Steel, or asbestos cement?
Corrugated asbestos cement, often called 'Super Six', is grey and cement-like rather than metal. Hardies' Super Six had 7 wide, deep ridges about 6 inches apart; the older 'Standard' sheet had 11. Hardies kept selling a non-asbestos Super-Six until at least 1992, so treat an unstamped sheet as asbestos until a lab says otherwise. Don't drill, cut, water-blast or walk on it. Our guide to Super Six roofing explains your options.
Corrugated in numbers
Lysaght calls Custom Orb the traditional Australian corrugated profile. Each sheet covers 762 mm of roof, the corrugations are 16 mm deep, and the lowest pitch is 5 degrees, a rise of 1 in 12.
It's light. In Colorbond at 0.42 mm it weighs 4.35 kg per square metre, against 47.25 kg for one of Monier's terracotta tiles. Sheets up to 24 m long can go on before an expansion joint is needed, so a typical house roof is covered in single lengths from gutter to ridge, with no end joins to leak.
Custom Orb is Lysaght's name, and Lysaght is a BlueScope business. Other makers roll similar sheets under their own names, and we aren't tied to any of them.
0.42 mm or 0.48 mm sheet?
| 0.42 mm BMT | 0.48 mm BMT | |
|---|---|---|
| Weight in Colorbond | 4.35 kg per square metre | 4.93 kg per square metre |
| Weight in Zincalume | 4.28 kg per square metre | 4.86 kg per square metre |
| Longest single span | 700 mm | 800 mm |
| Longest end span | 900 mm | 1300 mm |
| Longest internal span | 1200 mm | 1700 mm |
Why people choose it, and where it falls short
BMT means base metal thickness, the steel without its coatings. Thicker sheet spans further between battens, so on a re-roof the spacing already there decides which you need. Ask the roofer to measure rather than guess.
In its favour: it's light, familiar, comes in the full Colorbond and Zincalume ranges, and most roofers know it well, so repairs and matching sheets are easy to arrange.
The limits: it can't go below 5 degrees, and every screw is a hole through the sheet. That's why Lysaght says roofs are always fixed through the crests, never the valleys where water runs. The 2022 building code sets the minimum pattern, at the side lap and every second rib on end spans, every third on internal spans; states moving to the 2025 code may change that. And without a blanket underneath, rain on it is loud.
Curved and bullnose verandahs
Standard Custom Orb isn't meant to be machine curved. For bullnose verandahs and curved roofs, Lysaght uses Custom Blue Orb, a softer G300 steel with a slightly deeper 17 mm corrugation. The tightest curve it allows is a 300 mm radius, or 400 mm in Victoria. On a heritage verandah, make sure the quote names the curving-grade sheet.
What to ask a roofer
- Is my old roof steel or cement sheet, and how do you know?
- Which thickness suits my batten spacing?
- Will the sheets be full length and fixed through the crests?
- Does the verandah need curving-grade sheet?
- What screws are you using, and is a blanket going underneath?
What you can do
You can
- Look from the ground for lifted sheets, loose screws or rust stains around fixings
- Hose down the underside of gutters and other spots rain doesn't reach
Leave to a roofer
- Walking on it, which Lysaght says means stepping across at least two corrugations
- Replacing screws, sheets and flashings
- Anything on a roof that might be cement sheet
Our call
On a pitched home above 5 degrees, corrugated is a sensible, sound choice that most roofers know inside out. Before collecting quotes, we'd confirm the old roof is steel, because cement sheet turns a simple re-roof into a licensed removal job. And on a bullnose verandah, we'd check the quote names a curving-grade sheet.
Want a roofer to take a look?
Tell us the job and your postcode. We match it with a Find My Roofer certified roofer who specialises in that kind of work, and they call you to quote. Your number goes to them alone.