The ceiling assembly is fiberglass batt (R-19) in the rafters and drywall. I want to add 2″ layer of rigid polyiso (R-13) to the interior side of the drywall, then 1×3 furring, finishing with T&G pine. I know its should be R-49, but I think the extra R-13 and minimal impact on ceiling height will be worth the hassle. I’m in climate zone 4c. Is this feasible or will there be moisture issues between the foam board and drywall?