Are high-rises green?

High-rises use energy in ways that single-family homes don't
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GREEN CITY High-rises are popping up fast in San Francisco, altering the skyline from one month to the next. But are these giants environmentally friendly? Do they make San Francisco more green or less?

One of the major advantages of using tall buildings in city design is the potential to reduce suburban sprawl: building up instead of out lessens the demand for single-family homes, creates dense neighborhoods where cars aren't needed, and allows for more open spaces to be preserved.

Additionally, the concentration of people in high-rise clusters encourages the creation of acceptable transit systems. "The high density of high-rise neighborhoods — whether residential, office, or mixed-use — creates the necessary population density to support efficient transit service, allowing people to take transit rather than drive," said Lisa M. Feldstein, a local affordable-housing consultant who grew up in a residential high-rise in New York City's East Harlem. "The reason that bus service is poor in suburbs and rural areas is not that people in those areas don't like transit. It's that the population isn't sufficiently dense to support a fast, frequent, and efficient transit system, so people can't rely on it."

Density puts demands on transportation, but that doesn't guarantee public transit use. When people working in city centers like San Francisco can't afford to live there, that can create cross-commute situations that clog big-city roadways, which may be even more environmentally damaging than suburban-style development. In fact, San Franciscans drive to work alone more than they use public transportation to get there, according to a 2006 US Census Bureau study.

High-density residents tend to use fewer resources than their low-density counterparts. Because walls, pipes, and other materials are shared, it can take less energy, for example, to heat a high-rise unit than a single family home.

But high-rises use energy in ways that single-family homes don't — for example, in thousands of elevator trips from top to bottom every day. According to a study found on the US Department of Energy's Web site, elevators consume up to 10 percent of the total energy used to maintain tall buildings. Furthermore, these buildings are usually climate controlled (in part to counteract the heat created by their elevators), whereas opening and closing windows can more effectively regulate temperatures in single-family houses and low-rise units. High-rise buildings also include common areas that often leave lights burning 24 hours a day.

Not having private yards in high-rises reduces the water and the toxic chemicals used to maintain them and forces people into public spaces. But there is another environmental cost to this void, said Lisa Katz, a planner with Design, Community and Environment in Berkeley. "People living in high-rises have less connection to the land; for example, they can't grow their own food," she said. Raising food sources in agricultural communities and exporting them to cities uses exorbitant amounts of energy in the form of fuel and packaging.

High-rises, however, have the potential to achieve the highest level of green building ratings, according to Maria Ayerdi, executive director of the Transbay Joint Powers Authority, which on Sept. 20 approved the proposal for the new Transbay Transit tower, which will be the tallest building on the West Coast. "In tall buildings there are creative efficiency, recycling, and energy-generating opportunities that may not be possible in smaller buildings," she said.

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