Where metal roofs actually fail
Rarely in the middle of a sheet. Trouble starts where water sits or metals meet: the laps where sheets overlap, around screw heads, along the bottom edge into the gutter, and under flashings.
Screws are a common weak point. Old ones rust, and their rubber washers harden and split, so each screw becomes a tiny leak. On an older roof, replacing every screw is often part of a restoration.
Mixing metals causes trouble too. BlueScope says lead isn't compatible with ZINCALUME or COLORBOND steel, so old lead flashings need painting or separating. Copper does similar damage, including copper-rich water from a hot water system overflow, which BlueScope says should be piped past the roof, preferably to the ground.
Restore it or re-sheet it?
| Restore | Re-sheet | |
|---|---|---|
| Rust | Surface rust that brushes back to sound metal | Holes, or rust that flakes right through |
| How widespread | A few bad sheets among many good ones | Rust-through on many sheets or most laps |
| Fixings and battens | Screws rusty but battens solid | Battens or fixings corroded along the roof |
| Location | Well away from breaking surf | Close to the surf, where the original steel may not suit the site |
Near the coast? Check the steel as well as the paint
BlueScope's simple guide for homes says COLORBOND steel suits roofs more than 200 m from breaking surf, and COLORBOND Ultra suits those between 100 and 200 m. Closer than that, it recommends SUPERDURA Stainless. Distances are measured from the high water mark, and local conditions such as prevailing winds still matter.
If your roof is closer to the surf than its steel was meant for, early rust is the likely result, and a new coat won't change the steel underneath.
In cyclone areas, corrosion is about strength as well as looks. The Northern Territory Government warns that coastal corrosion attacks cladding, battens, screws and straps and weakens a roof's cyclone resistance, so a restoration up north should include checking the fixings.
What the restoration quote should cover
- How rust will be treated, for example wire brushing or grinding, then an anti-rust primer
- How many sheets, if any, are being replaced, and in what product
- Whether every screw is being replaced, or only the rusty ones
- Laps, flashings, ridge capping and gutters: which are sealed, repaired or replaced
- Swarf (metal filings from drilling) swept off daily, because BlueScope says it causes rust stains
- The primer and topcoat by name, both made for metal roofs
What you can check, and what to leave alone
You can
- From the ground, note rust streaks, lifted sheets and rusty gutters
- From inside the roof space, note any spots where daylight shows through
- Hose down the spots rain never reaches, like the underside of gutters and walls under the eaves. BlueScope suggests every six months, or every three near the coast
Leave to a roofer
- Any rust treatment or grinding up top
- Replacing screws, sheets and flashings
- Coating, which needs a metal primer and dry weather
- Roofs that might be corrugated asbestos cement, which can pass for metal from the street
Our take
If the rust is surface deep and limited to a few spots, we'd restore, and insist the quote covers screws, laps and flashings as well as paint. If the roof is fairly new, check its BlueScope warranty first, because overpainting voids it. If rust has eaten through many sheets, or the house is near the surf and rusting early, we'd get a re-sheet price alongside the restoration quote.
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.
