Cities | San Diego
San Diego Multiplex Rules 2026: ADU Bonus, SB 9 (2021) and Lot Splits
San Diego runs its own ADU Home Density Bonus Program, which allows more accessory dwelling units (ADUs) in eligible zones than state law requires. An ADU is a second, smaller home on a lot that keeps its main house. This page covers the city's version of SB 9 (2021), its 2025 ADU changes, the ADU Home Density Bonus Program after the 2025 changes to it, and the San Diego details that change what you can build.
San Diego in six facts
- San Diego calls an SB 9 (2021) two-home project a Multi-Dwelling Unit Development (MDUD, Municipal Code 143.1310) and the lot split an Urban Lot Split (Municipal Code 143.1315). Source: San Diego Information Bulletin 409
- Without a lot split, a San Diego lot may have up to two SB 9 homes plus up to two ADUs or junior ADUs, never more than four units. With a split and SB 9 homes, no ADUs are allowed. Source: Information Bulletin 409
- San Diego's 2025 ADU and junior ADU amendments took effect August 22, 2025 outside the Coastal Zone. Source: San Diego regulatory updates
- In single-family zones, the ADU Home Density Bonus Program now caps the total at 4 ADUs on lots up to 8,000 sq ft, 5 on lots of 8,001 to 10,000 sq ft, and 6 on larger lots, counting the state-law ADUs. Source: San Diego regulatory updates
- Outside a Transit Priority Area, San Diego requires one parking space per unit for the third and fourth units built on the original lot under SB 9. Source: Information Bulletin 409
- The US Census Bureau estimates the population of the City of San Diego at 1,406,106 on July 1, 2025. Source: US Census Bureau, Vintage 2025
Start With State Law
The state laws apply in San Diego as in every California city. SB 9 (2021) allows two primary homes on a lot in a single-family zone, a lot split into two, or both, approved by staff with no hearing. ADU law sets the ADUs 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 up to 1.5 acres. And San Diego County is one of the seven counties where SB 79 took effect July 1, 2026, allowing buildings of five or more homes near qualifying transit stops.
San Diego's own regulatory updates page lists the recent state changes the city is applying: the 60-day review deadline from SB 450 for both lot splits and SB 9 building permits, SB 1123 from July 1, 2025, and AB 1061 (2025), which narrowed the historic exclusion. The page says each lot split application and each building permit application for an SB 9 project now has its own 60-day review deadline under SB 450.
San Diego in Numbers
The US Census Bureau estimates 1,406,106 people in the City of San Diego on July 1, 2025. The California Department of Finance's E-5 estimate for January 1, 2026 counts 1,419,531 people and 589,685 housing units, with 46,210 of them in buildings of two to four units. The two agencies use different dates and methods.
In 2022, the first full year of SB 9, the Terner Center at UC Berkeley reported that the City of San Diego received seven applications for new SB 9 units. Los Angeles received 211 in the same year.
SB 9 in San Diego: Information Bulletin 409
The city's rules for SB 9 are in Information Bulletin 409 from Development Services. San Diego uses its own names. The two-home project is a Multi-Dwelling Unit Development (MDUD) under San Diego Municipal Code section 143.1310. The lot split is an Urban Lot Split (ULS) under section 143.1315. Both are allowed in the RS, RE, RX and RT zones, and in Planned District zones that permit single but not multiple dwelling units.
For small buildings, San Diego allows less than the state's 4-foot setback. "Newly constructed one-story dwelling units with a 16-feet height or less may abut the interior side or rear property line." A taller new unit needs a 4-foot interior side and rear setback next to residential property. Front and street-side setbacks follow the zone.
Parking depends on transit. Inside a Transit Priority Area, the city's mapped zone near major transit, no parking is required. Outside one, the bulletin says "one off-street parking space per dwelling unit is required for the third and fourth units (of any kind) constructed on the initial (unsubdivided) lot." Rentals must last at least 31 days. In the Coastal Overlay Zone, "A CDP is required for all MDUD and/or Urban Lot Split applications." A CDP is a Coastal Development Permit.
