BELFAST, Maine — Former U.S. Sen. George Mitchell grabbed a spade and dug right in Tuesday afternoon as the crowd attending a groundbreaking ceremony for the Belfast Cohousing & Ecovillage development erupted in cheers and whistles.

The moment has been a long time coming for the planned community, which began nearly five years ago.

“This project is unique in so many respects,” Mitchell said.

He ticked off ways that the 50-member, 42-acre community is different from typical housing developments, including its commitment to energy efficiency, its environmental concern and its “walkable” design. Mitchell said that while some may disagree that people need to work to fix real problems with the environment, he’s glad that the Belfast Cohousing members aren’t among them.

“The problem is so large and so vast in scope, there’s a tendency on the part of many individuals to say it’s too big for me to solve it,” he said. “We know it will take the combined efforts of millions and perhaps billions of people all over the world.”

Mitchell was joined in the groundbreaking by Belfast Cohousing members Pia Gibson, 8, and Mike Shannon, 76. Pia’s smile was the brightest thing on an overcast day as she threw a shovelful of rich soil onto the ground where the community’s common house will be built sometime over the next year.

When asked what her favorite part of co-housing is, she didn’t hesitate.

“Having my friends next door,” she said.

Her mother, Sanna McKim, is a co-founder of the group, and said that her daughter’s friends range in age from 1 to 76 years old, which is one of the attractive aspects of co-housing. She said she was glad to have the ceremony to mark a milestone for the group — finally building after years of planning.

“I’m thrilled to be able to build on the momentum of a bunch of really good design decisions,” she said.

Her husband, Alan Gibson, is a co-founder of the Belfast-based architecture and construction firm GO Logic, which is building the 36 energy-efficient houses which will make up the community.

The homes will be fitted with solar panels and in the middle of winter will require almost no supplemental heat, according to GO Logic. The houses are a selling point for the project, but new member Lindsay Verite of Camden said they weren’t what convinced her to sign up, along with her four young children.

“I have enthusiastically and with pride joined Belfast Cohousing,” she said at the ceremony. “Community is what I’ve bought. And the amazing, energy-efficient, well-thought-out house is a bonus.”

Work actually has begun on a few of the buildings, which are being framed out by construction workers before the ground freezes. The first residents are planning to move into their homes on May 15.

Margie Shannon, 75, who has been living off the grid in Knox for 22 years along with her husband, Mike Shannon, is among them. She said she is very excited to make the move.

“It’s the right thing to do,” she said, even though she’s scrambling to figure out where to put her collection of seven spinning wheels.

The view from her new place is expansive, encompassing a sweep of fields and forests. She was enthusiastic even though her house has yet to have walls and windows.

“It’s just going to be great,” she said. “Today, looking down at the house, I just had the urge to pick it up and hug it.”

The group is still seeking a few good members to join them and purchase homes, which have a base price range from $150,000 to $330,000, depending on size. In addition to their own houses, the members will share a common house with a big kitchen, 40 or so acres of land for farming, gardens, pathways and pasture, and the intentional community.

Many Belfast dignitaries came to the ceremony to lend their voices in the cheers that rose from the crowd. City Councilor Marina Delune was among them.

“It’s our goal to have Belfast be a very energy-efficient city, and this is thrilling,” she said afterward. “It’s something to be really proud of — and I think that this is the future of housing.”