Case study: How to install a green roof on a private home

The site: A more than 900-square-foot expanse atop a historic building in the Prospect Lefferts Gardens neighborhood of Brooklyn. The homeowner recently re-roofed the building, in anticipation of installing a green space, she had the roofer raise the skylights several inches and bring the waterproofing material up the sides of the roof’s walls. The plan: The homeowner envisioned a wide carpet of greenery in addition to a small space for growing some fruits and vegetables, as well as an area to hang out with friends. She hired architect and green roof pro Inger Staggs Yancey of Brooklyn Greenroof to bring her idea to life. The plants: The engineer’s assessment showed that the roof could hold 55 pounds per square foot—enough strength to support a full rooftop farm. For a time, the homeowner entertained the idea of installing a full rooftop farm but eventually decided to return to her initial concept of a low-maintenance green space with a few planters for edibles.

Several inches of edging material—typically stones or gravel—will then be used to form a root-free border separating the growing area from any vertical elements like walls or, in this case, the sides of the skylights. Metal slats placed between the rocks and the growth media help ensure separation while retaining drainage.

Over the moisture layer goes a filter fabric specially engineered to hold in the dirt while draining out any water. The timeline: Once Yancey and the homeowner finalized the plans for the roof, Brooklyn Greenroof applied for a permit with the city’s Department of Buildings. The entire installation took about five days in total, with a weekend between planting and finally putting in the edging. The homeowner also built a set of copper-covered planter boxes to sit on the raised cornice area near the front of the building, with Wooly Pockets planted with strawberries hanging down nearby.

The money: The average cost for a bare-bones green roof—including the design, permitting, and installation—will typically run between $18 and $22 per square foot.