US Patent 8470436 Roofing system including insulation and cover boards

A roofing system includes a plurality of insulation boards adapted for overlying a roof deck to form a layer of insulation, and a plurality of cover boards adapted for overlying the layer of insulation. Each insulation board includes a polymer foam material having a first density. Each cover board includes a material including polyisocyanurate, the material having a second density greater than the first. The foam material of the insulation boards may include, for example, polystyrene, polyurethane, or a phenolic material. The insulation boards and cover boards may include facers on top or bottom surfaces.