A capsheet is the final, top layer of a built-up felt roofing system. Its primary job is to protect the underlying waterproof layers from UV radiation, weathering, and physical damage. Most capsheets feature a mineral surface (often green, black, or brown) which provides the necessary UV protection and an attractive finish.
The importance of a mineral capsheet
Without a capsheet, the bitumen in the underlays would quickly degrade under the sun’s rays. The mineral granules embedded in the surface of the capsheet reflect heat and prevent the bitumen from becoming brittle. This ensures your flat roof remains waterproof for decades.