Investigation into the Performance Characteristics of Multi-Outlet Siphonic Roof Drainage Systems

Siphonic roof drainage systems have been in existence for approximately 30 years, and are becoming an increasingly common element of urban drainage infrastructure. In that time, the construction sector in most developed countries have been gradually persuaded of the benefits that these systems offer when compared to conventional roof drainage technologies. However, current design practice is based on steady-state theory and, arguably, simplistic assumptions. In response to perceived deficiencies in current design practice, a siphonic roof drainage research programme was initiated at Heriot-Watt University in 1996. This has led to a better understanding of the performance characteristics of siphonic systems, with particular reference to the priming of such systems (the purging of air from the system). This has resulted in the development of a numerical model capable of accurately simulating the priming phase of single outlet siphonic roof drainage systems. However, the majority of installed systems incorporate more than one gutter outlet, and the interaction between such outlets is not well understood. It was therefore recognised that further research was required to extend the applicability of the existing numerical model to multi-outlet applications. The work reported herein details an ongoing UK government funded research programme to investigate the performance characteristics of multi-outlet siphonic roof drainage systems. The experimental aims, apparatus and procedures are described, and results are illustrated. In addition, "real" data obtained from three installed siphonic roof drainage systems are discussed. Conclusions are drawn regarding the performance characteristics of multi-outlet siphonic roof drainage systems, and plans for future work are outlined.