PETERBOROUGH, N.H. – At a time when the housing market remains in a slump, consumer demand is growing for energy efficient homes that are kinder to the environment. And it’s not just individual homes that are going green. Increasingly, it’s entire neighborhoods.

With its mix of single-family, duplex and 4-unit buildings, organic farm, shared office space and common house, the Nubanusit Neighborhood here is an earth-friendly cohousing community, where residents own their own homes but share common space.

Lono Hunter, an aspiring architect who spent years studying green building construction and design, moved to the eco-village in April.

“It’s a little bit of an experiment,” Hunter says. “You can do it yourself – you can add features, you can add insulation – but in terms of actually living in a way that maybe has some potential to help the environment, I think you need the power of numbers.”

There are 113 co-housing communities around the country, and about 90 more in the works, said Craig Ragland, executive director of the Cohousing Association of the United States. Though sustainability has been a longtime trend in cohousing, Ragland said he’s seen increased interest in recent years toward the use of solar energy and other green building practices. Some communities have gone so far as to pay carbon offset fees, he said.

Meanwhile, builders of more mainstream developments also are embracing green neighborhoods.

Recent market research by McGraw-Hill Construction projects that the green building market could account for $20 billion in sales, or 10 percent of the overall homebuilding market, this year. Those figures are expected to double within five years.

Starting next year, the U.S. Green Building Council will begin applying a version of its Leadership in Energy Environmental Design rating system to entire neighborhoods rather than single buildings. A pilot program launched early last year attracted so much interest that officials accepted more than 200 proposals, twice the number they sought.

Nubanusit Neighborhood and Farm is not part of the pilot program, but its 29 homes are being built to the council’s highest certification standards.

The homes feature triple-glazed windows, seven inches of recycled insulation and other materials chosen for longevity. The neighborhood is heated by a wood-fired boiler using pellets from a neighboring town. Sixteen homes have sold, and residents began moving in last year.

Shelley Gougen Hulbert is one of the community’s co-founders and plans to move in after selling her current home, which features recycled insulation and solar panels but is not as green as her duplex at Nubanusit.

“We were aware of green but we’ve become so much more aware,” she said. “The idea was that if we were going to be developers, and we are whether we like it or not … we wanted to hold ourselves to the highest standards because not only did we recognize that we could lessen our carbon footprint and our impact on the environment, but we could have an effect on every other person who chose to buy in.”

The property once belonged to a former governor in the mid-1800s and later was home to a popular inn. But it had been abandoned for years when the Hulberts and another couple purchased it in 2004. They were motivated not only by the idea of farming within a close-knit community but by the prospect of preserving a large piece of open land, she said.

Ragland, the cohousing director, said that’s typical of such communities.

“A key idea that has become common in both rural and suburban communities is preserving natural green spaces, rather than just not destroying the land as badly, which is sort of what any development is – it’s scraping the life off the land and then putting cement and a thin veneer of life back on,” he said.

Builder Robert Thornton is building 350 homes in Ocean View, Del., following standards set by the National Association of Home Builder’s Green Building Program. Homes include high performance insulation and efficient furnaces inside, and irrigation systems outside with sensors tied to weather satellite information. Construction waste was kept to a minimum and recycled onsite.

Thornton said home buyers are clamoring for the high-end homes, though it has been difficult at times to persuade trade contractors to try new materials, work on waste reduction and pay attention to environmental concerns.

“A lot of the builders out there are nay-sayers,'” he said. “Once they see that’s where their economic impact is going to be most effective, they get on board. They see that’s what our customers are demanding.”

Thornton traces his decision to build a green neighborhood to a plane ride he took over the property soon after he acquired it.

“I looked at the trees from a Cessna a half mile up and I said there’s no way I can cut these things down,” he said. “At that time, green was just starting to come in, but I did it really for the right reason. I just didn’t have the heart to destroy it.”