Fifty-nine point seven million Americans were living in a multigenerational household as of March 2021, 18% of the U.S. population and a share that has quadrupled since 1971, according to Pew Research Center’s analysis of Census Bureau survey data. Buried inside that number is a specific, deliberate housing move that real estate agents and elder-law attorneys say keeps multiplying: parents and their adult children buy one property together, then use zoning tools such as an accessory dwelling unit permit or a formal duplex conversion to split it into two legally distinct living spaces under one roof and one mortgage. It isn’t a spare bedroom with a lock on the door. It’s two kitchens, sometimes two separate utility meters, and often two separate entrances, arranged so a father in his late sixties and his daughter in her thirties can own the same address without sharing a single morning routine. The math driving it is blunt. Buying alone at today’s prices is out of reach for a lot of people, and building two households under one roof is often cheaper than buying two separate houses in the same neighborhood.
The Money Behind the Move
Half of lower-income adults living in a multigenerational household say the arrangement helps them financially. That figure drops to 36% among middle-income adults and 24% among upper-income adults, according to the same Pew survey of more than 9,600 U.S. adults. Caregiving runs a close second: a third of people in these households cite caring for a relative as a major reason for the arrangement, and one in four point specifically to looking after an adult family member rather than a child. Money and caregiving are exactly what a legal unit split is built to solve at the same time. Splitting a house on paper lets a family share one down payment and one tax bill while still giving each generation a door it can close.
The Older Half of the Equation
The people moving in are getting older, too. Twenty-two percent of adults 65 and older lived in a multigenerational household in 2023, up from 17% in 1990. Among adults 85 and older, the share climbed from 18% to 25% over the same stretch, according to Pew’s most recent analysis, published in December 2025. The same research found a poverty rate of just 6% among older adults who don’t live alone, compared with 20% among those who do. That gap helps explain why living near family, instead of alone in an empty house or in assisted living, has become the more common outcome for people past 65. None of this is new information to a builder or a zoning office. What’s changed recently is the paperwork: more states have loosened rules around accessory units, which shortens the legal path to a second kitchen and a second address on one lot.
Photo: Nur Fadhillah Fajarudeen / Unsplash
What “Separate” Actually Means on Paper
The split usually takes one of two forms. Some families build or convert an accessory dwelling unit, a self-contained space on the same lot with its own kitchen and bathroom, permitted apart from the main house. Others go further and legally convert a single-family property into a duplex, so each generation holds a distinct, deeded unit rather than an add-on room. Either way, the goal is the same: a parent who wants adult children a short walk away, not on the other side of a shared hallway, and adult children who want to help without turning into an unpaid, on-call caregiver. Surveys on the subject keep landing on the same tension. Families want to be near each other. They also, genuinely, want to be left alone.
Boomers Complicate the Timeline
The scale of who’s aging matters here. There were 69 million Baby Boomers as of 2022, 21% of the U.S. population, and they still held 38% of the country’s owner-occupied homes, according to Freddie Mac’s economic and housing research group. Freddie Mac’s own modeling projects a gradual decline in Boomer-owned households over the next decade rather than a sudden one, which leaves adult children with a genuinely open question about timing. Move a parent now, on their own terms, or wait for a fall or a diagnosis to force the decision later. Buying and legally splitting a house is one way families are answering that question before it gets asked for them.
A legally divided house doesn’t fix the housing shortage, and it doesn’t make caregiving free. What it does is turn an emotional decision into a real estate transaction with its own deed and its own lock on a second door, which, for a growing share of the country, is starting to look less like a compromise and more like the actual plan.
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