Metal Roofing

Metal roofing covers a family of roof systems in which thin metal, rather than clay, slate, wood or asphalt, forms the weathering surface. The metal may be laid over a solid deck as a waterproof skin, or it may be rolled into profiled sheets stiff enough to span between purlins on their own. Common base metals are steel with a metallic coating (zinc, aluminium-zinc or similar), aluminium, copper, zinc alloy, stainless steel and lead.

Metal has been used on roofs for well over two thousand years. Lead and copper were the first choices because they were easy to work; iron became economical in the early nineteenth century, and the 1829 English patent for corrugated sheet opened the way for cheap, lightweight industrial and colonial roofs. Steel later replaced wrought iron, allowing thinner sheets.

Main system types

• Through-fastened (exposed-fastener) panels: corrugated or trapezoidal sheets screwed through the face into the structure.
• Standing seam: long pans joined by raised seams and held down by concealed clips, letting the metal move with temperature.
• Traditional seamed roofing: batten seam, flat (flat-lock) seam and related techniques used mainly with copper, zinc, lead and terne-coated metals.
• Modular products: metal shingles, shakes and press-formed tiles, including stone-coated steel.

Performance

Service lives of roughly 30 to 70 years or more are commonly cited for metal roofs, depending on metal, coating and climate, compared with about 12 to 20 years often quoted for asphalt shingles. Metal is noncombustible, lighter than many alternatives and widely recycled. Weak points are usually at fasteners, seams, cut edges and flashings, and at junctions with incompatible metals.

Regional terms

In the UK, Ireland, Australia and New Zealand, profiled steel is still often called "corrugated iron" or CGI, while North Americans may say "tin roof" or "metal roof". Trade names such as Galvalume, Zincalume and Colorbond have become everyday words in some markets.