“Green roofs are a great way to offer sustainability benefits while reducing the operating costs and impact on the environment,” Rowland says. “They help to reduce the heat island effect, decrease stormwater runoff and lower energy usage through greater building efficiency.”

But he adds, “One challenge to the success of a green roofing installation is ensuring proper drainage of the system.”

Roof slopes, drainage and soil and plant selection all play significant roles. A green roof that retains too much water can cause a variety of issues, such as water infiltration due to ponding water and disruptions to the establishment of the plantings, which impact the system’s efficiency and drainage characteristics. Also, in extreme cases, there can be structural issues due to increased water and ice load.

In addition, the microclimate at the roof level of a high-rise building will likely not be the same as the ground level climate, he says.

Firm in Focus

The DeMatteis Organization
820 Elmont Rd., Elmont, N.Y.
Principals: Richard and Scott DeMatteis
Founded: 1918
What’s New: One of the eight projects DeMatteis is doing for the New York City School Construction Authority—which all conform to the city’s Green Schools Guide—is PS 46X in the Bronx. A five-story, 77,000-sq-ft building is being constructed, with an 81,700-sq-ft renovation planned for an adjacent building. Joining old to new involved careful planning of structural tie-in work between both buildings. For the existing structure, which is more than 100 years old, extensive shoring supports were designed to enable removal of the exterior masonry wall so that new structural steel could be installed. PS 46X has a footprint that sits only feet away from the property line on three elevations, necessitating the use of mast climbers. Once completed, the new building will offer a modern green school, and the existing one will have ADA accessibility.