Green Roofs: Are They Worth the Expense?

May 19, 2009, 9:23 am
Green Roofs: Are They Worth the Expense?
By Kate Galbraith

Chicago Dept. of Environment

The green roof atop Chicago’s City Hall is blooming, but other cities think the concept is too costly.
Richard M. Daley, the mayor of Chicago, told a panel at the Harvard Club of New York on Monday that he aims to make his city the “most environmentally friendly city in the world.”

A key part of Mr. Daley’s vision involves “green roofs” — the idea of putting plants, and even a few trees, on top of buildings. Chicago already has more than 600 “green roofs,” the mayor said — including one over its City Hall, which even has a couple of beehives.

As well as giving workers from surrounding skyscrapers something pleasant to gaze at, green roofs help keep the city cool, and also filter stormwater so that it does not overwhelm drains.

New York has a few green roofs, but it has not prioritized them in the way that Chicago has (or Toronto, which is thinking of making green roofs mandatory for some new buildings).

The reason is cost, said Carter Strickland, a senior policy adviser in New York City’s long-range planning and sustainability office. “We found that street trees are more cost-effective than green roofs,” he told the panel.


New York City is also emphasizing “white” or “cool” roofs, with the ability to reflect rather than absorb the sun’s heat. Green roofs, Mr. Strickland said, might cost $25 to $30 a square foot; “cool” roof would cost “a fraction of that,” he added.

There are other impediments in New York — including a tough permitting process. Miquela Craytor, the executive director of Sustainable South Bronx, said that it took her organization two years to install a “green wall.”

And implementing Mayor Daley’s vision in New York, beehives and all, would face an even more fundamental hurdle, according to David Yassky, a New York City council member: “It’s illegal now in New York City to keep bees,” he said.

Mr. Yassky added that he hopes to change that through legislation

Tidal Power

Walk along the beach and watch the ocean. There’s a lot of power out there. Just ask the people whose beachfront houses get washed away in big storms. Engineers are investigating ways to harness that power and generate electricity.

It’s not a new idea. Prototypes of wave-power generators have been around for 100 years. But people have only started to get serious about it since the reality of global warming started to sink in.

The idea is simple. Anything that moves can power a generator. Water in the ocean moves, all the time. It’s easy to predict how that water will move, next week or next year. We can predict how tides will move in bays and rivers – several years ahead. And satellite images can tell us several days ahead of time how high the waves will be.

Engineers are already testing wave and tide-powered turbines. A turbine on the bottom of New York City’s East River already provides enough electricity to run a nearby grocery store and parking garage. A generator buoy bouncing in the waves off the Oregon coast is being tested, too. Engineers estimate that eventually, 300 buoys could provide power for almost 40,000 homes. Turbines in the Gulf Stream could provide electricity for more than 100,000 homes.