Ask your B.D. Most locales require 1/4" plywood or paneling to meet fire code. I would prime the boards for moisture protection, air seal the surface behind with the foam boards (and get a thermal break from the rafters).
Be safe, Gary
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The carsiding is 5/8" so it should work, but I'll check. My major barrier is is going to be how to insulate the vaulted part (2x6)of our garage reno with code acceptable R-value and getting my inspector to approve the removal of ceilings joists and addition of rafter ties.......although with all the info you supplied me with that shouldn't be much of an issue