Transforming schools, convents and motels makes the most sense because the original buildings are often the right size and layout to convert into housing, Mr. Keenan said.

“Our mission is to find a new purpose for abandoned properties,” he said. “The question we try to answer with every project is: How do we use real estate for social change?”

The organization spent $1.1 million to renovate and convert St. Peter’s convent into a building with 24 private bedrooms, shared bathrooms, a community dining room and a number of other shared-living spaces, such as the library, a television room, a sunroom, a front porch and a basement with a pool table. Building such a dwelling from scratch could have cost $5 million or more, Mr. Keenan estimates.

The decision to convert the convent into a shared-living space rather than carve it into separate apartments was made not only because it made architectural sense but also because Build With Purpose sees a need for a more diverse range of housing options for older adults, Mr. Keenan said.

While the elderly in Bergen and Passaic Counties might desire separate units, because they are accustomed to living on their own, Mr. Keenan believes their health and well-being might improve from being in a more communal setting, where residents can rely not only on each other but also on the building’s 24-hour staff.

“It’s worked out very well,” said one resident, Fran McKee, who moved in two years ago.

Ms. McKee acknowledged that eating every meal in a common dining room and spending so much time around others “definitely took some getting used to.” But she has come to really appreciate the ties to fellow residents and to St. Peter’s Elementary School, whose students visit often and invite the residents to their school plays and other events.

The home’s porch looks out on the school playground, and plans are in the works for a therapeutic garden, which the residents and the children could plant and maintain together.