Which material is commonly used in the construction of BUR roofs?

Asphalt or tar is the primary material used in the construction of Built-Up Roofing (BUR) systems. BUR roofs are characterized by their multiple layers of bitumen (asphalt or tar) alternated with reinforcing fabrics, creating a durable and waterproof membrane. The use of asphalt or tar helps to bind the layers together, forming a continuous and effective barrier against water infiltration. This makes BUR roofs particularly suited for flat or low-sloping surfaces where drainage is less effective.

In contrast, the other materials listed do not suit the BUR system. Metal sheets are typically used in standing seam or corrugated roofing systems, while single-ply synthetic membranes are separate roofing solutions often employed in commercial or industrial applications. Wood shingles are traditionally used in steep-slope roofing rather than flat systems like BUR. Thus, asphalt or tar stands out as the right answer due to its specific role and effectiveness in built-up roofing systems.