Cities | San Francisco

San Francisco Multiplex Rules 2026: Family Zoning Plan and Fourplexes

San Francisco has two local rules that allow more homes on house lots than state law requires. The first, from 2022, allows four units on any lot in an RH (Residential, House) district and six on a corner lot. The second, the Family Zoning Plan of 2026, removes density limits in residential areas and adds height on transit and commercial streets. This page explains both, how they meet SB 9 (2021) and SB 79, and the conditions that come with the extra units.

Start With State Law

State law sets a minimum in San Francisco as in every California city. SB 9 (2021) allows two primary homes on a lot in a single-family zone, a split into two lots, or both, with staff approval and no hearing. ADU law sets the accessory dwelling units (ADUs), the second smaller homes on a lot, that every city must approve. SB 684 and SB 1123 allow up to 10 lots with 10 homes on a multifamily-zoned lot or a vacant single-family lot of up to 1.5 acres.

Two state rules treat San Francisco differently. SB 79 took effect July 1, 2026 in San Francisco, one of seven counties named by HCD, and the city has its own plan to meet it (below). And AB 1751, the 2026 Missing Middle Townhome Ownership Act that starts January 1, 2027, does not cover the city: its text says "This section shall not apply to the City and County of San Francisco."

San Francisco in Numbers

The US Census Bureau estimates 826,079 people in San Francisco on July 1, 2025. The California Department of Finance's E-5 estimate for January 1, 2026 counts 845,658 people and 423,517 housing units. Of those, 81,408 are in buildings of two to four units and 66,283 are single detached homes, so the city already has more homes in small multiplexes than in detached houses.

SF Planning says state law requires San Francisco to plan for 36,000 housing units between 2023 and 2031. The Family Zoning Plan is the city's rezoning to allow them.

The 2022 Four-Unit Density Exception

Planning Code section 207(c)(8) came from Ordinance 210-22 (Board File 210866), introduced by Supervisor Mandelman, and took effect November 27, 2022. SF Planning's summary says: "In all RHD's, up to four units (not including any allowed ADU's) are allowed on all lots, and up to six units (not including ADU's) are allowed on corner lots so long as certain conditions are met."

ADUs are allowed on top of these counts. Before 2022, some districts allowed more units by conditional use. Source: SF Planning code summary.

The exception comes with conditions. A project using it:

• cannot also use the state density bonus, the state law that gives extra size to projects with affordable homes;
• cannot make a substantial adverse change to a historic resource;
• must replace demolished units, build at least as many units as it demolishes, and offer protected tenants relocation help and a right of first refusal, meaning they get the first offer;
• makes every unit above the base zoning subject to rent control;
• needs at least one new unit with three or more bedrooms, or at least one-third the size of the largest unit;
• requires the owner to have owned the lot for at least one year, with inheritance from close family counting;
• needs a rear yard of 30 percent of lot depth or 15 feet, whichever is greater, when it has four or more units.

One condition helps owners who will live there. Owners who sign a three-year residency affidavit get Historic Resource Assessment fees waived and can form condominiums through the new-construction process, so the units can be sold separately. The supplemental application lists these terms, and the Planning counter takes questions at 628.652.7300 or [email protected].

The 2026 Family Zoning Plan

Mayor Lurie introduced the Family Zoning Plan at the Board of Supervisors on June 24, 2025. The Planning Commission adopted it on September 11, 2025, the Board adopted it on December 9, 2025, and the Mayor signed it on December 12, 2025. According to SF Planning, the ordinances "will take effect on January 12, 2026," which met the state deadline of January 31, 2026 for a compliant rezoning. A Tenant Protection Ordinance was adopted in December 2025 as well.

Source: SF Planning, Family Zoning Plan.

For a house lot, the main line is the "Removal of density restrictions in residential areas off the corridors, so that projects may build additional units within the existing height limit (typically 4 stories)." A density limit caps the number of homes per lot. Without one, the building size rules (height, rear yard and similar limits) decide how many homes fit.

