What paint can and can't do for an iron roof
Roof paint keeps water and air off the steel. On iron that's still solid, a proper repaint (wash, rust treatment, primer on bare spots, then top coats) gives the roof another stretch of life for a modest outlay.
Once the steel has rusted through, there's nothing left for paint to protect. Painting over holes, or over heavy rust at the laps, hides the problem for a season or two before the stains and drips come back.
The Building Code backs up that split. Clause B2 expects renewable protective coatings to last at least 5 years with normal maintenance, and the building envelope, which includes the roofing, at least 15 years. Paint is the part you renew. The iron is the part you replace when it's finished.
How far gone is your iron?
| What you'll notice | What it usually means | |
|---|---|---|
| Faded or chalky paint | Colour washed out, streaky runoff | Repaint soon, before rust starts |
| Light surface rust | Orange spots or patches on otherwise solid steel | Treat the rust and repaint |
| Rust at laps and fixings | Rust lines where sheets overlap and around nail or screw heads | Treat and repaint if firm, replace those sheets if not |
| Rust through | Holes, flaking steel, daylight from the roof space | Replace sheets, or re-roof if it's widespread |
| Rust everywhere, plus leaks | Patches all over and drips in several rooms | Re-roof |
Corroded iron can give way underfoot
WorkSafe lists badly corroded metal roofing among the brittle roofs that workers shouldn't walk on. If trained roofers are told to stay off it, a homeowner checking the damage certainly should. Judge it from the ground and from inside the roof space, and leave anything on the roof to a roofer with proper fall protection.
When a repaint is the right call
A repaint makes sense when the sheets are firm and free of holes, rust is light and patchy, most fixings are tight, and the roof isn't leaking. It's the cheapest way to keep a sound iron roof going, and timing matters: paint applied before rust takes hold does far more good than paint applied after.
Most of a good repaint is preparation. Ask how they'll wash the roof, treat rust, deal with loose fixings and swarf (the steel filings left behind by drilling), and prime bare metal before the top coats go on.
Look closely at the parts the rain doesn't wash, like overhangs and unlined soffits. The metal roofing industry's Code of Practice says these collect salt and dust and corrode faster, especially near the sea, so they're often where rust starts first.
When a re-roof is the better money
Rust through the sheets, laps flaking apart, nails popping across the roof, or leaks you've already had patched more than once all point to a re-roof.
A re-roof is also the chance to fix things paint never will: replacing old nails with screws, fitting new underlay and flashings, and sorting the spouting (gutters) while the scaffolding is up.
After residential building work like a re-roof, the contractor must give you completion information, including copies of any product guarantees or warranties and the maintenance needed to keep them valid. Keep it with the house papers.
What makes each job bigger or smaller?
For a repaint, it's the roof's size and pitch, whether it's one or two storeys, and above all the preparation: how much rust needs treating, how many sheets or fixings need replacing first, and whether scaffolding or edge protection is needed.
For a re-roof, add stripping and disposal, new underlay and flashings, any rotten purlins found once the iron is off, spouting if it's being replaced too, and a consent if the system or purlins change. A good written quote lists each of these instead of lumping them together.
Consent, LBPs and the paperwork
A repaint is maintenance. It doesn't usually need a building consent or an LBP (Licensed Building Practitioner).
A like-for-like iron re-roof often doesn't need a consent either. Wairoa District Council's example is new corrugated iron replacing old with no change to the purlins, which doesn't need consent unless the old cladding failed within 15 years. Change the purlins, or switch to a different roofing system, and it does.
If the re-roof needs a consent, the roofing must be done or supervised by an LBP. And at $30,000 or more including GST, the contract has to be in writing, with the disclosure statement and checklist given to you before you sign.
Reading the quotes fairly
Ask for a quote rather than an estimate. Consumer Protection says an estimate is a best guess, and the final cost should generally land within 10 to 15% of it, while an accepted quote is a fixed price unless you agree to extra work or the scope changes.
There's no legal requirement to pay a deposit when you accept a quote. If one is asked for, Consumer Protection advises keeping it to 10% of the total or less.
Weighing it up, step by step
Get the condition confirmed
Ask a roofer to photograph the laps, the fixings, the eaves and the worst sheets, so you can see the steel for yourself.
Get both options quoted
A repaint (with any sheet replacements it needs) and a re-roof, on the same visit, each listing what's included.
Think about your timeline
If you're selling soon, a sound repaint may be all you need. If you're staying for the long run and the iron is tired, the repaint money may be better spent towards a new roof.
Count the repeat work
A repaint is a job you'll do again in future. A re-roof is a bigger cheque, written less often.
Check the consent position
Ask whether the re-roof is like-for-like and exempt, or needs a consent because the purlins or system are changing.
Pick a dry spell
Painting needs dry weather, so book it for the drier months where you can, and expect weather delays either way.
Your part, and the roofer's
You can
- Look over the roof from the ground with binoculars
- Check the roof space with a torch for daylight and rust flakes, standing only on the joists
- Note where and when any drips show up
- Keep branches trimmed back from the roof, from the ground or with an arborist
- Keep invoices from past roof work
Leave to a roofer
- Anything on the roof
- Washing and rust treatment
- Replacing rusted sheets and failed fixings
- Priming and painting
- A re-roof and any consent it needs
What we'd do with a tired iron roof
If the sheets are solid and the rust is light, we'd repaint now, before light rust turns into holes and a cheap job turns into an expensive one. If you can see daylight from the roof space or the laps are flaking, we'd skip the paint and put that money towards a re-roof. On the fence? A roofer's close-up photos of the laps and fixings usually settle 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.