What kind of materials are typically used for the top layer of a BUR system?

The top layer of a Built-Up Roofing (BUR) system is typically composed of colored gravel or reflective coatings. This choice is important because the top layer serves several critical functions, including protecting the underlying layers of roofing from physical damage, UV radiation, and weathering.

Colored gravel is commonly used since it can provide additional aesthetic benefits while reflecting sunlight, which can help in managing the roof's temperature and reducing heat absorption. Reflective coatings, on the other hand, enhance energy efficiency by reflecting solar radiation. This can contribute to lower cooling costs in buildings by minimizing heat buildup within the roofing system.

Other materials listed, such as rubberized membranes, plastic sheeting, and wood shingles, are not standard for the top layer of BUR systems. Rubberized membranes are usually related to single-ply roofing systems rather than BUR, plastic sheeting lacks the durability required for BUR applications, and wood shingles are traditionally used in pitched roof systems rather than flat BUR configurations. Overall, the materials chosen for the top layer of a BUR system provide crucial protective qualities and energy efficiency benefits, making the first option the most appropriate choice.