Tell us about the roof
Sheets are cut to the slope length (max 40 ft per sheet); longer slopes use two sheets with a 150 mm end lap. Effective cover 1000 mm per sheet after the side lap, plus 5 % for cutting. Ridge, gutters, screws and accessories are quoted separately.
Sheets, laps and thickness explained
Number of sheets = roof length ÷ effective cover width, rounded up, for each slope. A sheet is 1050 mm wide overall and covers 1000 mm once the side lap is made. A 40 ft (12.2 m) ridge therefore needs 13 sheets per slope.
Sheet length is the slope length from eave to ridge, plus a small overhang at the eave. We cut sheets to the exact length on our roll-forming line, so there is no joint along the slope for anything up to 40 ft. Longer slopes take two sheets with a 150 mm end lap.
Thickness is the base-metal thickness in mm. 0.40 mm is the common choice for houses and shops, 0.45 mm for industrial sheds and warehouses, and 0.50 mm where spans are long or wind loads are high. Thinner sheets cost less per sheet but need closer purlin spacing.
Colour-coated or galvalume? Both start as galvalume (aluminium-zinc coated) steel. Colour-coated sheets add a baked paint finish in the colour you choose; plain galvalume keeps the silver finish and is the economical option for sheds and back-of-house roofs.
The estimate adds 5 % for cutting and wastage. Ridge caps, flashings, gutters, self-drilling screws and foam fillers are listed separately on the quotation.
Which thickness is right?
| Thickness | Typical use | ≈ kg / m² |
|---|---|---|
| 0.30 mm | Temporary sheds, boundary cover | 2.54 |
| 0.35 mm | Sheds, cattle sheds, small godowns | 2.97 |
| 0.40 mm | Residential roofs, shops, godowns | 3.39 |
| 0.45 mm | Industrial sheds, warehouses (most common) | 3.82 |
| 0.50 mm | Heavy industrial, long spans, high wind | 4.24 |
Weights are approximate (base metal × 7.85 × profile factor). Actual colour may vary slightly from screen.
Roofing sheet specifications