own + buildsb 9 + adusupdated for 2026boyenga team at compass
The Build Lab
What state law lets you build on a California single-family lot: ADUs, two homes under SB 9, a lot split, or a small-lot subdivision on vacant land. Put in your lot and see which paths are open.
Lot checkerThe rulesHow they stackTimelineBy the numbers
- each SB 9 home800 sq ftat least, guaranteed
- to split a lot2,400 sq ftabout, under state minimums
- side and rear setbacks4 ftat most, for SB 9 homes
- city decision60 daysor it’s deemed approved
lot checker
What you can build on this lot
Answer ten questions about the lot. Each path shows whether it’s open, what to check and how many homes state law guarantees, and the diagram draws it.
…the most homes state law guarantees on this lot, from the paths that are open or worth checking
A schematic, not a site plan: the dashed line marks 4-foot side and rear setbacks. Your city’s front setback, objective standards, easements and utilities decide the real layout.
lot math
New lots must each be at least 1,200 sq ft and at least 40% of the original lot. Cities may allow smaller lots, not larger minimums.
State law sets the floor; your city’s objective standards, easements, utilities and costs decide what fits. Before you design, we can pull the city’s rules and recent sales of new homes and ADUs nearby.
the rules
The SB 9 rules
SB 9 (2021) gives owners in single-family zones two options, approved by city staff with no hearing and no CEQA review. You can use one or both.
Two homes on one lot
- Where it appliesSingle-family zones only, in cities that include part of a U.S. Census urbanized area or urban cluster.
- What it allowsUp to two homes on the lot: two new ones, or one new home added to an existing one. They can be attached or detached.
- Size and setbacksLocal rules can’t keep either home from being at least 800 sq ft. Side and rear setbacks are 4 ft at most, and none for an existing structure rebuilt in place.
- ParkingAt most one space per home, and none within half a mile of high-quality transit or a major transit stop, or one block of a car-share vehicle.
- Who can’t use itHousing rented to a tenant in the last 3 years, rent-controlled or rent-restricted housing, parcels with an Ellis Act withdrawal in the last 15 years, mapped hazard and protected land, and landmarks or contributing historic structures.
- RentingRentals must be longer than 30 days. There’s no owner-occupancy rule for two homes on one lot.
Splitting the lot
- Lot sizesTwo new lots of roughly equal size, each at least 1,200 sq ft and at least 40% of the original, so a 60/40 split at most.
- Once onlyA parcel can be split only once, and a city can refuse a split of an adjacent parcel by the same owner.
- The affidavitThe applicant signs an affidavit to live in one of the homes as a principal residence for 3 years from approval. Community land trusts and qualified nonprofits are exempt.
- Homes per lotUp to two homes on each new lot, and ADUs and JADUs count toward the two: up to four homes in all.
- What cities can’t requireRight-of-way dedications, offsite improvements, fixes to nonconforming conditions or park in-lieu fees. They can require utility easements and access to a public street.
- TimingA complete application is approved or denied within 60 days, or it’s deemed approved. A denial needs a written finding of a specific health or safety impact that can’t be mitigated.
how they stack
How SB 9 and ADUs stack
What state law guarantees on one lot. Cities can allow more.
| path | what the state guarantees | homes | the catch |
|---|---|---|---|
| ADU law only | Your house plus a converted ADU, a junior ADU and a new detached ADU | 4 homes | Two detached ADUs under AB 956, likely from January 1, 2027 |
| SB 9, two homes | Two homes plus an ADU and a JADU (HCD’s example) | up to 4 | SB 9 never requires more than 4 on one lot |
| SB 9, lot split | Two homes on each new lot; ADUs and JADUs count | up to 4 | The 3-year owner affidavit |
| Both SB 9 tools | Two homes on each new lot | up to 4 | A city doesn’t have to allow ADUs on top |
| Small-lot subdivision | Up to 10 parcels or homes on a vacant single-family lot | up to 10 | Vacant lots of 1.5 acres or less only |
Whether a city must allow a fifth home without a split (for example two homes, two ADUs and a JADU) isn’t settled; up to 4 is guaranteed, and more is up to your city.
the timeline
How the rules got here
- Jan 1, 2022SB 9 takes effect
Two homes and lot splits on single-family lots, approved by staff.
- Jan 1, 2024HCD can enforce SB 9
AB 434 gave the state housing department enforcement authority; it reviews local SB 9 ordinances.
- Jul 1, 2024SB 684 starts
Streamlined subdivisions of up to 10 parcels on multifamily-zoned lots.
- Jan 1, 2025SB 450 tightens SB 9
The 60-day deadline, standards that apply uniformly across the zone, and no more 25% demolition limit.
- Jul 1, 2025SB 1123 adds vacant single-family lots
Up to 10 parcels on vacant single-family lots of 1.5 acres or less.
- Jan 1, 2026AB 1061 narrows the historic exclusion
Only landmarks and contributing structures in historic districts are excluded.
- Sep 29, 2026AB 956, SB 1117 and SB 1116 signed
Two detached ADUs, ADU impact fees only above 750 sq ft, and changes to small-lot subdivisions. Confirm their start dates with your city.
by the numbers
How often owners use SB 9
Not often. The Terner Center’s first-year count, through November 2022, found activity limited or nonexistent in most cities it studied.
| city | lot splits filed | approved | two-unit filed | approved |
|---|---|---|---|---|
| San Jose | 10 | 5 | 1 | 0 |
| San Francisco | 4 | 2 | 25 | 4 |
| Saratoga | 21 | 2 | 15 | 1 |
Source: Terner Center for Housing Innovation, UC Berkeley, published January 2023. We found no official statewide count since.
