Siphonic Drainage

A siphonic system draining a roof or roof gutter normally consists of a series of specially-designed, grated drains or outlets each connected by small diameter tailpipes to a high level horizontal collector pipe leading to a vertical down pipe discharging at ground level. The drain benefits from the addition of air baffle to prevent the entry of air into the system and by ensuring that the pipework is assembled to specific dimensions, air can be totally removed from the system. This allows the system to fill entirely with water.


Siphonic Roof Drainage System
Siphonic Roof Drainage System

The unique features of siphonic drainage is its suitability for cutting edge architecture where conventional drainage would impair the aesthetics of the design.

RTC Siphonic drainage advantages are:

  • Fewer Siphonic drains are required therefore reducing roof penetrations.
  • Rows of vertical rainwater pipes inside a building are eliminated together with the extensive under floor drainage systems to serve them.
  • Fall or gradient is not required to transport a siphonic flow.
  • The location to siphonic drains on the roof or in a gutter is not restricted to column positions.
  • Siphonic systems can be integrated with roof, gutter and underground drainage design to produce optimum solutions to known parameters.
  • The discharge from each siphonic downpipe is a specific water volume at a pre-determined location in the building envelope.
  • Siphonic drains are performance tested and calibrated for flow capacity and operational water depth.



Architects, Consultants and Contractors continue to use this ground breaking siphonic system in large footprint buildings because it drains double the amount of rainwater using only half the pipe diameter.

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