Built-up roofing, which has been used for almost 150 years, is one of the oldest and most durable roofing systems. The system consists of multiple plies of reinforcing felts laid shingle fashion into continuous moppings of hot asphalt or cold adhesives. The system is then covered with aggregate set in an asphalt flood coat or final cold adhesive application. The plies can consist of organic membranes or glass fiber membranes.
Built-up roofs are particularly resistant to damage from wind, hail and snow. The multiple layers provide extra protection and perform well in extreme weather conditions.