Sustainability and green building mean different things to different people. Some believe a sustainable building is defined by its use of advanced technological features such as solar panels. Others rely on rain gardens, cool roofs or recycled materials to define sustainability. Perhaps the most simplistic definition of “sustainable,” however, means a building that is intelligently designed and built to operate efficiently and last a long time. No matter the definition, metal can help in achieving a sustainable building.
Metal boasts many attributes related to sustainability, including recyclability, longevity and reusability. Cool metal roofing is a common choice for buildings. Two properties dictate a cool roof’s performance: solar reflectance, which is the percent of sunlight reflected off the roof, and infrared emittance, which is the percent of the sun’s heat re-radiated from the roof to its surroundings. Cool metal roofing can reflect up to 70 percent of the sun’s rays to reduce heat transfer into a building, well exceeding the Energy Star minimum requirement of 25 percent. Using insulation in conjunction with a metal roof reaps additional benefits. A painted or granular-coated metal roof emittance can reach 90 percent. For every 1 percent increase of solar reflectance, 1 F (0.6 C) is saved in roof surface temperature. Painted metal roofing maintains 95 percent of its solar reflectance and thermal emittance values throughout its life. Unlike asphalt roofing, which offgases carbon dioxide while it degrades, metal roofing has no emissions.
Not only are metal products made out of highly recycled materials, they are re-recyclable at the end of their useful lives. Steel is the most recycled material in the world. More steel is recycled in one year than aluminum, paper and glass combined. Almost 76 million tons (69 million metric tons) of steel was recycled in the U.S. in 2006. Every ton of steel that is recycled saves 2,500 pounds (1134 kg) of iron ore, 1,400 pounds (635 kg) of coal and 120 pounds (54 kg) of limestone. New steel made with recycled material uses as little as 26 percent of the energy required to make steel from raw materials. Natural metals such as aluminum, zinc and copper also are highly recycled; copper has the highest scrap value of any building metal. Deconstruction—removing items from a building that can be salvaged—also is possible with metal. Panels can be removed and reused in their original state on a different building. Metal also is not downcycled, meaning that it does not lose quality as it is recycled many times over.
In addition to its inherent sustainable properties, metal also can foster other means of sustainability. For example, it is a good material to use with solar photovoltaic arrays. Companies are branching out and introducing metal products that accommodate the solar industry, such as solar standing seam metal roof systems and energy panels.
For examples of sustainable projects that use metal, see the “Building Green” section of metalmag in this issue and in previous issues by visiting www.metalmag.com.