Issue 541 to

Getting to Know Your In-Laws

Can a once marginal and almost completely invisible housing type help solve San Francisco’s current housing shortage?

Urbanist Article

Since the Department of Lands and Buildings erected 5,610 “refugee cottages” in camps all around the city after the 1906 earthquake, San Francisco has often relied on flexible housing types to meet the needs of residents, families and workers. Accessory dwelling units (or ADUs; also known as secondary units, in-laws or granny flats) offer a way to increase density while respecting neighborhood character. [1] Given the Bay Area’s housing crisis, in-law units are an important strategy for helping increase the supply of “naturally affordable” housing.

In 2014, two laws related to ADUs were passed by the San Francisco Board of Supervisors. One, authored by Supervisor David Chiu, created a process to legalize existing ADUs that meet certain parameters. The other, sponsored by Supervisor Scott Wiener, permitted the construction of new in-law units in the Castro neighborhood.

SPUR has long advocated for the ADU as one way to put a dent in the ongoing housing crisis. By utilizing existing infrastructure (such as walls, floors, roofs, and other elements) of the primary structure, they can be created at far lower cost than ground-up units (and are often rented at lower price levels than typical housing units, without government subsidy). [2] They can help homeowners better afford their homes, provide more affordable units for renters, and/or allow families to care for and support each other while maintaining independence. In some cases, the addition of an ADU may soon be completed in concert with seismic sustainability work — and rental revenues will help to offset that capital investment. On March 11, 2015, the Board of Supervisors passed Supervisor Wiener’s legislation to allow building owners to finance earthquake retrofits by converting garages and basements into apartments.

Legalizing Existing Housing

Anecdotal estimates put the number of ADUs constructed without permits at 30,000 to 50,000 across San Francisco. Supervisor Chiu’s 2014 legislation [3] permits the legalization of these units and establishes a process for legalization and parameters to relax some planning code requirements. While legalizing existing ADUs will not increase the housing
supply, Chiu’s ordinance maintains an existing source of “naturally” affordable housing, protects existing tenants, requires fixes to health and life safety hazards, increases property
tax revenue to San Francisco and provides a safe and clear path to legal status for property owners.

Since the law’s passage last year, San Francisco’s planning department has received approximately 90 legalization requests and approved 40 of them.

Creating New Housing

The ordinance authored by Supervisor Wiener permits the construction of new ADUs within the envelope of existing buildings in the Castro Street Neighborhood Commercial District or within 1,750 feet of the neighborhood boundaries. [4] The first new Castro in-law unit has been approved by the planning department. While the actual number of units may be small to start — the planning department estimated last year that 400 new units could be created — this program could eventually be implemented citywide and increase in scale. Were the law to be implemented across San Francisco, one could envision thousands of units being produced and inhabited with minimal effect on neighborhood character or congestion. This year, Supervisor Wiener also plans to bring forward similar legislation for the rest of District 8, including Glen Park, Noe Valley and Diamond Heights.

Many buildings in San Francisco are not built to their existing maximum potential. In 2008,
adoption of the Market and Octavia and the Eastern Neighborhoods Plans relaxed parking and density requirements to allow ADUs on any residential transit-oriented district property, but there has been very little interest to date. Similarly, in the Castro alone, there are over 1,000 single-family homes zoned for two or three units whose owners have not taken advantage of the expansion potential. In response to these findings, the city’s planning department will release a user-friendly handbook this spring intended to make the ADU legalization process more accessible to the general public.

Around the Bay and Beyond

Other cities around the region have had mixed success with, and demand for, ADUs. Oakland plans to look at its zoning regulations for ADUs this year; it appears interest is rapidly increasing, but the existing requirements may pose challenges for implementation. In San Jose, ADUs are allowed in single-family neighborhoods, but demand is fairly low,
likely due in part to restrictive parking requirements and the cost of construction. The city of Berkeley is known for championing ADUs, but last September’s proposal to loosen restrictions and make them easier to build as-of-right was deferred to this year for further discussion.

Several major cities have embraced ADUs. Vancouver, BC may have the strongest model, with ADUs making up perhaps a third of the city’s rental housing stock. In 2004, Vancouver began to allow ADUs in every residential district citywide and relaxed building requirements related to parking, ceiling height, fire sprinklers and electrical work. The city has steadily continued to refine its regulations in order to support the legalization and construction of ADUs; it is estimated that 60 percent of buildings constructed in 2000-2009 included an ADU. Portland, Oregon, is also seen as a leader in the realm of ADUs. In 2010, it waived significant building fees for ADUs and relaxed unit size limitations. As a result, the number of new ADU applications jumped dramatically but this still only amounts to a couple hundred units per year.

As ADUs offer an incremental approach to growing the housing supply, the question remains of whether they will eventually scale up to their potential. Despite the challenges, we believe the answer is yes given the ability of ADUs to provide a variety of solutions to meet the wide-ranging needs of families and individuals over time. The Bay Area has the opportunity now to learn from other cities that have put efforts into growing their ADU stock and to structure their policies accordingly to welcome and encourage further ADU construction.

Developing creative responses to the affordable housing crisis is imperative. The Bay Area must pursue as many different solutions as it can. While there has been some recent success in building high-density housing or transit-oriented districts around the region, we must do more. Building ADUs is one of the few strategies that can make an impact in neighborhoods where high-density or large-scale growth is neither possible nor appropriate. The ongoing efforts of accessory dwelling unit champions San Francisco Supervisor Wiener and Berkeley Mayor Tom Bates are a great start. Getting more ADUs legalized and built is
one of many options for growing and improving our in-law housing inventory and may lead to additional innovations in housing residents in San Francisco and more widely around the Bay Area.


[1] A residential unit added to an existing building, ADUs are independent units that have their own kitchens, bathrooms and living area and are generally developed using underutilized spaces within a lot, whether a garage, storage building, rear yard or an attic.

[2] “Accessory Dwelling Units in Planning and Policy,” by Kearstin Dischinger, Urbanism from Within catalog (February 2014)

[3] See “Authorization of Units Installed without a Permit,”

[4] See “Addition of Dwelling Units in the Castro,”

Kristy Wang is SPUR’s Community Planning Director.
Special thanks to Kearstin Dischinger and Mark Hogan.