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Roof Drainage System

Metal Gutter and Downpipe Systems

Drainage is an integral part of any roofing system. Prefabricated gutter and downpipe systems are a practical choice for many European- and American-style villas, multi-storey residential buildings and commercial properties.

These systems are easy to install and available in a wide range of profiles and colors. In addition to managing roof drainage, they also create a distinctive architectural line across the building façade.

What to Consider When Selecting a Metal Gutter System

Reliable performance and long-term resistance to outdoor exposure and corrosion.
Dimensional stability under changing climatic conditions.
Gutter and downpipe dimensions that provide sufficient drainage capacity for the roof.
A complete system with appropriately configured components and materials that comply with applicable domestic or international standards.
Profiles, colors and details that complement the building’s architectural style.

What EACHANCE Can Deliver

Efficient drainage of rainwater and snowmelt.
Controlled discharge that directs water safely away from the building.
Reduced risk of basement water ingress and damage to walkways, gardens and surrounding areas.
High structural strength to withstand accumulated snow and ice.
Limited thermal expansion and contraction as outdoor temperatures change.

Why Choose a Metal Gutter & Downpipe System?

Thermal expansion and contraction cannot be eliminated. Over time, excessive movement may deform gutters or cause leakage at joints, affecting system performance and increasing maintenance costs. Metal has a relatively low rate of thermal movement and therefore helps reduce these risks.

In addition to copper and titanium-zinc systems, RUIDAFENG aluminum-alloy gutters are available with either pre-coated or powder-coated finishes. Both processes use coating systems selected for outdoor weather resistance:

Pre-coated finish: PPG or BACKER
Powder-coated finish: AkzoNobel

Conventional PVC gutters may become brittle and crack as they age. Metal gutters retain their original profile and structural stability for longer, reducing replacement frequency and ongoing maintenance requirements. Over the complete service life of a building, a metal gutter system can therefore provide a cost-effective drainage solution.

Factors Determining Gutter and Downpipe Size

Roof drainage design requires careful consideration. Leakage from gutters or downpipes can cause serious damage to both exterior and interior walls, while remedial work can be costly. Low maintenance requirements, durability and service life are therefore important considerations when designing a gutter and downpipe system. A properly designed system can remain in good condition for many years with minimal maintenance.

The type, appearance and location of a building directly influence the selection of its roof drainage system. Together, these factors determine the roof area, roof pitch and applicable rainfall intensity.

In general, gutter and downpipe sizes are determined by the volume of water discharged from the roof. For a given rainfall intensity, the required drainage capacity is primarily affected by the roof area and roof pitch.

Using the actual sloping surface area of the roof as the basis for calculating runoff can produce an excessively high result. This may lead to oversized gutters and downpipes and unnecessary material costs. Research attributed to the U.S. National Institute of Standards and Technology (NIST) uses the following relationship:

Design Roof Area = Projected Roof Area × Roof Drainage Factor

Rainfall Intensity

Rainfall intensity is measured over a five-minute period and expressed in millimetres per hour (mm/h). The recorded five-minute intensity is converted into an equivalent hourly rainfall rate for drainage calculations.

Table 1 presents rainfall intensities for major cities in China. It also indicates the roof area that can be drained for each unit of downpipe cross-sectional area.

The calculation assumes a reference drainage capacity at a rainfall intensity of 25 mm/h. If the rainfall intensity doubles, the roof area that can be served by the same drainage outlet is reduced by half.

Once the local rainfall intensity and effective roof drainage area have been established, the gutter and downpipe system can be sized through the following steps.

Determine Downpipe Locations and Spacing

In addition to the building’s architectural style and façade appearance, the following factors should be considered when locating downpipes:

Each downpipe should generally serve no more than 15 metres of gutter. Allowance for the gutter’s thermal expansion and contraction may reduce this maximum length.
Where possible, avoid routing rainwater around corners before it reaches a downpipe.
In regions subject to freezing conditions, avoid locating downpipes on the north-facing side of the building wherever practical.

Determine the Gutter Size

Gutter dimensions are determined by rainfall intensity and the corresponding roof drainage area.

M = Gutter Depth ÷ Gutter Width

An initial value for M is assumed.

IA = Rainfall Intensity × Drainage Area

On the sizing chart, locate the intersection between the selected M value and the corresponding roof drainage area. Extend horizontally to the left until it intersects the vertical IA line. The value shown on the diagonal line at this intersection indicates the required gutter width.

If the intersection falls between two available sizes, select the larger size.

Gutter Depth = Gutter Width × M

Determine the Downpipe Size

Under normal design conditions, a downpipe should have a cross-sectional area of at least 45 cm². Its internal cross-section should remain consistent throughout the drainage path.

Standard Downpipe Sizes

Downpipe specificationCross-sectional area2 × 3 in rectangular downpipe48 cm²3 × 4 in rectangular downpipe75 cm²Ø80 mm round downpipe50 cm²Ø100 mm round downpipe78 cm²

North American K-Style

Popular throughout North America for decades, the K-style gutter remains a preferred choice for both residential and commercial buildings.

Metal Gutter and Downpipe Systems

Choose a metal gutter and downpipe system that complements your building’s architectural style.

European Half-Round

Widely used in European architecture, half-round gutters are typically paired with round downpipes to create a clean, classic appearance.

Custom Gutter Systems

Designed around your architectural requirements and visual preferences, our custom systems integrate closely with the roof edge for effective drainage and a cohesive exterior finish.