What is the function of cap sheets in BUR roofing?

Cap sheets in BUR roofing serve primarily as a waterproof barrier that features a granule surface. This function is crucial for protecting the underlying layers of the roofing system from water infiltration and environmental damage. The granulated surface not only enhances the waterproofing capability but also provides additional UV protection, which helps prevent deterioration of the roof materials over time.

The design of the cap sheet allows it to effectively shed water away from the roof, directing it into drainage systems, thereby minimizing the risk of leaks. Furthermore, the granules on the surface contribute to the durability and longevity of the roofing system by providing a level of resistance to physical damage and weather effects.

In contrast, while insulation against moisture is important in roofing systems, it is not the primary role of cap sheets. A decorative finish is also a secondary function but does not capture the primary purpose of the cap sheet. Additionally, although energy efficiency can be achieved with reflective materials, the primary characteristic of cap sheets in BUR systems is their waterproofing capability.