Filling in the ‘Missing Middle’: SB 9 and SB 10, Explained

One house on a few thousand square feet of land may not be the most efficient use of space, but it’s a common one. As the population boomed after World War II, single-family zoning spread across the United States.

In California, single-family, detached homes account for more than half of all housing units, according to the U.S. Census Bureau's California housing statistics. The next largest number of housing units are in buildings of 20 or more units, which account for about 12 percent of all housing units in the state.

Between the extremes of single-family, detached homes and mid- to high-rise apartment buildings is a range of housing options that are less common. Gov. Gavin Newsom last week signed two laws designed to provide more housing options—including the option to own and thereby build wealth—throughout the state.

The two Senate bills, SB 9 and SB 10, seek to address this housing range, known as the “missing middle.” The term, coined by Daniel Parolek, founder of Opticos Design, refers to house-scale buildings with multiple units in walkable neighborhoods. Think duplexes and fourplexes, cottage courts and townhouses—types of housing that fell out of favor after World War II. 

The two Senate bills are designed to increase density in areas where single-family homes already exist or where current zoning doesn’t allow more than one home on a lot, and they would do so largely by streamlining the permitting and approval process. They would make it easier for property owners to split their lots, build duplexes, and—if they live near transit or an urban center—build up to 10 units on one single-family lot.

Opponents fear the change to “neighborhood character.” Proponents, who have called the increase in density provided by the bills “modest,” “gentle,” and a “light touch,” argue that the moderate increase in density will not interfere with character, but will provide much-needed housing options.

Senate Bill 9

SB 9 would allow owners of a single-family home to build or convert their house into a duplex, as well as split their lot into two and build a single-family home or duplex on the second lot with only “ministerial approval.” That means the property owner would not need a discretionary review or hearing from the local jurisdiction such as a city planning commission.

SB 9, sponsored by Sen. Toni Atkins of San Diego, effectively allows property owners to develop new homes for rent or sale on existing single-family home lots. A report from the Terner Center for Housing Innovation, a housing think tank at the University of California, Berkeley, notes:

“This ability to create duplexes and/or split the lot and convey new units with a distinct title would allow property owners to pursue a wider range of financing options than are available for ADU [accessory dwelling unit] construction to build these new homes. In so doing, SB 9 could open up new homeownership opportunities at more attainable price points for prospective purchasers, who would be able to apply for a traditional mortgage to buy the home.”

The bill will also allow qualified developments or lot divisions to forgo reviews mandated by the California Environmental Quality Act, as CEQA does not apply to ministerial approvals.

To discourage speculation by corporate developers, the law requires the property’s owner to occupy one of the units on one of the properties as their principal residence for at least three years.

Certain projects would not be eligible for the ministerial approval of the increase in density, including those that local building officials determine will have  a specific adverse impact on health and safety or the physical environment that cannot be mitigated.

Other properties that do not meet the criteria include those in historic districts and homes that are rented out as affordable housing.

Senate Bill 10

With its provisions to upzone single-family lots to accommodate up to 10 units, SB 10 offers more potential to increase the housing stock. And zoning changes are left up to local jurisdictions, which addresses concerns about local control. SB 10 would allow a city or county to zone any parcel, including a single-family housing lot, for up to 10 units—but only if the lot is in an urban infill area or within a half mile of a major public transit stop or a “high-quality bus corridor,” which is defined as a route that meets specific service time intervals.

The bill was sponsored by San Francisco's Sen. Scott Weiner, who introduced three similar housing bills in the last legislative session—SB 1120, SB 50 and SB 827—all of which ultimately failed. SB 10 defines an urban infill area as a site that is within the jurisdiction’s boundaries and in which three-quarters of the lot is bordered by parcels with urban uses. At least two-thirds of the proposed development’s square footage must be for residential use.

SB 10 does not count accessory dwelling units—commonly known as granny or in-law units or backyard cottages—toward the total number of units allowed on the property.

This bill also allows local governments to increase density without going through CEQA review, which precludes project-delaying CEQA lawsuits. These lawsuits can sometimes hold up a project so long that they effectively kill it.

Housing development is not permitted on publicly owned land such as parks and designated open space areas. Parcels in high or very high fire hazard zones also do not qualify, unless they include fire hazard mitigation measures covered by existing building standards.

If the lot in question is subject to a voter-approved restriction on the use of the land, SB 10 allows the local jurisdiction to override that restriction if two-thirds of the members of the voting body—the city council, for instance—vote accordingly.

While SB 10 sunsets on Jan. 1, 2029, any ordinance that a jurisdiction adopts under the bill can extend beyond the sunset date.

Reality Check

Although these two bills streamline development policies to make it easier for property owners to increase the housing density on their land, there is no guarantee that homeowners with available lots will pursue the development opportunity. Even if property owners are willing, lots can be constrained by size or other physical barriers, and owners can be constrained by finances, time or a variety of other obstacles that can prevent the further development of available lots.

In the Terner Center’s analysis of SB 9 and how it might look in communities with more than 5,000 single-family homes, the report took market feasibility into account and found that SB 9 could lead to just over 650,000 new such units throughout California, a state with more than 6.8 million single family homes.

While 650,000 units may not be enough to solve the homelessness crisis, it’s a start. And advocates for affordable housing have even higher hopes for SB 10 and its potential to encourage housing growth in areas where some of its consequences—such as traffic congestion and pollution—can be mitigated.