Don't do it
I have had way too much experience with this crap. From an insulation standpoint., it's a great product,but from a drywall perspective it's a nightmare. Whenever you put something between the framing and the drywall,bad things happen. The worst part is trying to set the screws, because the cushion of foam makes it impossible to set the screws because 99% of the screws will tear the face paper thus losing their holding power. You can't glue it either because all the foam board I have seen has a "wrapper" of plastic. The other downside is that the foam board needs to be fastened as well as drywall because the drywall is not going to "tighten" the foam board. I have never even seen the foam board put up properly, so the drywall job becomes impossible to correctly. The last problem is windows and doors. I assume you rout your windows and doors, so you will need to put extension jambs on prior to hanging or hand cut the windows and doors and that is just crude. If you are that energy conscious, why not try foam insulation in the cavities? Expensive, but if done properly, it's the greatest.:thumbup::thumbup:
