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.