Daily Plant Masthead

Volume XXIII, Number 4768
Tuesday, Aug 12, 2008

The Roofs At Parks Are Going Green

On Earth Day 2007, Mayor Bloomberg released a comprehensive sustainability plan for the City of New York titled PlaNYC. In response to this visionary initiative, the Five Borough Technical Services division adopted its own short term sustainability task force. After extensive research, Five Borough discovered that installing a green roof, a thin layer of vegetation installed atop a traditional flat or pitched roof, can contribute significantly to the city’s sustainability effort. Now, virtually the whole west wing of the Five Borough Administrative Building roof is covered by a variety of green roof systems featuring different designs.

In Spring 2007, Technical Services constructed its first, rather modest, green roof module. Based largely on a standard design by Barrett Roofing, which donated about $3,000 worth of roofing material, it covers 800 square feet (measuring 40’ long x 20’ wide).

The current green roof systems planted atop the Five Borough Administrative Building now include nearly 7,000 square feet of vegetation. Unlike most traditional green roofs, the one on Randall’s Island is made up of 12 distinct systems, each one differing from the next in growing medium, plant type, or installation model. Thus, the Administration Building roof serves as an experimental station in which the performance of many different systems can be monitored and compared. The lessons learned from these comparisons can be applied to future installations around the city.

Technical Services’ roof at Five Borough is truly at the forefront of green roof technology with some of the most innovative systems available. One system, called Green Paks, consists of 195 woven polyethylene bags pre-filled with a mineral based growing medium that consists largely of heat-treated shale. The bags were placed side-by-side atop a rolled out root barrier and drainage mat layer. Then slits were cut into the black knit surface and sedum plugs were inserted into the growing medium. Another modular system is made up of 400 aluminum trays that cover 1,600 square feet of rooftop with plants. It offers flexibility in that each 2’ x 2’ tray can be removed, if necessary, to provide access to the roof below. The most recently installed system at Five Borough is made from 100 biodegradable planting trays that will soon decay, contributing organic material to the growing medium, and ultimately providing a monolithic system.

The green roof atop the Randall’s Island Administrative Building serves many ecological purposes, including storm water retention, mitigating the urban heat island effect (the absorption of heat by built structures that make cities 2 to 10 degrees Fahrenheit warmer than the surrounding suburbs or countryside), and energy conservation, to name a few. According to Green Roofs for Healthy Cities, in summer, depending on the plants and depth of medium, green roofs retain 70-90% of the precipitation that falls on them. Between the months of May and October, New York City receives on average of 24.1 inches of rainfall. If Five Borough’s green roof can retain 70-90% of this rain, it will be capable of absorbing about 64,000 to 84,000 gallons of storm water between May and October.

The Five Borough green roof serves as a working laboratory for green roof design and construction, providing knowledge to the rest of the agency and other groups while at the same time conserving and giving back to the City of New York. So far, this endeavor has been a great success and it is hoped that it will demonstrate the advantages and feasibility of installing green roofs atop all Parks buildings.

Questions and visits are welcomed. Please contact John Robilotti, Senior Project Manager, at 212-410-8908.

Submitted by Catherine Colwell


Eco-Friendly Tip of the Day

“During hot months, try to park your vehicle in a shady spot, which decreases the amount of fuel lost to evaporation and requires less air-conditioning when you get back in.”



“I know I am but the summer to your heart,
And not the full four seasons of the year.”

Edna St. Vincent Millay
(1892 - 1950)

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