Green urban rooftops blossoming

Green urban rooftops blossoming

Not so green yet in early spring, the roof of Target Center in downtown Minneapolis. Photo by Bill Klotz

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. The Minneapolis Central Library has green roofs on two floors.

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

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.

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.

System selection is the key to creating a successful vegetative roof, he explained, and they come in three varieties:

  • Extensive: The least expensive option offers 6 inches of soil or less and requires no irrigation system.
  • Semi-intensive: A more designed roof, this style has deeper soil, costs more and looks better. It works on roofs that are seen, such as those next to offices. But the roofs require a strong structure to carry the weight.
  • Intensive: Soil depths exceed 8 inches and offer greater variety of plants, grasses and even trees. They may have walking paths and other architectural features. More labor is needed for maintenance, and the underlying structure must be strong enough to hold a substantial amount of weight.


Topics: Architectural Firms, Building Owners and Managers, Construction Firms, Energy Saving Products, Engineering Firms, Exteriors, Great Commercial Buildings, Green Roofs / Garden Roofs, Roofing, Urban Planning and Design

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