Siphonic System

What Is a Siphonic System?

A siphonic system is a new-generation roof drainage solution that ensures the safe and reliable discharge of rainwater from buildings with large roof areas.

The system utilizes gravitational force along with a vacuum effect to discharge water rapidly. Thanks to this vacuum effect, the system’s piping does not require any slope, providing architects with greater design freedom, enhancing structural flexibility, and eliminating limitations caused by rainwater drainage requirements.

A siphonic system is designed based on meteorological data that indicates “maximum rainfall intensities observed over standard time intervals,” which varies by region. With high-performance roof drains developed by Egemek, the system requires significantly fewer downpipes compared to conventional drainage systems. Computer-aided designs and precise hydraulic calculations ensure flawless system operation.

Unlike conventional systems, a siphonic system does not operate on the principle of free flow. Pipes that are accurately sized according to hydraulic calculations fill within a specific time frame depending on rainfall intensity, creating negative pressure that rapidly draws water downward. This negative pressure not only accelerates drainage but also helps keep the piping system clean.

With its advanced engineering expertise and extensive experience, RAWD provides effective, durable, economical, and reliable solutions in siphonic roof drainage systems.

Operating Principle

Used for nearly forty years in numerous buildings across Europe, this system offers significant advantages over conventional drainage systems — primarily by eliminating the need for pipe gradients and enabling the use of smaller pipe diameters.

In a siphonic roof rainwater drainage system, the vacuum effect is achieved through the system’s operation in a fully filled state. By applying precise hydraulic calculations and designing the horizontal pipes with a minimal slope of approximately 0%, the system ensures that the pipes fill completely with water. Once the pipes are fully filled and air is eliminated from the line, the transition of water from the horizontal to the vertical section generates a vacuum effect. This vacuum increases both the velocity and flow rate of the water, allowing the pipes to fill entirely while reducing the number of vertical downpipes and the overall pipe diameters compared to conventional systems. Additionally, the high flow velocity enables the system to be self-cleaning. When the ratio of horizontal to vertical piping reaches up to ten-to-one, the system achieves cost optimization—and in some cases, this ratio can reach as high as twenty-to-one, further minimizing installation costs.

Design Criteria

The calculation of a siphonic system is based on meteorological reports indicating the “Maximum Rainfall Intensity Observed Over Standard Time Intervals.” Specifically, the design takes into account the highest rainfall value recorded over a five-minute period within the last hundred years.

The most critical component of the system design is the roof drain. Thanks to its vortex breaker structure, the drain prevents water from entering the system in a swirling motion—thus eliminating air intake—and ensures continuous operation through its multi-layered configuration.

The siphonic system, constructed with HDPE (High-Density Polyethylene) pipes, guarantees watertight performance through butt welding and electrofusion methods at the pipe joints. Since gasketed connections are not used, the system eliminates potential leakage issues that may occur over time due to gasket deterioration.

Advantages