As Route 170 branches to Route 169 and turns off onto West Springfield Road, the pavement ends, the forest canopy dilutes the sun, and the metallic sounds of civilization concede to nature’s pastoral murmurs in Carroll Plantation.

Only utility poles and the occasional jet contrail painted across the sky remind that the journey along the narrowing dirt roads of Maine’s backwoods is not a trip back in time as well. Then, at the end of a winding driveway, amid a large clearing in the timberland, stands a structure so strikingly modern that it evokes science fiction, like a glimpse of Jules Verne’s Earth circa 2153:

A geodesic dome.

“Interesting, isn’t it?” Cliff Severance says by way of greeting.

A 52-year-old electrical engineer from Oak Hill, Va., Severance has been building the dome on 150 acres overlooking Bog Brook during vacations since June 2006.

With its 46-foot diameter built atop a one-story foundation and a cupola soon to be added, Severance’s vacation home is massive, 4,100 square feet among two 1,600-square-foot bottom floors and a 900-square-foot top floor. Severance will build a 29-foot diameter dome, a garage, when the main house is done. The project will take two more years.

He fell into building his dome-icile almost by accident.

“I originally was looking at building a traditional log cabin up here,” Severance said, “but my wife is a little more contemporary.”

Also an electrical engineer, Mary Severance, 48, found Natural Spaces Domes of North Branch, Minn., on the Internet. Natural Spaces, at naturalspacesdomes.com, is one of a half-dozen large firms nationwide specializing in geodesic domes, company owner Dennis Johnson said.

“It’s not like what the rest of my neighbors would have in Maine. That was the first thing that hit me,” Mary Severance said.

Severance’s dome is among 50 the company does annually worldwide, one of four the company designed in Maine, Johnson said.

The Severances declined to price their dome, but Johnson said his buildings start at $40,000 to $50,000 for a geodesic cabin, with houses starting at $75,000 to $100,0000. The most expensive, an 8,000-square-foot triple dome outside Pittsburgh, cost $1.9 million, he said.

Johnson described the Severances as typical dome-sters: environmentally minded, well-educated build-it-yourselfers seeking the advantages domes offer over traditional homes. Not that their choice has drawn universal acclaim.

“One comment came from a truck driver who hauled in some of the supplies,” Severance said. “He took a look at it and said, ‘What the hell are you doing building a hippie dome?’ It’s got that stigma.”

Yet a dome’s advantages over traditional modern housing, Severance and Johnson said, include:

. Fewer building materials. The same square footage built by typical design would use one-third more materials.

“What we saved we spent on windows,” Mary Severance said. “In Maine, you don’t have a long or superhot summer, so I wasn’t afraid to put all kinds of windows and skylights in.”

. Superior sturdiness and insulation. Built on a network of struts arranged on great circles, or geodesics, lying on the surface of a sphere, the geodesics intersect to form triangular elements that are very rigid and yet distribute building stress and weight across the entire structure. That makes domes very tough, the only man-made structures whose strength increases proportionally as they increase in size.

“We have had domes go through hurricanes and tornadoes and survive without anything more than a broken skylight,” Johnson said.

His domes have an insulation value of R55 to R66. Dome owners, he said, have been known to spend only $450 annually on natural gas to heat their homes.

. Lovely natural light and acoustics. Not counting the cupola’s five bay windows, Severance’s dome will have 15 skylights and two emergency windows along its top, with six more windows on the side and three basement windows.

“In conventional houses, everybody wants a cathedral ceiling, and the dome’s got it naturally,” Johnson said.

“The quality of light should be spectacular,” Mary Severance said.

And while the bottom floor will have the squared rooms of a traditional home, “you have to really watch what you say. The way the dome is shaped, you can hear people across the room as if they’re standing next to you,” Severance said.

The natural light will save electricity, enough so that Severance probably will not have to pay for it when he installs a windmill generator, he said.

Building the dome has felt awkward, especially because it’s so high – no scaffolding – but it is not especially difficult, said Peter Amodio, 58, an industrial arts teacher from Salem, Va. Amodio is among a handful of friends and family, including Russell Felmey, Dustin Kecki, Les Severance and Jim Golden, who have helped out.

“It’s a challenge to build because there are so few corners. Everything is angular,” Amodio said. “It’s not as easy to build as a conventional home.”

Johnson provides customers a three-day dome building class in Minnesota, videotapes, instruction manuals, and sells the dome’s specialized parts.

Finding a contractor for a dome might be difficult, said Dennis Dunbar of Dunbar Custom Homes of Canaan.

“A lot of contractors are scared of them. They’re too nonconventional for most,” said Dunbar, who just built a Natural Spaces dome for Cynthia Greaton of Wayne.

“It wasn’t bad when I got into it. I thought it would be mind-boggling,” he said. “It took longer than a conventional house just because of all the angles to the dome. The finish work was tough.”

Shingling the dome meant treating each of its dozens of triangular surfaces as an individual roof.

“The shingling is, we’ll call it a nightmare,” Dunbar said. “You only have three full shingles and the rest have to be cut individually.”

Severance probably will contract out the shingle installation because it’s such a critical job, he said. His wife hopes to live in the dome nine or 10 months a year once they retire.

“I think we’re going to end up with a showplace, eventually, and being that I wanted something more contemporary, well, you can’t get much more contemporary-looking than this,” Mary Severance said. “One of the reasons we really wanted to do this was to leave a legacy for our son. Craig will have a home up there, if he wants it, after we’re gone, and I hope he can say, ‘Hey, my mom and dad did this for me.'”