Rooftop gardening provides environmental benefits in urban areas

By David Runk
Tuesday, July 27, 2010

Using heat from a forge that turns out car parts and hand tools, a Michigan manufacturer is developing an energy-efficient way to warm a year-round greenhouse on the company's roof.

David Moxlow, president of Trenton Forging, started growing fruit and vegetables atop his plant southwest of Detroit in November; he has already harvested greens, peppers, broccoli, strawberries and tomatoes, which are shared with employees and visitors. The company is among a number nationwide that are developing technology and techniques for rooftop gardening as interest in local and homegrown food grows.

Sky Vegetables aims to build hydroponic farms on roofs in New York and Washington and in the Boston and San Francisco areas to make more fresh produce available in cities. Another company based near Chicago, GreenGrid Roofs, sells a modular system of plastic bins that make it easier to install rooftop beds.

Rooftop gardens provide environmental benefits similar to traditional green roofs, in which plants are used to reduce storm-water runoff, filter pollutants and cut heating and cooling costs. The gardens also can make it easier for city residents to get fresh fruit and vegetables, which is seen as a way of improving public health.

Manufacturers, meanwhile, often have large, unused flat roofs but little land to spare.

Moxlow, who grew up gardening, built a plastic-covered greenhouse, known as a hoop house, on a stretch of his company's flat roof and used forced air and a hot-water heater to keep it warm during the winter. But he has designed and is testing a system to harness heat from the forging operation that would otherwise be wasted.

The forge heats metal to between 1,600 and 1,800 degrees. After pieces are formed, they are put into big bins and set outside to cool. Moxlow's system would roll some bins under a 4,000-gallon tank inside the plant to heat water to warm the greenhouse. In northern states where greenhouses often shut down for the winter because of the high cost of heating, the system could make year-round growing more practical, he said.

Sky Vegetables, based in Needham, Mass., says its hydroponic systems could help building owners save money on heat. Designed for roofs of at least 10,000 square feet, its systems would use solar panels to heat greenhouses where plants grow in water. The greenhouses should lower buildings' utility costs by absorbing sunlight in the summer and providing additional insulation in the winter, the company says.

Sky Vegetables may eventually license its technology, but right now it plans to rent roofs where it will install its greenhouses and then sell the produce to supermarkets and other customers.

GreenGrid, owned by Weston Solutions Inc. of Vernon Hills, Ill., makes gardening systems that can be used on smaller roofs.

-- Associated Press

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