Relatively few families occupy the Boston region’s family-size homes

Here’s another reason why housing is so expensive in the Boston area: A sizable share of larger homes—those with at least three bedrooms—are occupied by older households of only one or two people or by groups of unrelated roommates.

That is according to a comprehensive new analysis from the Metropolitan Area Planning Council, which crunched census date from 2012 through 2016, as well as real estate data, for 13 municipalities: Boston, Brookline, Cambridge, Chelsea, Everett, Malden, Medford, Milton, Newton, Quincy, Revere, Somerville, and Winthrop.

The major finding was that many, many larger apartments, houses, and condos were filled with people who might not really need the space. For instance, one-quarter of larger units—more than 50,000 for-sale and rental homes—were occupied by over-55 households with no more than a couple of residents.

What’s more, families with children occupied just 39 percent of all the larger for-sale and rental units in the 13 municipalities analyzed. And roommate households—pairs or groups of unrelated individuals—occupied more than one-third of the larger rental units.

Metropolitan Area Planning Council

Such realities help keep the Boston area’s rents and prices high compared with much of the rest of the U.S.—in particular for families, which have to compete with the roommate households and the older empty-nesters for those larger spreads. This goes a long way toward explaining why some municipalities in the region—Boston proper most prominently—are losing families with children.

“Our analysis confirms the dire situation for Greater Boston’s families with children,” the Metropolitan Area Planning Council report said. “They are disproportionately cost-burdened and overcrowded in their housing. Their problems don’t result from an absolute lack of units, but rather from who is occupying the family-sized units that do exist.”

The solution, though, lay not necessarily in building more condos and apartments with at least three bedrooms. According to the MAPC, it’s instead more about building the smaller units that developers are already keen on building because of what they see as stronger demand for such spreads and the construction costs for larger ones.

More studios, one-bedrooms, and two-bedrooms would provide more options for younger people otherwise sharing those larger units. And the smaller homes would also provide options for older residents looking to downsize, according to the MAPC. This would all open up more of those larger units to families with kids and decrease competition in that sphere—which might in turn being down rents and prices.

Of course, prospective buyers and renters would still face myriad other challenges, including an abundance of more affluent competitors—the Boston area has an unusually high share of renter households pulling in at least $100,000 a year, for instance—and those high construction costs. Never mind that many towns and cities have zoning regulations that discourage the sort of multi-family housing the region desperately needs.