SB 478

SB 478 will stop the misuse of floor area ratio and minimum lot size requirements that prevent the construction of multifamily buildings in areas already zoned to allow them.

Floor area ratio restrictions control how large a building can be, based on the size of the parcel of land. Many cities misuse this restriction to prevent multifamily housing: for instance city of Del Mar restricts floor area ratio to .35—meaning the building’s total floor space can take up only 35% of the total lot size. For example, a 2000 square foot lot would only be allowed to have a duplex that is 700 square feet total—350 square feet per home.

Minimum lot size requirements identify the smallest lot that can legally be created within a local jurisdiction. If the minimum lot size is large (in some areas as much as an acre) a builder must pay for a much larger piece of land than is needed—discouraging or preventing development.

SB 478 will establish a 1.5 floor area ratio standard for land zoned for missing middle housing (between 2 and 10 homes). This will help ensure multifamily housing can actually be built in areas that zone for it. The bill sets a minimum lot size for 2-4 home parcels and a separate, sustainable minimum lot size for 5-10 home parcels.

SB 478 is a part of the Senate’s Building Opportunities for All housing package. Learn more about this package of legislation here.


  • 9/28/2021: SB 478 was signed by Governor Newsom and chaptered by the Secretary of State. This bill will go into effect on January 1, 2022. Read our statement here.


Authors: Scott Wiener (D, SD 11)

Sponsor: California YIMBY

Press Coverage

Senator Wiener Introduces Four Bills to Spur Housing Production and Address California Housing Crisis – Davis Vanguard

San Francisco legislators push housing bills – Bay Area Reporter

Wiener aims to eliminate ‘poison pill’ to multifamily housing with new legislation – SF Business Journal

Could these bills help California build more affordable housing? – Cal Matters


  • California YIMBY (Sponsor)
  • Abundant Housing LA
  • Bay Area Council
  • California Apartment Association
  • California Building Industry Association
  • Chan Zuckerberg Initiative; Circulate San Diego
  • East Bay for Everyone
  • Fieldstead and Company, Inc.
  • Greenbelt Alliance
  • Greenlining Institute
  • Habitat for Humanity California
  • Housing Action Coalition
  • Lisc San Diego
  • North Bay Leadership Council
  • San Francisco Bay Area Planning and Research Association
  • Terner Center for Housing Innovation At the University of California, Berkeley