# Corrugated Iron (Corrugated Galvanised Iron)

> Corrugated iron is thin metal sheet rolled into parallel waves for stiffness. Patented in London in 1829, it became a roofing material used worldwide.

- URL: https://roof.wiki/corrugated-iron/
- Topic: Roofing Materials
- Also known as: CGI; corrugated galvanised iron; corrugated galvanized iron; corrugated steel; corrugated metal roofing; corrugated sheet metal; wriggly tin; wrinkly tin; corro; Custom Orb; pailing; zinc (Nigeria, Cyprus); mabati; tôle ondulée; Wellblech; chapa ondulada; calamina
- Regions: Global, Oceania, Africa, Europe, Latin America, South Asia, North America
- First published: 2026-11-01 · Last reviewed: 2026-11-01
- Cite as: "Corrugated Iron (Corrugated Galvanised Iron)." roof.wiki. https://roof.wiki/corrugated-iron/

## Key facts

- **Patent:** No. 5786, 1829, Henry Robinson Palmer (London Dock Company)
- **First commercial maker:** Richard Walker, Bermondsey, London (advertising by 1832)
- **Galvanising patent:** 1837, Stanislas Sorel (Paris); first applied to corrugated sheet c. 1843
- **Standard pitch of corrugations:** 76 mm (3 in)
- **Historic UK roofing sheet:** 18 SWG, about 1.2 mm (0.048 in)
- **Typical modern sheet (Australia):** 0.42-0.48 mm base steel, 762 mm cover, 4.3-4.9 kg/m²
- **Minimum pitch, NZ corrugate (16.5 mm deep):** 8°
- **Peak British exports:** c. 250,000 tons a year, 1890-1900
- **Surviving tin tabernacles in England:** 86 (fewer than 20 listed)

Corrugated iron is thin metal sheet that has been formed into a continuous series of parallel, rounded waves. The corrugations turn a floppy sheet into a stiff, lightweight structural skin: a sheet that would sag between supports when flat can span between widely spaced purlins once it is waved, and early versions were even used as self-supporting arched roofs with no framing at all. The fully protected form is usually called corrugated galvanised iron (CGI), because for most of its history the sheet was coated with zinc to slow rusting.[1][2] Although the base metal has been mild steel rather than wrought iron since the early twentieth century, and most modern sheet carries an aluminium-zinc coating or factory paint rather than plain zinc, the old name has survived in everyday speech across the English-speaking world.[10]

The material is known by many local names. In Australia trade names such as "Custom Orb" and the slang "corro" are used, British soldiers called it "wriggly tin", Caribbean English speakers say "pailing", and in Nigeria and Cyprus the sheets are simply called "zinc".[10] In East Africa the Swahili word *mabati* refers to iron roofing sheets in general. French builders speak of *tôle ondulée*, German of *Wellblech*, and Spanish speakers of *chapa ondulada* or, in the Andes, *calamina*.

## Definition and profile

A corrugated sheet is described by three numbers: its thickness, the pitch of the waves (the distance from one crest to the next) and the depth of the waves (the height from trough to crest). Over its history the pitch has ranged from about 25 mm (1 in) to 125 mm (5 in), but nearly all modern corrugated roofing has settled on a pitch of 76 mm (3 in).[10] That figure goes back a long way: by the late nineteenth century the British standard sheet already had corrugations 3 in apart and about ¾ in (19 mm) deep, with a sheet width of 2 ft 3 in (686 mm) and lengths from 4 ft to 12 ft (1.2 to 3.7 m) in one-foot steps.[1] Other patterns existed alongside it. A 5 in (127 mm) pitch was used for a royal ballroom at Balmoral in 1851, and a so-called "Canadian" pattern alternated flat sections 9 or 12 in apart with the waves.[1]

