What Zincalume is
BlueScope classes Zincalume as Type AM coated steel under AS 1397:2021. The magnesium, aluminium and zinc in the coating protect the steel by corroding in its place, which BlueScope calls sacrificial protection, and its Activate technology is designed to slow that corrosion down.
In Lysaght's Custom Orb and Klip-Lok, Zincalume is high-strength G550 steel with an AM125 coating, a heavier metallic layer than the AM100 minimum under Colorbond's paint. BlueScope says both products outperform old-style galvanised steel in most roofing.
Zincalume and Colorbond are BlueScope trade marks. We have no link with BlueScope; this page sets out what its published guidance says.
Zincalume or Colorbond?
| Zincalume | Colorbond (Classic finish) | |
|---|---|---|
| Finish | Bare metallic coating, silver | Metallic coating, primer and baked-on paint in 22 core colours |
| Distance from breaking surf or exposed salt water | More than 200 m | More than 200 m |
| Distance from calm salt water, such as harbours and estuaries | More than 100 m | Any distance |
| Solar absorptance (share of the sun's heat absorbed) | Treat as 0.50 to 0.60, and it shifts as the surface weathers | Set by colour: 0.28 for Dover White up to 0.95 for Night Sky |
| Painting it later | Voids BlueScope's warranty | Also voids BlueScope's warranty |
Heat and comfort
For the building code and NSW BASIX, BlueScope says to treat Zincalume as absorbing between 0.50 and 0.60 of the sun's heat, a mid-range figure. A light Colorbond colour absorbs less; a dark one, more.
Bare metal also has low thermal emittance, meaning it gives off less of the heat it has absorbed as radiation. BlueScope says that makes it behave differently from painted roofs for energy efficiency, so the insulation under it matters.
What it can't touch
This is where Zincalume roofs go wrong. BlueScope says lead, copper, stainless steel and copper alloys must not be used with it, and long contact with treated or green timber corrodes it too.
Lead flashings on an old chimney need painting or separating from the new sheets, because even run-off from lead attacks the coating. Copper is the sneaky one: water from a hot water system overflow carries copper, so BlueScope wants overflow pipes run beyond the roof, ideally to the ground. Galvanised gutters under a Zincalume roof can corrode early, so pair it with Zincalume or Colorbond gutters.
The 2022 building code also bans lead materials upstream of this kind of roofing. The 2025 edition, which states are adopting from 1 May 2026, may word that differently.
Upkeep, and painting it later
Rain keeps the open roof clean. Wash sheltered spots, like the underside of gutters, at least every six months, or every three months near the sea, and skip sugar soap, which BlueScope says shouldn't be used on bare Zincalume. For steel roofs generally, a NSW Government heritage schedule gives a life of 20 to 40 years.
You can paint it, but overpainting voids BlueScope's warranties. If you do, BlueScope suggests a household detergent wash, water-based acrylic, and a zinc-rich etch primer on any rusty patches. Our roof paint page has more.
What to ask before it goes on
- How far is the house from surf, exposed water or calm water, measured from the high-water mark?
- Are there lead flashings, copper pipes or a hot water overflow on the roof, and what will you do about them?
- Are the gutters galvanised, and will they be replaced to suit?
- Which profile and thickness are you quoting, and what goes underneath?
Yours, and the roofer's
You can
- Find where your hot water overflow pipe drains
- Hose sheltered spots under the eaves on schedule
- Note rust stains around flashings from the ground
Leave to a roofer
- Changing or separating lead flashings
- Rerouting overflow pipes off the roof (or a plumber)
- Any work on the sheets themselves
Our view on bare steel
If you're well clear of salt water and like the look, Zincalume is a plain, honest steel roof. We'd measure the distance to the water first, remembering the calm-water rule is stricter than Colorbond's. Then we'd ask the roofer to deal with any lead flashing, copper pipe or hot water overflow before the first sheet goes down, because those are what quietly eat it.
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.