This home was completed in late 1965 and originally had a gravel roof I was able to keep painted white. Insurance required replacing roof so now it is 30-year asphalt shingle. Old A/C having a hard time keeping up with heat load so I'm thinking of installing 2 inch foil backed polystyrene between the "rafter" portion of the trusses. This foam would be installed flush with the bottom side of the "rafters" leaving an airspace of one and one half inches between the upper surface of the foam and the lower surface of the roof planks/sheathing.
The new roof has a ridge vent and there are vented soffits along both of the lower roof portions. This looks to me like it would provide adequate venting of the heat built up during our sunny days. I'm wondering if the 2 inches of foam, along with the foil as a radiant barrier, will do enough to reduce the heat load in the attic to allow the A/C ductwork to operate more efficiently thereby keeping the living space more comfortable. The ceiling has original blown-in fiberglass at three and a half inches. Not great but that's all the space we have to insulate. Also, I am tempted to install this foam with the radiant barrier up since there will be a 1 & 1/2 inch airspace above for it to work. Any thoughts would be welcome.