WORLEY, Idaho – When the wind blows at Circling Raven Golf Course, it rustles through prairie grasses growing on the roof of the Stensgar Pavilion.
This bit of man-made habitat is so convincing that a killdeer has moved in. Visitors who climb a ladder to get a better view of the Idaho fescue and blue bunch grass on the roof also see the killdeer faking a broken wing, the bird’s maneuver to lead potential predators from her nest.
“It looks just like the Palouse Prairie around us,” said Bob Bostwick, a spokesman for the Coeur d’Alene Casino Resort & Hotel, which operates the golf course.
That’s exactly what architect Roger Gula had in mind. The Stensgar Pavilion’s roof changes with the seasons. It greens up when the snow melts, blooms with purple asters in the spring, and waves bronze seed-heads from ripened grass in the fall.
And aesthetics aside, “it really is a workhorse that provides a lot of benefits,” said Gula, who works for Mithun Inc., of Seattle.
The pavilion, which hosts corporate events, was built without air conditioning because the green rooftop provides so much insulation. The roof also muffles the roar of 18-wheel tractor-trailers barreling down U.S. Highway 95.
Green roofs are an old-new idea, with roots dating to the era of sod homes. Common in Scandinavian countries, they’re catching on in North America as city leaders, engineers and architects see the potential for lowering energy costs and reducing rainwater runoff.
In May, Toronto became the first North American city to pass a law requiring new developments to incorporate green roofs. The law, which will be phased in, applies to buildings of 6,000 square feet or greater. The requirement could push Canada’s largest city past Chicago as the urban area with the most green roofs, according to the nonprofit Green Roofs for Healthy Cities.
In San Francisco, where Mithun also has an office, city leaders encourage green roofs to mitigate lost wildlife habitat. Patches of rooftop vegetation provide resting spots for birds migrating along the Pacific Coast Flyway. Rooftop gardens also are seen as a vehicle for halting declines in San Francisco’s bee population, Gula said.
Green roofs pack the most benefits in highly urban areas, said architectural designer Burton Yuen, who also works for Mithun. The plants absorb rain and snowmelt, which means building owners spend less money capturing stormwater runoff.
Pockets of rooftop vegetation also lower temperatures in inner cities by reducing the heat radiating from pavement and roofs.
In the Inland Northwest, the Stensgar Pavilion is among a few buildings with green roofs. Executives of the Coeur d’Alene Casino, which is run by the Coeur d’Alene Tribe, wanted the pavilion’s design to harmonize with the rolling hills of the Palouse.
“There’s a feeling that this building is emerging from the landscape,” Gula said.
The drought-resistant grasses grow in six inches of soil on the roof, with wildflowers to add color in the spring. Rain that isn’t absorbed by the plants flows into a gutter. In the summer, a drip irrigation system keeps the grass green, reducing fire danger.
The plants and soil added about 150,000 pounds to the roof’s weight. Because the pavilion was designed for heavy snow loads, it was strong enough to handle the extra burden, Gula said.
Installing a green roof cost nearly twice as much as the high-end metal roof in the pavilion’s initial plans. Not having to install air conditioning helped offset the cost. The roof also will last longer, because the soil and plants protect the roof’s membrane from solar rays, Gula said.
“Going green is a commitment that means a few extra bucks upfront,” said Bostwick, the casino’s spokesman, “but it flows with the tribe’s long history of stewardship of this land.”