Roof failures due to ponding - a symptom of underestimated development
Delft University of Technology and Corsmit Consulting Engineers, Rijswijk (ZH), the Netherlands
In the Netherlands about 20 light-weight flat roofs collapse every year as a result of ponding of rainwater during heavy rain showers. Despite the fact, that in 1993 a new regulation came in force (Dutch Bouwbesluit) addressing the rainwater ponding on the light-weight flat roofs, the roofs built after this date continue collapsing seemingly in the same rate. From reports made by different institutions and bodies on these and other construction failure related subjects, it can be concluded that the collapses of light-weight flat roofs do not stand alone. They are one of the symptoms of a larger development on the building and construction market in the Netherlands. A development that is characterized by emphasis and focus on pushing the structural limits in order to save materials and costs in combination with declining priority concerning coordination, checking and site supervision. Also deregulation, resulting in less control instruments and procedures in practise and fragmentation of the design and construction processes, play here an important role.
Key words: Light-weight flat roof, rainwater ponding, structural failures, structural safety