David writes again from Arlington, Massachusetts: "Can I slide your foam board insulation between the roof rafter (16 inch on center - true 2x8) and the finished lath sloping ceiling? Or do you sell some other product that would work?"

Answer: We do not recommend FOAMULAR® insulation for this application. Instead, consider using PINK fiberglass insulation. Detailed installation instructions can be found at owenscorning.com on the project page for cathedral ceilings.