Too much insulation
Is there such a thing as having too much insulation?
My recent home addition has a 2×6 wall construction with 1.5“ polyiso on the exterior. So that’s already R10. Code for climate zone 2 is R13 for walls. I want to insulate the stud bays with open cell spray foam to act as my air barrier. Technically I would only need an inch to reach R13. Is there any benefit if I do more spray foam? It seems like a waste of space if I leave most of the stud bays empty. Would spraying the entire wall be overkill and a waste of money or is more insulation always better, regardless of climate zone? Spraying the entire cavity with ocsf would give me an R value of 30.
For context, my ceiling will be insulated to code, R 38. (2×6 construction filled fully with closed cell foam is the only way to reach code here since I missed adding exterior insulation to the flat roof and already have a deck installed on top.)
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