Rigid insulation location
Renovating my second floor and need to insulate the roof. Zone 5, Roof is existing so unable to locate insulation on the outside. Need to do it as an unvented given the configuration. Is it better to flash and batt or batt and run the rigid continuous on the inside of the rafters.
Had a dewpoint anaysis run starting on the inside with 1/2″gyp on 3/4″ furing over continuous 2″ polyiso R13 over 6″ rafters filled with rockwool insulation R24 with 3/4″ purlins, 3/8″ plywood and black asphalt shingles.
The analysis extreme was run with an outside temp of 12degF and inside of 72degF and 30percent humidity. No condensation was shown to occur. That said, concerned that the R13 rigid might not be enough to keep condensation out of the cavity in looking at charts that indicate that you need a R20 in Zone 5 to ensure no condensation occurs. Advice? Prefer not to use Sprayfoam.
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