QUICK ANSWER
SB 9 Lot Split vs ADU in San Jose: Which Path Fits Your Lot?
Choose an ADU if you want to keep one property and rent or house family; most Bay Area ADUs cost $150,000 to $400,000. Choose an SB 9 lot split only if you want a separate lot you can sell or finance: each new lot must be at least 1,200 sq ft, the smaller at least 40 percent of the original, and you sign an affidavit to live there for 3 years. In San Jose, each split lot is capped at two units, ADUs included.
If you own a larger single-family lot in San Jose, you have three real ways to add housing: build an ADU, build a second home under SB 9, or split the lot under SB 9 and sell or keep part of the land. The "SB 9 vs ADU" question is less about which law is better and more about one thing: do you ever want to sell part of the property on its own? Below, we compare the paths, San Jose's local rules, and the checks to run before paying for surveys or drawings.
A quick note before we start: this is planning guidance from a design-build team, not legal or tax advice. Lot splits create new legal parcels, so confirm your plan with the City of San Jose and a real estate attorney before you commit.
What does SB 9 actually allow on a San Jose lot?
SB 9 gives most single-family lots two ministerial options: a two-unit development on your existing lot, and an urban lot split that divides one lot into two. "Ministerial" means the city checks your plans against objective standards with no public hearing and no discretionary design review. The law took effect January 1, 2022 (SB 9 bill text).
Option 1: Two-unit development (no split)
Under Government Code 65852.21, the city must ministerially approve up to two primary units on a single-family lot if the project meets objective standards. Key state rules:
- The city cannot apply standards that would block two units of at least 800 sq ft each.
- Side and rear setbacks can be no more than 4 feet for new construction. An existing structure, or one rebuilt in the same footprint, needs no new setback.
- Parking can be capped at one space per unit, and none can be required within one-half mile of high-quality transit or a major transit stop.
- Any rental of a unit must be for more than 30 days, so short-term rentals are out.
Option 2: Urban lot split
Under Government Code 66411.7, you can split one single-family lot into two parcels through a parcel map. The state rules:
- Each new lot must be at least 1,200 sq ft, and the smaller lot cannot be less than 40 percent of the original. That is the "60/40" rule people mention.
- You must sign an affidavit that you intend to live in one of the units as your principal residence for at least 3 years from approval.
- The city must act on a complete application within 60 days.
- Each new lot can be limited to two units, and the statute counts ADUs and JADUs toward that two.
- Lots created by an SB 9 split cannot be split again under SB 9, and you cannot split an adjacent lot you own the same way.
Who is excluded
Both options are off the table if the project would demolish or alter housing that has been occupied by a tenant in the last 3 years, rent-controlled or deed-restricted affordable housing, or housing removed from the rental market under the Ellis Act within 15 years. Certain hazard and resource areas also restrict eligibility, such as very high fire hazard severity zones, earthquake fault zones, flood zones, and wetlands, with some exceptions where the site meets mitigation standards. Historic protections changed on January 1, 2026: AB 1061 narrowed the old historic-district exclusion so it focuses on designated historic resources and landmarks rather than entire districts. San Jose is updating its code to match through ordinance update PP25-007.
How does San Jose apply SB 9?
San Jose follows state law with a few local rules you need to know. The city adopted an SB 9 urgency ordinance on December 14, 2021, and its SB 9 overview page lays out how the program works today:
- Single-family lots only. SB 9 applies to lots in the city's R-1 single-family districts and some planned development (PD) districts. Lots that already hold a duplex or multifamily building do not qualify, though they may still add ADUs.
- Two units per lot after a split. On lots created by an SB 9 subdivision, San Jose caps development at two units per lot, ADUs included.
- Owner occupancy for splits. The applicant must live on one of the resulting parcels for 3 years from approval of the subdivision.
- Local frontage, depth, and access standards. The ordinance gives alternate lot frontage, depth, and access standards where the regular Subdivision Ordinance conflicts with SB 9. In practice this is where many lot splits succeed or fail.
- CC&Rs still matter. The city notes it cannot enforce private agreements, but your neighborhood's CC&Rs may still limit what you build.
The city is also working on changes. Its Zoning Ordinance Update (PP25-001) proposes extending SB 9-style two-unit projects to R-2 districts and revising objective design standards. For current application steps and checklists, start at the city's SB 9 Duplex Project or Subdivision page. Building permits are then filed through SJPermits.org, the same portal used for ADUs and remodels.
