Smooth Modified BUR, also known as “BUR,” is a traditional commercial roofing system that has been used in the United States for more than a century. BUR roofs are also commonly known as “tar and gravel” roofing systems, and they are composed of multiple alternating layers of bitumen (asphalt) and reinforcing fabrics, which combine to create a complete membrane. Rackley Roofing has been working with built-up roofing for more than four decades, and we have a trusted reputation for our experience and skill in built-up roofing installation, maintenance, and repair.