What the Building Code expects
Clause B2 Durability sets minimum lives, with normal maintenance, counted from when the code compliance certificate is issued. MBIE's Acceptable Solution lists roof cladding as needing at least 50 years where it's structural and at least 15 years where it isn't, which covers most house roofing. Easy-to-replace parts and renewable protective coatings, like roof paint, need at least 5 years.
These are legal minimums a product has to be able to meet, not a promise about your roof. MBIE's own example of consent-exempt work is replacing a 20-year-old metal roof that has lasted more than 15 years with a comparable product, which tells you roofs are expected to go past the floor.
What published figures say for each roof type
| What the published figure says | What wears it out early | |
|---|---|---|
| COLORSTEEL MAXAM longrun (NZ Steel warranty) | Roofing perforation warranty from 50 years (Mild) down to 20 years (Very Severe), and not recommended in Extremely Severe sites | Salt, unwashed areas, swarf, copper or lead runoff |
| Unpainted ZINCALUME (NZ Steel warranty) | 25 years in Mild sites, 20 in Moderate, and not recommended closer to the sea | Coastal salt and geothermal gases |
| Pressed metal tiles (BRANZ appraisal of Gerard) | Minimum expected life with cleaning and recoating: 40 years in exposure Zone B, 30 in Zone C, 20 in Zone D | Foot traffic, chip loss, salt |
| Concrete tiles (Monier warranty) | 30 years against manufacturing defects | Cracked tiles underfoot, ridge bedding, moss |
| Clay tiles (Level, from BRANZ) | Expected durability of 50+ years with correct installation and maintenance | Damage during maintenance work |
| Butynol (BRANZ appraisal) | Serviceable life of at least 20 years with proper maintenance | Ponding, movement in the structure below, punctures |
A warranty isn't a lifespan
Warranties are the closest thing to a published number, but read the conditions. NZ Steel's COLORSTEEL warranty needs its maintenance programme followed and documented, runs from when the material is delivered to site, and covers the steel only, not fasteners or other accessories.
It also excludes damage from swarf (the steel filings left from drilling and cutting), run-off from lead or copper, ponding water, failing to replace corroded fasteners, and storms, earthquakes and other extreme events. For COLORSTEEL roofing, normal rain washing is the maintenance NZ Steel asks for, but unwashed areas such as soffits, gutter undersides and spots under aerials and solar panels need washing by hand, and that's a warranty requirement.
For a COLORSTEEL roof, the honest answer to how long it lasts is: ask the roofer for the written warranty for your address, then do the maintenance it lists. Our COLORSTEEL guide explains the two products and their warranties.
Distance from the sea changes everything
NZ Steel sets its COLORSTEEL warranty categories by distance from the coast, with different distances for the east and west coasts. Mild typically starts 5 km from breaking surf and covers most of New Zealand. Severe sits 100 to 500 m from the east coast and 500 m to 1 km from the west coast. For anything within 100 metres of a saltwater body, NZ Steel asks you to contact COLORSTEEL to confirm the warranty.
Under NZS 3604, as summarised by BRANZ, exposure Zone D covers all areas within 500 m of the coast including harbours, and 100 m from tidal estuaries and sheltered inlets. BRANZ testing found winds can carry salt particles more than 20 kilometres inland, though the metal roofing Code of Practice says the main effect reaches just a few hundred metres from the shore.
Parts of a building the rain doesn't wash collect salt and dust and corrode faster. On a house within 500 m of the Auckland harbour, BRANZ found sheltered spots collected about 3 to 8 times more salt than exposed ones.
Other things that age a New Zealand roof
Geothermal gases. The Code of Practice treats buildings within 50 m of a geothermal fumarole as a geothermal microclimate, and says highly active areas such as much of Rotorua count as geothermal even without a local fumarole. BRANZ found aluminium-zinc coated steel appears to corrode more quickly in strong geothermal environments than marine ones.
Sun. Auckland's mean daily maximum UV Index at Leigh reaches 12.2 in January, NIWA says. Strong UV is hard on paint, sealing washers and membranes over time.
Snow and wind. In snow-prone areas, snow straps on gutters and extra fixings on flashings and chimneys are normal, because sliding snow pulls at them. Wind finds any loose sheet or flashing.
Earthquakes. After the Canterbury earthquakes, BRANZ found tiles on hill-suburb roofs had often come off their battens because they weren't tied down or their ties had corroded.
Neglect. Moss, lichen and blocked spouting (gutters) keep water sitting where it shouldn't. Decramastic tiles, popular in the 1960s and 1970s according to Gerard, lose their stone chips over time, exposing the bitumen and then the galvanised steel, which eventually rusts, Resene says.
Signs a roof is near the end
- Rust holes, or daylight through the roofing when you look up from the roof space
- Leaks turning up in new places after repairs
- Tiles cracking or crumbling across the whole roof
- Bare steel showing over large areas of a painted or decramastic roof
- Nails or screws lifting everywhere, with rust around the holes
- Splits, blisters or ponding on a butynol or membrane roof
- A sagging ridge or roofline
Old roofs and asbestos
WorkSafe says a home built before 1 January 2000 may contain asbestos, and lists asbestos cement roof sheeting and panels such as Super Six among the places to look. Health NZ warns asbestos-cement roofing breaks easily and you could fall through it. Don't walk on it, water-blast it or drill it. If you're not sure what your roof is made of, our asbestos roof guide explains how to find out safely.
How to tell where your roof is up to
Find out when it went on
Your council property file may show a re-roof consent, and old sale documents or a builder's report sometimes mention it. Neighbours with the same era of house can be a clue too.
Check your exposure
Ask a roofer which NZS 3604 zone and COLORSTEEL category your address falls in. It changes what counts as normal wear.
Look from the ground
On a dry, bright day, use binoculars to look for rust, bare patches, cracked tiles, moss and lifted fixings.
Look from the roof space
With a torch, look for daylight, drips or water stains on the timber after rain. Step only on the joists.
Get a roofer's report every few years
Monier, for one, suggests a roofing professional inspect a tile roof ideally every five years. A written report with photos gives you a baseline. Our roof inspections page covers what's in one.
If a newer roof fails early
You have rights. You can notify the contractor of defects within 12 months of completion, and they must fix them within a reasonable time; the defect is presumed to be theirs unless they prove otherwise. The implied warranties in every residential building contract say the work must be done properly with suitable materials, and MBIE says you can take action within 10 years if they aren't met.
A contractor isn't liable for a defect caused by failing to do normal maintenance, which is one more reason to keep receipts for roof washes, moss treatments and spouting cleans. And insurance won't pay to replace a roof that has simply worn out: house policies commonly exclude wear and tear, rust and gradual deterioration.
What you can do to help a roof last
You can
- Hose down soffits, gutter undersides and other unwashed areas you can reach from the ground
- Keep branches trimmed back, from the ground or with an arborist
- Keep copper pipes and lead flashings from draining onto a steel roof
- Check the roof space after heavy rain
- Keep receipts and reports in one folder
Leave to a roofer
- Inspections and written condition reports
- Washing and moss treatment on the roof itself
- Replacing corroded fasteners and lifted flashings
- Recoating before the steel is exposed
- Advice on when a re-roof makes more sense than repairs
How we'd get the most years out of a roof
Know your exposure zone, keep the warranty paperwork and do the maintenance it asks for. Get a roofer to look at it every few years and after any big storm, and fix small things while they're small: a lifted flashing, a few popped nails, a blocked outlet. On the coast, we'd keep the unwashed parts clean and repaint before rust starts, because that's where steel roofs usually give out first.
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.