Standing in her living room, Margaux Jansen looks across the street with anxiety. She’s worried, she said, about what life in this quiet Paoli neighborhood will be like if a luxury assisted-living facility got approval to move in across the street.

“It just doesn’t fit. It doesn’t work," she said. “It’s going to change everybody’s lifestyle here."

Jansen and dozens of her neighbors have banded together to oppose a developer’s plan to build a three-story, 127-unit assisted-living facility in their community.

They worry about how Solera Senior Living would fit into this sleepy slice of suburbia off Lancaster Avenue. Even though the plan is in its early stages, residents are concerned about stormwater runoff, encroachment on privacy, parking, bright lights, traffic congestion, the risk of wandering dementia patients, and the burden that another senior facility will place on volunteer firefighters and EMS, a group already stretched thin.

These folks have told Tredyffrin Township officials their concerns about the proposal for the Russell Road parcel, currently occupied by vacant office buildings, and have met with developers at Alterra Property Group, which Jansen and her neighbors credit with trying to work with them and address concerns.

“We have met with the neighbors, planning commission, and various stakeholders several times,” Matthew Pfeiffer, director of acquisitions for Alterra, said in a statement, “and we are working in good faith to incorporate comments and feedback to create a project that is well-received by the community and fits with the context of the neighborhood."

This conflict comes at a time when the market for senior-living communities is growing to fill the needs of an aging population, one that needs not only physical assistance but also care for Alzheimer’s and dementia. The Solera property is set to include a memory-care unit.

“The demographic trends of aging in the immediate area and across the country are undeniable, and will continue to support a need for more senior-living facilities to address our aging population,” Pfeiffer said. “Also, increasingly more elderly people want to live in facilities that are near their children and grandchildren.”

In all, there are nearly 29,000 assisted-living communities — with almost a million licensed beds — in the United States, and 1,000 such facilities in Pennsylvania, according to the National Center for Assisted Living. Assisted-living complexes offer a lower level of care than nursing homes or skilled-nursing facilities, but more than independent-living complexes.

Steve Monroe, managing editor of the SeniorCare Investor and an industry expert, said these communities are more popular in the greater Philadelphia area than in other parts of the country. Episcopal and Presbyterian senior-living homes, as well as high-end continuing-care retirement communities on the Main Line, started the trend.

“For years, it’s been extremely well-accepted" in the region, Monroe said. “It’s been around, and success begets success.”

He doesn’t see the popularity decreasing anytime soon, he said, but “the whole industry is questioning what the baby boomers are going to do."

In Paoli, existing senior communities include Highgate at Paoli Pointe, Sunrise of Paoli, and Daylesford Crossing, just across Lancaster Avenue and the train tracks from the proposed Solera site. A couple of miles down the road in Wayne, Brightview “resort style” senior living is set to open in April. In neighboring Malvern, crews are working on Echo Lake, a retirement community featuring an “amazing setting, innovative lifestyle, with a focus on aging well," according to its website.

On Russell Road, residents said they wonder whether another community is needed.

“Are there advantages of putting so many facilities in a community?” said Jeff Hyson, who has lived there for 19 years. “What are the costs and benefits of the township promoting ALF [assisted living facility] development?”

One cost: a strain on emergency workers, said Eamon Brazunas, the chief of the Berwyn Fire Company.

“Unfortunately, there’s a need for these type of facilities, no doubt,” he said, “but the people that really get hurt by this are us.”

When it comes to these kind of communities, fire and EMS officers usually expect to respond to one call per bed per year, he said. But that isn’t always the case. In the first year that Daylesford Crossing was open, for example, Berywn and Paoli fire companies exceeded that number, he said.

The openings of Brightview, Echo Lake, and perhaps later Solera are "going to be impactful,” said Brazunas, whose squad works closely with other volunteer departments in Paoli and Radnor.

Neither Brazunas nor Russell Road residents say they harbor hard feelings toward Alterra. Pfeiffer, its director of acquisitions, pointed out that the facility would increase tax income without putting pressure on the school system.

“They’re willing to work with us,” said Bruce Walk, who has lived in the neighborhood for 24 years.

Jansen added with a laugh: "It’s not their fault they bought the wrong property.”

Now, she said, she just hopes Tredyffrin officials do right by the neighborhood residents, especially because such a facility is permitted there.

In 2012, the township changed the zoning code to allow for assisted-living facilities in the commercial district, according to Matt Baumann, assistant township manager and director of planning and zoning. Since then, two communities — Daylesford Crossing and soon-to-open Brightview — have been constructed in the commercial zone, he said in an emailed statement. The township declined to comment on the preliminary plans for Solera, which would be the third such facility constructed in the commercial district.

To Jansen and her neighbors, the zoning change allowed these facilities to move in without officials giving much thought to how they fit in with the surroundings, she said.

“Code doesn’t always mean it’s working,” she said. The neighbors said their narrow street, with a 25-mph speed limit, doesn’t look much like a commercial area to them.

Jay Halsey, another neighbor, said: “We’re not against development. We’re just looking at the effect of this ALF in this township.”

Ultimately, Jansen said, her group — which totals 60 to 70 neighbors — knows Solera will likely be built in some form.

“Our goal is to continue to voice our concerns," she said. “We just don’t want to go, ‘Oh, well.' ”

Solera currently manages the Preserve at Clearwater, a Florida community offering assisted living and memory care for nearly 90 residents, and is in the process of opening properties in Denver; the Chicago suburb of Highland Park; and Kensington, Md. The price and details of the Paoli development were not yet available.