Green roofs popping up in big cities

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Nevertheless, Mark Thomann, design director at the New York landscape design firm Balmori Associates, said high construction costs, a lack of government support, and limited expert availability are still combining to thwart many ambitious green roof plans. “We imagined doing 50 of these a year, and the reality is we do one to two a year,” he said. In cities like New York, zoning laws haven’t yet accounted for green roofs, relegating them to awkward spaces between traditional buildings and landscaping. Plant specialists, Thomann said, often don’t have the equipment for roof access, whereas contractors often don’t know enough about plant-friendly construction practices.

Even so, his firm has been trying to push the envelope on design. “Most of the green roofs have been flat green surfaces, which are great, but we’ve been looking at different ways of making those roofs three-dimensional,” Thomann said. One of his company’s completed projects, the roof of New York’s Earth Pledge Foundation, features a vegetable garden.

Other design firms are teaming up with ecologists to build roofs that incorporate hollows, small cliffs, scattered rocks, dead wood and varied vegetation to mimic everything from riverbanks to high mountain meadows. The result has been a surprising burst in habitat for urban wildlife —and more aesthetically interesting roofscapes that building owners can use to attract human tenants as well.

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Endangered beetles and spiders have found refuges in Basel, Switzerland, where a city mandate requires green roofs to accompany all new flat-roofed buildings. Endangered rooftop orchids thrive in nearby Zurich, while London has created new habitats for its small population of black redstart birds with crushed-brick “brown roofs” that mimic the derelict urban sites they favor. And in San Francisco, several acres' worth of dramatically sloping rooftop on the California Academy of Sciences have been designed as native habitat for the threatened bay checkerspot butterfly.

In New York, a planned visitors’ center at the Brooklyn Botanic Garden is allowing staff to likewise experiment with a wide range of vegetation that might work as “living roof” plantings to fit the building’s sinuous profile. Patrick Cullina, the garden’s vice president of horticulture and science research, pointed out that green roofs need not be monolithic, especially ones that are meant to be seen.

The rooftop garden on Bill Clinton’s Presidential Library in Little Rock, Ark., includes yellow roses, a sentimental favorite. Cullina hopes the more publicly accessible Brooklyn rooftop will include visually interesting colors all year long. He also hopes to challenge the paradigm of which plants can be used in a living roof system, using nearby seashore and pine barren environments as inspiration.

Moving beyond simple cost-benefit calculations can pay particular dividends for an institution hoping to marry aesthetics, research and community leadership. It helps when a chartreuse rooftop grass turns a particularly vivid shade of reddish-orange during an otherwise dreary New York winter.

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