This article is part of The Rooftop, a blog and multimedia series from New America’s Future of Land and Housing program. Featuring insights from experts across diverse fields, the series is a home for bold ideas to improve housing in the United States and globally.
Three-quarters of the United States’ residential land is zoned for single-family homes. As the housing affordability crisis has grown, many housing advocates, government officials, and residents point to this exclusive zoning as a barrier to creating more housing and thus affordability. But despite the urgent need to build more housing, many residents are reluctant to transform their communities’ look and feel from single-family homes into a dense mix of housing types.
Enter accessory dwelling units (ADUs)—the technical term for smaller, independent dwellings such as backyard cottages, in-law suites, and basement apartments that exist on the same lot as the primary dwelling. By legalizing ADUs, communities can retain the primacy of single-family homes while adding new housing stock. As of 2024, 14 states had authorized ADUs, including blue states such as California and Massachusetts, and red states such as Utah, Montana, and Arizona. Beyond state-level zoning reform, dozens of cities, such as Durham, North Carolina, and Madison, Wisconsin, have created allowances for ADUs.
By including ADUs in the zoning code, and through legislation that has gotten successively better at minimizing neighborhood or government interference, ADU construction has gone from a fringe phenomenon in the 20th century to a major part of the housing economy in the 21st. ADUs account for more than one-fifth of all housing permits in California, and in 2023, San Diego permitted more accessory dwelling units than single-family homes.
The popularity of ADUs as a housing solution is well-earned: They enable multigenerational living and caregiving, homeowners can better afford their homes by renting out their ADUs, and lower-income households can afford to live in neighborhoods where primary residences are out of reach. And yet, an estimated 40 percent of ADUs in the U.S. are not used as long-term, primary residences. Monthly rents for ADUs are often higher than similarly sized units in multifamily buildings. And while the rental income from ADUs may help homeowners afford their properties, having an ADU on a property, or even the ability to build one, raises property values, making it harder for newcomers to buy such homes.
“An estimated 40 percent of ADUs in the U.S. are not used as long-term, primary residences.”
These downsides, among others, suggest that while ADUs are a critical way to address the housing shortage, they may not be the most effective way to bring down housing costs. Indeed, rather than transcending the primacy of single-family homes, are ADUs helping to reinforce it while also diverting the public’s attention away from the inevitable need for more density to meet demand?
At the same time, a major success of ADUs is the way this housing type has attracted a spectrum of political factions to support building new housing. Coalitions to legalize ADUs have combined the support of urban and rural politicians, progressive and libertarian factions, and professional groups ranging from developers to teachers. In addition, the housing community has landed perhaps its largest lobbying group ever—AARP, the nation’s top advocacy organization for older Americans—as ADUs are their signature housing policy to encourage aging in place and intergenerational living. Finally, as zoning reform authorizing ADUs has arrived in hundreds of communities across the country, they have forced a conversation about housing, increasing Americans’ housing policy literacy.
This raises a key question: Could the political infrastructure and public momentum behind ADUs be leveraged to advance housing solutions that are more impactful?
As a fellow at the Johns Hopkins Stavros Niarchos Foundation (SNF) Agora Institute’s Center for Economy and Society, I study four options for increasing housing supply and affordability: (1) repurposing government property, (2) home repair programs, (3) splitting up lots, and (4) building code reform. Each of these solutions could benefit from some of the same politics, narratives, and stakeholders that have made ADUs so popular.
Repurposing Government Property
In March, the Trump administration revealed a list of 443 federal buildings positioned for sale and created a task force to explore using federal lands to develop affordable housing, signaling a federal interest in repurposing government-owned property. At the local level, there is also an appetite for repurposing government-owned property, particularly for use as housing. Atlanta, for example, owns 40 public properties in various stages of development, and has formed the Atlanta Urban Development Corporation to identify publicly owned properties and partner with private developers to add hundreds of long-term affordable units to the area’s housing stock. New York City recently issued an executive order to explore repurposing government property for housing development. Cities such as San Francisco and Philadelphia have used land leases, where the government retains property ownership but receives revenue during the lease, to not only accelerate housing development but also ensure that some units are set aside for below-market rents.
Like constructing ADUs, repurposing government property into housing can achieve goals that have appeal across the political spectrum, such as reducing government spending, creating public-private partnerships, and lowering housing costs.
Home Repair Programs
Beyond politics, ADUs have tapped into residents’ concerns about aging in place and maintaining property values. Home repair programs could likewise enable older adults to stay in their homes longer, while increasing the value of their homes, particularly in low-income neighborhoods where the housing stock is older and disinvestment has led to years if not decades of deferred maintenance. Local organizations partnering with private banks to provide low-interest loans could ensure these home repair programs don’t rely solely on government dollars and could also support local contractors and other small businesses in the process.
Similar to the coalitions that have lobbied for ADUs and zoning reform, statewide home repair programs such as Pennsylvania’s have garnered a range of political and stakeholder support. This includes housing and environmental nonprofits such as Habitat for Humanity and Natural Resources Defense Council (NRDC), as well as local preservation and transportation advocacy groups, such as Preservation Alliance and 5th Square. Because the need for home repairs also transcends urban/rural divides, these programs tend to have statewide bipartisan appeal.
Splitting Up Lots
One reason ADUs have been so successful in places such as California is that they have enabled homeowners who have a lot of equity, but not a lot of cash, to access the full value of their property. A new California law, SB684, also taps into homeowners’ eagerness to monetize the latent value of their property, but supercharges the opportunity. Rather than legalize building one small ADU, SB684 streamlines the development process to create up to 10 lots from one single property. This legislation can enable pocket neighborhoods—small groupings of housing with some shared infrastructure and land. With planning guidelines and architectural design, pocket neighborhoods can retain the single-family home character of a neighborhood while adding density. The shared infrastructure of a pocket neighborhood could also support aging in place with small-scale senior living communities.
As SB684 enables property owners to split their land into multiple parcels, it is also likely to result in “starter homes” with rents or purchase prices below typical newly constructed single-family homes that are larger and have more private land. As states consider ADU reforms, they should consider broadening the policy discussion to include lot subdivision. Particularly at a moment when government support for housing programs is low, lowering the cost of land can help make housing development financially feasible for developers.