I am in the midst of a re-roof that was spawned by water damage. We’re taking off concrete shingles and putting on a metal roof (futureroof.com). I am looking for the best insulation that creates a vapor/moisture barrier. I was about to use closed-cell foam.

One cathedral ceiling has 2×4 roof joists that will be shimmed to 4 and a quarter inches. In some places on this roof the original skip sheathing is in place which could be left in place (at least most of it) while removing the batt insulation. This is a nonvented space.

The other cathedral ceiling has 2×12 roof joists. This has some soffit vents but no ridge vent. When we put on our new roof (Futureroof.com) which is a metal roof that is supposed to be a cool roof, we could put on a ridge vent. My hope is that we can make it a non-vented space as well. I’ve learned about how venting was simply a solution to wet batts but that it brings in cold air, brings in moisture, and brings in air movement—all which lead to condensation.

Both ceilings have to be insulated from the deck down. The roof with 2×12 joists has some exposed bays from the bottom so that could have up and down spray if up spray is preferable.

Also, we have not yet purchased our underlayment but were going to use 2; the first affixed to the top of the roof decking while waiting for the new roof was to be Titanium UDL. The second which would be put on as the new roof is installed has a locking property: MRN 1/4″ FFF Thermal Liner (don’t know brand name).

Thanks.