I happen to have several square feet (2,576) of rigid foam insulation laying around that I'm not sure I'm going to use (it came with an order of stuff I will certainly use). I have a small house that I'm redoing (down to studs and back). The roof currently has 2 layers of composition shingles, and a roofer friend indicated the current top layer is about 12-15 years old. I think I also might have a leak in the valley over the front porch - I'll know for sure in the next week or so when I rip the porch ceiling out.
I was wondering, if I do choose to replace the roof, which would involve removing both layers and going back with either shingles or metal, would applying this 2" polyiso on top of the existing roof deck (1X6 T&G pine) make any difference whatsoever in the temp of my attic during the summer or winter in Texas? The 3 gabled ends would not have any insulation, and the will have new gable vents. Inside the attic, the ceiling would have blown (new) insulation. The polyiso is not foil faced.
Thanks, Todd