Technical Canlon | Active Drainage, Integrated Prevention and Drainage – The Evolution of Roof Water Management Logic Behind Canlon's Siphon Drainage Patent

On June 5, 2026, Canlon was granted an invention patent, "A Test Device for a Siphon Drainage System of a Membrane Metal Roofing", patent number ZL202311789137.5. This marks the formal integration of "active drainage" into the core capability of the membrane metal roofing (Fusion® integrated panel) system, in addition to "waterproofing"—the "integrated waterproofing and drainage" concept has moved from a theoretical concept to a testable and verifiable engineering practice.

Conventional thinking in roofing projects: prioritizing waterproofing over ventilation

For a long time, the technical focus of roofing projects has been on "prevention"—that is, if the waterproof layer is in place, water can't get in and everything is fine. Article 2.0.1 of GB 55030-2022 "General Specification for Waterproofing of Building and Municipal Engineering" proposes the waterproofing principle of "adapting to local conditions, prioritizing prevention, combining prevention and drainage, and comprehensive management". However, in engineering practice, "drainage" is often simplified to the structural design of the slope layer—ensuring that the drainage slope is not less than the standard value, and that water can flow to the gutter by gravity.

The problem is that gravity drainage depends on the slope. T/CECS 1668-2024 specifies a minimum slope of 2% for integrated panel roofs. However, in actual projects, the slope may deviate from the design value due to factors such as structural deformation, insulation layer compression, and construction errors. When the slope is insufficient to overcome water flow resistance, localized water accumulation occurs on the roof.

The impact of water accumulation on the waterproofing layer is gradual: long-term immersion accelerates the migration of plasticizers in the membrane, winter freeze-thaw cycles create alternating stress on the lap welds, and the deposition of dust and microorganisms in waterlogged areas further weakens the weather resistance of the membrane surface. A roof that never dries out causes its waterproofing layer to age faster—even if water doesn't actually "leak in," its chronic wear and tear on the roofing system has already begun.

The meaning of "integrated prevention and drainage" in engineering

"Integrated waterproofing and drainage" is not simply a combination of waterproofing and drainage. Its core principle is that the waterproofing layer ensures "no leaks," and the drainage system ensures "no water accumulation"—the two are complementary and parallel, not primary and secondary. A truly integrated waterproofing and drainage roof should have the ability to quickly guide rainwater away from the roof through organized drainage, even under zero-slope conditions, preventing water from lingering on the roof for longer than the necessary runoff time.

This concept aligns perfectly with the principles of sponge city construction . The "Guiding Opinions on Promoting the Construction of Sponge Cities" (Guo Ban Fa [2015] No. 75), issued by the General Office of the State Council in 2015, proposed a six-character policy: "infiltration, retention, storage, purification, utilization, and drainage." Among these, "drainage" is an indispensable final stage—when rainfall intensity exceeds infiltration and storage capacity, excess rainwater must be safely and orderly discharged into the municipal pipe network; otherwise, the sponge city will transform from "water absorption" into "waterlogging." As the first interface for rainwater reception in a building, the roof's drainage capacity determines the building's hydraulic safety under heavy rainfall conditions.

A testing device, which piece of the puzzle did it complete?

This testing setup consists of five units: a unit with membrane-coated metal panels on both sides to simulate the actual roof structure, a gutter unit to collect incoming water, a siphon unit to create negative pressure to drive full-pipe flow, a simulated rainfall unit to provide a controllable water source, and a testing unit to record siphon pressure and drainage performance. Working together, the five units reproduced the complete operating conditions of the entire roof siphon drainage system under laboratory conditions.

The unique value of this device lies in three "adjustable" features: adjustable gutter cross-section, which allows testing of drainage efficiency for gutters of different sizes, providing a basis for design selection; adjustable roof slope, which verifies the change in runoff time from zero slope to different inclination angles, answering the design question of "what minimum slope is required to ensure drainage within a specified time"; and interchangeable rainwater hopper models and pipe diameters, which allows comparison of the performance differences of different drainage components on the same platform, avoiding common engineering errors such as "large pipe with small hopper" or "small pipe with large hopper" caused by component mismatch.

These three capabilities all point to the same goal: to shift the design of siphon drainage systems for integrated panel roofs from "experience-based selection" to "data-driven" approaches. Previously, designers could only determine pipe diameters and hopper types based on empirical formulas and manufacturer samples—a process whose reliability significantly decreased when the roof area exceeded a certain scale or the building's design resulted in complex drainage paths. With this system, drainage solutions for any specific project can be tested and verified before leaving the factory, transforming system performance from "relying on the manufacturer's claims" to "being tested."

The natural advantage of integrated roofing panels – a weldable, continuous waterproof surface

Siphonic drainage systems are not a new technology. They have been used for decades in concrete flat roofs. However, siphonic drainage under metal roof conditions faces a special challenge: there are overlaps between the metal panels. If the overlaps are not completely watertight, the siphonic negative pressure will draw air in from the gaps, disrupting the full-pipe flow state. Siphonic drainage is essentially a negative pressure system that requires the system to be airtight.

This is the inherent compatibility logic between integrated roofing panels and siphon drainage systems: the integrated roofing panels, through hot-air welding of the surface polymer roll material , construct a seamless waterproof membrane on top of the metal sheet. This membrane not only solves the problem of "water leaking down," but more importantly, it ensures the airtightness required for the siphon system to operate—air cannot enter the pipes along the overlap seams, the negative pressure state can be maintained stably, and the siphon efficiency is not affected by gaps in the metal sheet structure. From another perspective: the fully welded waterproof surface of the integrated roofing panels is a prerequisite for the "transplantation" of siphon drainage systems from concrete roofs to metal roofs. The two are not simply a combination of products, but a deep compatibility of systems.

From patents to systems: a closed loop of full-chain capabilities

The true value of this patent lies not in the device itself, but in the closed-loop capability it creates. Prior to this, Canlon's technological accumulation in the integrated panel field focused on three aspects: materials—the factory integrated process of polymer rolls and metal sheets; products—jointly editing the T/CECS 1668-2024 group standard; and applications—engineering verification in industrial plants such as the Yanjing Beer Danjiangkou base. The siphon drainage patent completes the fourth aspect: system verification. This forms a complete chain of "material patent → product standard → engineering implementation → system testing."

Yanjing Beer Danjiangkou Base Project

In industry terms, the deliverables of a roofing solution are no longer just a stack of roof panels and a set of construction drawings, but rather "tested and verified system performance indicators"—under specific design parameters, the drainage system of this solution can drain water from the roof within a specified time, with stable siphon operation and continuous full-pipe flow. For the owner, this means that "integrated drainage and waterproofing" has transformed from a corporate slogan into a verifiable technical commitment.

Conclusion

Technological advancements in roofing engineering sometimes don't manifest in the invention of new materials, but rather in the serious attention paid to an old problem. Drainage is to roofing what is a long-neglected fundamental skill—everyone knows it's important, but technically, it's been limited to the experiential level of "just make sure the slope is right." When the industry begins to establish quantifiable testing standards and verification methods for roof drainage systems, it indicates that roof water management is evolving from a hastily handled construction step into a subsystem requiring independent design and verification.

This patent for a testing device doesn't boast about a material revolution or claim to have disrupted anyone. It does something more fundamental: it transforms the question of "how quickly and how cleanly water is drained" from a subjective one into a data-driven one. This is precisely the kind of question an industry will first ask when it's transitioning from extensive to intensive development.