The old roof has to go and you’ve settled on steel. Then the quote throws up a question you weren’t expecting: Zincalume or Colorbond? Both are BlueScope steel, both go down with the same screws, and on the rack the sheets look the same apart from the finish. So which one belongs on your house?
We get asked about Zincalume vs Colorbond roofs on most of the metal re-roofs we price around Nowra. Neither one wins every time. They are the same steel set up for different jobs. The right pick depends on where the house sits, what else is on the roof, and how much the neighbours will care about glare.
If you’re still deciding between steel and tiles, our Colorbond vs tile comparison is the better place to start. This post assumes steel is already the plan.
Colorbond is Zincalume with a paint system on top
This is the part that surprises people. Colorbond is not a different metal. It starts as a steel sheet with the same type of metallic coating Zincalume has, a zinc and aluminium alloy that does the real work of keeping rust out. BlueScope then adds a pretreatment, a primer and a baked paint finish over that coating.
Zincalume stops at the metallic coating. What you see on the roof is the alloy itself. It’s bright silver when new and slowly dulls to a softer, mottled grey.
So the useful question is never “which steel is stronger”. It’s whether those extra layers earn their keep on your particular roof.
Zincalume earns its place on sheds, inland blocks and tight budgets
Zincalume is usually the cheaper sheet, because there’s no paint system to pay for. On a big, simple roof that adds up.
On a house re-roof it matters less than most people expect. The sheet is one line on the quote. Removing the old roof, flashings, ridge capping, sarking, gutters and labour make up the rest, and those cost the same whichever finish you choose. Our guide to what a Nowra roof replacement really costs walks through those lines one by one.
Raw metal also hides scratches well. A scuff on Zincalume just looks like more Zincalume. That makes it a practical choice for farm sheds, carports and workshops where ladders and gear get dragged across the sheets. Out on the rural blocks around Cambewarra and Falls Creek, a silver shed roof is about as normal as it gets.
And some people simply like the look. Plain metal roofs were on Australian houses long before coloured steel came along, and a silver roof still suits some older weatherboard cottages and farmhouses.
Salt air tips the balance towards Colorbond
A good share of the area we cover sits within reach of sea spray: Culburra Beach, Shoalhaven Heads, Greenwell Point and the streets near the river mouth. Salt lands on the roof, and wherever rain doesn’t rinse it off, it sits there holding moisture against the coating.
Both products rely on the same metallic layer underneath. On Colorbond, the primer and paint put an extra barrier between that layer and the salt. BlueScope rates its products by how far a building sits from breaking surf and other corrosive sources, and for the harshest sites it points people to Colorbond Ultra or Colorbond Stainless rather than the standard sheets.
The spots that fail first on coastal roofs are rarely the open sheets. It’s the sheltered places rain never reaches. Under the lip of a flashing. The overlap between two sheets. The underside of the eaves. When we look at an old roof near the coast, those areas tell us what the new one will be up against.
If you live close to the water, ask whoever quotes which BlueScope product they’re specifying and whether it suits your distance from the surf. Getting it wrong can shorten the life of the roof and cause problems with the manufacturer’s warranty.
The shiny silver roof is not always the cooler one
New Zincalume reflects a lot of sunlight, which sounds perfect for a Shoalhaven summer. The catch is that bare metal is poor at letting go of the heat it does absorb, and it reflects less as the surface dulls. Colorbond paint uses BlueScope’s Thermatech technology to reflect solar heat, and a light colour will often keep the roof space cooler over the life of the roof. Dark charcoal and black Colorbond roofs still run noticeably hotter, so colour choice matters as much as the product.
Glare is the other issue. That silver finish can throw sunlight straight into a neighbour’s window, especially from a low pitch roof sitting below houses on a slope. Councils can restrict reflective roofing in some areas or through development conditions. If your re-roof is part of an extension or new build, check your approval before you settle on bare metal.
What already drains onto your roof matters more than the sheet
Both products react badly to some other metals, and copper is the one that catches people out. Water running off copper pipe, an old copper solar hot water unit or copper flashing will corrode Zincalume and Colorbond below it. The wrong screws and fixings can cause similar trouble at every fixing point.
This is why we look at the whole roof before we price anything. Laying new sheets is the easy part. Working out what else drains onto them is what decides whether they last.
When we quote a metal roof replacement, the product and colour go on the written quote along with what is included and what is not. You shouldn’t have to guess which steel you’re paying for.
Painting Zincalume later is possible, but rarely the cheap option
Some owners plan to go silver now and add colour later. Zincalume can be painted, as long as it’s properly cleaned and primed with a system made for metallic coated steel. It is still a paint job done on the roof, though, and it won’t match a factory baked finish for durability. If you know you want colour, it’s nearly always better value to buy it on the sheet.
How we’d choose for a Nowra home
Every roof gets looked at on its own, but this is roughly how the decision falls out on the jobs we see:
- Near the beach or river mouth: Colorbond, in the grade BlueScope specifies for your distance from the surf
- Inland, in suburbs like West Nowra or Cambewarra Village: either works, so choose on looks and budget
- Shed, carport or workshop: Zincalume is hard to beat on price
- Copper anywhere upslope: deal with that first, whichever sheet you pick
- Extension or new build: check council conditions on reflective roofing before ordering
Ryan Bruce leads our team, with more than 10 years of roofing experience behind the work, and we are fully licensed and insured. If you’re weighing up Zincalume against Colorbond for your next roof, we’ll come out, look at the roof and where it sits, explain what we find in plain English and give you a free written quote for replacing your steel roof.
Common questions about Zincalume and Colorbond
Is Zincalume cheaper than Colorbond?
The sheet usually is, because it has no paint system. On a full house re-roof the gap shrinks, since removal, flashings, gutters and labour cost the same either way. Ask for both options on the same written quote and compare the totals.
Does Zincalume last longer than Colorbond?
No. Both start with the same kind of metallic coating, and Colorbond adds primer and paint on top. Inland, either can give a long life. Near the coast, Colorbond in the right grade for your site generally holds up better.
What is Colorbond made of?
Colorbond is BlueScope steel with a zinc and aluminium alloy coating, a pretreatment layer, a primer and a baked paint finish. In other words, it is Zincalume steel with a factory paint system added.
What are the disadvantages of a Zincalume roof?
Glare is the big one, and some councils restrict reflective roofing. It has fewer options for harsh coastal sites and comes in a single finish. Like Colorbond, it corrodes when water runs onto it from copper.
What Colorbond colour is closest to Zincalume?
No standard Colorbond colour copies the metallic look. People who want a light grey roof that sits close to weathered Zincalume often look at Shale Grey or Windspray. Check a real sample outdoors, because colours read differently on a roof than on a chart.
