Corrugated Iron (Corrugated Galvanised Iron)

Corrugated iron is thin metal sheet formed into a regular series of rounded ridges and troughs. The waves give the sheet much greater stiffness across the corrugations, so it can span between widely spaced supports with little framing. The galvanised version, often abbreviated CGI, is coated with zinc against rust. Although almost all modern sheet is steel, and usually carries an aluminium-zinc coating or paint, the name "iron" has stuck.

History

Henry Robinson Palmer, engineer to the London Dock Company, patented corrugated metal sheets in 1829 and soon roofed a shed of about 40 ft (12 m) span with it. Galvanising, developed in France in 1837, made the material far more durable. By the 1840s British firms were exporting fully prefabricated corrugated iron buildings to Australia, South Africa and other colonies, and suppliers such as William Cooper and Boulton & Paul sold kit churches and chapels, now known in Britain as "tin tabernacles". John Lysaght introduced it to Australia within about a decade. Mild steel replaced wrought iron from about the 1890s.

Profile

Nearly all modern corrugated sheet has a pitch of 3 in (76 mm) between crests. Historic roofing sheets were often about 18 SWG (1.2 mm) thick, considerably heavier than today's sheets, with profile pitches of roughly 3 to 5 in.

Global use

Corrugated sheet is still a mainstream roofing material in Australia, New Zealand and Argentina, including in cities, and is ubiquitous on rural and informal buildings in Africa, Latin America and South Asia because it is light, cheap and easy to transport and fix.

Conservation

Historic corrugated buildings suffer mainly from neglect. Corrosion often starts at overlaps where moisture is held by capillary action. Regular painting greatly slows rust, and repairs should match original sheet size, gauge, profile and fixings.