What are cap sheets primarily used for in BUR roofing?

Cap sheets in Built-Up Roofing (BUR) systems serve a crucial function by acting as the top layer of the roofing assembly. They are specifically designed with a granule surface that provides several benefits, which aligns with the selected answer.

The granules on the cap sheet not only enhance the aesthetic appearance of the roof but also offer protection against ultraviolet (UV) rays and help to extend the life of the roofing system. This surface layer improves durability and resistance to physical damage, contributing to the overall effectiveness of the roofing system.

While cap sheets do contribute to waterproofing by forming a part of the overall roofing membrane, their primary defining characteristic is the presence of a granule surface that serves to protect the underlying layers and enhance the system's performance.