Modern roll-formed sheet follows the same geometry but is far thinner and is supplied in long, custom-cut lengths. An Australian sheet of the classic type, for example, has a cover width of 762 mm (30 in) and a profile depth of 16 mm (about ⅝ in), and is made from steel with a base metal thickness of 0.42 mm or 0.48 mm (about 0.017 to 0.019 in). It weighs roughly 4.3 to 4.9 kg/m² (0.9 to 1.0 lb/ft²).[4] A heavier version of the same profile in 0.60 mm and 0.80 mm steel is made for curved roofs and water tanks.[4]

Corrugation is not limited to steel. The same waved profile is produced in stainless steel, aluminium and copper, and plastics such as fibreglass-reinforced polyester and polycarbonate are corrugated to make translucent rooflights that match the metal sheets.[10]

## History

### Invention in London

Corrugated metal sheet was patented in Britain by Henry Robinson Palmer, engineer to the London Dock Company. His patent, number 5786 of 1829, described metal plates in "a fluted, indented or corrugated form" and envisaged self-supporting roofs riveted to cast-iron ridge and gutter plates.[1][8] In 1830 Palmer roofed a dock shed in London with self-supporting corrugated iron spanning about 40 ft (12 m).[2] The commercial side was taken up by Richard Walker, whose Patent Corrugated Iron business was advertising by 1832 and had a factory in Grange Road, Bermondsey, by 1833.[1] Walker was already offering bow-roofed warehouses in 1832, the ancestor of every curved corrugated shed that followed.[1] The early sheets were pressed one flute at a time, so a works could make only a few sheets a day; roller corrugating, developed in the mid-1840s by John Spencer of West Bromwich and patented in a similar form by Edward Morewood and George Rogers in 1845, made mass production possible.[1]

### Galvanising

Bare iron rusts quickly, and the material only became durable once zinc coating was available. The Parisian Stanislas Sorel took out the first patent for hot-dip galvanising in 1837, and the process was brought to Britain the same year; a company to exploit it was established at Southwark in 1838.[1][3] John Porter of Southwark is credited with first galvanising corrugated roofing sheet in 1843.[1] Wrought iron remained the preferred base metal for decades, partly because zinc bonded to it more readily than to early steel. Thin steel sheet suitable for corrugating was not developed until the 1890s, after which steel steadily displaced iron.[1]

### The export trade and prefabrication

Because the sheets were light, stackable and could be fixed by unskilled labour, corrugated iron became the material of choice for prefabricated buildings sent around the British Empire and beyond. By the 1840s complete kit buildings were being made in Britain, many of them for Australia and South Africa.[2] Laycock's of Liverpool built an iron palace in 1843 for King Eyambo of the Calabar River in present-day Nigeria, and Spencer's works sent an iron market house to Honduras in 1846.[1] Edward Bellhouse of Manchester shipped prefabricated cottages and warehouses to California and Australia during the gold rushes of 1849 to 1851 and showed prefabricated buildings at the Great Exhibition of 1851. Prince Albert then ordered from him a corrugated iron ballroom for Balmoral, 60 ft by 24 ft (18.3 by 7.3 m), made of 18-gauge sheet; it cost £194 10s and was ready about three months after it was ordered.[1]

Large firms grew up around the trade. Frederick Braby & Co., founded in London in 1854, later had works at Deptford, Liverpool and Glasgow, and its Glasgow Eclipse Works employed up to 1,700 men. A. & J. Main & Co. of Possilpark, Glasgow, published catalogues that by 1894 included curved agricultural buildings.[1] British production for export peaked between about 1890 and 1900, at roughly 250,000 tons a year.[1]

In Australia the material was taken up almost immediately. John Lysaght brought corrugated iron to Australia within about ten years of its development in England, and settlers valued it because it could be carried long distances, even by camel, and assembled into whole buildings from numbered sheets.[9] From the 1840s it also spread to rural areas of the United States, Argentina, Spain and New Zealand, and later to India.[10]

