SENBO Building Materials supplies color-coated steel downpipes as part of its metal building drainage product range. These pipes are designed for use with external gutter systems on steel structure buildings, collecting and discharging roof rainwater. They are commonly used in industrial plants, logistics warehouses, and large-span public buildings.
Color-coated steel downpipes are architectural drainage pipes with rectangular or square cross-sections. They are manufactured from color-coated steel sheets using cold-working processes such as roll forming and interlocking.
The product uses color-coated steel sheet as its base material, typically grades such as Q235B or DX51D+Z. Surface coating options include PE (polyester) or PVDF (fluorocarbon) to meet varying weather resistance requirements.
According to inspection and acceptance standards, the zinc coating weight for Al-Zn or galvanized substrates is generally at least 150 g/m². The PVDF fluorocarbon coating thickness is at least 25 μm, and the polyester coating is at least 20 μm.
Raw material testing is primarily based on GB/T 12754 "Color-coated steel sheet and strip." Acceptance of finished products and installation refers to CECS 380-2014 "Technical Specification for Application of Metal Profiled Sheet Roofing and Wall Engineering" and GB 50242 "Code for Acceptance of Construction Quality of Building Water Supply, Drainage and Heating Engineering."
Standard machine-formed products primarily feature rectangular or square cross-sections, such as 95×133 mm and 144×108 mm. Wall thicknesses typically range from 0.4 mm to 0.6 mm, and 0.8 mm thick products can also be custom-made. Standard lengths are 6 meters or 12 meters, and custom lengths are available to meet project requirements.
Colors can be selected based on the RAL standard color chart to ensure visual harmony with the exterior walls of steel-structure buildings.
Products are categorized by manufacturing method into two types:
Machine-formed downpipes: Standard-specification products manufactured in batches on production lines, offering high efficiency and consistent dimensions.
Custom-fabricated downpipes: Produced using manual bending and mechanical seaming techniques to meet requirements for special specifications or oversized dimensions.
Unlike standard PVC pipes, color-coated steel downpipes do not suffer from aging, cracking, or bursting caused by thermal expansion and contraction. In extremely cold regions such as Northeast and Northwest China, PVC pipes are prone to freezing and cracking due to low-temperature brittleness. Color-coated steel downpipes leverage the low-temperature resistance of metal and have not suffered freeze damage even in extreme cold. The expected service life is 15–20 years, which is three to five times longer than that of PVC pipes.
Standard factory-formed specifications meet the needs of most conventional projects. For specialized engineering projects involving large roof drainage volumes, non-standard sizes can be custom-fabricated.
For the YTO Express Logistics Park project, the vast roof area and extreme drainage volume during heavy rainstorms meant that the largest standard specification (180×125mm) was insufficient. The manufacturer used manual bending and mechanical seaming techniques to produce custom 245×200mm extra-large downspouts, paired with large elbows nearly 1.8 meters high. The installation used a double-riveting process for structural stability. Post-installation, drainage efficiency improved by 40% compared to the original design.
The installation of color-coated steel downspouts must meet the following acceptance criteria. Vertical deviation must not exceed 3mm per story height. Pipe clamps must be evenly spaced at intervals of no more than 2m. The overlap length for connections must be at least 30mm. Joints must be secured with blind rivets or bolts.
Water flow tests must show no leakage or reverse slope issues. Any leakage detected during post-installation testing requires rework. Final acceptance is granted only when no pressure drop or leakage points are observed during the stabilized pressure period.
Designed for use with steel-structure buildings, these downspouts offer a clean, streamlined appearance. Colors can be customized to match the building's exterior walls, ensuring visual harmony with the steel roofing and wall cladding. A variety of fittings such as S-bends, single bends, and pipe clamps are available to accommodate complex wall system installations.
From an engineering perspective, these downspouts form a cohesive system with color-coated steel gutters and wall panels, ensuring consistent service life. This offers an advantage over stainless steel alternatives, which often involve higher costs and visible welded joints.
