Developing green roofs for colder climates

A 2-year green roof study conducted at the Univ. of Minn. looked at developing guidelines for low maintenance plants that could survive the cold and often dry Minnesota weather and still reduce building energy costs. Horticulture graduate student Jonathan Hensley and professor John Erwin sought to create a low maintenance roof that could reflect light and absorb heat during the summer and insulate buildings during the winter. Hensley and Erwin trialed a variety of grasses, bulb crops and perennials on the roof of the university’s Williamson Hall.

Hensley said the savings are hard to quantify especially since a green roof can cost 2-3 times as much as a conventional roof. However, a green roof can last 2-3 times longer.

Erwin, who is a commissioner of the Minneapolis Parks and Recreation Board, has supplied the city with a list of approved plants to develop a city-recommended green roof guide. The Target Center in Minneapolis has a 2½-acre green roof that was completed in September 2009 and cost $5.3 million.

University landscape architect Tom Ritzer said the results of Hensley’s and Erwin’s research will be a part of the school’s facility management discussion about the practicality of green roofs. He said the key to the university installing other green roofs will be cost effectiveness.