Built-up roofs (BUR) are traditional roofing systems consisting of multiple layers of bitumen (asphalt or coal tar) alternated with reinforcing fabrics such as felt. These layers create a durable and waterproof membrane, offering excellent protection against the elements. Gravel or mineral surfaces are often applied on top for additional weather resistance and UV protection. BUR systems are known for their longevity and strength, making them a reliable choice for flat or low-slope roofs.