California Takes a Big Step Toward Legalizing 'Missing Middle' Housing

Legislators advance bills that would allow duplexes statewide and make it easier for local governments to legalize small apartment buildings.


The headline-grabbing fights in California housing politics over the past couple years have generally been over big, ultimately unsuccessful state bills that would override local zoning restrictions to allow for apartments near transit and job centers.

This year, the state's pro-development YIMBY (Yes In My Backyard) activists and legislators devoted their energy toward wonkier, slightly more marginal reforms. The strategy appears to have paid off.

Last week, the California Assembly passed two housing reform bills. One legalizes duplexes in single-family neighborhoods across the state, and the other makes it easier for local governments to allow "light-touch" density on their own.

"We're headed to an era when we're going to see more of that gentle in-fill housing that was legal in California up until the 1970s and '80s," says Matt Lewis, communications director for California YIMBY. "This is really sort of a Back to the Future week for California housing policy."

The duplex bill, S.B. 9, passed out of the state Assembly on Thursday. It allows homeowners to split single-family-zoned lots and then build two units on each—effectively legalizing the construction of four homes where only one was allowed before. The legislation would also require local bureaucrats to "ministerially" approve permits for lot splits and duplexes, meaning they wouldn't have the discretion to deny or condition those permits.

This follows a growing trend of states and cities legalizing more "missing middle" housing—i.e. two-, three-, and four-unit homes—in what were once neighborhoods of exclusively single-family houses.

Minneapolis legalized the construction of triplexes citywide in 2020 (although the city's preservation of height and massing restrictions means the change has led to very little new housing). Starting this month, developers in Portland, Oregon, are now able to build up to four-unit homes almost everywhere in the city.

The lot-splitting streamlining in California's S.B. 9 is probably the more impactful than the duplex legalization, says the Sightline Institute's Michael Anderson.

"Many banks and credit unions struggle to figure out how to value a lot with an extra rental on site, and therefore can't always offer good loan terms to people looking to build a backyard cottage or remodel into a duplex," Anderson writes. "But every lender knows exactly how to value a little lot with a new house on it. This would make mortgage financing easier."

The bill doesn't apply to lots that are less than 2,400 square feet or that are in historic districts or wildfire zones. It also requires that a homeowner who applies to split up his or her lot also agree to live on-site for at least three years. And it doesn't allow homes to be converted to duplexes if they'd been rented in the last three years.

These provisions were added to pacify critics who claimed the bill would lead to a flood of "greedy and disruptive" investors snatching up single-family plots and displacing tenants in a mass redevelopment campaign.

An analysis by Berkeley's Terner Center for Housing Innovation—before the owner-occupancy requirement was added to the bill—found that S.B. 9 would enable roughly 700,000 new units of housing in the state, particularly in coastal counties and larger cities.

Potentially setting the stage for even more development across the state is California's S.B. 10, which passed out of the Assembly last Monday. On its face, the bill doesn't legalize any new housing. Rather, it makes it easier for local governments to do that themselves.

Typically, local governments trying to change their zoning codes—to allow for denser housing, say—would first have to produce a study on the environmental impacts of the proposed changes. Those studies can cost millions of dollars and take years to complete. State law also enables third parties to sue if they think a study wasn't thorough enough, delaying things even more.

S.B. 10 would speed things up by allowing local governments to legalize 10-unit developments on urban parcels of land without also having to go through the environmental review process.

"You can make a real argument that that kind of housing does not need the same kind of environmental scrutiny," state Sen. Scott Wiener (D–San Francisco) told Reason in January. "It allows cities to do what they want to do, or need to do, quickly and not have to spend ten years doing [environmental impact reports] and getting sued."

Both S.B. 9 and S.B. 10 will now head back to the California Senate, where they already passed, for final approval. That will have to happen before a September 10 deadline. Then the bills will go to the governor for his signature.

Lewis notes that ending California's shortage of affordable housing will require deeper reforms still.

"We're so deep in the hole in terms of the housing shortage that we're still going to need to do more comprehensive reform for even denser buildings particularly near transit and job centers," he says. "What we saw this week is a recognition that the neighborhoods that we have now, which already have duplexes, triplexes, and small apartment buildings are not the end of the world."