### Churches, huts and shelters

In Britain the best-known products of the trade are the prefabricated "iron churches", nicknamed tin tabernacles. The first is thought to have been put up in London in 1855, and they were popular from the late nineteenth century until the First World War.[3] Makers such as Samuel Hemming of Bristol, William Cooper of London and Francis Morton of Liverpool sold them from catalogues.[3] Morton's St Mark's, Birkenhead, of 1867 was designed to seat 500 and cost about £2,000.[1] Historic England counts 86 surviving corrugated iron churches in England, fewer than 20 of them listed; one, St Chad's Mission Church, has been re-erected at the Blists Hill museum in Shropshire.[3]

Military needs created two further icons. Captain Peter Nissen designed the Nissen hut during the First World War, a semicircular corrugated shell that could be erected quickly and moved, and after the war such huts became common farm buildings in Britain.[1][2] In the Second World War about 1.5 million Anderson shelters, curved corrugated steel shelters dug into gardens, were distributed in Britain.[2] The Italian Chapel on Lamb Holm, Orkney, built inside a Nissen hut by prisoners of war, is the only corrugated iron structure in Scotland with the highest (Category A) listing.[1]

### The twentieth century and after

Corrugated iron was also used in prestigious buildings. It appeared at Chatham Dockyard, Liverpool Lime Street station and Brunel's Paddington station, and the Herd Groyne lighthouse at South Shields (1881) is clad in it.[2] In Australia, BlueScope's predecessor introduced technology for bonding paint to galvanised steel in the 1950s, and the first coil of pre-painted COLORBOND steel came off the line at Port Kembla in 1966, after which coloured corrugated roofs spread through Australian suburbs.[9] Plain galvanised corrugations have since largely been replaced, in industrialised markets, by aluminium-zinc coated and coil-painted steel, often in more complex trapezoidal profiles.[10]

## Materials and coatings

Modern corrugated sheet is cold roll-formed: steel coil is fed through a series of rolling dies that progressively form the waves, and the sheet is sheared to the ordered length automatically.[10] The steel itself is protected by a metallic coating applied at the mill:

- **Galvanised (zinc) coating.** The traditional finish. Zinc protects the steel sacrificially, corroding in its place, but a pure zinc coating is consumed faster than alloy coatings and is the least suited of the common options to salty coastal air.[6]
- **Aluminium-zinc coating.** Usually about 55% aluminium by mass, sold under names such as Galvalume and Zincalume. It forms a more durable barrier than zinc alone, but it too is gradually consumed and is thinnest at cut edges.[6][10] Australian sheet of this type is made to AS 1397, with a minimum coating mass designation of AM125 for unpainted aluminium-zinc-magnesium sheet.[4]
- **Pre-painted coatings.** Coil-applied paint over a metallic coating, made in Australia to AS/NZS 2728; heavier metallic coatings (for example AM150) are specified under the paint for severe coastal or industrial sites.[4]

Aluminium corrugated sheet is a lighter alternative that does not rust, because it contains no iron and its oxide film re-forms when scratched; it is often chosen for coastal buildings where steel coatings are short-lived.[6]

Historic sheets were much heavier than modern ones. British roofing sheet was commonly 18 SWG, about 1.2 mm (0.048 in) thick and weighing around 1.2 kg per square foot, roughly 13 kg/m² (2.6 lb/ft²); a modern sheet of similar area weighs a fraction of that.[2] British builders used gauges from 16 BWG (1.65 mm) to 22 BWG (0.71 mm), while thinner 24 and 26 gauge sheets were made mainly for export.[1]

## Design rules and standards

Corrugated sheet sheds water well when it is laid steeply enough, but its shallow waves make it more sensitive to low pitch than deep trapezoidal or standing-seam profiles. Requirements differ by country:

- **New Zealand.** The industry Code of Practice sets the minimum cladding pitch for conventional corrugate (about 16.5 mm deep) at 8°, falling to 4° for 21 mm deep corrugate and 3° for 35 mm deep "big corrugate". It explains that low pitches slow drainage and make side and end laps more vulnerable to wind-driven water.[5]
- **Australia.** Design and installation of metal roof and wall cladding is governed by AS 1562.1, with performance checked against AS 4040.1 (concentrated loads) and AS 4040.2 (wind pressure), and wind loads calculated to AS/NZS 1170.2.[4] A typical Australian corrugated sheet with an anti-capillary side lap is rated down to 5° (about 1 in 12).[4]

Span tables are tied to sheet thickness. For the Australian sheet described above, the maximum roof purlin spacing is 900 mm (35 in) for an end span and 1,200 mm (47 in) for an internal span in 0.42 mm steel, rising to 1,300 mm and 1,700 mm (51 and 67 in) in 0.48 mm steel; the unstiffened eaves overhang is limited to 200 to 250 mm (8 to 10 in).[4] Long sheets expand and contract with temperature, and for this sheet an expansion joint is needed only once a roof run exceeds 24 m (79 ft).[4]

## Installation

The basic method has changed little since the nineteenth century, although fastenings and sealing have improved:

1. **Framing.** Sheets are laid over timber or steel purlins (on roofs) or girts (on walls) at the spacing allowed by the span table for the sheet thickness and the local wind load.[4]
2. **Underlay and insulation.** Modern roofs usually add an underlay and insulation over the purlins; the details follow local codes such as the New Zealand Code of Practice.[5]
3. **Side laps.** Adjacent sheets overlap by about one and a half corrugations.[10] Modern profiles may have a shaped "anti-capillary" side lap that stops water being drawn between the sheets, which is what allows lower pitches.[4]
4. **End laps.** Where one sheet cannot cover the full slope, the upper sheet overlaps the lower by about 150 mm (6 in), more on low pitches.[10]
5. **Fixing.** Sheets are fastened through the crests of the corrugations, where water does not run, with self-drilling screws or nails fitted with sealing washers. Historic sheets were often fixed with bolts, nails with lead or bitumen washers, or hook bolts to steel purlins.[2]
6. **Flashings and ridge.** Ridge cappings, barge (verge) flashings and apron flashings are cut or rolled to the profile. Historic roofs often had decorative cast or pressed ridge pieces.[2]

Corrugated sheet can be curved. Thicker grades can be machine-curved to radii as tight as 300 mm (12 in), with a straight section of at least 100 mm (4 in) left at the end of each curve; thin standard grades are not intended for curving.[4] Curved corrugated roofs are characteristic of Nissen huts and of many farm buildings.[1]

## Performance

**Weight and economy.** A modern corrugated steel roof weighs only about 4 to 5 kg/m² (under 1 lb/ft²), far less than clay or concrete tiles, which keeps framing light and makes the sheets cheap to transport.[4] This low weight and ease of fixing, rather than durability, explain its worldwide spread.[10]

**Durability and corrosion.** Service life depends mainly on the coating and the environment. Corrosion is fastest near the sea, in areas of acid rain and where sheets are kept damp.[2][10] Typical failure points on old roofs are:

- **Laps.** Water held in the narrow gap between overlapping sheets by capillary action sets up corrosion that is hidden from view.[2]
- **Fixings.** Holes from moved fixings let in water, damaged fixings let sheets lift, and fixings of a different metal cause galvanic corrosion.[2]
- **Buried edges.** Cladding that ends up below ground level after changes to the ground corrodes rapidly.[2]
- **Coating loss.** Once the zinc layer is consumed or damaged, the steel beneath rusts; galvanising quality on old sheets was variable.[2]

Regular painting is the single most effective way to extend the life of a galvanised roof, and most historic corrugated iron was painted at some point.[2]

**Heat and comfort.** Thin, uninsulated metal sheet has almost no thermal mass, so rooms beneath it heat up quickly in sun and cool rapidly at night. In thermal simulations of informal steel-clad dwellings in Tshwane, South Africa, combining added thermal mass with shading was more effective at reducing heat stress than the measures usually proposed for such homes.[7]

