Going Beyond ADUs to Make Housing More Affordable

ADUs are really popular -- can other housing types get some of that love?

Hey readers,

I wanted to share a little bit of writing that’s a result of my fellowship at Johns Hopkins’s Center for Economy & Society this year. The piece, which was originally published this week in New America’s new housing-focused newsletter, The Rooftop, looks at how the politics, narratives, and stakeholders that have enabled an ADU lovefest can be extended to other housing strategies: repurposing government property, home repair programs, splitting up lots, and building code reform.

I’ve written about some of these ideas already this year, such as building code in general, and single stair building code reform in particular, as well as repurposing government land. Below is an excerpt of the piece, with a link to the full story on The Rooftop.

I also have been spending part of this week prepping to celebrate my two years of writing this Substack at the end of May! I’ve been reaching out to engaged readers to nudge them to subscribe and hit my goal of 400 premium subscribers by June 1 — for the next month only I’ve reduced the price of a full-year premium subscription. Take advantage of this deal before it ends by subscribing here!

I’m also doing an Ask Me Anything and will be responding to all your questions in my anniversary piece, so drop an anonymous question about anything related to cities, writing a Substack, me, living in 2025…whatever!

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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: ADUs 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.

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.

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The ADU lovefest is just getting started

Building Code is the New Zoning Reform

The Huge Potential of Repurposing Government Property

Are Single-Stair Buildings the New ADUs?