Syphonic Roof Drainage – How does it work?

Originally developed in Scandinavia over 40 years ago, syphonic roof drainage systems have been in use in the UK since the early 1990’s. Since then, many large projects have used the syphonic system to overcome installation problems which would have been difficult to solve using a traditional gravity rainwater system.

Siphonic drainage is actually very simple in principle and all systems work in exactly the same way. Baffle plates inserted in the outlets restrict air entering the top of the system which, when combined with carefully sized pipework, causes the system, horizontal and vertical, to run full. In a very similar way to a simple tube siphon (such as you would use to empty a fish tank), the action of water dropping down the downpipe will cause a negative pressure to form at the top. This negative pressure can be harnessed to suck water along a collector pipe installed horizontally connecting the outlets at high level.