Foam It Green is saying I can put 3 inches of foam and then attach the drywall to the rafters (leaving 2.5 inches of space). Is this viable? I don't see a lot of Foam It Green comments. Looking at investing a significant amount of money (for us) and just don't want to get burned...I presume I'd need to use a good vapor barrier prior to the drywall.
I know there are no shortage of varying opinions on foam use, but thought I'd try to get some (valuable) input.