Corrugated iron has been New Zealand’s classic roof for more than 150 years, and until the 1980s it was the country’s most common roofing material. This guide covers what the product is today, its sizes and minimum pitch, how long it lasts, and what it involves and costs to replace an old corrugated iron roof.
Short answer: today’s “corrugated iron” is steel, not iron. It’s coated with zinc and aluminium and usually pre-painted, such as COLORSTEEL MAXAM®. Standard corrugate has 17.5 mm deep waves at 76 mm spacings, covers 762 mm per sheet and needs a roof pitch of at least 8°. Inland Waikato homes, Hamilton included, get MAXAM’s longest warranty: 50 years against corrosion. Replacing the old iron on a typical single-storey, three-bedroom home with new corrugate costs about $18,000–$26,000.
What is corrugated iron?
Corrugated iron is steel sheet rolled into regular waves, which makes a thin sheet stiff enough to span between the roof framing. It was invented in Britain in the 1820s and was available in New Zealand as early as 1843. Until the 1980s it was the country’s most common roofing material.
The name is older than the product. The sheets were always steel, galvanised by dipping them in molten zinc. The zinc slowly corrodes in place of the steel, so the coating wears away over the decades. Today’s sheets use an aluminium-zinc coating (ZINCALUME®), which New Zealand now uses more than any other coating on steel roofing, usually with a factory paint finish such as COLORSTEEL® on top.
The profile itself has changed only once, according to the NZ Metal Roofing Code of Practice. In the 1960s, the steel changed to a much stronger grade, and each sheet went from 8 to 10½ corrugations so it could be laid either side up. So “corrugated iron”, “corrugate” and “longrun corrugate” now mean the same roof. See is longrun the same as corrugated iron?
Sheet Sizes and Coverage
| Standard corrugate | Size |
|---|---|
| Wave depth and spacing | 17.5 mm deep at 76 mm centres |
| Cover width (after the side lap) | 762 mm |
| Sheet width | 851 mm |
| Steel thickness | 0.40 mm or 0.55 mm |
| Weight | About 4 kg per m² (0.40 mm) to 5.6 kg per m² (0.55 mm) |
| Sheet length | Rolled to order, to the length of the roof |
Sources: NZ Metal Roofing Code of Practice and Dimond’s corrugate data. Exact figures vary slightly between manufacturers.
Because the sheets are rolled to length, most house roofs go on in one piece from ridge to spouting, with no end laps. Very long runs are another matter. The Code says to check standard corrugate’s water-carrying capacity once a run passes 15 m. See how long longrun sheets can be. There’s also a miniature version, known as mini-corrugate, baby iron or sparrow iron, which is mostly used for walls and small roofs.
Minimum Pitch and Drainage
Standard corrugate needs a roof pitch of at least 8°, which is about 1 in 7. Below that, the side laps can’t be relied on to keep water out. Deeper corrugated profiles and trapezoidal rib can go lower:
| Profile (minimum rib height) | Minimum pitch | Check capacity after a run of |
|---|---|---|
| Standard corrugate (16.5 mm) | 8° | 15 m |
| Deep corrugate (21 mm) | 4° | 20 m |
| Trapezoidal rib (27 mm) | 3° | 40 m |
Source: NZ Metal Roofing Code of Practice, minimum pitch for generic metal roofing. The pitch that counts is the pitch of the sheets once they’re laid, not the pitch on the house plans.
Most villas, bungalows and 1950s–70s homes have main roofs well over 8°, so corrugate suits them. Where it often fails is on a later lean-to, deck cover or extension that’s close to flat. On a re-roof, those sections may need rib even if the main roof stays corrugate.
How Corrugated Iron Holds Up Over Time
An old galvanised roof lasts as long as its zinc. As the zinc wears away, you see white powdery corrosion, then red rust, usually starting at laps, nail holes and the areas rain doesn’t wash. Until 1980 these roofs were fixed with lead-head nails, which back out over time and let water in. The Code of Practice now recommends screws on every roof.
