Siphonic Rainwater Systems
Advantages of Siphonic Rainwater Systems
Gravity Rainwater Systems
Rainwater Harvesting
Soil, Waste & Ventilation
Project Management
Rainwater System Maintenance

1. In general fewer siphonic outlets than conventional outlets are required thus reducing roof penetrations.
2. The need for rows of vertical rainwater pipes inside a building is virtually eliminated together with the extensive under floor drainage systems to serve them. For example in a long valley gutter twelve or more siphonic outlets may be connected to a single collecting pipe. The combined rainwater flow may then be discharged via one vertical down pipe at the boundary of the building.
3. The fall or gradient that would be required by a conventional pipe designed to flow part full is not necessary to transport a siphonic flow. When filled siphonic pipework operates under a pressure regime that differs from atmospheric and the lateral collecting pipe(s) can be installed horizontally immediately below the roof structure. This characteristic alone allows significant savings to be made in the construction of large industrial or commercial buildings. Also great flexibility in the use of the space within open-plan buildings is enabled by providing large areas uncluttered by down pipes.
4. The location of siphonic outlets on the roof or in a gutter is not restricted to column positions as with conventional rainwater downpipes. Outlets can be installed for example at planned roof / gutter low points or even in extreme cases to compensate for unplanned roof / gutter deflection.
5. Siphonic systems can be integrated with roof, gutter and underground drainage design to produce optimum solutions to known parameters.
   5.1. The discharge from each siphonic downpipe is a specific water volume at a pre-determined location in the building envelope.
   5.2. Siphonic outlets are performance tested and calibrated for flow capacity and operational water depth.
6. The current British Standard, BS EN 12056-3:2000 "Gravity drainage systems inside buildings Part 3: Roof drainage, layout and calculation" incorporates design parameter recommendations for siphonic systems. The meteorological data therein can be used to determine dimensional rainfall for both siphonic and conventional systems.