Two city forms matter. Form DS-3063 is the SB 9 eligibility declaration. Form DS-3062 is the owner-occupancy affidavit for a lot split, which the record owner signs before the parcel map records. The parcel map is the recorded map that creates the two new lots.
How Units Combine in San Diego
| Plan | What is allowed | Maximum |
|---|---|---|
| SB 9 homes, no lot split | Up to 2 MDUD homes plus up to 2 ADUs or junior ADUs | 4 units |
| Urban Lot Split plus SB 9 homes | Up to 2 units on each new lot. No ADUs or junior ADUs. An existing ADU or junior ADU must be removed or converted. | 4 units (2 per lot) |
| State ADU law, single-family home | 1 junior ADU, 1 converted ADU and 1 detached or attached ADU | House plus 3 |
| ADU Home Density Bonus, lot up to 8,000 sq ft | Bonus ADUs in eligible zones, counting the state-law ADUs | 4 ADUs |
| ADU Home Density Bonus, lot 8,001 to 10,000 sq ft | Bonus ADUs in eligible zones, counting the state-law ADUs | 5 ADUs |
| ADU Home Density Bonus, lot over 10,000 sq ft | Bonus ADUs in eligible zones, counting the state-law ADUs | 6 ADUs |
| Existing multifamily building | Up to 8 detached ADUs (no more than the existing units) plus conversions up to 25 percent of units | Depends on existing units |
Sources: Information Bulletin 409 and San Diego regulatory updates. Bonus caps apply in single-family zones where the program is still allowed.
The bulletin is direct on the main choice: "If the project proposes a lot split using the ULS provisions and construction of MDUD units, then no ADUs/JADUs would be permitted." A JADU, or junior ADU, is a unit of 500 square feet or less inside the house. If you keep one lot, you can have two SB 9 homes and up to two ADUs or JADUs, and never more than four units. The city's preferred option is to "Propose units and an Urban Lot Split concurrently," meaning in one filing. A 2026 code update, effective July 2026 outside the Coastal Zone, also says a JADU must be removed or converted into one of the homes when both the MDUD and lot split rules apply.
The 2025 ADU Changes
San Diego's 2025 ADU and JADU amendments took effect August 22, 2025 outside the Coastal Zone. For a lot with a single-family home, the city now says: "One JADU, one converted ADU (e.g., a garage conversion), and one detached or attached ADU are permitted on properties with an existing or proposed single-family home." On a lot with an existing multifamily building, up to eight detached ADUs are allowed, but no more than the existing number of units, plus conversions of existing space up to 25 percent of the units.
Two earlier city rules still help. The 2024 Land Development Code update, adopted July 16, 2024, says a front yard setback "can not be used to prohibit the construction of an ADU home that is 800 square feet or less." And San Diego lets owners turn ADUs outside the bonus program into condominiums: "ADUs may be converted into separate condominium homes that can be sold individually." That is the local option state law offers under AB 1033, and every lender on the property must consent.
Starting January 1, 2027, state law changes. AB 956 requires every city to approve two detached new ADUs on a single-family lot, where the August 2025 San Diego rules list one detached or attached ADU. HCD's handbook had not yet described AB 956 when this page was checked. Ask Development Services how it will apply the 2027 rule before you file a permit after that date.
The ADU Home Density Bonus Program After the 2025 Changes
The ADU Home Density Bonus Program lets owners in eligible zones build more ADUs than state law requires. The 2025 changes, listed on the city's regulatory updates page, changed it in seven ways.
- Fewer zones. The program no longer applies in the RS-1-1, RS-1-2, RS-1-3, RS-1-4, RS-1-8, RS-1-9 and RS-1-10 zones, and one more zone the city's page writes as "RS-11", unless the site is designated residential and lies in a High or Highest California Tax Credit Allocation Committee (CTCAC) Opportunity Area. Ask the city for your lot's rating.
