Insulation for attic of Cape Cod house
I insulated the 'attic' of my cape cod house 2years ago. The attic joists are 2x6s, as are the rafters. The attic is only 3ft high, so I did my best to add 6' kraft-faced insulation between the joists, and then 9' unfaced insulation laid perpendicular to the joists. Of course, it was impossible to get new insulation from the attic down to the knee walls (between the joists): just too difficult no matter how I pushed/pulled. Now that Hurricane Sandy damage requires me to strip off and replace all sheetrock and insulation, I want to do a good insulation job along the sloped ceiling/wall too (i.e. from the knee wall to the attic). These upper rooms get unbearably hot in the summer, radiating heat from the sloped wall/ceiling. I can't afford spray foam. Is rigid XPS foam board between the joists better than fiberglass batts? Maybe 2 layers of 2' thick, which would leave 2' air gap between the XPS insulation and the roof deck? I'm also thinking about adding 1' XPS between the joists and the sheetrock, to act as a thermal break, but I'm concerned about popping screws.
Your advice greatly appreciated.
Here is a link that might be useful: