Sustainable Cities Promote Growth On Rooftops
Transforming useless, black rooftops into prosperous, green gardens — that is the goal of Dr. Paul Mankiewicz. As director of the Gaia Institute, an environmental research group in New York City, he has designed a unique greenhouse which solves the complexities of gardening on rooftops and will provide fresh produce for thousands of residents below.
By using a lightweight soil, a simple steel-frame structure wrapped in plastic, and a unique planting and harvesting system, this new greenhouse could add a new facet to agriculture. And that has the biologist excited.
“If we have a system that can purify the air and lower the amount of traffic needed to ship produce — and have that system in cities where pollution problems are serious — that is certainly a big improvement for society,” he said. “And by having a new center of economic activity right in the cities, it makes for a much greater increase in wealth for those urban areas.”
After seven years of research and development, Mankiewicz has applied for a grant from the Environmental Protection Agency to build a prototype greenhouse on a building owned by the Cathedral of St. John the Divine, New York City’s fifth most popular tourist attraction.
Tied to the grant is New York City’s Recycling Division, which will help supply the ton of solid waste the greenhouse will use every day. Food scraps and other waste material will be composted in large bins, Mankiewicz said, then slurried up to the roof where the material will be used in both the soil and the nutrient system.
The greenhouse’s soil is the unique feature that makes the system work. Most soils are too heavy to use on rooftops, he said, and building additional reinforcement is too expensive.
However, he has created a super lightweight soil by using both synthetic and organic materials, including recycled styrofoam. The styrofoam works as filler — the purpose sand and clay serve in most soils.
Feeding the crops involves a series of underground tubes linked to a controller, which delivers precise amounts of water, nutrients, microbes, carbon dioxide and oxygen to maximize plant growth.
Covering the plants will be a lightweight steel frame covered with a thin glazing of plastic. By his calculations, Mankiewicz said the amount of petroleum needed to produce all the plastic used in the greenhouse would get a truckload of produce only 300 miles down the road from California.
For planting and harvesting, a space-saving gantry system will span the garden and roll over the top of the growing space. Workers will be able to work from above, he said, eliminating the need for aisles and increasing crop yields by 30 to 90 percent.
On a larger scale, Mankiewicz envisions rooftop greenhouses eventually adorning the tops of shopping malls. With tens of thousands of square feet available, a shopping mall greenhouse could supply all the produce for an entire community. And by increasing the profits of both store and mall owners, he said the technology could leap ahead, becoming a new green layer of the urban environment.