The green roof on the Dearborn Truck Plant in Michigan spans more than 10 acres. It’s the largest one on a single, freestanding building in North America.
The expanse of sedum plants atop The Republik Building at 211 Rigsbee Ave. doesn’t quite compare, being a little more than 2,000 square feet, but it serves as a demo for potential clients of Xero Flor America, the company that provided the green roof materials for the truck plant.
Xero Flor America’s headquarters are in the Rigsbee building, which the company moved into last year. The company, which has several offices, changed its headquarters from Lansing, Mich. to Durham in 2006.
The company installed the green roof atop the 1940s structure this year.
“It has the potential to be a landmark in the greening of downtown Durham, especially to show how green roofs can help solve the area’s stormwater problem,” said Clayton Rugh, general manager and technical director for Xero Flor America.
The company focuses on the use of green roofs to improve water quality by reducing the amount of rainwater running off impervious roofs and picking up pollutants.
Peter Raabe, North Carolina conversation director for American Rivers, a national river conservation organization, sees green roofs as a significant tool for improving the quality of the city’s drinking water.
“Our office in Durham is on the fifth floor of the Snow Building on Main Street. Looking out my window during storms, I see the rain pounding down on the roofs of downtown buildings and surging into the streets. That runoff then rushes through the city’s stormwater drains that flow right into the creeks that feed the Falls and Jordan reservoirs,” Raabe said.
The greenery also extends the life of a roof by protecting it from the sun and the expansion and contraction from temperature extremes. The shade and insulation reduces heating and air conditioning costs. And the roofs require minimal maintenance and can thrive with little supplemental irrigation in most temperate climate zones.
The pre-vegetated mats for the company’s Southeast region are grown in fields in northeast Durham County. They are planted mostly with moss and sedum, a flowering perennial that is lightweight and has shallow roots. Sedum can handle drought and is tolerant of a wide range of temperatures. Seedum also provides food for pollinators.
Atop the Rigsbee building, different colored sedum flowers bloom from spring through fall, and the plants turn red while dormant in the winter.
Beneath the vegetation there are several layers: growing medium, water retention fleece, drain mat and root barrier. Some of the materials are produced in the North Carolina towns of Enka and Hildebran. The mats are rolled out like sod onto roofs.
The company sells the mats for jobs of every size and for both residential and commercial buildings. Usually a contractor installs the roof, but Xero Flor staff sometimes will do the smaller jobs. Recently the staff gave a chicken-coop’s roof a makeover. The cost ranges from $8 to $20 per square foot.
Xero Flor America is one of about 20 different Xero Flor sister companies around the world under the company Xero Flor. It is the exclusive U.S. distributor for the Xero Flor Green Roof System, which was engineered in Germany. Rugh estimates that about 20 percent of new construction in Germany has new roofs, largely due to government incentives.
Rugh said municipal involvement is crucial in encouraging property owners to purchase green roofs. Some governments offer reduced taxes, grants or creative incentives such as allowing a developer to build a taller apartment building. The green roof atop the Rigsbee building alone can prevent more than 50,000 gallons of stormwater runoff annually, he estimated. And over the years, less stormwater means longer lasting water plants and less government spending, Rugh said.
In the United States, the cities of Chicago, Washington D.C. and New York City are leaders in green roofs, and Rugh hopes Durham will join that list.