Blog > SB 9 in Silicon Valley: what lot splits mean for buyers
property nerd guide · buyers
SB 9 lets many Silicon Valley single-family lots hold two homes, or split into two lots. Here is what the law allows, what to check on a listing and how it can change what a home is worth to you and to the neighbors.
By the Property Nerds® of the Boyenga Team at Compass · NextGenAgents™
the short version
SB 9 changes what a single-family lot can become
Since January 1, 2022, California's SB 9 has required cities to approve qualifying two-unit projects and lot splits in single-family zones ministerially, without a public hearing. Since January 1, 2025, they have had 60 days to decide.
For buyers, that cuts two ways. A lot you buy may have options the last owner never used. And the lot next door may have them too. Our SB 9 explainer covers the basics for owners; this guide looks at the law through a buyer's eyes.
units per lot
after a lot split
smallest new lot
city decision
the rules
SB 9 in plain English
Two-unit projects
A lot in a single-family zone can hold up to two primary homes, either two new units or one new unit beside an existing one (Government Code §65852.21).
Urban lot splits
A lot can be split into two of roughly equal size. Neither can be smaller than 40% of the original, and each must be at least 1,200 sq ft unless the city allows smaller (§66411.7).
Owner-occupancy for splits
The applicant signs an affidavit stating they intend to live in one of the units as their principal residence for at least three years from approval.
No short-term rentals
Any rental of an SB 9 unit must be for a term longer than 30 days.
Size and setbacks
City standards can't stop two units of at least 800 sq ft. Side and rear setbacks can't exceed four feet, and none is required for an existing structure rebuilt in place.
Parking
A city may require up to one space per unit, but none within a half mile of a major transit stop or high-quality transit corridor, or within one block of a car share vehicle.
what's excluded
When SB 9 doesn't apply
A project can't demolish or alter housing that has been occupied by a tenant in the last three years, that is rent controlled or that carries an affordability covenant. Individually listed historic properties and many historic district properties are excluded, as are sites with certain environmental constraints, such as some fire, flood and earthquake fault zones. A lot created by an SB 9 split can't be split again, and an owner who split an adjacent lot under SB 9 can't split the next one.
| Option | Units | Owner-occupancy | Separate sale |
|---|---|---|---|
| SB 9 two-unit project | Up to 2 primary units, plus ADUs if no split | Not required by SB 9 without a split | Stays one parcel |
| SB 9 lot split | Up to 2 units on each new lot | 3-year affidavit from the applicant | Two parcels that can be sold separately |
| ADU and JADU | A converted ADU, a JADU and a detached ADU on a single-family lot | None for ADUs; JADUs only if they share sanitation facilities with the house | Generally not, unless the city allows ADU condos |
sb 450
What changed on January 1, 2025
SB 450 (Chapter 286, Statutes of 2024) tightened the process. Cities must approve or deny a complete application within 60 days, or it is deemed approved. A denial must come with a full set of written comments and a way to fix them. Local standards must apply uniformly across the zone, unless they are more permissive. And the old limit on demolishing more than 25% of exterior walls is gone.
listing checklist
What to check on a listing
- The zoning: SB 9 applies to lots in single-family residential zones.
- Historic status. Palo Alto's Greenmeadow and Green Gables Eichler tracts, for example, are National Register historic districts.
- Whether a tenant has lived in the home in the last three years.
- The Natural Hazard Disclosure, for fire, flood and earthquake fault zones.
- Lot size, shape and frontage: can both new lots meet the 40% and 1,200 sq ft rules and still fit two homes?
- Easements and recorded restrictions on the preliminary title report.
- Sewer, water and electrical capacity, plus protected trees under local ordinances.
- The city's own objective SB 9 standards, which differ from city to city.
value
How SB 9 can affect value, for buyers and neighbors
On paper, more units sounds like more value. In practice, design, engineering, utility work, fees and construction all come before any benefit, and a lot split brings the three-year occupancy promise. For some lots the option matters; for many, the numbers don't work. We treat SB 9 potential as a question to study, not a feature to pay extra for.
If you're buying next to a large lot, ask what the neighbor could build. Two units with four-foot side and rear setbacks can change light, views and privacy. That isn't a reason to pass on a home, but it belongs in your thinking.
property nerd note
SB 9 is a math problem first. Before you count on a split, sketch the lot with real dimensions: two parcels at 40% or more, four-foot setbacks, a driveway or access path, utility runs and any protected trees. Then call the city's planning desk with the address. If the sketch doesn't work, the option doesn't exist.
nextgenagents™
How the Boyenga Team helps
Lot screening
We pull zoning, hazard disclosures, title and permit history for the lots you're considering.
Project experience
Our team manages restoration and pre-listing projects, so we know how plans, permits and contractors fit together.
Clear-eyed pricing
As NextGenAgents™ we price homes from what has sold, not from what a lot might become someday.
talk to a property nerd
Wondering what a lot could hold?
Send us the address. We'll pull the zoning, the disclosures and the city's SB 9 rules so you can decide with real information.
faq
SB 9 for Silicon Valley buyers: FAQ
How many homes can SB 9 allow on one lot?
Up to two primary units on a lot that isn't split. After an urban lot split, each of the two new lots can hold up to two units, for up to four in total.
Do I have to live on the property?
For a lot split, yes. The applicant signs an affidavit of intent to live in one unit as a principal residence for at least three years from approval.
Can I rent the units?
Yes, but not as short-term rentals. Any rental of an SB 9 unit must be for longer than 30 days.
How long does the city have to decide?
Since January 1, 2025, 60 days from a complete application, or the application is deemed approved. Design, engineering and building permits take additional time.
Sources: California Government Code §§65852.21 and 66411.7 (current as of January 1, 2026, via FindLaw) · SB 450 (Chapter 286, Statutes of 2024) · California HCD ADU Handbook, March 2026 (hcd.ca.gov) · City of Palo Alto Historic Districts (paloalto.gov). General information, not legal advice. Each city sets its own objective standards; confirm with the city's planning department.