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Thoughts on Proposed Air/Vapor Barrier for New Construction

leon_g | Posted in General Questions on

We had some discussions with our architects about air and vapor barriers, but I wanted to get some feedback on what they are proposing.  I’m attaching a detailed view of a proposed wall assembly, which shows a WRB and a Smart Vapor Retarder.  Also attached are some more details of wall and roof assemblies.  The house will be in Portland OR, CZ 4

I read in numerous GBA articles that the architect should clearly show the air barrier path, as a continuous path from foundation to roof, with the comments along the lines of “if the architect can’t show how the air barrier should be achieved, how can we expect the builder to put in the proper air barrier”.  I’m attaching a drawing of an example of air barrier details to be used in construction drawings.

Looking at the drawings I attached, I don’t see the continuous air barrier in the proposed plans.  I don’t see a sill seal at the sill plate, I don’t see any caulking (other than at windows), etc.

In our discussions with the architects, they want to rely on tightly sealed drywall and the smart vapor retarder as the air barrier.  I don’t disagree with that, but we may end up opting for recessed lights (don’t shoot me), which would obviously penetrate the drywall/SVR barrier.  Even if we went for the surface mounted lights that they recommend, there would need to be wiring to these lights, which would have to penetrate the assembly.  Along the same lines, it seems like the numerous electrical boxes in walls will do the same – penetrate drywall and SVR barrier.

My questions are two-fold – 1.  Do the attached drawings adequately show the air-barrier, or do they need to be updated?  2.  Is relying on well sealed drywall as an air barrier a good strategy, given all the expected penetrations, or does an exterior air barrier make more sense?  If it’s the latter, we  have lots of rigid insulation on the roof to serve as an air barrier, but I am not sure about the walls.

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