishing up a full kitchen remodel that pretty much required me to rebuild 25′ of exterior wall in my 1600 s.f. 1950s ranch located in Portland, Oregon (zone 4 marine). It is a 2×4 wall with R-15 fiberglass, existing 1×8 shiplap board sheathing (less some areas with wood damage, yes we do have termites in the NW), window and door rough openings flashed to a Tyvek primary WRB and air barrier. I would like to add 1-1/2″ of rigid foam with taped seams and a 1/2″ rainscreen before replacing my cladding.
Given that the Tyvek is already my primary drainage plane, should I bother to caulk the perimeter and rough opening edges of the foam to the Tyvek?
Dave
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Replies
David,
You wrote that the Tyvek is an air barrier, implying that you installed it conscientiously. That's good -- but experienced builders have learned that Tyvek isn't a very good air barrier. It's easy for ladders to leave rips in the Tyvek, and there are countless fastener penetrations.
So you still need to do everything you can to limit air leakage. The Tyvek is your WRB, but Tyvek alone -- even taped Tyvek -- shouldn't be depended on as your air barrier.
Q. "Should I bother to caulk the perimeter and rough opening edges of the foam to the Tyvek?"
A. Yes.