Which materials are commonly used as the surfacing layer in BUR?

The correct choice identifies materials that are commonly used as surfacing layers in Built-Up Roofing (BUR) systems. Gravel, modified bitumen, and reflective coatings serve specific purposes in BUR applications.

Gravel is often used as a protective layer, providing ballast that protects the underlying layers from UV radiation, physical damage, and weathering. It also helps with drainage, preventing water accumulation on the roof surface. Modified bitumen can serve as both a waterproofing layer and a surface, offering durability and flexibility, especially in areas subject to temperature fluctuations. Reflective coatings are critical for increasing energy efficiency, as they help reflect sunlight, reducing heat absorption and mitigating the urban heat island effect.

Selecting these materials ensures the roof is durable, water-resistant, and energy-efficient, fitting the unique needs of BUR systems.