Flat Roofs & Built-up Roofing
A roof that is nearly level or slightly pitched is called a low-slope roof or flat roof. No roof should be dead level flat; it must have at least a slight slope to drain. Problems in low-slope roofs are common and more difficult to diagnose than pitched roof problems or steep slope roofs because the path of water leakage through flat roofs is often quite hard to trace.
One of the most reliable ways for waterproofing a flat roof is called built-up roofing or BUR. Built-up roofs are composed of several layers of roofing material. Usually a 2 ply system is used consisting of one base sheet and one cap sheet. The base sheet is installed first and the cap sheet is installed over the base sheet. A 3 ply system can be offered with two base sheets for a longer warranty.
Built-up roofs vary greatly in life span, but those used in residential houses usually last about 15 – 20 years, depending on their quality, exposure, number of plies, and the adequacy of their drainage.