Polyiso versus XPS Foam for a roof??
So I need to replace a section of a low slope roof on our ranch (1925 built) immediately. We are going to add on to the back of the house and have a cathedral ceiling kitchen in a few years so i want to do a test on this part that will not be disturbed.
I have read and read for years about the possible applications and have old articles that i can adhere to. However i do not truly understand the difference between the 2 products and if it really does not matter on the roof. It will not get wet after i do the job correctly so does it matter that i use some XPS in conjuntion with the polyiso?
I will probably go with the suggested 6 inches of material but am not sure if i will incorporate the venting or not between the last layer of plywood and the roofing material.
Mainly because i am just not sure how i am going to attack fastening the material and furring strips just yet.
Anyone have any thoughts?? I see the polyiso has a little more r value but i am thinking it may be worth saving some money and only using 1 layer of that. We live in north jersey so i am thinking we are in Zone 6 or on the edge where i see it should only require 2 inches of closed cell foam to stop the dew point.