An expanded perlite insulation board having an integrally attached scorch-resistant layer is provided. During formation of the perlite insulating board using a traditional Fourdrinier manufacturing process, a liquid slurry of mineral wool and clay is applied to the still-wet perlite board, forming a coating thereon. Upon completion of the manufacturing process, the coated layer protects the underlying perlite board from scorching during installation of the outer modified bitumen layer when using the open flame, propane torch method of installation.