SB 9 vs ADU: side-by-side comparison
The biggest difference is ownership: an ADU stays on your one parcel, while an SB 9 lot split creates two parcels that can be sold separately. Everything else follows from that.
| Factor | ADU (+ JADU) | SB 9 two-unit (no split) | SB 9 urban lot split |
|---|---|---|---|
| Approval path | Ministerial ADU permit under state ADU law | Ministerial, objective standards only | Ministerial parcel map, then building permits |
| Can you sell part separately? | Generally no. Only as a condo where a city has adopted AB 1033 | No, still one parcel | Yes, each lot gets its own title |
| Owner-occupancy rules | None for an ADU. A JADU requires the owner to live in the JADU or main home | None in the state statute for the two-unit option | Affidavit to live in one unit for 3 years |
| Typical max units | Main home + ADU + JADU, more in some setups | Two primary units, and San Jose allows ADUs with a duplex | Two per new lot, ADUs counted |
| Main cost drivers | Size, foundation, utility runs, finishes | Second full home, utilities, site work | Survey, parcel map, separate utilities and laterals, then construction |
| Timeline factors | Design, permit review, build | Design, permit review, build | Map approval and recording before or alongside building permits |
| Financing | Against your one property (HELOC, cash-out refi, construction loan) | Against your one property | Each lot can be financed or sold on its own once recorded |
A note on the "up to four units" claim you may have read online. It can be true on paper in some scenarios, such as two lots with two units each, but the statute lets a city cap each split lot at two units including ADUs, and San Jose does. On an unsplit lot, a duplex plus ADUs is possible in San Jose, but the exact count depends on the current ADU ordinance and your site. Confirm the number with the city for your parcel rather than planning around a headline.
Which path fits your goal?
Start with what you want the property to do in 10 years, not with the law.
Goal 1: Keep everything and rent part of it
An ADU is usually the simplest fit. You keep one parcel and one title, there is no owner-occupancy rule on the ADU, and the permit path is well worn. A typical Bay Area ADU runs $150,000 to $400,000 depending on size and site. Our Bay Area ADU guide covers sizes, costs, and rent math, so we will not repeat it here.
Goal 2: House family on the same property
For parents or adult kids, an ADU or a JADU usually wins on cost and simplicity. If family members need a full-size home with its own yard, an SB 9 two-unit development lets you build a second primary home without splitting the lot.
Goal 3: Sell part of the land
This is the main reason to choose an SB 9 lot split. It is the only one of the three paths that creates a separate legal lot you can sell or finance on its own. The trade-offs are the 3-year owner-occupancy affidavit, the cost of the parcel map and utility separation, and a smaller remaining lot. If you only want to sell a small unit, compare the condo route in our AB 1033 guide. San Jose has been one of the early adopters of that path, but confirm the current program with the city before you design around it.
Goal 4: Build a new home
If your existing house is near the end of its life, a lot split can pair with new construction: keep or rebuild one home, and build a second on the new lot. Before you choose, run the remodel vs rebuild math in our remodel vs rebuild guide. New custom construction in the Bay Area typically runs $400 to $700+ per sq ft.
What drives the cost of an SB 9 lot split?
A lot split adds a layer of soft costs and site work before any home is built. We are not publishing a single dollar figure because these costs swing widely by site. The main drivers are:
- Boundary and topographic survey. Needed to draw the new line, confirm the 60/40 ratio, and locate easements.
- Parcel map preparation. A licensed surveyor or civil engineer prepares the map that the city reviews and records.
- City application and review fees. Check San Jose's current fee schedule for the parcel map and building permits.
- Utility separation. Each lot typically needs its own water, sewer lateral, and electric service. A long sewer run, an upgrade at the street, or a new meter can be a large line item.
- Access. A rear lot may need a driveway or access easement that meets the city's access standards.
- Legal and title work. Easement agreements, new legal descriptions, and lender consent if you carry a mortgage on the original lot.
Plan a 10 to 20 percent contingency on the construction side, as you would for any major project.
Feasibility checklist before you spend money
Most SB 9 plans are decided by the lot, not the law. Check these six items first, ideally with someone who has built on San Jose lots before:
- Lot size and shape. Can both lots reach 1,200 sq ft with the smaller at 40 percent or more? Odd shapes and flag lots get harder.
- Frontage and access. Can each new lot meet San Jose's frontage or access options? A narrow lot with one curb cut may only work as a flag lot with an access easement.
