A tar and gravel roof is a flat roofing system commonly used on commercial and residential buildings. Several layers of bitumen, usually tar, make up this kind of roof. For further protection, gravel or crushed stone is placed on top. In addition to acting as a ballast to keep the roofing materials in place, the gravel protects the tar from UV rays. The resilience of tar and gravel roofs to severe weather conditions is well-known.