The following parameters are based on standard production and relevant standards. Customization is available to meet specific project requirements.
| Performance Indicator | Parameter/Specification | Standard / Notes |
|---|---|---|
| Base Material | Color-coated steel sheet (Q235B / DX51D+Z) | Galvanized or Al-Zn coated substrate |
| Base Material Standard | GB/T 12754 | Color-coated steel sheets and strips |
| Finished Product Standard | CECS 380-2014 | Technical specification for metal profiled sheet roofing and wall engineering |
| Common Wall Thickness | 0.4–0.8 mm | Standard machine-made: 0.4–0.6 mm |
| Zinc Coating Weight | ≥150 g/m² | Double-sided coating |
| Coating Thickness | PVDF ≥25 μm / PE ≥20 μm | Selected based on weathering grade |
| Standard Specifications | 95×133 mm, 108×144 mm, 130×100 mm, 180×125 mm | Rectangular or square cross-section |
| Single Unit Length | 6 m (standard) / 12 m (max) | Customizable |
| Salt Spray Resistance | ≥500 h | Requirement for outdoor use |
| Service Life | 15–20 years | Suitable for cold regions |
| Pipe Clamp Spacing | ≤2 m | Evenly distributed |
| Vertical Deviation | ≤3 mm/story height | Installation acceptance requirement |
1. Cold and Frost Resistance. The metal material overcomes the inherent flaws of PVC pipes, such as aging due to thermal expansion and contraction and low-temperature brittleness. It withstands freezing temperatures in the extreme cold of Northeast and Northwest regions, with a service life of 15–20 years.
2. Flexible Specifications. Machine-formed products cover standard market needs, while manual customization accommodates extra-large specifications (e.g., 245×200 mm) and non-standard sizes for special drainage requirements.
3. Architectural Coordination. Colors can be customized according to RAL standards to match the exterior of steel-structure buildings. A variety of accessories ensures the drainage system integrates with the building's aesthetic.
4. Verifiable Material Standards. Manufactured in compliance with GB/T 12754 and CECS 380-2014. Features include a galvanized layer of at least 150g/m², coating thickness meeting weather-resistance requirements, and salt spray resistance of at least 500 hours.
5. Clear Installation and Acceptance Criteria. Specifications include vertical deviation of no more than 3mm per story height, pipe clamp spacing of no more than 2m, and an overlap length of at least 30mm. Acceptance is based on a leak-free water flow test after installation.
For cold climates: Select color-coated steel downpipes over PVC to avoid low-temperature brittleness. Confirm that the zinc coating weight and coating type are suitable for local weather conditions.
For large roof areas: Calculate the required drainage capacity based on local rainfall intensity and roof area. If standard specifications are insufficient, consider custom-fabricated large-size downpipes.
For coastal or industrial environments: Verify that the coating type (PE or PVDF) and zinc coating weight meet the corrosion resistance requirements. Salt spray test reports are available upon request.
During installation: Follow the acceptance criteria for vertical deviation, pipe clamp spacing, and overlap length. Use blind rivets or bolts for joints, and conduct a water flow test to confirm no leakage before final acceptance.
1. Organized roof drainage systems for industrial steel plants and logistics warehouses, compatible with color-coated steel external gutters.
2. Metal roof drainage for large-span public buildings, including stadiums, exhibition centers, and large supermarkets.
3. Roof drainage in cold regions, serving as an alternative to PVC pipes in Northeast and Northwest China.
4. Large-area roofs and projects requiring high drainage capacity, with customizable non-standard large-diameter specifications.
Color-coated steel downpipes are less prone to low-temperature brittleness and cracking compared to PVC. They also offer better coordination with steel-structure building exteriors and a longer service life. PVC may be lighter and less expensive, but steel downpipes provide greater durability in extreme climates.
Non-standard sizes can be custom-fabricated using manual bending and mechanical seaming techniques. For example, extra-large downspouts such as 245×200mm have been produced for large logistics parks. Contact our technical team with your drainage calculations and we can recommend an appropriate custom size.
Key checkpoints include vertical deviation of no more than 3mm per story height, pipe clamp spacing of no more than 2m, and overlap length of at least 30mm. A water flow test should be conducted after installation to confirm there is no leakage or reverse slope.
Yes. Colors can be selected from the RAL standard color chart to match the building's exterior walls, steel roofing, and wall cladding. This helps the drainage system integrate visually with the overall building design.
Please provide the pipe size, wall thickness, length, color (RAL code if available), quantity, and whether machine-formed or custom-fabricated products are preferred. Also indicate the project location and any special environmental conditions such as coastal exposure or extreme cold.
Tianjin SENBO Building Materials Technology Co., Ltd. is a manufacturer of color-coated steel downpipes, color-coated aluminum downpipes, FRP daylighting panels, and other metal envelope products. Our production base is located in Jinghai Economic Development Zone, Tianjin, China, equipped with automated production lines and a four-stage quality inspection process. For more information about our factory, certifications, testing capabilities, and project references, please visit our About Us page or contact our engineering team.
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No. 17 Guanghai Road, Jinghai Economic Development Zone, Tianjin, China
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