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Call (916) 436-3776SB 9 Lot Splits & Duplexes North Bay & Wine Country
How Does an SB 9 Lot Split or Duplex Work in the North Bay & Wine Country?
In the North Bay, Sonoma, Napa, Marin, SB 9 lets you add units to a qualifying single-family lot by right: build a second unit (a duplex or a house plus an ADU), split the lot into two parcels, or both, up to four units on what was one single-family lot. Approval is ministerial when the objective criteria are met. Eligibility depends on single-family zoning, an urban location, a 40/60 lot-size split, tenant-protection rules, and local standards, so feasibility must be confirmed with your city first. Serve First checks feasibility and handles the real estate; Ashlar Lending finances the build; Ashlar LDA prepares the documents.
North Bay & Wine Country SB 9 snapshot (2026)
Up to 4 units
Lot split + a duplex on each new lot
40% minimum
Smaller parcel in a lot split
Ministerial
By-right approval, no hearing
No Prop 13 hit
The split itself isn't a reassessment event
Figures reflect 2026 rules and change over time. SB 9 eligibility and local development standards vary by jurisdiction and must be confirmed with your city or county. Serve First Realty is a licensed California real estate brokerage, not a lender, contractor, or law firm.
How an SB 9 project works in the North Bay & Wine Country
SB 9 offers two tools that can be used separately or together. Here's how they work and where Serve First, Ashlar Lending, and Ashlar LDA come in, starting, always, with a feasibility check:
Understand the two SB 9 paths
SB 9 gives you a two-unit development path (add a second unit so a single-family lot holds a duplex, or a house plus an ADU) and an urban lot split path (divide one lot into two). Use them together, split, then put two units on each new lot, and a single parcel can become up to four homes, all by right.
Confirm your lot actually qualifies
This is step one, and it's where projects succeed or fail. The parcel must be zoned single-family and sit in an urbanized area or urban cluster; a lot split must leave the smaller parcel at least 40% of the original (a 60/40 split at most) with no minimum lot size. It can't require demolishing rent-controlled, deed-restricted, Ellis-Act-withdrawn, or recently tenant-occupied housing, and historic properties are excluded. Fire and flood zones trigger extra review rather than automatic disqualification. Serve First helps you assess eligibility of a North Bay & Wine Country lot before you spend.
Know the owner-occupancy affidavit
For an urban lot split, SB 9 requires the applicant to sign an affidavit agreeing to occupy one of the units as their primary residence for at least three years. That shapes whether a split fits your goals, it's built for owners, not quick-flip speculators. (The two-unit development path on its own generally doesn't carry this.) Ashlar LDA can prepare the affidavit and related documents at your direction.
Finance the build
Adding units is a construction project. Ashlar Lending can arrange construction or renovation financing sized to the build, and model the cost against the rent or resale value the new units will produce, so you go in knowing the project pencils. New units can generate rental income or be sold, depending on your plan.
Decide: hold, rent, or sell
An SB 9 project can create a rental, a home for family, or a new parcel or unit to sell. Serve First helps you weigh the options for your North Bay & Wine Country property and market the new lot or finished units to the right buyers when the time comes.
Confirm feasibility with your city before you commit a dollar. SB 9 is state law, but eligibility and objective development standards, setbacks, unit size, access, and how each rule is applied, vary by jurisdiction, and some cities interpret them more restrictively than others. A North Bay & Wine Country parcel that looks eligible on paper may not pencil once local standards, lot geometry, and tenant-protection rules are applied. Serve First helps you run that feasibility check first, so you build on facts, not assumptions.
One family. Land, financing, and paperwork.
Turn one lot into more, with the whole project supported
An SB 9 project can add units and value to a single-family lot, but it takes feasibility, financing, and documentation. The Ashlar Brands family helps across all three:
- Serve First Realty helps you find an SB 9-eligible lot to buy, assess whether your current property qualifies, and sell the newly created lot or the finished units to the right buyers.
- Ashlar Lending Inc. (NMLS #2699657) can arrange construction or renovation financing to build the new duplex or second home, and model the numbers: build cost against rent or resale, so the project pencils.
- Ashlar LDA, Inc., a bonded and registered Legal Document Assistant, can prepare deeds, the owner-occupancy affidavit an urban lot split requires, and related documents at your direction.
These are separate businesses in the Ashlar Brands family. Serve First is a real estate brokerage, not a lender, contractor, or law firm. SB 9 eligibility and local standards vary by jurisdiction and must be confirmed with your city or county. A Legal Document Assistant prepares documents at your direction and is not a substitute for an attorney.
Doing an SB 9 project in the North Bay & Wine Country: the steps
Start with a feasibility check
Before anything else, Serve First helps you confirm whether your North Bay & Wine Country lot qualifies under SB 9 and the city's local standards, the single most important step.
Model the financing and the numbers
Ashlar Lending sizes construction financing to the build and models cost against rent or resale, so you know the project works before you start.
Handle the paperwork
Ashlar LDA prepares deeds, the owner-occupancy affidavit a lot split requires, and related documents at your direction.
Build, then hold or sell
Complete the units, then rent them, house family, or have Serve First sell the new lot or finished homes to the right buyers.
Frequently asked questions
How many units can SB 9 add to my lot?
Potentially up to four. SB 9 lets you put two units on a single-family lot (a duplex, or a house plus an ADU) and separately split the lot into two parcels. Combine them, split, then two units on each new lot, and one single-family parcel can become as many as four homes, all with ministerial (by-right) approval when the criteria are met. Local standards can affect what actually fits.
What are the basic eligibility rules?
The lot must be zoned single-family and located in an urbanized area or urban cluster. A lot split must leave the smaller parcel at least 40% of the original (a 60/40 split at most), with no minimum lot size. The project can't require demolishing rent-controlled, deed-restricted, Ellis-Act-withdrawn, or recently tenant-occupied housing, and historic properties don't qualify. Every city applies its own objective standards on top, so confirm locally.
Do I have to live on the property?
For an urban lot split, yes, SB 9 requires you to sign an affidavit agreeing to occupy one of the units as your primary residence for at least three years. This is designed to favor homeowners over short-term speculators. The two-unit development path by itself generally doesn't carry an owner-occupancy requirement. Ashlar LDA can prepare the affidavit at your direction.
Will an SB 9 lot split raise my property taxes?
The split itself is not a Proposition 13 reassessment event, so dividing the lot doesn't automatically reassess your retained property. New construction on the lot is assessed as new value, and a sale of a newly created parcel is its own event. Tax treatment can be nuanced, so confirm the specifics for your situation with a tax professional.
Is SB 9 available everywhere in California?
SB 9 is state law that applies to qualifying single-family parcels in urban areas, but how it's implemented varies by city and county, and some jurisdictions apply the rules more restrictively than others. Because of that variation, feasibility has to be confirmed with your specific city or county before you rely on it. Serve First helps you check whether a given North Bay & Wine Country property qualifies.
Exploring an SB 9 project in the North Bay & Wine Country?
Serve First Realty Inc. is a licensed California real estate brokerage that helps North Bay & Wine Country owners assess SB 9 feasibility, buy eligible lots, and sell the units or parcels they create.
California DRE# 02133513
SB 9 guides for nearby areas
Or start with the statewide overview: SB 9 Lot Splits & Duplexes in California.
More guides for this area: all North Bay & Wine Country real estate guides.