- Associated Press - Saturday, March 8, 2014

ST. PAUL, Minn. (AP) - Twin Cities residents walk past Angie Durhman’s work every day, but few of them are likely to notice it.

Durhman’s one-woman business designs and maintains greenroofs - roofs that are topped with a layer of vegetation - in the metro area and nationally.

Greenroofs have become increasingly common, as developers pursue sustainable design incentives and environmental certification. Durhman is part of an industry that is growing up around this trend.

“It’s still ‘nichey,’” Durhman told the St. Paul Pioneer Press (http://bit.ly/1fD2hLv ). “But the general public usually knows what a greenroof is now, even if they haven’t installed one before.”

Durhman has been designing and maintaining greenroofs in the Twin Cities for a year, under the name AD Greenroof, based in Minneapolis.

After spending seven years managing greenroof construction and maintenance for Tecta America, an Illinois-based contractor that entered the industry when it was in its infancy, she decided to move to the Twin Cities in 2012.

She now maintains one residential and two commercial greenroofs in the metro, including 2.5 acres on top of the Target Center arena in Minneapolis - one of the largest greenroofs in the country. But she’s hoping to contract for several more.

“They don’t need a whole lot of maintenance, but they do need some so the weeds don’t take over,” said Nathalie Shanstrom, a landscape architect with Kestrel Design Group, which designed the Target Center’s greenroof.

During the months it isn’t blanketed by snow, Durhman visits it and the other greenroofs she maintains periodically to ensure the vegetation cover is holding up.

During the rest of the year, Durhman has kept busy with the design side of her business - greenroofs can take up to three years to implement. Presently, she’s designing two greenroofs, one in Florida and one in Nebraska.

From a distance, a greenroof might not look much different than an average backyard, but it’s very different - right down to the soil.

Rather than the loamy topsoil found at ground level in much of Minnesota, a greenroof is rooted in a layer of pea-sized, porous rocks. These absorb and retain water, and are less likely to blow away than soil.

And the vegetation isn’t standard Minnesota fare, either.

“Greenroof systems … have to grow in more of an extreme climate,” Durhman said. “You have to think in terms of alpine conditions.”

She says the plants that thrive on a greenroof are usually heartier succulents called sedums, or stone crops like chives.

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