Spray foam retrofit from the exterior?
I’m re-siding a house built in the 60’s with minimal fiberglass insulation in the walls. Many of the rooms are quite cold. I am considering two options below: (Note: removing the interior finish, or even blowing in from the inside is not an option)
1) removing the siding, sheathing, and insulation, then applying open cell spray foam in the stud cavities from the outside, then sheathing with R6 zipwall.
2) just removing the siding, applying the R6 zipwall
Obviously option 1 is more work because of removing the sheathing, but I get a higher R value. However, I’m concerned about not having a vapor barrier on the inside of the wall. I know I will have to deal with the windows if I remove the sheathing, but that is part of a more complicated discussion which is better not discussed for clarity.
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