Advisability of Continuous Interior Rigid Foam
Hello. I have been considering continuous interior rigid foam as an option to increase the efficiency of my 1950’s home in southern Ontario, Canada in zone 5. 2×6 construction, 16″ on centre. Brick exterior with a weeping gap between brick and the sheathing/stud walls. 2′ roof overhang, so wind-driven moisture on the exterior walls is rarely an issue.
Exterior continuous rigid foam insulation is not an option. The old brick look is not something to be covered, apparently.
There has been an article or two here and there, and the odd mention in other threads about interior continuous rigid foam use. However, I am having trouble finding any definitive answer as to whether it is advisable. It seems wise in the sense that it decreases thermal bridging from the studs and is also a vapour barrier, which is required anyway but has the added bonus of insulation. Partition walls can be dealt with, as the overall gains would likely compensate for any thermal bridging there. Horizontal furring on top is a consideration.
However, my main issue is not the practical application, but theoretical side. Some threads have pointed to the possibility that it would cause increased condensation in the wall cavity since we do heat the house for more or less half the year. This means the exterior walls are cold and form condensation where it meets the warm rigid foam, correct? So basically, the thicker the foam the better, so we would need no less than 2″ foam to keep the interior wall cavities from reaching the dew point, if I am correct in understanding?
If it is semi-permeable, is that better to allow some breathing?
My knowledge of how condensation works inside walls is limited, mind you. I am a DIY’er.
Another option I’ve considered is rigid foam strips along the studs to reduce thermal bridging (Bonfiglioni, I believe) and spray foam in the wall cavities. This seems the most tested in my mind as spray foam is known for its effectiveness in cavities and the rigid strips would minimize thermal bridging.
I don’t foresee electrical and plumbing utilities as an issue with interior rigid foam as we plan to do all (or mostly) exposed utilities as stylishly as possible because hidden utilities seem unnecessarily annoying and troublesome.
I am mostly musing at this point, as the inefficiency of the house is tolerable but eventually making it more efficient is the goal.
Thanks for any insight.
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