thermal bridging in spray foam wall
Five years ago I replaced a full exterior wall of an old house (year of building unknown, guessing at 70 years, likely someone’s old 3-season chalet converted to 4). We built the new wall using 2×4 and used full cavity spray foam (I’m not sure if it was open or closed cell- it is very rigid). There is Tyvek, then Maibec wooden siding. On the interior there is drywall and paint.
There were also ceiling issues caused by inadequate insulation and a low shed roof over this area of the house (was possibly a porch that had been turned into a bathroom), so after re-building the wall, there was still moisture at the top of the wall, on the ceiling, and obvious roof melt causing ice dams. In late 2019, fixed this issue by adding an “insulation heel” using custom built trusses and basically building it over the existing roof and filling it with more spray foam insulation. No more ice dams! However, the top plate of the wall, where it meets the new “heel”, is still showing signs of interior moisture at several points along the wall. I can feel cold on the walls in those spots on cold days. It is possible that the spray foam guys missed some small areas and there are pockets of empty roof cavity there. At any rate, there is thermal bridging happening and I would like to address it. My concern is that there is moisture on the inside of the drywall caused by either a gap in sprayed insulation or an inadequate “fit” between the old roof assembly and the new.
Here comes the question…can I simply spray foam the exterior of that zone where old and new meet (currently remains un-sided)? Or is there something to do on the inside?
I am located in southern Québec, zone 4 (for plant hardiness, sorry, can’t find if that’s the same for insulation or not!).
Thanks for any advice you can offer!
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