The City of New York’s Randall’s Island Green Roof is a 30,000 sq. ft. living laboratory for green roof design. It’s home to 30 different green roof systems, the largest of which is 6,000 sq. ft. of Xeroflor planted in sedum.
Artie Rollins, Assistant Commissioner for Citywide Services, New York City Parks Department hosted a tour for Cities Alive in early October with intern Max Lerner.
All planting beds are replenished annually with ground up wood chips after perennials are cut back. Soon, some of that will be replaced with compost produced onsite. The building recently began a composting program for paper from the offices below and vegetative material from the roof. Since starting mid-summer it’s reached 1,000 pounds of feedstock.
One immediate benefit of the roof is the opportunity to save money downsizing the building’s air conditioner that’s scheduled for replacement. Because of the cooling effect of the green roof, the new unit will be a 15-ton unit (downsized from a 25-ton unit).
The department is working with Columbia University to monitor green roof plots on 10 different recreation centers. Some plots have 4” of mineral based soil, others 6”. Now in year 5, the study is looking at soil microorganisms and how they interact with native plants on the roofs and in adjacent gardens/grounds. For more information, see “Digging the New York City Skyline: Soil Fungal Communities in Green Roofs and City Parks” in Plos One, http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0058020
If the NYC Parks Department covered all their space with green roofs, it would add 1 million sq. ft. to the city’s green roof inventory. Maintenance is an issue Artie, said, estimating that the annual expense would run about $1/sq. ft. based on the experience at Randall’s Island.