A new roof starts in a different place. COLORSTEEL MAXAM®, which replaced Endura® and Maxx® in 2025, is warranted by environment:
| Where the house is | Corrosion warranty | Paint warranty |
|---|---|---|
| Inland, 5 km or more from surf (Hamilton, Cambridge, Te Awamutu) | 50 years | 18 years |
| Moderate coastal | 40 years | 18 years |
| Severe coastal | 30 years | 15 years |
| Very severe coastal | 20 years | 15 years |
Source: COLORSTEEL warranty tables, checked November 2026. For the distances behind each coastal category, see steel roofs near the coast. For more on the steel itself, see COLORSTEEL roofs explained.
Replacing a corrugated iron roof: what’s involved
Replacing roofing iron is one of the simpler re-roofs, because the new steel weighs about the same as the old iron and goes back onto the same framing. A typical job runs like this:
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- Strip back to the framing. The old iron, nails and lead flashings come off. Lead isn’t compatible with modern coated steel, so none of it goes back.
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- Check the battens and purlins. Timber that has taken in water over the decades can be soft or split. Anything that can’t hold a screw is replaced before the new roof goes on.
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- New underlay. The Building Code requires a permeable, absorbent underlay under profiled metal roofing on lined homes. Many old roofs have tired underlay or none. The Code of Practice recommends a synthetic, self-supporting, fire-retardant underlay for houses.
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- New corrugate, screwed down. Sheets are rolled to length and fixed with screws rated for your area, with sealing washers. The Code sets Class 4 as the minimum for exposed fixings.
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- New flashings at the ridge, barges, valleys and around chimneys and vents, folded from the same steel as the roof.
Replacing iron with comparable steel in the same position usually doesn’t need a building consent. Changing the structure or the roof’s shape can. See Hamilton City Council consent for a re-roof. If you own an older Hamilton home, re-roofing Hamilton’s 1950s–70s homes covers what usually turns up under the old iron.
What it costs to replace a corrugated iron roof (2026)
These are CTR Roofing’s guide prices for Waikato homes replacing old iron with COLORSTEEL MAXAM®:
| Home | Approx. roof area | Job | Typical range |
|---|---|---|---|
| Single-storey 3-bedroom | 140–170 m² | Old iron to corrugate | $18,000–$26,000 |
| Single-storey 4-bedroom | 180–230 m² | Old iron to trapezoidal rib | $24,000–$34,000 |
| Two-storey home | 130–170 m² | Old iron to corrugate, scaffold included | $26,000–$36,000 |
That’s roughly $110–$220 per m² of roof. Steep roofs, two storeys, hard access and replacing rotten battens push a job up the range. Spouting is usually a separate line. For the full breakdown, see what a metal re-roof costs in the Waikato.
Insulation and Noise Control
Rain is louder on steel than on tiles, and an old iron roof with no underlay and little ceiling insulation is louder still. The Code of Practice says the best way to reduce rain noise is more insulation in the ceiling space. A re-roof is a good time to top it up, while the roof is open. New underlay also helps.
Steel can also creak or tick as it heats and cools. The Code puts this down to the roof, flashings and fixings moving at different rates. Correct fixing and flashing details keep it to a minimum.
How Corrugated Iron Compares to Other Roof Types
Corrugated iron vs trapezoidal rib
Both are longrun steel in the same COLORSTEEL MAXAM® range, so the choice comes down to the look and the pitch. Corrugate keeps the classic wave of a villa, bungalow or 1960s home. Trapezoidal rib has bolder, flat-topped ribs, carries more water and can go down to 3–4°, so it suits low-pitched roofs and modern homes. See longrun roofing in the Waikato for the full comparison.
Corrugated Iron vs Tile
Concrete and clay tiles are far heavier than steel, so a tiled roof needs more framing. Going from tiles to steel costs more than replacing iron ($28,000–$40,000 for a single-storey, three-bedroom home), mainly because there’s more to strip and take away.
Corrugated Iron vs Membrane Roofs (flat roofs)
Corrugate isn’t a flat-roof material. Below 8° you need a deeper profile, and below 3° you’re into membranes or specialist trough-section roofing.
