Built-up roofing (BUR) or more commonly known to the layman as “tar and gravel” roofing, consists of multiple layers of #15lbs Asphalt felt paper (usually 4-5 ply), bonded together with hot bitumen. Another layer of hot asphalt is poured on top and clean crushed stone is embedded in the hot asphalt. The stone is simply there to prevent the sun’s UV rays from deteriorating the asphalt. BUR is the heaviest and most robust flat roofing system. It is not easy to damage a multi-layer system.