US Patent 9404261 Roofing systems and methods

According to one aspect, a roofing system includes a plurality of insulation boards adapted for overlying a roof deck to form a layer of insulation. Each of the plurality of insulation boards includes a first polyisocyanurate foam having a first foam density. The roofing system further includes a plurality of cover boards adapted for overlying the layer of insulation. Each of the plurality of cover boards includes a second polyisocyanurate foam having a second foam density, and the second foam density is greater than the first foam density. Each of the insulation boards and cover boards may have a facer on at least one major surface. The second foam density may be selected to provide the cover boards with a compressive strength to resist deformation.