Siphonic Roof Drainage Explained: Risks, Advantages and Design Considerations

14. February 2024 | 6 min read

Siphonic roof drainage systems are the most effective rainwater discharge technology for flat and low-gradient roofs. Compared to gravity systems, siphonic drainage boasts at least twice higher flow rate, offering better protection from leaks and overflows. However, to function correctly, siphonic drainage solutions must be impeccably designed. We talked with our expert, Maciej Teterka, and our recent customer, Tadmet Company, about the importance of proper design and other key considerations in ensuring optimal performance and long service life of siphonic drainage solutions.

The most effective rainwater discharge technology for flat and low-gradient roofs

What Is Siphonic Roof Drainage and How It Works

Siphonic drainage systems rely on negative pressure to create a vacuum effect and rapidly remove rainwater from rooftops. In contrast to traditional gravity-based systems, the air does not enter the downpipes, resulting in a higher flow rate, larger volumes of water removed and reduced risks of water accumulation on rooftops.

In addition, siphonic roof drainage systems save space. Rather than being installed with a slope, the connecting pipes can run parallel to the ceiling, and smaller diameters can be used without sacrificing drainage efficiency.

Yet, to function correctly, each siphonic roof drainage system must be designed, considering the building specifics and precipitation patterns in the respective area. 

“Any error at the design stage can result in the entire installation operating with reduced efficiency or, worse, not working at all,” says Maciej Teterka, Technical Support Specialist at Pipelife Poland. “Thus, it is essential for the design of the siphonic roof drainage system to be handled by someone with significant knowledge and expertise in this technology.”

Weather Conditions: Decisive Design Factor

Every siphonic roof drainage system is tailored for a specific precipitation amount. If the actual rainfall intensity happens to be lower, the system will function like a traditional gravitational system. In case the rainfall intensity considerably exceeds the anticipated amount, the system may struggle to cope with the large influx of rain and even fail.

Therefore, typical precipitation amounts for the area must be accounted for already in the design stage. The size of the system is also determined by considering how often the typical rainfall intensity is likely to be exceeded.  

“It is not optimal to install a system for precipitation amounts that may occur only once every few decades,” Teterka sums up. “For such cases, designing emergency overflow systems is a better and more cost-efficient solution.”

The most effective rainwater discharge technology for flat and low-gradient roofs

Designed by Experts: Siphonic Systems Backed by Experience 

To ensure customers can always count on fast, expert-level design services, Pipelife is working with highly experienced designers specializing in building services and boasting extensive experience in siphonic drainage solutions. The design services are available for Pipelife’s customers in all markets. 

In just a few days of receiving information on roof plan drawings and cross-sections, Pipelife’s experts prepare an optimized system design and share it with the customer. Several designs have already been completed and installed, boasting high client satisfaction.

The most effective rainwater discharge technology for flat and low-gradient roofs
The most effective rainwater discharge technology for flat and low-gradient roofs

From Idea to Installation: Siphonic Roof Drainage Case Study

Last autumn, Tadmet Company, a wholesaler based in Kościerska Huta, northern Poland, reached out to Pipelife regarding a siphonic roof drainage system for a new warehouse hall. The massive building with a floor area of over 7,700 m² and a roof height of about 14 m required a long-lasting, highly reliable and efficient roof drainage to protect the stored goods even in extreme weather.

In response to the customer’s request, Pipelife’s experts prepared a project fully tailored to the building specifics and Kościerzyna County’s rainfall patterns. Considering the architectural plan of the new warehouse, a system design with 27 heated rainwater inlets and four vertical downpipes was identified as the best solution.

“We were impressed by the speed, responsiveness and service quality offered by Pipelife,” says Dariusz Ostrowski, the Owner of Tadmet Company. “The system design we received was individually tailored and professionally made yet, at the same time, easy to understand.”

To ensure the longevity and faultless performance of the system, Pipelife Poland supplied an end-to-end product package for the building, including rainwater inlets, nearly 600 meters of drainage pipes, more than 370 fittings and complementary mounting systems. Pipelife’s technical support representative remained in contact with the customer throughout the installation process to provide assistance in case of questions or uncertainties.

The building was finished in December, and Ostrowski is pleased with the outcome:

“The installation went smoothly, attesting to the high product quality and the excellent customer support. The installed drainage system has been operating as expected and without issues. We are very satisfied with the result and our decision to put our trust in Pipelife.”

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