Interior and exterior rigid foam
Hello, Wade here from Fairbanks, Alaska (Zone 8) with a rigid foam insulation question.
Currently working on an addition to a current single bedroom house. The current structure will remain the heart of the new home, and I will extend a wing off each end of the house.
Current wall profile of the existing structure from inside to outside: drywall, horizontal 2×4 furring strips, 1.5″ rigid XPS, 6 mil vapor barrier, 2×6 wall with fiberglass batt, tyvek, fiber cement siding. I was meticulous when insulating the original structure 10 years ago and it has proven to be quite a good envelope.
For the new wings I plan to recreate the same wall profile (sprayed open cell foam in 2×6 wall cavities instead of fiberglass batts). However recently I have been toying with the idea of trying make things even more efficient. The new structure is much more complicated, has structural steel columns, lots of engineered LVL’s stacked in it, and I am worried that I am going to have places where the interior XPS is going to be my only defense against the cold. Its a large house (4900SQFT) and I plan to be living in it for the next 30 years, so I am willing to spend the extra money on insulation now because I believe it will pay me back over the life of the house.
So my thought is to put 3 inches of rigid XPS insulation on the exterior of the house. That should give me R-15 and provide a warm OSB surface to prevent frost build up, right?
Siding will be a combination of fiber cement, T&G cedar, and EFIS. Fiber cement and cedar will be applied to vertical furring strips to get a little bit of rain screen effect.
Should I move forward with this plan or am I asking for trouble? I appreciate all the help.
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