JoAnna and Ken Allen wanted to relocate from suburban Baltimore to the East Bay to be closer to their three children and four grandchildren. But JoAnna was reluctant to give up the friends and activities she had established after 45 years in Maryland and didn’t know what she’d do out here. “I was imagining living in an apartment and reading books all day long,” she said.

The couple heard that a new senior cohousing project called Phoenix Commons was going up in Oakland, so on the way to the airport after a visit to the Bay Area in 2015, they stopped in to see it. “By the time we landed, I had already decided to buy in,” JoAnna said. Two weeks later, they came back to select a unit, and in 2016, they moved in.

Cohousing is a community where people own their individual homes plus a share of common areas such as outdoor space and a clubhouse with kitchen, living and dining rooms. They typically prepare and share meals several times a week and become more than just neighbors.

They are usually structured as a condominium with a homeowners association, but are self-managed. Owners (called members) collectively make decisions, usually by consensus. Committees oversee the financial, administrative, maintenance and other work normally handled by a management company, although they may hire outsiders for some jobs. Each member is expected, and in some cases required, to pitch in, whether it’s cooking, cleaning or fixing the Wi-Fi.

Senior cohousing is a newer type designed for people who want to avoid the isolation that can happen when families move away and friends die. “There is a natural loss of community as you age. There is no way to replace it with jobs or schools,” said Christian Zimmerman, whose company developed Phoenix Commons, where he also lives.

JoAnna Allen called it “a great antidote to the loneliness that hits a lot of people.” She was familiar with cohousing, but her husband, Ken, was less gung ho. He came around “once he realized he could still have his privacy and independence,” she said.

The couple purchased their 880-square foot unit for $636,000 with cash from the sale of their former home and a loan from First Republic Bank.

“Everything I did in Baltimore, it’s better here,” JoAnna said. She is teaching meditation in a prison, joined a writing group and bought a kayak, which she can launch from the Phoenix Commons boat dock. Ken found his niche as the community’s tech guru, and doesn’t mind walking away from communal meals “when he’s had enough chitchat,” she said.

Ken’s only complaint is that “there are sometimes too many meetings,” he said.

There are 168 established cohousing communities in the United States including 14 that are senior-focused, said Karin Hoskin, executive director of the Cohousing Association of the U.S.

Some of the senior communities have minimum age requirements; others don’t but end up with mostly seniors because they lack the space and amenities most families want. In California, senior housing developments generally can exclude residents younger than 55 if they have at least 35 units and meet other requirements.

The senior cohousing communities in California are Phoenix Commons, Mountain View Cohousing Community, Glacier Circle in Davis, Wolf Creek Lodge in Grass Valley (Nevada County) and Walnut Commons in Santa Cruz.

When members get sick, other members usually will help with meals or trips to the doctor, but “this is independent living. There is nobody there to take care of you if you really need greater levels of care. We are very clear about that,” said Katie McCamant, owner of CoHousing Solutions, a development and consulting firm.

Most cohousing communities are created by a group of people who find a property, put up cash to buy it, deal with planning and zoning, hire an architect and contractor and get a construction loan. As people buy homes, the construction loan is paid off. This can take three to seven years.

Anne Geraghty started organizing a cohousing community five years ago but “it went much slower than I expected,” she said. Her original group disbanded in 2015, but now a second group is purchasing land in Sacramento to build cohousing called Washington Commons, most likely for seniors.

“Most people want to stay in their home as long as possible, because they want to control their own life. And then they go into a place where their life is controlled by others,” Geraghty said. “I love the idea of deciding what my future’s about and not being run by a corporation.”

Phoenix Commons, which opened in March 2016, is unusual because it was led and financed by a developer. Zimmerman’s company, AEC Living, had built nursing homes and assisted-living facilities. Zimmerman, 70, wanted to retire in senior cohousing so he developed one, with help on social aspects from early members.

The four-story project sits on the tidal canal that separates Oakland from Alameda, hard by the Park Street Bridge and Bay Trail. At least one owner of each unit must be at least 55.

It has 42 units, including a two-bedroom guest suite. Common areas are on the ground floor, for security. Units are one floor with extra-wide doorways, no-threshold showers and other aging-friendly features. Units range from 732 to 1,104 square feet. Some have balconies; all have washer-dryer hookups.

There are 10 units on the market at prices ranging from about $520,000 to $730,000. Homeowners association fees are about $650 per month. The complex has 36,000 square feet of common space, including a kitchen and dining room, gym, hot tub, waterfront promenade, central laundry, dock and garage with single and tandem parking options. A freight train comes by several nights a week, but units with sound issues have triple-pane windows.

About half of its members are still working, including a teacher, lawyer, physical therapist and social worker. Joan Taylor had been living in a “very nice condo” in Alameda, but “I felt isolated. I lived there two years and never knew anyone,” she said. At Phoenix Commons, “there is accessibility and community.”

Owners can sell cohousing units to whomever they want as long as they don’t violate antidiscrimination laws. Buyers must meet age requirements in senior communities that have them.

Cohousing is “a peculiar market,” said Bob Miller, a member of Wolf Creek Lodge. Buyers “are not buying real estate. They are buying into a very special community. It’s not going to work for everybody.”

Prices at his 30-unit community range from $300,000 to $500,000. “For Grass Valley that’s not cheap,” he said. “It’s significant to buy in,” but ongoing expenses are “very economical.” Association fees run about $360 per month.

There’s no solid research on cohousing resale values, but in 2010, Davis appraiser Lee Bartholomew did a limited study looking at new and resale prices at five all-age cohousing communities in Northern California. Initially, they sold for more per square foot than standard condos, but they also have green-building features that add to construction costs and appeal to cohousing buyers. From 2008 through 2010, they appreciated faster than standard condos, he said.

Lee hasn’t updated his research, but said, “My instinct is that premium is gone,” perhaps because as projects age they lose some luster. However, he added, “I suspect that as we have more housing shortages in highly developed urban areas, this concept will get more cachet. It’s an interesting housing model at a time when our country is so divided. These projects force people to relate.”

The challenge for senior cohousing is keeping it vibrant as members age. That’s an issue for all retirement communities, but more so for cohousing because members do so much.

“It’s a lot more work than we ever realized. It’s a good thing most of us are retired,” said Paul Berry, a member of Mountain View Cohousing, a “de-facto” senior community that opened in 2015. Members of the 19-unit complex are not sure how they will keep it going strong. “It’s a serious risk,” he said.

In Denmark, they deal with this by requiring new people moving into senior co-housing to be 65 or younger, said architect Charles Durrett, who has designed many co-housing projects.

When Glacier Circle in Davis, the oldest senior co-housing project, started organizing in 2002, its youngest member was 72. When it was finished in 2006, “there were quite a few of us who were able to do stuff. We formed a garden committee, an architecture committee, the fun committee,” said Stan Dawson, a founding member. “As people aged, we had to rely more and more on hiring people to do things.” It now has a cook who prepares four or five meals per week and someone else who cleans up.

Four of the eight units are owned by the original members. One three-bedroom unit, now priced at $525,000, has been on the market since August. It originally sold for $464,500.

Dawson misses the men who died, and as president has more work than he’d like. The community rarely plays boules, a game like bocce ball, anymore, but members still share meals and attend weekly meetings. “We are friends, sometimes trying to be family,” Dawson said.

Kathleen Pender is a San Francisco Chronicle columnist. Email: kpender@sfchronicle.com Twitter: @kathpender