## Conservation of historic corrugated buildings

Heritage bodies increasingly treat corrugated iron buildings as significant. Of roughly 43,000 listed buildings in Scotland, only 12 were rural corrugated iron structures, and a 2003 survey of 72 such buildings in the Highlands and Islands found 44% empty, deteriorating or ruinous.[1] Neglect, rather than any inherent weakness of the material, is the main threat.[2]

Recommended practice is to research and record the building first, then repair as little as possible. Light rust can be removed with wire brushes or abrasives and treated with a rust converter; heavy corrosion may need controlled low-pressure blasting, ideally after the sheets are removed so that lead-based paint dust can be contained. Badly holed sheets can be patched by welding in metal cut from a sacrificial sheet from the same building. Any replacement sheet should match the original in size, weight and profile, and fixings should match the original type.[2] Gutters, downpipes and the ventilation of timber floors also need regular attention, since the timber joinery of iron buildings often decays first.[2]

## Around the world

- **Australia and New Zealand.** Corrugated roofing is part of the national cultural identity and remains a mainstream urban roofing material.[10] Both countries have detailed industry standards for its use.[4][5]
- **Argentina.** Corrugated iron is still a common roof material in Argentine cities.[10]
- **Africa.** Iron sheets are very widely used for informal and low-cost housing, where uninsulated steel cladding is common.[10][7]
- **South Asia, Latin America and the Caribbean.** Corrugated sheet is everywhere on rural houses, market buildings and informal settlements because of its low cost and easy transport.[10]
- **United Kingdom and United States.** Use is now mostly agricultural and industrial, alongside conserved historic buildings such as tin tabernacles and wartime huts.[3][2]

## Sustainability

Steel and aluminium sheets are readily recyclable at the end of their life, and old corrugated iron has long been reused, which partly explains how many historic buildings have been moved and re-erected.[3] Against this, steel production is energy-intensive, and the poor thermal performance of uninsulated sheet can increase cooling needs or heat stress where it is used without insulation or shading.[7]

## Sources

1. Corrugated iron buildings (Thompson), Proceedings of the Second International Congress on Construction History, vol. 3, pp. 3097-3116 — University of Cambridge, Department of Architecture. https://www.arct.cam.ac.uk/system/files/documents/vol-3-3097-3116-thompson.pdf
2. Corrugated Iron Architecture — Building Conservation Directory. https://buildingconservation.com/articles/corrugated-iron-architecture/corrugated-iron-architecture.htm
3. What is a Tin Tabernacle? — Historic England (Heritage Calling). https://heritagecalling.com/2022/06/09/what-is-a-tin-tabernacle
4. LYSAGHT CUSTOM ORB and CUSTOM BLUE ORB brochure — Lysaght (BlueScope). https://cdn.dcs.lysaght.com/download/custom-orb-and-custom-blue-orb-brochure
5. NZ Metal Roof and Wall Cladding Code of Practice: Roof Pitch — New Zealand Metal Roofing Manufacturers Inc.. https://www.metalroofing.org.nz/cop/roofing/roof-pitch
6. Aluminum vs. Galvalume vs. Steel Roofing — interlockroofing.com. https://www.interlockroofing.com/kb/aluminum-vs-galvalume-vs-steel/
7. The efficacy of roof-based adaptations to reduce heat stress exposure in informal dwellings — Acta Structilia, University of the Free State. https://journals.ufs.ac.za/index.php/as/article/view/8154
8. Henry Robinson Palmer — Grace's Guide to British Industrial History. https://www.gracesguide.co.uk/Henry_Robinson_Palmer
9. History of COLORBOND steel — BlueScope. https://steel.com.au/resources/articles/history-colorbond-steel
10. Corrugated galvanised iron — Wikipedia. https://en.wikipedia.org/wiki/Corrugated_galvanised_iron
11. Preservation Brief 4: Roofing for Historic Buildings — U.S. National Park Service, Technical Preservation Services. https://www.nps.gov/orgs/1739/upload/preservation-brief-04-roofing.pdf