Living Roofs the Rage in Europe and Japan, Coming Soon to U.S. Homes

By Alastair Bland

The oldest hobby of stationary human societies - gardening - forms the groundwork for one of the latest trends in urban architecture: living roofs.

Also called green roofs, these structures are layered with six inches to two feet of soil and planted with grasses, trees or vegetables. They may provide benefits for the homeowners who live below, for the community and for the environment while enhancing the aesthetic beauty of urban areas.

Nations overseas are already moving far ahead in mandating the installment of living roofs in new building projects, but the trend is just catching on in California.

The premiere local example of a living roof can be found at the California Academy of Sciences in Golden Gate Park. Frank Almeda, the Academy's senior curator of botany, is overseeing the installment of a large living roof project at the new facility, which is scheduled to reopen in the Fall of 2008 after four years of construction.

"This is a living, native garden, which will attract wildlife and serve as a corridor in an urban area," he said. "By using native species we're promoting the local flora as well as creating an environment beneficial to animals, like birds and butterflies."

Living roofs cost more to build than standard roofs, as they must support tremendous amounts of weight in soil, water and plants, but advocates point out many boons.

Firstly, urban areas tend to be much warmer than surrounding rural areas - cities are sometimes dangerously hot during summer heat waves - and living roofs can help reduce this "urban heat island" effect by absorbing moisture and releasing it as vapor into the air.

Living roofs also absorb rainwater, thereby reducing runoff and alleviating the impact on sewers in times of heavy precipitation. They serve as very effective insulators, as well, keeping buildings cooler in the summer and warmer in the winter.

According to Almeda, they will last longer, too; the tar, metal, wood and synthetic structure beneath a rooftop garden does not experience the same degree of impact from wind, rain and other elements as does a standard roof. "

Whereas a traditional shingle roof might last 15 years before it requires replacing, a living roof can go 40," he said.

On July 16, at the Hall of Flowers in Golden Gate Park, Glen Patterson of Vancouver, British Columbia, gave a presentation to more than 100 amateur gardeners, horticulturalists and plant enthusiasts on the benefits of green roofs.

Patterson, 85, stands among the leading figures in this field as the owner and caretaker of a 2000-square-foot garden on the patio of his third-story apartment in downtown Vancouver. Grown thick with numerous plant species, including a 100-year-old maple and bonsai-style conifers, Patterson's garden even features three small streams populated by large coi.

"It's a natural, self-propagating system," he said. "I have no lawns to mow or hedges to cut. There's nothing to be fertilized. The leaves fall and naturally mulch into the required nutrients, and the water recycles and the fish waste breaks down into nutrients. It's a real oasis here in downtown Vancouver, with all the pavement and streets and traffic."

Jesse Markman of Sasaki Associates, a multidisciplinary design firm in San Francisco, has worked on several large-scale green roof projects in the Bay Area, including, currently, a project at UC Davis. He sees an upward swing in the trend, though it is most marked in Europe, Japan and the American midwest, especially Chicago, where municipal governing bodies grant financial incentives to architects and homeowners who invest in living roofs.

"San Francisco doesn't really have anything like that yet," he said. "A lot of developers want an instant payback, and with green roofs they won't see that because it may take more than 10 years for the cost benefits to show themselves."

The Gap headquarters in San Bruno laid a 70,000-square foot green roof on its facility in 1997, says Markman. The cost ran 80 percent higher than that of a standard roof and architects and engineers predicted that 11 years would pass before utilities savings caught up with the price tag. It ended up taking eight years. Patterson said his roof cost $30 per square foot to build before buying the plants.

"People ask, 'How can you spend so much on a roof that's 2000 square feet?' But some of those are people who've just bought a new Mercedes. It depends what your values are. Some want gardens on their roof. Others want a Mercedes."

For more information on green or living roofs, visit the Web sites at www.greenroofs.org or www.greenroofs.com.