Corrugated Metal Roofing Sheet Buying Guide: Galvanized vs Galvalume vs PPGI — How to Specify Roofing Sheet by Profile, Thickness, and Coating
Corrugated metal roofing sheet is the cheapest roof over a structure and the one most often bought on price alone — which is how projects end up with sheets that rust at the cut edge in three years, or a profile that does not reach the purlin spacing the engineer designed. Thickness, zinc weight, profile, and coating are what actually decide roof life. Specify them and a thin sheet outlasts a thick cheap one.
This guide compares the coatings, profiles and thickness, fixing practice, and a complete RFQ checklist.
Coating Comparison: GI vs GL vs PPGI
| Coating | Composition | Corrosion life (rural) | Best for |
|---|---|---|---|
| Galvanized (GI) | Zinc | 10–25 years | General roofing, budget projects, industrial sheds |
| Galvalume (GL / Al-Zn) | 55% Al, 43.4% Zn | 15–30 years | Coastal, hot climates, long-life roofs — 2–4x Gi life at cut edges |
| PPGI (pre-painted) | Zinc + paint system | 10–20 years | Visible roofs, color matching, residential and commercial |
Thickness and Zinc Weight: What to Look For
| Base thickness (BMT) | Typical use | Minimum zinc |
|---|---|---|
| 0.13–0.20 mm | Economy sheds, temporary structures | Z20–Z60 (thin coat acceptable only indoors) |
| 0.25–0.35 mm | Standard roofing — the export default | Z100–Z180 |
| 0.40–0.60 mm | Long-span, coastal, load-bearing roofs | Z180–Z275 (or AZ150 for GL) |
Note the difference between BMT (base metal thickness) and TCT (total coated thickness): paint adds 20–40 µm per side. Quote in BMT and verify with a micrometer — “0.3 mm” in the trade can mean either.
Profile Guide
| Profile | Character | Use |
|---|---|---|
| Sine wave (corrugated) | Classic wavy profile | General roofing, walls, agricultural buildings |
| Trapezoidal (box rib) | Tall ribs, wide coverage | Industrial roofs, long spans, better water shedding |
| Tile profile | Simulates roof tiles | Residential and aesthetic projects |
| Standing seam | Concealed fixings | High-end architectural roofing |
Fixing and Installation Essentials
- Fix at the crest of the corrugation, never the valley, or water tracks through the screw hole.
- Overlap: one corrugation side lap minimum; end laps 150–200 mm with the upper sheet lapped over the lower.
- Purlin spacing must suit the sheet thickness — 0.3 mm sheet on wide purlin spans deflects and oil-cans.
- Use self-drilling screws with EPDM washers and do not over-tighten — crushed washers leak.
- Thermal movement: metal roofing expands and contracts; use slotted or flexible fixings on long runs.
Cut-Edge Corrosion (The Detail That Ends Roof Life)
- Cut edges have no coating — keep sheets cut-to-length at the factory where possible.
- Touch up cut edges with zinc-rich or matching paint on site, especially for GL and PPGI.
- Avoid contact between metal roofing and untreated timber or dissimilar metals — use washers and barriers.
Common Applications
- Factory and warehouse roofing and cladding.
- Residential roofing and roofing retrofit over old sheets.
- Agricultural sheds, poultry houses, and grain stores.
- Carports, container shelters, and temporary structures.
RFQ Checklist
- Coating: GI (zinc g/m²) / GL (AZ) / PPGI (paint system + color)
- Thickness: BMT in mm, and confirm the standard (0.25/0.30/0.35/0.40)
- Profile: sine wave, trapezoidal, tile — plus effective width and rib height
- Length: cut-to-length (recommended) or standard 2–12 m; quantity in tons/sheets
- Packing, certs, destination / Incoterm
FAQ
GI or GL for coastal roofs? Galvalume (AZ150) — its aluminum content resists chloride much better than plain zinc at the same coating weight.
What thickness do I need? 0.30–0.35 mm BMT covers most industrial and residential roofing; go thicker for wide purlin spans and coastal exposure.
Why did my roof rust at the edges first? Cut edges without touch-up and fixing holes without washers — both are site issues, not coating failures.
Why Source Roofing Sheet from Yihang Metal
Yihang Metal supplies corrugated metal roofing sheets in galvanized (Z60–Z275), Galvalume (AZ50–AZ150), and PPGI (PE/SMP/PVDF systems) at 0.13–0.60 mm BMT, in sine wave, trapezoidal, and tile profiles, cut to length on request, with coating weight certificates and export packing. Container loads typically ship in 20–30 days.
Ready to specify your roofing sheet? Send us the coating, thickness, profile, length, and quantity, and we will confirm mill availability and lead time with a fixed-price quote and coating certificate. Email [email protected] or use the quote form on this page — our team replies within one business day.