PAST A DRAB TWO-STORY Bozeman motel, its parking lot jammed with pickups and a marquee out front announcing GUN SHOW TODAY, past the pawnshop with whitewater kayaks stacked in the window, past the gingerbread-trim Victorians just off Main, past the SEE GRIZZLY BEARS, EXIT NOW! billboard on Interstate 90 and the nouveau timber mansions squatting resolutely on the bald land, a dirt road leaves the pavement and veers up a gravel drive through a keyhole in the hillside. Only then do you see it: a long, narrow house with a vaguely wavy metal roof, improbably modern, settled into its grassy hollow like a snowdrift and wearing its honey-gold siding like a skin. Surrounded by rural, ranchy Montana, it is the sleek new incarnation of sustainable architecture.

But as incongruous as it seems, it's not the only house of its kind around here. Its owners, husband-and-wife designers Brett Nave and Lori Ryker, have conceived half a dozen such homes in and around Livingston, about 30 miles south of Bozeman, as part of their crusade to modernize western architecture—and green it up in the process. This house is their personal laboratory of sustainable building, and the boxy, wood-clad studio adjacent is their architectural HQ. Ryker, who wrote the book on modern sustainable design with 2005's Off the Grid: Modern Homes + Alternative Energy, calls their aesthetic "contemporary vernacular," drawing on Montana's frontier-cabin legacy but spiffing it up with a slew of cool eco-finds like denim insulation, sunflower-seed plywood, and wheat-board cabinetry.

"One of our big goals is to make beautiful buildings and help people understand that green materials don't predetermine a certain style," says Ryker, whose new book, Off the Grid Homes, is due out in May from Gibbs Smith. "Yeah," Nave translates, "we're not talking about Earthships."

Nave, 36, has thinning brown hair, a puckered chin, and a slow, mumbly drawl left over from his childhood in Birmingham, Alabama; he's funny in an understated, joke's-on-him kind of way. All of which makes him the alter ego of Ryker—sunny-blond and serious—who was raised in Texas and has a master's in architecture from Harvard. The couple met in Auburn, Alabama, more than a decade ago, started Ryker/Nave Design in 1995, and moved to Livingston three years later. In addition to her design work, Ryker, 43, teaches Remote Studio, a field program for architecture students that combines hands-on design with backcountry adventure to explore, as she puts it, the "intersection between nature and creativity."

When it came time to build their own live/work compound on 40 acres of khaki wheatgrass just west of Livingston, in 2004, they chose a rutted-out old cow wallow as their construction site, deliberately building low—the 2,300-square-foot house steps down seven feet from west to east, and the roof is 18 feet tall at its highest—so that the complex is all but invisible to their neighbors.

As much as the house belongs to this ridge, and to the Montana prairie wavering off in all directions, stylistically it's a surprise: part wooden houseboat, part luxe and streamlined lean-to, part modern ranch—Lincoln Log brown and as skinny as a double-wide. Nave and Ryker hunted for local, recycled, and sustainable products that were practical without being boring, innovative but not exorbitant. All told, the 4,000-square-foot project cost roughly $175 per square foot, excluding the cost of the land. Nave estimates that the national average to build green today is about $225 per square foot—only about 10 percent more than the conventional route, although where you live is a big factor.