TRENTON, Mich. – Using heat from a forge that turns orange-hot metal into 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.
Trenton Forging President David Moxlow started growing fruit and vegetables atop the plant southwest of Detroit in November and has already harvested greens, peppers, broccoli, strawberries and tomatoes that 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 Inc. aims to build hydroponic farms on roofs in New York, Washington, D.C., and 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.
Gayla Trail, author of “Grow Great Grub: Organic Food from Small Spaces,” has gardened for a decade on the roof of the three-story apartment building where she lives in Toronto. In that time, she has seen growth in automatic watering systems and other products geared toward rooftop or balcony gardeners.
“When I started, I didn’t know anybody else that was doing what I was doing,” she said. “Finding the information to deal with the extreme of that (rooftop) environment was next to impossible.”
Trail, 36, said gardening makes people better consumers because they’re more aware of how food is produced. She started growing on the roof because it was her only option for a place to garden, and that’s true for many urban residents with small or no yards. Manufacturers, meanwhile, often have large, unused flat roofs but little land to spare.
“If you’re landlocked, your only option is to go up,” Moxlow said.
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. But the gardens also can make it easier for city residents to get fresh fruit and vegetables, which is seem as a way of improving public health.
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 they’re formed, pieces 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.
