A building’s roof drainage system is an important design consideration regardless of the building type or location. Siphonic roof drainage systems—when compared with standard drainage methods—increase efficiency and result in significant initial cost savings.
How Siphonic Roof Drainage Works
A conventional gravity-type drainage system collects rainwater from a roof surface where gravity forces the water flow out through pitched horizontal and vertical pipes. Large roof surfaces generally require many vertical pipes, which are limited by the capacity of natural gravity-induced water flow within the pipes.
A siphonic drainage system prevents air from entering pipes, so during a rainfall, horizontal pipes prime full of water. The water then accelerates down through the vertical pipes inducing a negative pressure flow, hence the siphonic name. This siphonic effect results in high-flow velocities, which efficiently remove water from the roof while offering many other benefits.
Benefits of Siphonic Drainage
The resulting flow of water at such high velocity can equate to smaller pipes, less vertical piping, and potentially less underground piping. Compared to conventional gravity systems, a savings of nearly 45% is commonplace.
The siphonic effect allows for horizontal piping to be installed without a gradient, which further simplifies the installation and allows for more efficient use of the space at the ceiling. In some instances, the roof can be lowered solely due to the use of a siphonic roof drainage system. Additionally, since the horizontal piping does not need to be installed with a downward pitch in the direction of flow, it is easier to route the piping to achieve a more aesthetically pleasing installation. This is a huge benefit for areas with exposed construction.
Siphonic roof drainage systems can expel water from large facilities at a much faster rate than conventional gravity systems. They typically are self-cleansing, due to the high velocity at which water flows through the pipes, demanding a low level of maintenance in normal conditions. Rainwater harvesting also is more cost-effective and flexible with siphonic drainage than conventional systems. It’s possible to store water in above-ground tanks, minimizing the need for deep underground tanks.
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