Is a 2×8 wall better than a 2×6 wall with exterior insulation?
I am working out the wall assembly four out new build and I am trying to figure out whether it is better to go with a 2×6 wall or a 2×8 wall. Here is what I got for both
Home is in climate zone 5
2×6 wall (from inside to out)
– Gypsum board/sheetrock
– 2×3 service cavity
– 2×6 framing with dense packed wood fiber (~ R-20)
– Zip sheathing
– 5.5 inches of wood fiberboard (~ R-19)
– Rain screen
– Cladding (Vertical aluminum on 1st floor and horizontal Shou Sugi Ban wood on second floor up to peak)
Basically the same assembly but without the 2×3 service cavity. In this case we would maybe use some 1x strapping (maybe with the 2×6 wall too) for the service cavity.
– Dense pack wood fiber in the 2×8 (~ R-27)
– 4 inches wood fiber board on the exterior (~ R14)
I think the 2×8 with thinner exterior sheathing might be more manageable form a construction standpoint especially when it comes to attaching the rain screen and cladding. My understanding is that having a vapor open insulation on the outside also gives me some leniency with the amount on the outside although I think, in both scenarios, my rations are good.
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