What’s Under the Green Roof?

A green roof makes a pretty emblem for making ecological reform profitable in urban real estate. But we often approach the idea with a weedy sense of its scope.

When four experts addressed New York’s Urban Green Council about green roofs’ role , they all  agreed: more green roofs make a healthier city, but only those with greenbacks to spare should invest in them. Said Laurie Kerr, a policy adviser in Mayor Michael Bloomberg’s sustainability corps: “A city study found that a green roof’s payback period runs four to five times as long as a cool roof”s, out to hundreds of years” before recovering its investment. Green roofs are nice, and meaningful, but they’re luxuries. This accord may have stymied the discussion’s sponsor, which billed the evening as part of a series called “Oppositions.” But it clarifies priorities for the rest of us.

The installations, which entail a moist membrane and soil and plants on a building’s roof, lower a building’s temperature and can snatch some carbon dioxide from the air. But they cost extravagant amounts, making them most logical as amenities for developers to offer status-minded tenants or ones with special health needs. As a talon of policy, so-called “cool roofs,” which use nothing lovelier than white paint to reduce heat absorption, scratch deeper into carbon output and lift investment values. If you want to clamp a fix across cities that lowers carbon and its associated costs, require building owners to make their roofs light in color or otherwise able to reflect the sun. And if you want to sex up the idea of occupying urban real estate, put cattails and hydrangeas and whatever else looks alluring on the rooftop.

“As a matter of policy, the real value of green roofs is what I’ll loosely call the real estate value,” said Leslie Hoffman, who runs a firm called Earth Pledge that proselyted green roofs in the late 1990s and now advises affordable-housing developers on installing them. “The creative design, the ability to look down on a garden, elderly people doing exercise around the perimeter or sitting in wheelchairs gardening in boxes- those are wonderful if they’re real. But what happens a lot is projects are proposed and then value-engineered out because they’re expensive.”

Now, green roofs sponge up stormwater and thus play some role in keeping sewers running cleanly. But so do street trees. Green roofs advance a green economy by glamorizing a methodical change in how owners track their buildings’ energy performance.

But anybody who tells you they stand as the work unit of the green urban property market would also have tried to sell Art Deco cornices to every investor in the Depression. And any such person either wants to skim off the top of the green economy or wants to see the green economy wilt.