Rooftops covered with plants go back hundreds, if not thousands, of years. In China there is the roof iris, Iris tectorum, so named because it flourishes on sod. In Northern France and England there is an old rural tradition of growing moss, ferns, and hens-and-chicks (or live-forevers) on the roofs of houses, covered entryways, and out-buildings.
While the East End may be in the vanguard of many trends, it is playing catch-up on green roofs. However, green roofs are arriving here, albeit slowly, as at the new house Arthur Beckenstein and John O’Rourke built overlooking Three Mile Harbor in East Hampton, where one was installed on the garage and entrance roofs in late May.
The house is on a steep slope with glass walls opening to a view of the harbor on three sides. The rectangular masses of garage and entrance are on the street side and can be seen from the interior staircase.
Mr. Beckenstein, who in his college years studied architecture and graphic design at the Rhode Island School of Design, brought in a landscape architect early in the process. Thomas Woltz, principal of Nelson Byrd Woltz Landscape Architects, which is based in Virginia, is known for incorporating environmental sustainability into design; his newest project is at Hudson Yards on the west side of Manhattan.
The Bridgehampton firm Barnes Coy, the house’s architect, planned the necessary structural reinforcement after Mr. Woltz suggested a planted roof. A 900-square-foot raw visual element has now been transformed into a carpet of mixed sedums, a mosaic of texture and color that is a lovely and harmonious foreground to the woods around the house.
The green roof was used to solve an aesthetic and design challenge, but it also has an ecological benefit: It reduces and slows stormwater runoff, and it filters pollutants from rainwater before it drains into Three Mile Harbor.
Houses and commercial structures with green roofs installed over the entire roof have the potential to reduce energy use and lower the costs of heating and air conditioning by as much as 60 percent, according to George Irwin, president of Greenliving Technologies, an international company with a growing facility in Rochester, which the owners selected for the job. The vegetative layer absorbs heat and acts as an insulator, reducing the temperature of the roof surface and the surrounding air.
Greenliving Technologies has a patented modular system for installing green roofs and the project would have taken only a day, if Mr. Irwin had been happy about the quality of the first batch of sedum. It had been transferred from a refrigerated truck to one that was not refrigerated for the final stretch of delivery, and the plants were stressed. A fresh shipment arrived the following morning.
The growing medium is an engineered soil of aggregate, mycorrhizae and organic compost the company has developed with Long Island Compost, a firm on Long Island that also markets green roofs as well as growing walls and vertical farms. The aggregate improves drainage and the mycorrhizal fungi increase the holding power of nutrients in the soil.
A roof covered with sedum performs best with a four-inch layer of soil; other plants appropriate for roof installations require a thicker layer. The soil is bagged and mats of a mixture of various low-growing sedum are wrapped in netting and put on pallets to simplify transportation and lifting them to the work areas. (Details and illustrations can be seen on the Greenliving website, agreenroof.com.)
Sedum are workhorses that give a lot and ask little in return. Their roots are light-weight and don’t need much depth and their evergreen leaves provide solid coverage, preventing weeds from finding a toehold. They flower at different periods and some of their foliage becomes ruby red in winter, changing the colors of the mosaic mixture over the course of the year.
In this small installation, manual subsurface drip irrigation was installed, although in larger areas automatic systems with pop-up and overhead sprays are used. Fifteen minutes of irrigation every couple of weeks should be sufficient during the worst of midsummer heat and drought, and overwatering is a greater problem than underwatering. And, as an added advantage, not much weeding is necessary.