MJC,

Sorry, the thread is indeed old but if you are still out there, the foil face is rigid 'isocyanurate' type insyulation.

In recent years it has been getting much less expensive than styrofoam (here in NH), and gives better R-values. Especially if the reflective faces are used with a small air-gap.

Pete

I have done just what you described. Our layers were as follows (top to bottom):

-Shingles.
-#15 felt paper.
-1/2" plywood sheathing.
-2x4 strapping (flat) 16" OC.
-3 layers of 1-1/2" Firestone PolyISO polyurethane foam (staggered joints).
-1 layer of Ice & Water Shield directly on top of the pine t&g for our vapour barrier.

The 2x4 strapping was secured to the timbers with 10" screws (to sandwich the foam in place).

This proved to be an easy (and inexpensive) way to close in and insulate the roof system.

I'm interested in the technique,, but dont' have anything to add,,

I think they covered it well. I use the same system with some slight variances. I'm very pleased with how it works and performs. Tim

Do you need ventilation between the foam and the sheeting as you would with fiberglass insulation, or not?

Water vapor is far less likely to reach the dew point and condense at some point during its migration through foam, than it might be as it migrates through glass...

And IMO it is unwise to put a convection current (the ventilation) next to such a potentially volatile fuel supply as foam, as hot cinders my very well be drawn into a cold roof during a potentially beatable fire -

I typically sheath tight to foam and provide a secondary cold roof above it

Jim, I be building a similar roof on my home. If you have any installation information, drawings, photos etc... I'd appreciate receiving them as well. You can email me at: mauricep1@xplornet.con