Last reviewed: August 11, 2026. Planning ranges are based on contractor experience and are not city service guarantees. Rules and lender requirements vary by property, jurisdiction, and program.
SB 9 and ADU law provide different ministerial housing pathways. An urban lot split generally creates two approximately equal parcels, with neither parcel smaller than 40% of the original and each parcel at least 1,200 square feet, unless the local agency has adopted a smaller minimum allowed by statute. After a qualifying urban lot split, state law does not require a local agency to permit more than two total units on either resulting parcel. For this rule, primary dwellings, SB 9 units, ADUs and JADUs count as units. A local agency may choose to allow more. An ADU keeps the lot whole. The appropriate path depends on parcel eligibility, existing units, objective standards, owner-occupancy and rental restrictions, title, financing and the owner's goals.
Homeowners keep asking us whether they should “do SB 9” instead of building an ADU. Fair question — the two laws get mixed together in every news story. Here is what each one actually does, and how to tell which fits your property.
01What SB 9 actually allows
Senate Bill 9 (in effect since 2022) gives owners of single-family lots in urbanized areas two ministerial rights:
- Two units on one lot — a duplex (or a second primary unit) where one house stood, approved without a hearing.
- The urban lot split — under Government Code section 66411.7, an urban lot split generally creates two approximately equal parcels, with neither parcel smaller than 40% of the original and each parcel at least 1,200 square feet, unless the local agency has adopted a smaller minimum allowed by statute. After a qualifying urban lot split, state law does not require a local agency to permit more than two total units on either resulting parcel. For this rule, primary dwellings, SB 9 units, ADUs and JADUs count as units. A local agency may choose to allow more.
A qualifying urban lot split includes statutory eligibility conditions and generally requires a three-year owner-occupancy affidavit, subject to the statute's stated exceptions. Protected categories, existing uses, prior splits, objective standards, easements, access, utilities and the parcel geometry can affect eligibility. Confirm the current parcel-specific requirements before assuming that a split is available.
02What an ADU does instead
An accessory dwelling unit adds an independent dwelling on the existing lot and may be detached, attached, above a garage, or converted from existing space. ADUs are available on many qualifying residential lots, subject to state and local standards. A permitted ADU may be rented on a term longer than 30 days after required permits, inspections, and occupancy approvals are complete, subject to applicable restrictions. Project-specific cost drivers are explained in the cost guide.
03The real comparison
| ADU | SB 9 lot split | |
|---|---|---|
| What you end up with | One lot with an additional dwelling pathway | The resulting parcels may generally be conveyed separately after an approved and recorded split; verify title, financing, and local requirements |
| Owner-occupancy | Generally not required for an ADU; a JADU may require owner occupancy when sanitation is shared, subject to statutory exceptions | A three-year affidavit is generally required for a split, subject to statutory exceptions |
| Lot requirements | Available on many qualifying residential lots, subject to state and local standards | Neither resulting parcel may be smaller than 40% of the original and each is generally at least 1,200 square feet, unless a smaller local minimum is allowed by statute; other exclusions apply |
| Process weight | One building permit path | A subdivision map plus building permits — surveyors, utilities per lot, more time and fees |
| Decision factors | Housing goals, site feasibility, existing units, utilities, schedule and financing | Parcel eligibility, owner-occupancy, title, access, utilities, financing and long-term ownership goals |
The interaction depends on whether the property uses an urban lot split. After a qualifying urban lot split, state law does not require a local agency to permit more than two total units on either resulting parcel. For this rule, primary dwellings, SB 9 units, ADUs and JADUs count as units. A local agency may choose to allow more. Without a split, separate SB 9 and ADU/JADU entitlements may apply, but the allowable combination still depends on the statutory pathway, existing units, objective standards, and local implementation. Confirm the parcel-specific configuration before representing a three- or four-unit outcome. See the current California HCD SB 9 fact sheet.
04How to decide for your lot
Compare parcel eligibility, existing and proposed units, lot geometry, objective standards, access, utilities, title, financing, owner-occupancy and rental restrictions, and long-term ownership goals. Neither pathway is categorically better. A parcel-specific feasibility review should identify which statutory path, if any, fits the property before a unit count or separate-conveyance outcome is represented.
Quick answers
What is SB 9 in California?
Is an ADU better than an SB 9 lot split?
Can I do both SB 9 and an ADU?
Why don't SB 9 splits work on small lots?
SB 9 and the ADU path answer different questions, and it is worth reading them side by side. California ADU law gives you a second unit on the lot you already own, with ministerial approval and no owner-occupancy requirement. SB 9 splits the parcel itself, which is a bigger, slower move with its own affidavit. If you are only comparing to decide what to build, the rules table shows how each city treats an ADU, and the permit guide covers the submittal either way.