What is the purpose of an overlap in BUR construction?

The function of an overlap in Built-Up Roofing (BUR) construction is fundamentally to create a watertight seal between layers. In BUR systems, multiple layers of roofing felt are typically used, which are adhered together with asphalt or similar adhesive materials. The overlaps ensure that water is directed away from seams and prevents leaks from occurring at these critical points. By overlapping the edges of these layers, a continued barrier is formed, effectively sealing the roof against water penetration, which is essential for the durability and longevity of the roof system.

While insulation, aesthetic appeal, and installation time are important factors in roofing, they do not fundamentally address the primary purpose of overlaps in BUR construction. The paramount concern in designing a roof system is to ensure it is waterproof, and overlaps play a crucial role in achieving that goal.