There’s a coming population boom in the United States that is going to put its housing stock—and maybe its entire housing system—to the test.

There are currently more than 58 million people in the U.S. aged 65 or older, a number that’s expected to climb to over 80 million by 2040. Within the next decade, there will be 25 million people who are older than 75. According to a new report, the places where these older adults live are simply not designed for the needs of an aging population.

The report, Housing America’s Older Adults, was issued by Harvard University’s Joint Center for Housing Studies (JCHS). It explores the many ways the housing stock of the U.S. has been built without the needs of older people in mind, from a lack of accessibility features for those with mobility challenges, to geographic isolation from services, to the sheer dearth of affordable housing for those with limited means.

“We have deficits on all these fronts,” says Jennifer Molinsky, who led the creation of the report as project director of the Housing an Aging Society Program at the JCHS. “We worry about the safety of the house, the accessibility of the house, and also its connection to all the things that you need in a community and a neighborhood.”

These issues are concerning because the vast majority of older adults live in their own homes either as owners or renters, and only tend to leave when they are forced to by poor health. Despite the high prevalence of ambulatory challenges among older adults, very few of these homes are designed to accommodate what the report calls the “three foundational features” of accessible housing: single-floor living, no-step entries, and wide hallways and doorways. According to the most recent data, less than 4% of homes nationally have all these features. Less than 1% are wheelchair accessible.

Age-appropriate homes do exist, of course. The report notes that four million older households live in age-restricted, or retirement, communities. Another 1.4 million older adults live in nursing homes. These options, though, are often financially unattainable to older adults who tend to live on fixed incomes. While many homeowners have wealth associated with their home equity, non-white homeowners tend to have few other resources, according to the report. Renters, particularly non-white renters, have even less net wealth. For most older adults, moving to a home suited to their old age is unrealistic.

Some alternatives are emerging, including compact accessory dwelling units that cities are increasingly allowing to be built on the lots of single-family homes, or various forms of cohousing where older residents can share building amenities and access to health services. “A lot of those are a little bit niche right now,” Molinsky says.

But maybe they shouldn’t be. “House sharing is a great example,” Molinsky says, referring to the estimated 913,000 older adults who live exclusively with unrelated roommates, a figure that’s doubled since 2006. “It’s a particularly great idea because it doesn’t require building new houses. We’re just using what we’ve got more efficiently.”

The report highlights a few promising models for rethinking how older adults can live their later years. One is a kind of cooperative housing organization known as a “village,” where paying members band together to share access to caregivers and medical assistance while also building community to combat social isolation.