Green roofs are nothing new. In their book, Planting Green Roofs and Living Walls, Nigel Dunnett and Nñel Kingsbury report that the idea has “been [around] for centuries.” Historically, say the authors, people in present-day Turkey, Iraq and Iran built homes of mud or earth with grass-covered rooftops.
The ancient practice is enjoying a resurgence. In the U.S., noteworthy green examples include the Pentagon, Chicago’s City Hall, a Ford assembly plant in Dearborn, Michigan and nu-merous buildings in Portland, Oregon.
Roofs: The Last Frontier
There are many benefits to a “living” roof, says Steven W. Peck, founder and president of Green Roofs for Healthy Cities, a Toronto-based association. “The roofscapes of our cities are the last urban frontier—from 15 percent to 35 percent of the total land area—and the green roof industry can turn these wasted spaces into a force for cleaner air, cleaner water, energy savings, cooling, beauty and recreation,” he says.
But given the importance of curb appeal, particularly in today’s turbulent real estate market, not everyone will want to cultivate their rooftops. Zoning laws could be an obstacle, sloped roofs pose challenges, and even flat roofs require a rugged, waterproof, puncture-resistant membrane to protect the living space and its contents from seepage and leaks. Then there is the increased cost and weight of many green roofs.
There are alternatives to an overhead garden, including a “cool” roof. Accor-ding to the Cool Roof Rating Council (CRRC) “a cool roof reflects and emits the sun’s heat back to the sky…”Cool-ness’ is measured by two properties, solar reflectance and thermal emittance.”
Long life should be a goal of all eco-friendly roofing. Tom Hutchinson, a principal in Hutchinson Design Group and a technical consultant for the EPDM Roofing Association, says, “The best environmental solution is a sustainable roof system, one that can last 30 years or more. There are way too many poorly designed cool and garden roofs that are consequently not environmentally friendly at all.”
Possibly the longest-lived roofs are those made of slate, though the material can be expensive to work on. The Slate Roofing Contractors Association reports that sea green slates can last anywhere from 110 to 120 years, de-pending on the quarry of origin. Green slate from Vermont, they say, “could last 200 years or more.”
A Long Life, then Recycled
To the extent possible, the roofing material should come from recycled products and be recyclable at the end of its life span. Metal is one option. Scott Kriner, president of Green Metal Consulting, says, “A metal roof can be energy efficient, contain a high amount of recycled material, be inert, have low overall life cycle costs and be highly durable.” In addition, he says, metal roofs are “ideal for catching rainwater.”
Weight is critical in roofing materials. According to Frank Lane, president of ArmorLite Roofing Technology, lighter weight contributes to safety not only at the time of installation but in the event of fire, earthquake or high winds. Environ-mentally, he claims, a lighter roof requires less energy in the manufacturing process, as well as in transporting materials from factory to jobsite.
ArmorLite roofs, Lane says, originate from 85 percent recycled materials that are, in turn, 100 percent recyclable. The key ingredient is lightweight polymers that are strong enough to provide 50 years of useful life at a weight of just 3,500 pounds for a typical residential rooftop. This compares, he says, with 30,000 pounds for a conventional roof. Often, says Lane, because of its light weight, an ArmorLite roof can be installed over an existing conventional roof, thus eliminating removal waste altogether.