Unvented cathedral ceiling condensation issues
I received a call form one of my Architect clients. His friend recently re-built his roof and now has major condensation issues; so I went to take a look. Here is the constructed assembly as best as I can figure, pictures attached.
Inside to Outside
1. Heavy timbre with wood cladding in between
2. 6mm poly that wasn’t removed attached to the heavy timbre’s with acoustical sealant and staples
3. From here the old roof was removed from the outside. Between the heavy timbre’s polyiso was tuck taped to the timbres to give the foamer something to spray against.
4. 4″ of closed cell spray foam was applied from the outside, again see pictures. Foam applied over heavy timbres and in between the 2×6’s running parallel and perpendicular on top of the heavy timbres. 2×4’s then on top of the 2×6’s.
5. plywood sheathing
6. felt underlayment
7. Armadillo metal roof
The home owner had condensation issues before the roof repair, now the condensation issue is worse. We are in a 7A zone, Prince Edward Island Canada so I know the R26 from the foam is just not cutting it.
I have a few concerns, first is the double vapor barrier. When we took down a section of the interior cladding to take a look, there was no signs of condensation between the 6mm poly and the poyiso.
Second is the fact that there is a void area between the roof sheathing and the spray foam.
My original thought was the condensation was due to air leakage and freezing on the warm side of the roof sheathing. I was hoping we could take off the metal roof, slap some xps foam in three layers on the roof sheathing, re-install the roof and that would take care of the issue. However I was informed by the roofer that the new roof is not coming off without destroying it.
Now my approach would be to add additional interior insulation and a smart vapour retarder.
Am I missing something or am I on the right track. I would like a second opinion and also think a WUFI analysis wouldn’t hurt as well.
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