Is this a good exterior wall design for climate zone 5?
I’m building a house and want very energy efficient, durable (100 yr), efficient to build and not outrageously expensive. I’m willing to pay up for an insulation system, but am not convinced that very high R values are economically justified in the way that good design and better materials are. So I have been debating a conventional frame 2×6 24″oc, sheathing, 1.5″ cc spray-foam outside and over rim joist, 3″ foam inside stud bays and rim joists, and rest of stud bay left empty. Seems this would give good insulation, eliminate bridging, compensate for fine flashing mistakes, eliminate condensation and vapor driven issues and not require design changes outside the norm of our local builders knowledge. 1. is this sound? 2. how durable is spray foam? relative to foam board? exterior applications? 3. if real R value diminishes quickly with additional inches of insulation, is leaving the rest of the stud bay empty better for durability? 4. are there siding attachment issues thru spray foam?
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