How bad is it?
| What it usually means | Where it usually leads | |
|---|---|---|
| Light orange speckles or staining, coating mostly intact | Surface rust on sound steel | Treat and paint the affected areas |
| Rust rings around screws, or rust along the laps | Old screws, and water trapped at the joins | New screws, resealed laps and treated rust |
| Rust streaks running down from a flashing, pipe or aerial | A different metal reacting with the roof | Separate or replace the cause, then repair the sheet |
| Bubbling paint, flaking layers, or pinholes of light from inside | Rust right through the steel | Those sheets replaced |
| Holes or flaking on many sheets | A roof near the end of its life | A re-roof priced alongside any restoration |
Why it's rusting
Fixing rust without fixing its cause means paying twice. These are the usual reasons.
Age. Steel roofs don't last forever, and an old galvanised roof that's rusting all over may simply be finished. For a replacement, BlueScope rates Colorbond and Zincalume ahead of galvanised steel for most roofs.
Salt air. BlueScope's guide for homes recommends standard Colorbond for roofs more than 200 m from breaking surf, and Colorbond Ultra between 100 and 200 m. A roof closer to the surf than its steel was made for will rust early however often it's painted.
Contact with other metals. BlueScope says lead and copper corrode Colorbond and Zincalume. That includes run-off from old lead flashings and copper-rich water from a hot water system overflow, which it says should be piped past the roof, preferably to the ground.
Filings left behind. Metal filings from drilling and cutting, called swarf, rust where they land. BlueScope says swarf causes rust stains and can shorten a roof's life.
Places the rain doesn't wash. Salt and grime build up where rain can't rinse them off. BlueScope's October 2026 maintenance bulletin says to wash those areas every six months at least, or every three months near the coast.
Rusty roofs can give way
Safe Work Australia says every roof should be treated as fragile until a competent person says otherwise, and lists corroded metal sheets among the materials likely to be fragile. Rusted sheets and battens can collapse under a person's weight, so nobody without the right safety gear should be up there. If an old corrugated roof might be asbestos cement rather than steel, which is possible on homes built before 1990, don't let anyone grind, wire-brush or water-blast it until it's been checked.
Treat, restore, re-sheet or replace
Treat a few spots on a roof that's otherwise fine. BlueScope doesn't recommend touch-up paint on Colorbond, and says overpainting voids its warranty, so check whether yours is still covered before anyone gets the brush out.
Restore a roof with surface rust in many places but sound steel. The value is in the rust treatment, new screws and resealed laps, with paint going on last. Our pages on metal roof restoration and painting a metal roof cover the work.
Re-sheet sections where rust has gone through in patches but most of the roof is sound.
Re-roof when holes are widespread, the battens or fixings are rusting too, or the steel was never right for how close you are to the coast. Our guide to Colorbond roofing explains the choices.
How to size up the rust before calling anyone
Photograph the worst areas from the ground
Use a phone's zoom. Note whether the rust sits at screws, along the laps, at the bottom edge near the gutter, or out in the middle of the sheets.
Look for light from the roof space
On a sunny day, look from the manhole with the lights off. Pinpricks of light mean holes.
Look for a cause nearby
A lead flashing, a copper pipe, a hot water overflow, an aerial or an air conditioner sitting above the rusty patch is a strong clue.
Find the paperwork
When was the roof put on, and is there a BlueScope warranty? BlueScope says a warranty claim needs documents showing the product's age, proof of purchase and photos.
What you can do, and what to leave
You can
- Photographing rust from the ground
- Checking for pinpricks of light from the manhole
- Hosing down areas the rain misses, like under the eaves, from the ground
- Digging out the roof's age and any warranty papers
Leave to a roofer
- Grinding, wire-brushing and treating rust
- Replacing screws, sheets and flashings
- Separating lead or copper from the roof
- Judging whether the battens and fixings are still sound
What we'd do with a rusty roof
We'd find out why it's rusting before choosing the fix. Surface rust from age on a roof well back from the beach, we'd treat and paint, as long as the quote covers screws and laps too. Rust from a copper pipe or an old lead flashing, we'd fix the cause first. And if the roof is rusting through all over, or it's the wrong steel for the coast, we'd put the paint money towards new sheets.
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.