Key takeaways
- Trapezoidal generally spans further than corrugated for the same thickness, because its ribs are deeper and more angular.
- Corrugated tolerates higher minimum pitch and has a shallower, more traditional appearance.
- Fixing is through-fixed in both cases; the difference is where the screw lands and how the side lap seals.
- Market convention often decides the answer before engineering does — check what your buyers specify.
The essential difference
Corrugated sheet is a sinusoidal wave: smooth curves, no sharp corners. Trapezoidal sheet is angular: flat pans between ribs, with straight-sided folds. Both are through-fixed and both are lapped at the side, but the geometry drives everything else.
Because trapezoidal ribs are deeper and have angular corners, the section resists bending more efficiently per unit of steel. In practice that means a trapezoidal sheet spans further between purlins at the same thickness, or achieves the same span at a thinner gauge.
| Criterion | Corrugated | Trapezoidal |
|---|---|---|
| Section shape | Sinusoidal wave | Angular ribs with flat pans |
| Cover width | 762 / 900 / 1000 mm | 900 / 1000 / 1070 mm |
| Minimum pitch | 10–15° | 5–10° |
| Spanning capacity | Lower for same thickness | Higher for same thickness |
| Fixing | Through-fix, in the crest | Through-fix, in the crest |
| Appearance | Traditional, softer | Modern, more defined |
| Typical markets | UK, Ireland, Australia, Africa | Europe, Middle East, Asia, Latin America |
Span and thickness
Because trapezoidal sections are structurally more efficient, they let you either reduce purlin spacing or reduce sheet thickness. Neither is free: thinner sheet is more easily damaged on site and less tolerant of foot traffic.
The practical rule most producers apply is to check the cladding supplier's span table rather than reasoning from the profile. A 0.5 mm trapezoidal sheet and a 0.5 mm corrugated sheet have different allowable spans, and the table is the only reliable source.
Pitch, water and the lap
This is where the two profiles diverge most in practice. Corrugated has a high, rounded crest and a side lap that interlocks over one full wave; trapezoidal has a lower, flatter rib and a side lap that depends on the shape of the rib edge.
Because of that geometry, corrugated generally tolerates a slightly higher minimum pitch than trapezoidal — counter-intuitively, since trapezoidal is the stronger section. The reason is the lap, not the strength: the trapezoidal side lap relies more on the rib edge for its seal, so at very low pitch capillary action can draw water through.
Both profiles are unsuitable for genuinely low-pitch roofs. If the pitch is below about 5°, the answer is usually standing seam rather than a choice between these two.
What the profile choice does to the machine
The comparison so far has been about the finished sheet. The other half of the decision is what each profile asks of the line, because that is where the money and the changeover time sit.
Corrugated is a sinusoidal wave, and a smooth curve is formed by many small successive bends, so a corrugated machine carries more forming stations for the same cover width. Trapezoidal profiles have flat pans and straight-sided folds, which form in fewer, heavier passes and therefore in a shorter machine with a lower station count.
That matters if you intend to sell both. Corrugated and trapezoidal are different profile families, so they cannot share a roll cassette — running both means either a second machine, an interchangeable cassette set on one base frame, or a double layer configuration. Settle which of those you want at the order stage: cassette interchangeability is a specification decision, not an upgrade added afterwards.