Gardeners mop sweat pouring from their foreheads, rummaging through their utility belts, yanking small plants from pots to prepare them for the soil. In late Spring, it is not unusual for gardeners to be planting, but these gardeners aren’t working on the ground—they are planting vegetation on the rooftop of a housing development project in San Francisco that embraces green living.
Green roofs are covered with soil and vegetation—a concept developed in Germany in the 1960s that has since spread around the world.
Rooftop gardens are not just a pretty place to escape the concrete jungle. They increase a roof’s life span, reduce storm water run-off, filter pollutants out of air and rainwater, and can be used as a garden to grow fruits and vegetables.
And green roofs are already common in Chicago, Atlanta, and Portland and are becoming popular in the San Francisco Bay Area.
Construction is underway at the California Academy of Sciences to complete the largest living green roof in California, which will span two and a half acres atop a new building in Golden Gate Park. It is scheduled open to the public in October of 2008.
Renzo Piano, a renowned Italian architect who has won several architectural prizes and awards, designed the building to reflect San Francisco’s ambiance. The roof’s hilly terrain mirrors the topography of the city and will have many of the plants that grow in Golden Gate Park.
The 1.86 million dollar project, both privately and publicly funded, broke ground in September of 2005. The roof spans over four-and-a-half acres, two-and-a-half of which are covered with vegetation and host only native Bay Area plants. Visitors will not be allowed to stroll through the gardens but can enjoy the roof from an observation deck, from which the entire span of the garden and the cityscape of San Francisco are visible.
Green roofs consist of several different layers of soil and vegetation that are placed over a waterproofing layer that seals off the roof. They are expensive and can cost anywhere from five to thirty dollars per square foot. A standard asphalt roof costs one to two dollars per square foot. But ecologically, the benefits of a green roof outweigh the expense.
In San Francisco, street drains and sewers are combined systems, and during heavy rains street runoff and raw sewage combine and end up in the ocean. However, green roofs can retain seventy-five percent of that water and release it back into the air through condensation, reducing runoff and diminishing the workload typically required of treatment plants.
Green roofs also reduce the urban-heat-island effect—when metropolitan areas become significantly warmer than surrounding regions. Urban buildings suck in the sun’s radiation and spit it back out as heat, block the view of the cold night sky, and provide various surfaces for the reflection and absorption of sunlight. Materials used in large buildings, such as concrete and asphalt, retain more heat than smaller buildings. Green-roofed skyscrapers are roughly twenty-five to eighty degrees cooler than buildings without.
Rooftop gardens also improve a roof’s insulation value. Studies showed a twenty-five percent reduction in summer cooling needs and a twenty-five percent reduction in winter heat losses.
Most importantly, green roofs provide a home for native plants, insects, and other creatures that have trouble surviving in urban communities filled with cars, concrete, and pollution.
San Francisco is becoming a leading city of the green movement, from housing developments to cars and eco-friendly household items. Hopefully, within a couple of years, the moniker will both figuratively and literally reflect the city’s color