- Utilities. Where are the sewer main, water main, and electric service? Each lot needs its own path to them, on its own parcel or in an easement.
- Easements and title. Pull a preliminary title report. Existing utility or access easements can cut buildable area.
- Hazard zones and historic status. Check fire, flood, fault, and historic designations for your parcel before design.
- Trees. San Jose regulates ordinance-size trees, and a mature tree in the middle of the lot can shape the whole layout.
What we have learned building on San Jose lots
We have not published an SB 9 lot split in our portfolio, so we will not claim one. What we can show is how San Jose lots behave when you add a lot of house to them.
At 1285 Curtiss Ave in San Jose, we demolished a roughly 1,200 sq ft house and built a roughly 4,000 sq ft custom home in 2019. That is the same core work as the "build a new home" path: demolition, new utilities, a new foundation, and a full city permit set.
At 1440 Bird Ave in San Jose, we took a home from about 1,046 to about 2,207 sq ft on a 7,405 sq ft lot in 2021, with a new porch, rear patio, and attached garage. On paper, a lot that size could split near 60/40 into parcels of about 4,440 and 2,960 sq ft, well above the 1,200 sq ft minimum. Whether that works in real life depends on frontage, access, and utilities, which is exactly why the checklist above comes first.
Because UniqHaus handles architecture, 3D design, permit-ready drawings, city coordination, and construction as one team, a feasibility study and a build plan can come from the same people who will price and build it. Our pricing is itemized, and once you approve it, the price is fixed. Changes you request after approval are priced as change orders.
How to move forward
This order keeps costs low while you decide:
- Write down your 10-year goal and run the feasibility checklist.
- Review San Jose's SB 9 page and the ADU permit process side by side.
- Talk to a real estate attorney if you are considering a split or a sale.
- Get a site visit and a concept plan before paying for a full survey.
If you want an ADU, see our ADU design-build service. If the plan includes a new home, see our custom homes service. For how we work locally, visit our San Jose page.
Frequently Asked Questions
Can I build an ADU and use SB 9 on the same lot in San Jose?
On a lot you do not split, San Jose says its ADU ordinance allows ADUs on a property with a duplex, so an SB 9 two-unit project plus ADUs can be possible. If you split the lot, San Jose caps each new lot at two units total, ADUs included. Confirm the exact count for your parcel with the city's SB 9 page.
What is the minimum lot size for an SB 9 lot split?
Under Government Code 66411.7, each new lot must be at least 1,200 sq ft and the smaller lot must be at least 40 percent of the original. That means the original lot needs at least 2,400 sq ft, and in practice frontage, access, and utilities decide far more splits than area does.
Do I have to live on the property after an SB 9 lot split?
Yes. State law requires an affidavit that you intend to live in one of the units as your principal residence for at least 3 years from approval, and San Jose applies that rule. The two-unit option without a split has no owner-occupancy requirement in the state statute. Ask a real estate attorney how this affects your plans.
Can I sell an ADU separately in San Jose?
Not as a separate lot. An ADU stays on your parcel. The only route is a condo conversion under AB 1033 in cities that adopt it, and San Jose has been an early adopter. See our AB 1033 guide and confirm current rules with the city.
Does SB 9 apply if I rented my house in the last 3 years?
Often not. SB 9 excludes projects that would demolish or alter housing occupied by a tenant in the last 3 years. If part of your home was rented, check eligibility with the city before paying for a survey or drawings.
Is SB 9 still in effect in San Jose after the 2024 court ruling?
Yes, according to the city. The April 2024 ruling applied to five Southern California charter cities, and San Jose states SB 9 remains in effect locally. Check the city's SB 9 overview for any update before you apply.
Key Takeaways
- An ADU keeps one parcel; only an SB 9 lot split creates a separate lot you can sell.
- Each SB 9 lot must be at least 1,200 sq ft, with the smaller lot at 40 percent or more of the original.
- A lot split requires a 3-year owner-occupancy affidavit, and San Jose caps each split lot at 2 units including ADUs.
- Check frontage, access, utilities, easements, hazard zones, trees, and 3-year tenant history before spending on a survey.
NEXT STEP
Not sure if your San Jose lot should get an ADU or an SB 9 split?
Start a conversation with our team. We will look at your lot, your goals, and the rules, then tell you which path makes sense. Call (650) 866-5665 or contact us.