Most corrugated roofs come down to three choices that drive performance and cost: sheet thickness, support span, and fasteners. Use the tables and rules below to place a clear PO and avoid rework on site.
Before you order
- Environment: coastal wind/salt, industrial fumes, or inland.
- Loads: wind zone, snow (if any), occasional foot traffic.
- Pitch: lower slopes need longer end laps and better sealing; very low slopes prefer trapezoidal profiles.
- Profile depth: deeper ribs carry longer spans at the same thickness.
Thickness vs span (typical)
| Rib height | Thickness (mm) | Purlin spacing (mm) | Notes |
|---|---|---|---|
| 18–20 mm | 0.35 | 600 | Light sheds |
| 18–20 mm | 0.40 | 700–800 | Mild wind |
| 18–20 mm | 0.45 | 800–900 | Dent resistance |
| 25–30 mm | 0.50 | 1000–1200 | Factory standard |
| 25–30 mm | 0.60 | 1200–1500 | Stiffer panels |
Always check your profile maker’s data; increase thickness or reduce spacing for high wind, heavy traffic or roof accessories.
Coatings and base metal
- Galvanized: Z275 is common outdoors; inland projects may use Z180.
- Al‑Zn (Galvalume): AZ150 has strong corrosion resistance and good heat reflectance.
- Pre-painted: Polyester/SMP are economical; PVDF holds color best under UV.
Fasteners and placement
- Type: self-drilling screws with EPDM washers; stainless/coated with AZ or stainless sheets.
- Where: fix on crest for roofs (keep washer out of ponding water); valley fix more common on walls.
- Count: at each purlin—2 screws at edges, 1–2 interior depending on width and wind.
- Stitching: side laps every 300–500 mm; add butyl tape on windy or low-slope roofs.
Laps, pitch and sealing
- Side lap: 1 corrugation typical; 1.5 + sealant for low slopes/high wind.
- End lap: 150 mm; 200–250 mm for pitch < ~5° or exposed sites; always run butyl along the lap.
- Pitch: 5° practical minimum for corrugated; go trapezoidal if lower.
Spec you can copy
- Profile: corrugated 25 mm rib
- Thickness: 0.50 mm (base metal)
- Coating: AZ150 or Z275; topcoat PVDF 25 μm (or Polyester 20 μm)
- Cover width: 1000 mm; cut-to-length per layout
- Fixing: crest-fix screws with EPDM; side-lap stitch 400 mm c/c + butyl
- Supports: purlins at 1100 mm (adjust to site)
- Accessories: ridge/barge flashings with foam closures
FAQs & internal links
Q: AZ150 or Z275 near the coast?
A: AZ150 + PVDF is a durable combo; see coastal guide.
Q: How many screws?
A: Depends on wind zone and width; use two at edges per purlin, at least one interior; check local code.
Baoli Engineering Team · Reviewed Oct 31, 2025