I recently got a bunch of polyiso foam pieces that I want to use on the outside of my house. The outside of the house has 4″ of foil faced polyiso, but I have many attached porch roofs that have nothing between the rafters where they attach to the house. I was going to cut and cobble pieces in these spaces and can foam the edges. Here lies the issue, the foam I just got is 3″ thick so I was going to double them up but I’m not sure about the facing. One side is a layer that looks like tarpaper and the other side looks like 1/2″ of sound board, seems similar to suspended ceiling tile material. Can I safely use this? I was thinking of facing tarpaper towards the wall and 2nd one have tarpaper facing out, so the “sound board” sides would be in the middle against each other. Is moisture an issue ? Would the tarpaper and can foam seal this? I tried to cut the layer off so it would be just foam but it is firmly attached and would take a lot of time to do it. Anyone work with this before?