What material is typically used to create the reinforcing layer in BUR systems?

The reinforcing layer in Built-Up Roofing (BUR) systems is typically made from fiberglass or polyester mats. These materials provide strength and support to the roof system, enhancing its durability and resistance to various environmental factors, such as moisture, UV exposure, and temperature fluctuations.

Fiberglass mats are known for their lightweight and high tensile strength, making them ideal for roofing applications. They offer excellent dimensional stability and resistance to tearing, which is crucial during the installation and maintenance of the roofing system. Polyester mats, on the other hand, provide increased flexibility and resistance to punctures, contributing to the overall robustness of the BUR system.

In contrast, the other materials listed have limitations that make them unsuitable for the reinforcing layer in BUR systems. Foam boards, while useful as insulation, do not provide the structural reinforcement needed. Wooden sheets may enhance support but are prone to rot and decay, especially in wet conditions, which could compromise the roofing system's integrity. Metal grids, while strong, are not typically employed in the layering structure of BUR, as they do not offer the same compatibility with roofing materials and tend to be heavier and less flexible.