On top of the outermost layer of your roof (or the waterproof membrane, as it is known in roofing parlance), a protective mat or layer of insulation is laid down. That is followed by a root barrier (to keep the plants from growing down into your bedroom), a drainage layer, soil and, finally, the plants.

Sedum, that spongy, low-growing succulent, is favored by many green roofers in the Northeast for its short roots and drought-resistant properties.

“Sedum is so resilient that it will not need to be replaced each spring,” said Ms. Yancey of Brooklyn Greenroof. “It actually lives through each harsh New York winter by going dormant and turning a reddish-brown color. In spring, it bounces back better than ever, having rested and recharged over the winter. And because we always plant a mix of different sedums, it flowers in different colors, over an extended period of time, all through the summer and into fall.”

How Much Will It Cost?

The upfront costs of planting a living roof can be considerable, from about $10 a square foot to $40 a square foot, depending on the size and complexity of the project. Over time, however, green roofs can reduce energy and maintenance costs by protecting your rooftop and building equipment from excessive exposure to sun during the warmer months and increasing heat retention during the cooler ones.

Andrew Franz, an architect in Manhattan, installed an expansive living roof for clients with a three-bedroom TriBeCa penthouse. The layers of soil and vegetation created an “insulated building envelope” that significantly reduced their heating and cooling costs, said Mr. Franz, who worked with Plant Specialists, a landscape consultant, to develop and install the green roof.

“The apartment is now 10 degrees warmer in the winter and 10 degrees cooler in the summer,” he said, “creating a far more comfortable and energy-efficient residence.”