Here is a typical insulation detail for a rafter framed roof. We’re showing a 1” polystyrene baffle to provide airspace between the roof sheathing and rigid insulation for required roof ventilation. Under that is a 2” spray foam insulation with an R-6.9 per inch thermal value. The remaining rafter bay is filled with Spider fiberglass batt insulation which has a built-in adhesive, and has an R-value of 4.3 per inch. In a typical 11-7/8” rafter bay, this entire assembly provides an R-value of 52, well above the min. R-45 we show on our plans and the min. R-38 required by code.
