The Greening of Minnesota’s Urban Rooftops

Vegetative roofs have become more common in Minnesota and across the country as developers and building owners go green on their crowns to save money and reduce their environmental footprints.

Downtown Minneapolis boasts one of the largest green roofs in the country atop the Target Center, which features a 113,000-square-foot spread of sedum and other plants at 600 First Ave. N. The Minneapolis Central Library, 300 Nicollet Mall, has green roofs on two floors.

Plenty of planning goes into putting together a green roof in difficult climates and dense urban areas, according to Thomas Hanzely, national sales manager for the SkyScape Vegetative Roof Program at the Indianapolis-based Firestone Building Products division.

In recent years, more customers have installed manufactured modular systems rather than hiring designers, notes Minneapolis landscape architect Nathalie Shanstrom, who has worked on the Target Center roof and other projects.

Vegetative systems “are no longer about throwing plants on a roof and hoping they’ll survive,” Hanzely said at a recent event for the American Institute of Architects Minnesota chapter in Minneapolis. “They are about creating useful space people can enjoy, use and even harvest, as well as being a great tool to help people manage water.”

For communities, green roofs can reduce stormwater runoff into sewer systems. For building owners, they can cut energy consumption by acting as a buffer against the sun, slicing air conditioning costs and roof maintenance, Hanzely said.

A Con Edison study of a green roof in Long Island City in the Queens borough of New York revealed a 40 percent savings in energy consumption in summer and lower average heat loss in winter compared with black rubber roofs, said Hanzely. That’s enough savings to achieve a return on investment in just five to seven years for a vegetative roof, he said.

Some cities offer incentives for building owners to add green roofs. Minneapolis offers a reduction of at least 50 percent, and potentially more, in stormwater utility fees for building owners who install green roofs, according to the city’s website. The Minnesota Pollution Control Agency’s website also offers information on several vegetative roof projects in the state and suggests costs from $10 to $30 per square foot are common. No state subsidies for green roofs are available.

There are several additional benefits. Green roofs mitigate the heat island effect caused by density in cities such as Chicago and Washington, D.C., where they are popular, Hanzely said.

Building owners will find the roofs can last two to three times longer because plants reduce exposure to ultraviolet light and buffer extreme temperatures. And some owners are even harvesting crops on the rooftops, Hanzely added.

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