The 2026 plan changed density rules in residential areas after the 2022 exception took effect. The conditions listed above come from the 2022 code summary. Before you design, ask the Planning counter whether the 2022 exception and its conditions still apply to your lot, and which rules your project will be reviewed under.

SB 9 or the Density Exception?

An RH lot owner can compare two options. SB 9 (2021) is state law and comes with a 60-day decision deadline. The density exception is local and allows more homes on one lot. The table sets them side by side.

Sources: SF Planning code summary, Gov. Code 65852.21 and Gov. Code 66411.7.

SB 9 covers only lots in a single-family residential zone. HCD tells cities with more than one single-family zone to look at each zone's purpose, and says lot size or hillsides should not decide the question. Ask SF Planning whether your RH district counts as a single-family zone for SB 9 before you compare the two options. SB 9 also brings state limits the density exception does not list: side and rear setbacks of 4 feet at most, and no city rule that keeps either home under 800 square feet. The SB 9 page has the full list.

Adding ADUs to an Existing San Francisco Building

San Francisco has 81,408 homes in buildings of two to four units, and state ADU law gives those buildings their own rules. HCD treats "a structure with two or more attached dwellings on a single lot" as a multifamily dwelling, so an existing duplex, triplex or fourplex qualifies. On such a lot, a city must allow up to eight detached ADUs, but no more than the number of existing units. It must also allow ADUs inside existing space that is not lived in, such as storage rooms, boiler rooms, attics, basements and garages: at least one, and up to 25 percent of the existing unit count.

For an existing fourplex, that means up to four detached ADUs plus at least one conversion. State fee rules apply too: an ADU of 750 square feet or less pays no impact fees. Lenders treat ADUs differently from cities. Fannie Mae does not allow an ADU on a two- to four-unit property, while Freddie Mac allows one ADU on a one-, two- or three-unit property. See the ADU law page and the financing page.

SB 79 and the Family Zoning Plan

SB 79 lets residential, mixed and commercial lots within a half mile of qualifying transit stops hold buildings of five or more homes at 30 or more units per acre. A city may meet SB 79 with an "alternative plan" that keeps the same total zoned capacity but places it differently. SF Planning's factsheet says the Family Zoning Plan would qualify as San Francisco's alternative plan.

The same factsheet gives the scale: "More than three-quarters of properties in San Francisco (120,000 parcels) fall within areas subject to SB79. Over 60% of these properties (75,000 parcels) are within the geography of the Family Zoning Plan." It adds that "From July 2026 until 2032 (one year after San Francisco's next Housing Element is due), SB 79 provides temporary exemptions for certain properties," including parcels whose zoning already allows at least 50 percent of SB 79 density, among other conditions.

SF Planning says the plan keeps the existing 40-foot height limit in many residential areas near transit, where SB 79 itself would allow 55 to 95 feet. The factsheet was written while the plan was still proposed, and HCD issued a "Preliminary Review and Substantial Compliance Letter" on it in September 2025. If your lot is near a rail or frequent bus stop, ask SF Planning whether SB 79 or the plan's rules apply to it.

Rent Rules and Loan Limits

Rent rules matter more here because of the rent control condition above. The statewide cap in Civil Code 1947.12 uses the Consumer Price Index for the San Francisco-Oakland-Hayward area for San Francisco. Increases are limited to 5 percent plus that change, or 10 percent, whichever is lower, and local rules can be stricter. The rent and tenant rules page covers the state rules and the Ellis Act.

The Federal Housing Finance Agency's 2026 conforming loan limits for San Francisco are $1,249,125 for one unit, $1,599,375 for two, $1,933,200 for three and $2,402,625 for four. Ask SF Planning for its local SB 9 and ADU procedures and its current permit fees before you set a budget.

Where to Go Next

Related on VanPlex: California SB 9 in the global multiplex zoning comparison and the duplex to fourplex guide.

Frequently Asked Questions

Official sources (checked October 2026)