“They were a group of single women, empty-nesters, who each lived in a single-family home and didn’t want to live alone anymore,” Ms. Powers said. Aria, which opened in August, now includes men and residents of every age.

The self-determination of Aria’s founding residents is a hallmark of cohousing, along with clusters of houses or living spaces gathered around shared public areas. The heart of each community is the common house, or a space, where group meals are offered once or twice a week, together with activities and events. Houses are connected by pathways. Instead of a lawn mower in every garage, there often are no attached garages. Cars are exiled to peripheral parking areas, while a single, shared lawn mower suits the needs of everyone.

The common house is also where residents gather to make decisions about governance. Cohousing communities are most commonly set up as homeowners’ associations, with residents adhering to legally binding bylaws. Yet with cohousing, there is one critical difference.

“We are our own board, since most cohousing communities operate by consensus,” said Karin Hoskin, executive director of the Cohousing Association of the United States and a resident of Wild Sage, a cohousing community in Boulder, Colo. Though typically not required, residents are expected, or at least encouraged, to attend the group dinners and pitch in where they feel most comfortable: maintaining the grounds, for example, or serving on committees. When it comes to finalizing decisions about maintaining common areas, or questions like noise levels in public spaces after certain hours, the entire community must agree. The objective, Ms. Hoskin said, was to regain a lost sense of community.