By now, the story of California’s sky-high housing costs has moved from “excuse for not moving to America’s land of plenty” to “cliché used to lead an op-ed.” But two decades into one of the greatest policy-induced problems in American governance, we’re seeing the first signs that recent reforms to the state’s housing market are working. This precedent could serve as a model for other states that need to take the first steps toward creating a more affordable, inclusive housing market that has homes available for families of all shapes and sizes.

At issue are locally mandated single-family zoning laws. These laws take a range of forms, but what ties them together is that they all prevent landowners from having more than one unit of housing on a given lot. They ban construction of large, multifamily buildings as well as smaller, less-intrusive types of housing, down to garage apartments and backyard condos. These “accessory dwelling units,” commonly referred to as ADUs, are one of the cheapest, least politically fraught types of new housing, but they’ve faced widespread local bans in the United States for decades.

Fortunately, legislators have wised up to this opportunity in recent years. In 2016, the California Legislature passed SB 1069, a bill that prohibited local governments from adopting ordinances that preclude ADUs. Further changes in 2018 prevent towns from adopting fees or parking requirements to maintain pre-existing ADU bans, while changes in 2019 allowed illegally-constructed ADUs to be made legal with local inspection and limited other mechanisms that localities use to ban ADUs, like setback requirements and mandated lot-coverage ratios. The combined effect of these and other ADU laws has been to turn California’s single-family zones into places that allow two families per property rather than one.

These mandatory ADU laws are not a new concept—Washington passed a limited ADU law in 1993—but what is new is the effort to ensure such laws are universal, as well as to limit localities’ ability to prevent ADUs with restrictions like parking and lot geometry.

The changes California implemented have worked. Thousands of secondary dwellings have been built in the state since 2016. While the data are still new, they imply that there’s plenty of latent housing potential in single-family zones. But don’t take my word for it; new research from the American Enterprise Institute shows that abolishing single-family zoning in favor of “light touch density” that allows two to four units could add 10 percent to the nation’s housing stock.

This research is notable for another reason: Single-family zoning reform is typically seen as a leftwing or even a progressive issue. But AEI’s research reminds us that there’s also little love for mandatory low-density zoning among those on the political right.

There’s a lot to like about the way California legislators went about bringing an end to the eight or so decades where widespread single-family zoning was law. They started with the desire to address the state’s high housing costs and worked to legalize the smallest, least-controversial type of new housing: basement, backyard, and garage apartments. As reactionary municipalities found ways to maintain their ADU bans, legislators revisited the issue each year and closed loopholes, ensuring that their intent—preserving a statewide right to build a second home on one’s property—was not rendered moot by parking, lot geometry, and utility-access restrictions.

California should be seen less as a special case and more as a bellwether of future housing debates elsewhere. Rents in Los Angeles may be eye-popping to some, but for those who live in other high-cost places, they can seem relatable. Taking the first step in housing reform—allowing ADUs everywhere—will help. But that alone will not be enough to end single-family zoning. Doing so will require oversight with follow-up action once municipalities intent on stopping even the most mundane development prevent the new homes from reaching the market. That’s a multi-year commitment to an effort to improve housing costs. Hopefully some outside California see their peer’s success as opportunity to make changes in their states as well.