How to avoid trapping moisture in a wall with interior and exterior gypsum?
I live in a wildfire zone in California and am building a shed with metal siding. With metal siding, FEMA’s recommendation and local county codes require a thermal break between the wood framing and external siding. The details are shown here:
My concern with this setup is moisture being trapped in the wall. My layers from inside-out will look like this:
interior gypsum -> framing/insulation -> plywood sheathing -> exterior gypsum -> wrb -> metal siding
If I understand gypsum correctly, it acts as an air barrier. Recommendations from the above source recommend taping all seams of the exterior gypsum. Given this setup, it seems like the wall is going to be airtight and wouldn’t be able to breathe.
Am I right, or am I worrying about nothing? If this is an issue, how can I avoid this issue? Would a rain screen between the sheathing and external gypsum be the way to go?
Thanks for any advice on this!
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