Why so few
- CostHigh construction costs, and most homeowners aren’t builders.
- Local limitsCity rules on size, height and design.
- Fewer perks than ADUsSB 9 homes don’t get ADU fee limits.
- The split affidavitThe 3-year owner-occupancy promise for lot splits.
- Process and riskSubdivision Map Act costs, construction-defect liability, planning staff shortages and interest rates.
- Where it workedMore activity in places with larger lots, homes set in the middle of the lot, and high prices, such as Saratoga.
city notes
City notes
- San FranciscoSB 9 applies in RH-1, RH-1(D) and RH-1(S) zones. Lots must be at least 2,400 sq ft to split, with new lots between 40% and 60% of the original. The city adopted SB 9 design standards on November 14, 2024.
- CupertinoA ministerial permit for up to two homes and a ministerial subdivision for a split, with lots of at least 1,200 sq ft and about equal size. The Director’s decisions can’t be appealed. Standards in Ordinance 22-2246 (November 15, 2022).
- Unincorporated San Mateo CountyApproved two small-lot subdivisions on single-family land in 2026: a 9-home project on May 22 and a 5-home project on July 1.
- Every other cityEach city applies its own objective standards within state limits. Check the current ordinance for the address before you design.
City pages lag the law. San Francisco’s SB 9 bulletin, for example, still describes the historic-district exclusion as it read before AB 1061 took effect in 2026.
questions
Questions we hear
Can I split my lot and sell the new one?
SB 9 creates a lot that can be sold, but the applicant signs an affidavit to live in one of the homes as a principal residence for three years from approval. A parcel can be split only once.
How small can the new lots be?
Each must be at least 1,200 sq ft and at least 40% of the original lot, so you need about 2,400 sq ft to start. Cities can allow smaller lots, not larger minimums.
Do I have to add parking?
A city can require at most one space per home, and none within half a mile of high-quality transit or a major transit stop, or within one block of a car-share vehicle.
Can I rent the new homes?
Yes, for terms longer than 30 days. Short-term rentals aren’t allowed for SB 9 homes.
How long does approval take?
The city has 30 days to say whether the application is complete, then 60 days to approve or deny it. If it misses the 60 days, the application is deemed approved.
Is an ADU or SB 9 the better route?
It depends on the lot and the goal. ADUs get fee limits and no owner-occupancy rule; SB 9 creates full homes and, with a split, separate lots. Start with the checker above, then price both.
sources
Sources
State law, state housing department guidance and city pages behind this page, checked October 2026.
- HCD: Duplexes and Lot Splits (SB 9) fact sheetApril 2026www.hcd.ca.gov/sites/default/files/docs/planning-and-community/lot-splits-and-duplexes-sb-9.pdf
- HCD: SB 9 fact sheetSeptember 2024www.hcd.ca.gov/sites/default/files/docs/planning-and-community/sb-9-fact-sheet.pdf
- Government Code 65852.21: two homes on a single-family lotCalifornia Legislative Informationleginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV§ionNum=65852.21
- Government Code 66411.7: urban lot splitsCalifornia Legislative Informationleginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV§ionNum=66411.7
- Government Code 66499.41: small-lot subdivisionsCalifornia Legislative Informationleginfo.legislature.ca.gov/faces/codes_displaySection.xhtml?lawCode=GOV§ionNum=66499.41
- HCD: ADU handbookMarch 2026www.hcd.ca.gov/sites/default/files/docs/policy-and-research/adu-handbook-update.pdf
- Governor’s office: housing bills signed September 29, 2026AB 956, SB 1117, SB 1116www.gov.ca.gov/2026/09/29/governor-newsom-signs-housing-legislation-cementing-californias-record-progress-to-reduce-unsheltered-homelessness-and-build-more-homes/
- Terner Center: SB 9 Turns OnePublished January 2023ternercenter.berkeley.edu/research-and-policy/sb-9-turns-one-applications/
- SF Planning: Director Bulletin No. 8Updated September 2025sfplanning.org/resource/planning-director-bulletin-no-8-streamlined-housing-development
- City of Cupertino: Senate Bill 9City pagewww.cupertino.gov/Your-City/Departments/Community-Development/Planning/Residential-Planning/Senate-Bill-9
- San Mateo County: SB 684/SB 1123 small-lot subdivisionsCounty pagewww.smcgov.org/planning/sb-684sb-1123-small-lot-subdivision-and-housing-development
more to learn
Keep going
- ADU GuideADU rules, costs and a payback calculator.
- SB 9Lot splits and duplexes on single-family lots.
- Investor ToolkitCash flow, 1031 timing and rent rules.
- Property tax calculatorWhat new construction does to your bill.
- Disclosure DecoderEvery document in a California disclosure packet.
- Market PulseHomes for sale and 12 months of sale prices by city.
General information about California law as of October 2026, not legal or architectural advice. Your city’s ordinances, objective standards and permit staff decide what you can build.
talk to a property nerd
Thinking about building or buying to build?
We’ll pull the city’s rules for the address, look at recent sales of new homes and ADUs nearby, and help you weigh the options. Commissions are negotiable, and we offer bundled services, so ask us what’s included.
