Mexico, one of the world’s most polluted cities, is the latest to adapt the green roof concept. The government recently launched a program named “Azoteas Verdes” or “Green Rooftops” with a goal to convert 6,000 hectares of rooftops in the city to gardens by 2030.
Once upon a time, the skies of Chicago were black with smoke from factories and filled with sounds of the guns of Al Capone. But today, Chicago has shrugged off that unflattering image. The Windy City is touted to be the greenest in the U.S., thanks to the profusion of green roofs over its buildings.
Green roofs? Contrary to the image of a green-painted roof that jumps to mind, green roofs are those that are covered with plants or other vegetation, resembling a mini-garden. But the benefits of green roofs, also known as ‘living roofs’ or ‘eco-roofs,’ go beyond what meets the eye.
Buildings with green roofs are better insulated. In summer, they absorb and reflect heat while in winter, they retain warmth, cutting energy costs. Typically, around 15% of the heat in a building escapes through the roof, which a green roof can restrict. Further, rooftop gardens play an important role in storm water management, acting as mammoth sponges during rainstorms. They also extend roof life by providing protection from harmful UV rays. But most crucially, green roofs purify the air. According to research by Michigan State University horticulturist Kristin Getter, green roofs can capture 55,000 tons of carbon in an area with one million people. That is equivalent to “removing more than 10,000 mid-sized SUVs or trucks off the road a year,” she says. Also, green roofs lower air temperature by as much as 16 degrees Celsius per unit area.
Though Chicago popularized the concept in the U.S., green roofs were born in Europe. Traditional turf roofs found in many European countries are believed to be the predecessors of the green roof. But its modern avatar originated in Germany when Berlin University researcher Reinhard Bornkamm published his work on green roofs in 1961. Roughly 15 years later, the Landscape Research, Development & Construction Society, which today sets green roof standards and regulations, was founded in Bonn. It did not take long for the concept to catch on in Europe. But it was only in 1998 that green roofs made an appearance in the U.S. when Chicago Mayor Richard Daley brought them to the city.
The size of a green roof can vary from the small turf-covered thatch atop a home to large-scale roofing projects that include vegetable plants, designer gardens, and even trees. There are two kinds of green roofs – intensive and extensive. Intensive roofs are spread across a large space and they are landscaped with a variety of plants and trees, requiring hours of maintenance. Extensive roofs on the other hand are lighter on the upkeep because they are smaller in size and have less vegetation. In another variation, green roof foliage can be either grown on the roof or cultivated elsewhere and then rolled out on the roof like a pre-grown lawn.
The Millennium Park in Chicago has the distinction of being one of the
largest green roofs in the world. The lush area, spread over 24.5 acres,
is set atop an underground car park.
Despite such convenient options, green roofs are not as popular in the U.S. as they are in Europe. This is because, unlike in the U.S., green roofing is a well-supported government endeavor in Europe. In fact, Switzerland, Germany, France, and now Copenhagen have all made it mandatory for roofs with certain specifications to be converted to green roofs. In the U.S., Chicago provides monetary assistance to promote green roofs. Incidentally, Toronto was the first city in North America to adopt green roof legislation in 2009.
Costs have been the major deterrent to the proliferation of green roofs. They cost at least 10% more than traditional roofs. Getter and her team have found that the initial cost incurred on a 21,000 square feet green roof is approximately $464,000 while laying a normal roof costs just $335,000. “There’s no argument that painting a roof white is cheaper than installing a green roof,” emphasizes Chris Brunner, co-founder of New York Green Roofs. Yet, in the long run, the green roof can potentially save around $200,000 through deflated energy bills and efficient storm water management. What’s more, green roofs add oxygen into the air.
Green roofs cannot be an alternative for forest cover. But what they can do is act as mini ‘carbon sinks,’ absorbing ambient greenhouse gas and bringing down global temperatures. Rooftops make up a large amount of area in cities and utilizing this space would be an invaluable carbon management strategy. If green roofs continue to proliferate, it won’t be long before the world becomes green, not with envy, but with pride.
Image Credit: Erik Christensen at Wikipedia under a Creative Commons license