# Closed cell poly iso roofing material for residential



## KurtP (Sep 12, 2010)

I recently acquired several 3 3/4" x 4' x 8' closed cell poly iso foam core faced with heavy black fiber-reinforced organic felt (non-asphaltic) on both sides. The brand name is AC Foam II. This material is apparently used to insulate commercial buildings with 'hot asphalt or coal tar BUR, modified bitumen, and single-ply membrane systems'. I was wondering if I can used it to insulate my pitched roof by putting it between the sheathing and roof shingles instead of cutting it to size and putting it on the inside between the rafters, which would lower an already low headspace in the attic even more. I know two big issues are getting fasteners long enough to reach the sheathing and covering up the exposed ends. Can this work?


----------



## TarheelTerp (Jan 6, 2009)

kurtp2 said:


> 3 3/4" x 4' x 8' closed cell poly iso foam core (@ 6-7 R per inch =R24)...
> ...putting it between the sheathing and roof shingles...
> ...putting it on the inside between the rafters,
> Can this work?


How about laying it between/over the ceiling joists (or truss chord)?


----------



## Windows on Wash (Aug 30, 2011)

You can do that is you decide to create a "hot" roof but you will need a nail-able base (another layer of plywood) applied to the top of the foam.

You should not use it and nail directly through the foam to attach the shingles. It never works properly that way.

Also, make sure you are applying a suitable thickness to the roof when you do it.


----------

