What does the term "ply" refer to in roofing materials?

The term "ply" refers to the number of roofing layers in a roofing system. In the context of built-up roofing and certain types of membrane roofing, the term indicates how many individual layers of material are used to create the roofing assembly. Each additional ply contributes to the overall strength, durability, and waterproofing properties of the roof. For example, a single-ply membrane system would have one layer, while a multi-ply system might have two, three, or even more layers, which can be beneficial in providing enhanced protection against weather elements and extending the life of the roofing system. Understanding the concept of "ply" is essential for roofing professionals, as it affects installation methods, maintenance considerations, and potential material costs.