Zip Wall, air gap, and unprimed cedar shingles
I am about to build an 1800 sqf home right on the coast in RI. The general framing plan is 2×8 studs 24″ oc with 1/2″ Zip.
The insulation will be 1.37″ closed cell foam right up against the sheathing then high density fiberglass bats. Should be about r30.
(I understand this insulation and framing combo is not exactly logical. Its a compromise between several parties its not changing.)
Siding is unpainted cedar shingles over 1/4″ obdyke cedar breather.
My concern is solar driven moisture wetting the OSB zip wall. Building Science Corp recently published an article describing how solar driven moisture can rot OSB siding. I believe that zip wall is sufficiently permeable to allow drying,and the obdyke breather is a good start. I am slightly concerned that the sheathing will stay very cool and therefore damp because of the thickness of the walls and have no way to dry inward.
Do I need a larger air gap?
I had also been considering using a felt paper WRB as cheap insurance, but I am coming around to thinking this is unnecessary and will only prevent drying.
Thanks for your thoughts,