Oct 30, 2026
GRP (fibreglass) roof lights typically last 8–12 years. Replace when any of these appear:
• Visible yellowing or whitening with transmission dropping enough to darken the interior
• Exposed fibres and a rough, "furry" surface
• Leaks, with staining or dripping visible inside
• Brittle edges that crack under foot traffic or snow clearing
Corrugated polycarbonate is the mainstream replacement: higher transmission than aged GRP, far better impact resistance, similar weight, and no structural modification.
This is the single most common failure. They all look like "wave sheets", but a 2 mm difference in height or a 5 mm difference in pitch means the panels will not close.
Measure three numbers:
1. Pitch — centre-to-centre distance between crests
2. Height — vertical distance from crest to trough
3. Effective width — coverage after overlap
Then confirm the existing sheet thickness and fixing method. With those numbers a supplier can tell you whether a mould already exists.
SINHAI currently holds more than 70 corrugated moulds, covering trapezoidal profiles (such as type 1000), wave profiles (such as 1060), Roman, diamond-embossed and mini-embossed patterns. Common profiles run without a tooling charge; special profiles require a mould, typically 15–30 days. Put that lead time into the programme — do not discover it after the old roof is off.
|
Thickness |
Application |
Note |
|
0.8 mm |
Temporary structures, small canopies |
Lowest cost, limited snow/wind capacity |
|
1.0 mm |
Standard industrial roof lights |
The value mainstream |
|
1.2 mm |
Wider spans, higher snow load |
Check purlin spacing against the span table |
|
1.5 mm |
High-spec industrial, public buildings |
Better impact and stiffness |
|
2.0 mm |
Large spans, severe wind and snow |
Approaches solid-sheet stiffness, higher cost |
The selection driver is purlin spacing plus local snow and wind load, not "thicker is better". An under-specified sheet deflects under snow, ponds water, deflects further and eventually collapses — the classic failure sequence for single-skin roof lights.
Overlap. At least 200 mm along the slope (300 mm below 5° pitch), and one corrugation laterally. The overlap must run with the prevailing wind, or gusts drive rain into the joint.
Fixings. Screw at the crest with a sealing washer, hole 2–3 mm larger than the screw to allow expansion. Do not over-tighten — a flattened washer no longer seals. Increase fixing density within 1 m of purlin ends and sheet ends.
Thermal expansion. PC expands at about 6.5 × 10⁻⁵/K; a 6 m sheet moves roughly 23 mm across a 60°C range. Use slotted holes at sheet ends and leave allowance at ridge and eave.
Flashings. Ridge, eave and gable must use matching flashings and closure strips. These three locations account for most leaks.
Single-skin corrugated sheet does not insulate, and rain noise is noticeable. Where either matters (offices, residential proximity), two alternatives:
• Replace with multiwall (8 mm / 10 mm) — better insulation and lower rain noise, but it needs aluminium framing rather than reusing the original screw positions;
• Build a double layer: corrugated below, multiwall above, with an air gap between.
Which one applies is a building-use question, not a sheet question.
Provide photos of the existing profile, height/pitch/effective width, purlin spacing, location and the required glazed area. We will return a proposal covering profile, thickness, accessories and container loading. A short sample of the old sheet gives the highest matching accuracy.
Corrugated or solid for a roof light?
Depends on span and use. Corrugated suits direct replacement of steel or GRP roofing with no structural change and low cost. Solid suits applications demanding stiffness, impact resistance and appearance, such as public canopies and walkways. Neither single-skin option insulates.
Can I replace only the damaged sheets?
Yes, if the profile is still available and the damage is isolated. But if the roof has been yellowing for five years or more, new and old sheets will differ visibly in transmission and colour, and the result looks patched. Full replacement is usually the better decision.
Will PC corrugated sheet yellow in a few years like GRP?
Not at the same rate. The UV layer is decisive: proper products use a co-extruded UV layer rather than a surface coating, and commonly last beyond ten years outdoors. The typical failure of cheap product is a thin or single-sided UV layer, with yellowing starting in two to three years.
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