Ford Motor Co. last month unveiled a huge green roof at its new truck plant in Dearborn, Mich.
The roof is covered with 10.4 acres of sedum, a genus of perennial plants that tops a 3-in.-thick, four-layer system incorporating a root-resistant membrane, a drainage layer, a fleece mat, and a vegetation blanket (see schematic). The top inch-thick "growth substrate" consists of expanded shale, sand, peat, compost, and dolomite. The vegetative roof is supported by a modified bitumen roofing system.
Ford says the drought-resistant ground cover can absorb up to 4 million gallons of water per year, thereby relieving drainage systems that ultimately discharge into the adjacent Rouge River. Storm water will flow into a box culvert only if not absorbed by the roof or by ponds or vegetated swales on the site, says Roger Gaudette, manager of engineering and construction at Ford's Rouge Center manufacturing complex. The roof will also promote energy conservation by reducing heat gain.
Southfield, Mich.-based Arcadis was architect and Detroit-based Walbridge Aldinger Co. was construction manager. William McDonough + Partners, Charlottesville, Va., was the environmental consultant.
Ford initially investigated German vegetative roof systems that were typically 4 in. thick, according to Gaudette. Structural steel for the plant was ordered on that assumption, although the thinner system subsequently was selected. This followed work with the horticulture department at Michigan State University, which tested alternate growing and drainage mediums. The weight of the system, fully saturated, is about 10 pounds per sq. ft.
The roof incorporates 13 varieties of sedum, says Donald Russell, Ford's manufacturing sustainability manager. They were selected for qualities such as durability and resistance to disease and drought. The vegetation is not expected to grow to a height of more than 4 in.
The sedum was planted in the spring of 2002 on nearby Ford-owned land by Xero Flor, a German company. It was installed on the roof, which slopes 1/8 in. per ft., last October.
Ford expects the roof to last about 40 years, or double the life of a conventional system — largely by reducing the impact of UV degradation and freeze-thaw cycles.
Ford's sustainable design efforts are more immediately apparent in its 30,000-sq.-ft. visitor center, designed by Southfield, Mich.-based HarleyEllis, which adjoins the plant. It received a Gold LEED rating from the U.S. Green Building Council. The center has a photovoltaic system that provides some electricity for use within the building.
The plant, for which design work began four years ago, has some features that would contribute to LEED certification, but it was not designed with this in mind.
Ford's storm water management system extends to an adjoining parking lot, which was paved with an asphalt mixture that contains no small aggregate components. This creates a porosity that lets water seep into the ground, eliminating the need for catch basins in the paving. In three years of testing, Ford has found that the result is a surface on which water does not pond and snow melts more readily. A 16-acre lot where cars driven off the assembly line are stored awaiting shipment will be paved in this manner.
Ford anticipates that at some future time the company may be held responsible for treating and controlling storm water that originates on its property, and this could require construction of a costly treatment plant. "We'd rather be on the forefront of that, rather than on the back end.," Gaudette says.
Sustainable features at the Rouge complex, which opened in 1918, also include a gray water system. It consists of a 12,500-gallon cistern that collects rainwater and recycles it for exterior irrigation and flushing toilets, and "vertical landscaping" — the use of vegetation that grows on trellises mounted to exterior walls to shade the building and reduce heat gain.
"Ford incorporates LEED practices because they're environmentally friendly and are good business," says Tim O'Brien, VP of corporate relations. The company has spent about $5 million to date on storm water-related management systems.