WRB and SIP walls
I’m designing a 3 season cabin at 8300 feet in the Colorado mountains. Climate zone is 4a, with yearly 13 inches of rain, and 64 inches of snow. Humidity averages 60% over the year. Typical temperature swings over 24 hours will be 35 degrees. IOW a dry, cold, semi-desert.
The structure will be built of SIPS, consisting of a sandwich of two pieces of 7/16” OSB wrapping 3-7/8” of closed-cell foam. The sandwich is rated at R28, with 2 perms/inch. All the joints will be taped.
The exterior will be cement lap siding. (James Hardie indicates I don’t need a wrb in Colorado.) The roof will be standing seam metal.
I’ve been considering Benjamin Obdyke’s Hydrogap SA on the walls for both a WRB and air gap. However, I’ve got a tendency to over design things, and wonder if I’m doing too much. Not using it would simplify construction and lower the cost. I’m also concerned about the high altitude UV exposure on any WRB I put on.
One interesting opinion can be found here. Written by some folks from Edmonton, Alberta, Canada.
Should I install a WRB on the walls?
Should it be drainable?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part