Infill Development Equips Cities to Face the Reality of Demographic Change
American households are changing and housing policy needs to change too.
America’s housing needs are changing because American households are changing and housing policy needs to change too. Our current housing markets consist of products that overlook a wide variety of life stages and consumer needs. Communities need housing types that match the households people actually live in today.
For much of the 20th century, local housing policy was built around a specific type of house and a narrow assumption about who would be living in that home: a married couple with children living in a detached single-family house. That household type still matters and communities should support families with children, but it is no longer the only pattern we should be building for.
In 2024, the U.S. Census Bureau reported that about 64% of U.S. households were family households, down from 79% fifty years earlier. The Census also found 38.5 million one-person households, making up 29% of all U.S. households, compared with 19% in 1974. The share of householders aged 65 and older has also increased from about one in five householders 50 years ago to more than one in four in 2024. (Census.gov)
This shift matters for development because housing demand is measured in households, not just population. A city can have stable or modest population growth and still need many more homes if fewer people live in each home. When the average household gets smaller, the same number of people need more housing units. That is especially important in older neighborhoods where large houses may be occupied by one or two people, while younger residents, workers, seniors and small households struggle to find attainable options nearby.
A housing market made up mostly of large detached houses and large apartment complexes leaves out a huge range of real needs: a retired widow who wants to stay near her church and friends but no longer needs a large house; a young teacher who wants a small apartment near work; a divorced parent who needs a modest home close to children; an adult child caring for an aging parent.
This is where incremental infill matters. The “missing middle,” a term popularized by Daniel Parolek and Opticos Design, describes house-scale buildings that provide more housing choices while fitting into walkable neighborhoods. ADUs, duplexes, triplexes, fourplexes, cottage courts, live-work units and small mixed-use buildings are not niche products. These are the housing forms that allow a community’s physical pattern to catch up with its demographic reality. These types are especially important when communities need more small and moderate-sized homes, rather than more large detached houses. (Pew Research Center)
In addition to supporting traditional nuclear families, housing policy can also provide options for other kinds of arrangements including intergenerational homes, smaller ADUs for single-parent homes near schools and jobs. A neighborhood with only one housing type is not family-friendly over a full life cycle. A neighborhood with many housing options can support people as their life seasons, styles and needs change.
The aging of the population makes this even more urgent. Harvard’s Joint Center for Housing Studies has warned that the number of older adults living alone in their 80s and 90s is projected to grow substantially, creating new demand for smaller, accessible, well-located housing. (Joint Center for Housing Studies) AARP has similarly emphasized the role of ADUs and age-friendly housing options in helping people remain near family, caregivers and community support. This last point matters because aging residents need not just affordability but also proximity to social infrastructure. Smaller homes in existing neighborhoods can reduce isolation and make it easier for people to age in place without being trapped in homes that no longer fit their needs.
From a policy perspective, this requires updating zoning policies that still assume an outdated household model. Most zoning codes allow one large home per lot but prohibit a small backyard cottage. They allow expensive detached houses but ban duplexes, require more parking than small households need and force every new unit through processes designed for larger, more complicated projects. These rules mismatch the housing stock with the population and make normal demographic change look like a crisis.
Our position is that communities should respond to shrinking household sizes by legalizing and supporting more incremental infill. That means allowing ADUs by right, legalizing missing middle housing in residential neighborhoods, reducing parking mandates, supporting adaptive reuse and creating predictable approval paths for small projects. It also means training local developers, lenders, builders, city staff and elected officials to understand that smaller households require more flexible housing choices.
Demographic change is not a temporary trend. It is a structural reality. Communities that continue to build primarily for yesterday’s household model will worsen scarcity, increase costs, isolate older adults and make it harder for workers and younger residents to stay. Communities that allow incremental infill can adapt without erasing themselves. They can add homes gently, make better use of existing infrastructure and create neighborhoods where people can remain through every stage of life.
Additional Resources
U.S. Census Bureau — Nearly Two-Thirds of U.S. Households Are Family Households
Key source for 2024 household composition, one-person households, and the long-term decline in family households.
https://www.census.gov/newsroom/press-releases/2024/families-and-living-arrangements.htmlU.S. Census Bureau — Home Alone: More Than a Quarter of All Households Have One Person
Useful Census explanation of the rise and geography of one-person households.
https://www.census.gov/library/stories/2023/06/more-than-a-quarter-all-households-have-one-person.htmlPew Research Center — The American Family Today
Helpful broader context on smaller families, changing household composition, delayed marriage, cohabitation, and fewer children.
https://www.pewresearch.org/social-trends/2015/12/17/1-the-american-family-today/Harvard Joint Center for Housing Studies — The Number of People Living Alone in Their 80s and 90s Is Set to Soar
Strong source on aging, solo living, and future housing demand for older adults.
https://www.jchs.harvard.edu/blog/the-number-of-people-living-alone-in-their-80s-and-90s-is-set-to-soarOpticos / Missing Middle Housing — The Types
Clear explanation of the housing types that can meet demand from smaller households while fitting into existing neighborhoods.
https://missingmiddlehousing.com/the-types/AARP — Accessory Dwelling Units, Defined
Useful public-facing explanation of ADUs and their role in flexible, age-friendly, multigenerational housing.
https://www.aarp.org/livable-communities/housing/info-2019/accessory-dwelling-units-defined.html