A New York City postal processing facility that was contaminated during the 2001 anthrax attacks is now the site of the largest "green roof" in Manhattan.

The 65,000-square-foot roof area at the Morgan Processing and Distribution Center on Ninth Avenue between West 29th and West 30th streets cost $5 million to install in 2008. It affords views of such landmarks as the Empire State Building and is one of several pilot green roofs in the metropolitan area. During the anthrax attacks, the Morgan facility was one of 23 U.S. Postal Service facilities to be contaminated, according to a 2004 U.S. Government Accountability Office report. The site remained open for work during decontamination (as a processing facility, it is not open to consumers), but most of the site's 5,000 employees received precautionary antibiotics. Today, security at the facility is tight, but the seventh-floor green roof is open for employees to visit on breaks.

The Morgan facility's green roof and other new energy-saving measures there, such as replaced windows, have saved the Postal Service more than $1 million in energy expenses so far, Tom Samra, Postal Service vice president of facilities, said in a prepared statement. The location is on track toward a target to reduce storm water runoff by 75 percent in summer and 40 percent in winter, he added.

New York City has an estimated 1 billion square feet of roof space, according to Columbia University climate scientist Stuart Gaffin, that could be converted from black tar to "green," which is just one solution to the problems that conventional city roofs generate—they contribute to the urban heat island effect by storing and trapping solar energy and they collect storm water that ends up overwhelming the city's sewers and thereby polluting the waterways surrounding the city.

Buildings contribute 80 percent of all the greenhouse gas emissions in New York City mainly as a result of their associated electricity consumption, burning of fuel oil or natural gas to provide heat in the cold months and burning of non-electric cooking fuels such as gas. "We should think of them as polluting devices just like we think of automobiles, in terms of the climate problem," Gaffin says.

New York's Mayor Michael Bloomberg has committed city funds to converting some of the area's black tar and stone roofs into highly reflective white roofs, which reduce temperatures on roofs and cooling costs but fail to address the storm water runoff problem. So-called blue roofs, in which water drains are slowed down, are proposed by some to deal with the latter issue, Gaffin says. U.S. cities that have more aggressively embraced green roofs include Chicago, Seattle and Portland.

Gaffin is collecting data on all these approaches, as well as easy-to-install tray systems for green roofs, to see which are the best for decreasing a roof's temperatures and runoff.

Other green roofs have been installed at the Bronx County Courthouse (10,000 square feet), Ikea in Brooklyn (70,000 square feet), Ethical Culture Fieldston School (two roofs, measuring 5,100 square feet and 1,500 square feet, in the Bronx), a Con-Edison building in Long Island City (a quarter of an acre, or about 10,000 square feet) and Hackensack Hospital in New Jersey (about 5,000 square feet). All these projects will be eclipsed in size by a seven-acre green roof project set to go atop the Javits Center within the next two years.

Green roofs typically feature plants in a growing medium made of inorganic heat-expanded shales and clays that become very lightweight and porous so they can retain a lot of water. Plant roots adapt to these high-mineral-content media that are much lighter than conventional topsoil.

The lightest professionally installed roofs involve a four-inch planted medium on top of several layers of protective membranes atop the original roof. The layers start with a waterproof membrane (possibly PVC) other than the roof itself, then a geotextile filter cloth to prevent the medium from penetrating too far down, a root penetration barrier, a drainage layer, a second geotextile cloth for water retention, the rooftop growing medium and finally drought-tolerant vegetation.

To get the 2,000 cubic yards of growing medium required up to the seventh-floor roof of the Morgan facility, Tecta America's Brian Singley worked with specialized sub-contractors to devise a new approach. The team loaded the medium, which had been dumped by trucks into a holding pen constructed on West 30th Street adjacent to the postal facility, into the hopper of a large vacuum truck that is normally used to remove stones from roofs. By reversing the suction on the vacuum, the medium was blown onto the roof.

View a slide show of plants and vistas at the Postal Service's Morgan facility "green roof"