In the early 20th century, after being used for military purposes in the trenches and for Nissen or Quonset huts, "CGI" roofs were widely used but had low status. In the later 19th century, steel mills replaced iron works, and the product using steel could be made thinner for the same span and stiffness performance, but the term "CGI" remains in the UK and Australia up to the present. Īfter Palmer's patent expired in 1843, " corrugated galvanized iron" (CGI) became a world-wide favorite roofing material. This allowed the sheet iron to be self-supporting when used as a roof a contemporary account praised the material as "the lightest and strongest roof (for its weight) since the days of Adam". In 1829, Henry Palmer, engineer of the London Dock Company, patented "indented or corrugated metallic sheets" which added additional stiffness to bending in one direction in the manner of a beam. Terne became popular for roofs and weather-resistant farm items. Terne, an iron plate dipped into a solder of 80-90% lead with only the remainder tin, was cheaper than tinplate made in the same way, and the lead was more resistant in long-term outside use than tin or zinc alone. It was later determined that iron corrosion ( rust) could be stopped or at least slowed by dipping the hot iron sheets into molten tin or zinc, forming a metallurgically-bonded coating which protected it. When iron smelting became widespread in the early 19th century, although the smelting process was complicated, ore was so plentiful that iron became cheaper than lead, and much cheaper than copper. The copper on the tower was renovated in 2009. The roof at Kronborg, one of Northern Europe's most important Renaissance castles (immortalized as Elsinore Castle in Shakespeare’s Hamlet) was installed in 1585 CE. Mary's Cathedral, Hildesheim, installed in 1280 CE, survived until its destruction during bombings in World War II. Centuries later, copper and its alloys were integral in European medieval architecture. The Romans used copper as roof covering for the Pantheon in 27 BCE. In the 3rd century BCE, copper roof shingles were installed atop the Lovamahapaya Temple in Sri Lanka.
As a by-product of silver smelting, in Roman times it was readily available and relatively cheap. Lead was one of the first and easiest metals to smelt and with a low melting point, it could be easily formed to be watertight. Lead and Copper have played a significant role in architecture for thousands of years (see: copper in architecture). The metal pieces may be a covering on a structural, non-waterproof roof, or they could be self-supporting sheets. It is a component of the building envelope. A metal roof is a roofing system featuring metal pieces or tiles exhibiting corrosion resistance, impermeability to water, and long life.
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