One layer of exterior foam in climate zone 5
I’m sourcing materials for a project in the Seacoast area of New Hampshire.
I’d planned on standard 2×6 construction with an engineered roof. My intention was 2 layers of 2″ foam on the walls (not too partial to type of foam) and 6″ of foam on the roof. Cavity insulation of some sort, cost dependent. I’d even be OK with 2×4 construction for a total all R value somewhere around R30. I’m building this house to sell.
The quandary: I’ve found an excellent price on 1.5 lb factory second 4″ EPS. I could use it beneath the slab, on the exterior foundation walls and continue it up the outside walls of the house and use two layers on the roof. How much do I have to worry about the joints opening if I were to only have one layer of foam on the walls? Could I spray foam and tape the joints and be OK? The cost savings of using 4″ EPS throughout is half. Price is $19 for a 4″ 4×8 sheet.
Could be possible to use a layer of 1″ or 1.5″ of ISO inside of the EPS, but I wouldn’t be psyched to deal with trim and wall cladding of any sort over nearly 6″ of foam.
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