Who Should Choose Corrugated Iron
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- Villas, bungalows and character homes, where corrugate is the original roof and keeps the house looking like itself
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- 1950s–70s homes in suburbs like Fairfield, Enderley, Nawton and Dinsdale, where like-for-like keeps the street’s look
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- Homes in character areas, such as parts of Cambridge, where it’s worth checking with council before changing the roof’s profile. See metal roof replacement in Cambridge.
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- Farm sheds and rural buildings. See rural roofing.
It’s the wrong choice for any roof under 8°.
Questions to ask before you replace your iron roof
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- Which profile and which steel is on the quote? It should say something like “corrugate, COLORSTEEL MAXAM®”, not just “iron”.
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- What thickness is the steel, 0.40 mm or 0.55 mm?
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- Is new underlay included, and which one?
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- How will rotten battens or purlins be priced if you find them?
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- Are new flashings included, and are they the same steel as the roof?
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- What screws are you using, and are they rated for my area?
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- Is the roofer a Licensed Building Practitioner? See does a roofer need to be an LBP?
To compare quotes line by line, see how to compare re-roof quotes.
How CTR Roofing replaces corrugated iron
CTR Roofing has been roofing in the Waikato since 2010 and is a RANZ member. Every roof uses COLORSTEEL MAXAM®, in corrugate or trapezoidal rib. Our installers hold LBP Roofing licences, we supply a Record of Work on every consented job, and most homes are re-roofed in 2–4 days. See metal roof replacement in Hamilton and the Waikato.
Get your re-roof measured and priced
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Frequently asked questions
What is corrugated iron roofing?
Steel sheet rolled into regular waves, used on New Zealand roofs since the 1840s. Old sheets were galvanised with zinc. Today’s are coated with an aluminium-zinc alloy and usually pre-painted, such as COLORSTEEL MAXAM®. Despite the name, it has always been steel.How long does a corrugated iron roof last in New Zealand?
A new COLORSTEEL MAXAM® corrugate roof is warranted against corrosion for 50 years on inland sites such as Hamilton, and for 20–40 years on coastal sites, depending on distance from the surf. Many original galvanised roofs on Waikato homes are now 50 to 70 years old.Is corrugated iron noisy in heavy rain?
It’s louder than tiles. The NZ Metal Roofing Code of Practice says the best way to reduce rain noise is more ceiling insulation. A re-roof is a good time to add it, along with new underlay.What is the minimum pitch for corrugated iron?
8° (about 1 in 7) for standard corrugate, according to the NZ Metal Roofing Code of Practice. Deeper 21 mm corrugate can go to 4°, and trapezoidal rib to 3°. Below 8°, standard corrugate’s side laps can’t be relied on to keep water out.Can corrugated iron be used on old houses?
Yes, and it’s usually the original roof. New corrugate is the same wave profile, so a like-for-like re-roof keeps the look of a villa, bungalow or 1960s home. New steel weighs about the same as the old iron, so the framing takes no extra load.How much does reroofing with corrugated iron cost?
In the Waikato in 2026, replacing old iron with new corrugate costs about $18,000–$26,000 for a single-storey, three-bedroom home and $26,000–$36,000 for a two-storey home with scaffold. That’s roughly $110–$220 per m² of roof.What coatings are best for coastal Waikato sites?
Pre-painted steel suited to the site’s environment category. COLORSTEEL MAXAM® covers sites from mild to very severe, with shorter warranties closer to the surf. Unpainted ZINCALUME® is only for the least corrosive zones, and beachfront sites need ALTIMATE® or aluminium.What size is a sheet of corrugated iron in NZ?
Standard corrugate covers 762 mm per sheet, with a full sheet width of about 851 mm. The waves are 17.5 mm deep at 76 mm centres. Thickness is usually 0.40 mm or 0.55 mm, and sheets are rolled to the length of the roof.Sources: Te Ara: roofing and glazing · Code of Practice: corrugate profile · Code of Practice: minimum pitch · Code of Practice: coatings · Code of Practice: nails · Code of Practice: underlay · Code of Practice: roof noise · Dimond: corrugate · COLORSTEEL: warranty and maintenance
Related: Metal roof replacement in Hamilton · Longrun roofing · What a re-roof costs · Hamilton’s 1950s–70s homes
Written by Corey and the CTR Roofing team, Hamilton. Updated November 2026.