In 1990, the sum invested in new flat roof construction amounted to €600 million, with an additional €1.7 billion spent on refurbishment work. The roof is thus a cost-intensive element in building and one subject?to considerable damage. Very often, the decision in favour of a particular form of roof construction will be based solely on the initial investment required, and the cheapest solution available will be chosen. The negative effects of this reveal themselves later, with the client frequently having to pay for rehabilitation work within a relatively short time. Aspects such as constructional efficiency and long life are just as important as initial costs. In this respect, the interests of the client and of society coincide for once, since a roof with a long life will have a more positive ecological balance. (Bobran Ingenieure)