- A cap by lot size. "On lots up to 8,000 square feet, a maximum of 4 ADUs are allowed. On lots between 8,001 to 10,000 square feet, a maximum of 5 ADUs are allowed. On lots over 10,000 square feet, a maximum of 6 ADUs are allowed. These limits are inclusive of the ADUs allowed under state law."
- Smaller floor area. Floor area ratio (FAR), the building floor area divided by the lot area, is now calculated on a lot size capped at 8,000 square feet.
- Fire sprinklers. "All bonus and affordable ADUs constructed through the ADU Home Density Bonus Program must include an automatic fire sprinkler system."
- Parking. One space per bonus ADU outside a Transit Priority Area.
- Fire zones. In high or very high fire hazard severity zones, the site must be on a public street with two evacuation routes, and it cannot be on a cul-de-sac.
- Fees and penalties. A Community Enhancement Fee applies to bonus and affordable ADUs under 750 square feet. The penalty for charging more than the allowed rent on an affordable ADU went up by $10,000 per month.
One more limit affects resale: ADUs built through the bonus program cannot be sold as condominiums while their deed restriction is in force. A deed restriction is a recorded rule that stays with the property when it is sold. The city's summary did not list a dollar amount for the Community Enhancement Fee, so get the current figure from Development Services before you compare the bonus program with SB 9.
Fees, Rent Rules and Loan Limits
Information Bulletin 409 says "MDUDs are subject to payment of School Fees, Development Impact Fees, and the Regional Transportation Congestion Improvement Program Fees (RTCIP)." The city publishes the fee lists in Information Bulletins 501 and 502. The state sets the ceiling on school fees: the 2026 maximum Level I fee is $5.38 per square foot of assessable space, and a district may charge less. ADUs of 750 square feet or less pay no impact fees under state law. See the impact fees page.
The statewide rent cap in Civil Code 1947.12 uses the Consumer Price Index for the San Diego-Carlsbad area to measure the cost of living in San Diego County. Yearly increases are limited to 5 percent plus that change, or 10 percent, whichever is lower, and homes with a certificate of occupancy from the previous 15 years are exempt.
The Federal Housing Finance Agency's 2026 conforming loan limits for San Diego County are $1,104,000 for one unit, $1,413,350 for two, $1,708,400 for three and $2,123,100 for four. The financing page explains how lenders treat ADUs.
Best For
- ✓ Owners in eligible single-family zones who want more ADUs than state law requires and can meet the sprinkler rule.
- ✓ Owners who want to keep one lot and build two SB 9 homes plus two ADUs.
- ✓ Lots inside a Transit Priority Area, where no SB 9 parking is required.
Usually Fails When
- ✕ The lot is in RS-1-1 to RS-1-4 or RS-1-8 to RS-1-10 and outside a High or Highest Opportunity Area.
- ✕ The plan combines a lot split, SB 9 homes and ADUs on the same lot.
- ✕ The lot is in a fire zone on a cul-de-sac or without two evacuation routes, for bonus ADUs.
What To Verify Before Spending Money
- → Your lot's zone, Transit Priority Area status and opportunity area rating with Development Services.
- → The Community Enhancement Fee and Development Impact Fee amounts in the current bulletins.
- → Whether the lot is in the Coastal Overlay Zone, which needs a Coastal Development Permit.
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
How many ADUs can I build in San Diego?
What changed in San Diego's ADU bonus program in 2025?
Is the San Diego ADU bonus program still allowed in my zone?
Does San Diego require parking for bonus ADUs?
What does San Diego call SB 9 projects?
Can I combine an SB 9 lot split with ADUs in San Diego?
What fees apply to SB 9 homes in San Diego?
Can I sell an ADU separately in San Diego?
Do I need a coastal permit for an SB 9 project in San Diego?
How many people live in San Diego?
How close to the property line can an SB 9 home be in San Diego?
Official sources (checked October 2026)
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