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Spray Foam from the outside - how to air seal and complete vapor barrier?

TedBarnhill's picture

Hi folks.  We are working on a remodel of a 100+ year old home into a high-performance, green building in Minnesota.  The exterior walls will be spray foamed from the exterior by removing existing siding and insulation.  (The inside approach wasn't taken due to extensive, beautiful wood paneling and trim.)  Closed cell foam is being used, on top of which will go Dow SIS - 1/2 foam sheathing which, when taped, will act as sheathing and exterior air barrier (also provides an additional R-3 insulation)

The SPF will provide the home's vapor retarder behind the uncertain plaster and paneling surfaces.  However, there is some disagreement about the best approach for the joints between studs, and around headers.  In high-performance new home construction, these thin cracks are caulked on the inside to prevent vapor or vapor-laden air from leaking through between the studs.  Does anyone have thoughts on whether or not to caulk these joints?  They aren't foamable gaps, just thin cracks.  One opinion is that caulking these cracks at the exterior face of the wall may create moisture/condensation problems at that location.  Thoughts?


You are better off (post #203156, reply #1 of 1)

posting this question at

Lots of discussions of energy retrofit applications over there... few if any here...