Built-up roofing consists of waterproof membrane constructed on the roof by bonding together two or more layers of bitumen felt in hot bitumen. This system of roofing has been in existence for some 75 years or more and has been used succesfully on countless flat and pitched roofs.

Bitumen is an inherently durable material and has been used in tanking work since the construction of the pyramids. Although degraded by exposure to sunlight, if protected by a suitable surfacing, bitumous roofing membranes can provide an extremely long service life. When first introduced the original membranes were installed on uninsulated concrete and solid timber decks. With the advent of lightweight construction and the use of highly efficient plastic foam insulants the earlier materials were found to be vulnerable to substrate movement and the need for improved roofing membranes arose.

In recent years there have been numerous developments in roofing including a much better understanding of the stresses imposed on membranes and how they react. At the same time work in other fields such as condensation and moisture transfer through building systems led to predictive methods enabling designers to avoid problems due to intersatial condensation.

Stronger and more flexible reinforcements were introduced in the early seventies. More recent elastomeric and modified bitumen compounds have also been developed to give membranes better resistance to substrate movement.