How we supply it: Roofing sheets are arranged through a partner sheet supplier or fabricator who quotes, supplies and bills them and pays us a referral commission. The column footings for the shed use our 20 mm jalli and M-Sand, and the steel sections can be arranged with the sheets.
In one line: A metal roofing sheet is a profiled steel or aluminium sheet, coated against corrosion and often colour-coated, fixed over purlins to form a light roof.
What you are buying in a roofing sheet
A metal roofing sheet is a profiled steel or aluminium sheet, coated against corrosion and often colour-coated, fixed over purlins to form a light roof.
Two numbers matter: the base metal thickness (BMT) of the steel and the metallic coating, such as AZ150, which means 150 g/m² of aluminium-zinc on both faces together.
Thickness by use
| Use | Thickness (BMT) | Note |
|---|---|---|
| Light sheltered covers, utility lean-tos | 0.35 mm | Dents easily; avoid walk-on areas |
| Car porch, terrace cover, house shed | 0.45 mm | A sound balance |
| Windy or coastal sites, longer spans | 0.50 mm | With a higher coating |
| Skylights and light panels | Polycarbonate | Lets light through; UV-protected grade |
| Insulated roofs | Sandwich (PUF) panels | Cuts heat under the roof |
Choosing the sheet material
| Sheet | Strength | Near the sea | Heat |
|---|---|---|---|
| Al-Zn coated colour steel | High | Good with higher coating | Hot without insulation |
| GI (zinc) coated steel | High | Rusts sooner at cut edges | Hot |
| Aluminium | Lower | Very good | Reflects heat |
| Polycarbonate | Low | Good | Lets heat and light in |
| Fibre cement (non-asbestos) | Brittle | Good | Cooler |
Fixing and slope
Spacing and slope above are typical; the maker's tables for your profile govern.
- Space purlins as the sheet maker's span table allows, commonly about 1.2–1.5 m for 0.45–0.50 mm sheets.
- Keep a slope of at least about 5–10° for trapezoidal sheets so laps do not leak.
- Overlap end laps by about 150 mm and side laps by one full profile.
- Fix with self-drilling screws and EPDM washers at the crests, per the fixing plan.
- Fit ridge caps and flashings where the roof meets walls.
Checks on roofing sheets
- Get the BMT and coating class (for example AZ150) in writing; a TCT figure alone can hide thin steel.
- Measure thickness with a micrometer at a cut edge, scraping the paint to read the bare steel.
- Read the printing on the underside: thickness, coating, batch.
- Look for scratches in the paint and remove the protective film soon after fixing.
- Check that screws carry EPDM washers and are tightened without crushing them.
Storing sheets
- Store bundles raised, sloped and covered; water trapped between sheets leaves white stains and early corrosion.
- Lift sheets off the stack; dragging scratches the coating.
- Peel the protective film within days of fixing.
Roofing mistakes
- Comparing a TCT quote with a BMT quote.
- Mild-steel screws without washers near the sea.
- Too flat a slope, so laps leak in heavy rain.
- Cutting with an abrasive disc whose hot sparks burn the coating; use shears or nibblers.
- Purlins spaced wider than the span table allows.