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Cases

Roof Rainwater Drainage Systems

Franta provides siphonic roof drainage systems for large industrial plants and long-span buildings, supporting rapid drainage from large roof areas, optimized system design, and reliable long-term operation.

Typical Cases

Challenges in Siphonic Roof Drainage Systems

Large industrial plants, logistics and warehousing centers, exhibition venues, and other long-span buildings typically feature extensive roof areas and large rainwater catchment zones. During short periods of heavy rainfall, large volumes of rainwater can enter the roof drainage system within a short time, placing high demands on drainage capacity, piping layout, and connection reliability. Compared with conventional roof drainage systems, large industrial buildings must consider not only how to discharge rainwater efficiently, but also factors such as roof catchment area, local design rainfall conditions, roof outlet layout, pipe sizing, building height, structural steel space, and connections to the external stormwater drainage system.

Common challenges mainly include the following three aspects:

1. Large Roof Areas Create High Drainage Demand During Heavy Rainfall

Industrial plants, logistics warehouses, and similar buildings often have continuous roof areas covering thousands of square meters or more. During heavy rainfall, large volumes of rainwater can accumulate within a short period. If the number or location of roof outlets is insufficient, or if the piping network lacks adequate drainage capacity, water may accumulate on the roof and increase pressure on the waterproofing and building structure. Therefore, large roof drainage systems should not simply be configured like conventional drainage pipelines, but should be designed through project-specific hydraulic calculations.

2. Complex Overhead Space Can Conflict with Conventional Drainage Piping

The space below industrial roofs often contains structural steel, fire protection systems, HVAC systems, electrical cable trays, production equipment, and other mechanical and electrical services. Conventional gravity drainage systems generally require sloped horizontal pipes and multiple vertical stacks, which can occupy valuable overhead space in long-span buildings and increase coordination difficulties between different building systems. Reducing the number of vertical stacks and optimizing horizontal pipe routing are therefore important considerations in large industrial roof drainage design.

3. Long Overhead Pipelines Increase Leakage and Maintenance Costs

Roof drainage pipelines are usually installed at high levels beneath the roof or steel structure. If connection leakage, pipe corrosion, or support system problems occur, inspection and repair can be difficult. In operating industrial facilities, maintenance of overhead piping may also affect equipment and normal production below. Therefore, roof drainage systems must consider not only drainage capacity, but also pipe durability, connection reliability, and long-term operating stability.

Franta Siphonic Roof Drainage Solutions

To address large roof catchment areas, high instantaneous drainage volumes, limited overhead space, and complex piping layouts in large industrial buildings, Franta provides siphonic roof drainage system solutions.

Based on project-specific roof conditions, Franta develops a complete solution from roof rainwater collection to the external drainage connection through rainfall analysis, hydraulic calculations, siphonic roof outlet layout, pipe sizing, piping route design, and stainless steel piping system configuration.

1. For Large Roof Areas: Hydraulic Calculations Determine System Drainage Capacity

Siphonic roof drainage design is not simply a matter of increasing pipe diameters or adding more roof outlets. The system needs to be designed according to the actual project conditions.

Franta can perform hydraulic calculations based on factors including local design rainfall conditions, roof catchment area, roof zoning, building height, roof outlet locations, pipe length and routing, and connection conditions to the external stormwater drainage system. Based on the calculation results, the number of roof outlets, pipe diameters, and piping layout can be determined so that rainwater from different roof areas is collected and discharged in accordance with the system design.

2. For Limited Overhead Space: Siphonic Drainage Reduces Slope Requirements and Optimizes Piping Layout

Siphonic roof drainage systems use specially designed siphonic roof outlets to control air entry. Under design operating conditions, the pipelines gradually develop full-bore flow, using the pressure difference created by building height to transport rainwater rapidly. Compared with conventional gravity drainage systems that mainly depend on pipe slope, horizontal suspended pipes in a siphonic system can be routed more flexibly across the top of a building when system design requirements are met.

For steel-structure industrial plants, logistics centers, and other long-span buildings, this approach can reduce the impact of roof drainage piping on clear building height and other mechanical and electrical systems, while allowing vertical stacks to be arranged more strategically according to the building structure.

3. For Long-Term Operation: Stainless Steel Piping Improves System Durability

Franta uses stainless steel pipes and compatible connection products to form the roof rainwater drainage network. Stainless steel offers good corrosion resistance and is suitable for roof areas, overhead industrial environments, and pipelines that remain in long-term contact with rainwater, helping reduce maintenance problems associated with corrosion in conventional metal piping.

According to pipe diameter, building location, and installation conditions, suitable pipes, fittings, and connection methods can be selected based on the system design. Proper pipe clamps, hangers, and fixing measures can also be used to provide reliable support for horizontal suspended pipes, vertical stacks, and directional changes.

Key Advantages of Franta Siphonic Roof Drainage Systems

Professional Hydraulic Design

Rather than supplying pipes alone, Franta performs system hydraulic calculations based on roof catchment area, rainfall conditions, building height, and piping network layout.

 Higher Drainage Efficiency

Siphonic roof outlets and full-bore flow system design improve pipeline drainage capacity, making the system suitable for concentrated roof drainage in large industrial buildings.

 More Flexible Piping Layout

Reducing dependence on continuous pipe slopes helps optimize overhead piping coordination in large industrial buildings and allows the number and location of vertical stacks to be optimized.

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