Aluminum roof on Oklahoma's Council on Law Enforcement and Training facility in Ada, Okla.
Most metal roofing products consist of steel or aluminum, although some consist of copper and other metals. Steel is invariably galvanized by the application of a zinc or zinc/aluminum coating, which greatly reduces the rate of corrosion. This is why steel is used when building metal barns, which need to be able to withstand the weather and corrosion.
Metal roofing is available as traditional seam and batten, tiles, shingles, and shakes. Products also come in a variety of styles and colors.
Metal roofs with solid sheathing control noise from rain, hail, and bad weather just as well as any other roofing material. Metal roofing can also help eliminate ice damming at the eves. And in wildfire-prone areas, metal roofing helps protect buildings from fire should burning embers land on the roof.
Metal roofing costs more than asphalt, but it typically lasts 2 to 3 times longer than asphalt or wood shingles.
Solar reflectance and thermal performance of metal roofing
As may be seen from the table below, bare aluminum and steel may have a solar reflectance of roughly 60%, and a low emittance. The reflectance and emittance of bare metals are very sensitive to the smoothness of the surface and the presence or absence of surface oxides, oil film, etc. Usually, bare metals are not very cool in the sun. For example, in one outdoor experiment carried out Lawrence Berkeley Laboratory, a bare clean sheet of galvanized steel with a solar reflectance of about 0.38 reached temperatures nearly as high as a reference black surface.
Metal roofing is available with pigmented polymeric coatings, similar to paint, that are factory applied. These coatings are used to protect the metal panels, and for appearance's sake; they can also keep the roof cooler. The third and fourth entries below are examples of metal roofing with cool white coatings. Even a thin white coating "hides" the low emittance of the metal underneath, and produces a solar reflectance nearly as high as the thicker white coatings applied on site.
|Product||Solar reflectance||Infrared emittance||Temperature rise||Reflectance index|
|New, bare, galvanized steel||0.61||0.04||55°F||46|
|MBCI siliconized polyester white||0.59||0.85||37°F||71|
|Atlanta Metal Products Kynar Snow White||0.67||0.85||28°F||82|