Color-coated Steel Roofing Sheet

Color-coated Steel Roofing Sheets made from pre-painted steel coil are shaped by cold roll forming into a corrugated profile. Each sheet combines a steel core, a metallic coating on both sides, and a cured organic finish. The base metal is usually Q235B or DX51D, and the protective metallic layer can be zinc or aluminum-zinc with a coating weight from 40 g/m² to 275 g/m² per side. The paint system typically includes a primer and a polyester topcoat of at least 20 μm, while PVDF is reserved for sites with stronger UV exposure or salt spray. SENBO carries out incoming checks on coil thickness and coating weight, and the roll forming lines are set to verify rib geometry and effective width during production.

Common Profiles and Dimensions

• YX35-125-750: rib height 35 mm, rib spacing 125 mm, effective width 750 mm.
• YX25-210-840: rib height 25 mm, rib spacing 210 mm, effective width 840 mm.
• YX15-225-900: rib height 15 mm, rib spacing 225 mm, effective width 900 mm.

Sheet length is cut to order, and continuous lengths are possible when transport permits. The choice of profile affects span capacity, drainage behavior, and appearance.

Parameter Table

Test Data and Project Feedback

Mechanical Behavior

The substrate must show a tensile strength of at least 270 MPa. For YX35-125-750, the compressive strength is around 200 MPa, which is adequate for non-load-bearing and secondary structural envelopes. Thickness variation is controlled to ±0.02 mm, and flatness is limited to 3 mm per meter to avoid water retention on the finished roof.

Adhesion and Corrosion Resistance

Cross-cut testing requires that coating detachment area stays at or below 5%. Salt spray performance is typically specified as no red rust after 500 hours for standard material. Higher zinc coating weights improve this result. The actual requirement should be matched to the project location and atmospheric corrosion category.

Water Drainage

The corrugated shape channels rainwater through the troughs to the eaves. Overlap joints are sealed with waterproof washers and sealant. A minimum slope of 5% is recommended. Correct purlin alignment and fastener placement help prevent ponding and leaks.

Thermal Performance Example

A pilot project in Chongming District, Shanghai applied a heat-insulating coating over existing color steel roofing. After treatment, the surface temperature decreased from 63°C to 33°C, and the indoor temperature fell by about 8°C. While the insulation coating provided the main benefit, the case shows how the metal sheet can be combined with additional surface treatments for energy savings.

Installation Speed

Factory-produced sheets can be installed quickly on site. Daily output from roll forming can reach 3,000 meters. When paired with a steel frame, canopy and warehouse roofs can be completed in a short time. Long sheets reduce the number of end laps, which also lowers the potential leak points.

Design and Installation Notes

• Keep coils and sheets dry before installation. Outdoor storage requires ground clearance and a breathable cover to prevent condensation.
• Use cutting tools that do not produce high heat. Shears and nibblers are preferred over abrasive discs.
• Touch up cut edges and scratches immediately with a compatible repair paint.
• Select fasteners and washers that are compatible with the coating to minimize galvanic corrosion.
• Follow the specified side lap and end lap details. In high-wind areas, increase fastener density near edges and ridges.
• Check purlin spacing and alignment before placing sheets. Misaligned purlins can cause visible waviness and stress the ribs.

Questions from Projects

What slope is needed for a roof without a waterproofing membrane?

A slope of 5% or more is typical for single-skin profiles. Lower slopes may be used in special cases, but additional sealing and drainage measures must be designed and reviewed by the project engineer.

How do I choose the zinc coating weight?

The atmospheric corrosivity category of the site should be evaluated first. Mild rural areas may be fine with 40 g/m² to 90 g/m². Coastal or industrial zones often require 150 g/m² or more, or an aluminum-zinc coating with equivalent performance.

Can the sheets be installed on curved roofs?

Some profiles can be curved to a large radius. The minimum radius depends on the rib height, sheet thickness, and coating flexibility. The manufacturer should confirm the forming limit before the order is placed.

What causes color variation between batches?

Color variation can occur when coils come from different production runs. For a large roof or wall, it is safer to order all material for the same surface from one coil batch. When this is not possible, request a color reading and set a tolerance, such as ΔE ≤ 1.5.

Purchasing and Inspection Checklist

• Confirm substrate grade and coating weight on the mill certificate before production.
• Request a sample of the actual paint color and approve it before coil slitting.
• Check sheet thickness, rib height, and effective width at receiving. Reject material outside tolerance.
• Inspect the coating for scratches, coil breaks, or uneven color. Minor damage can be repaired, but large areas of damage should be replaced.
• If the roof must meet a specific wind uplift rating, request test data or calculations for the selected profile and fastener layout.
• For projects where fire performance is a concern, remember that a single metal sheet is non-combustible, but the complete roof assembly may include combustible insulation or underlayment that must be evaluated separately.