Senate Bill 9 (SB 9), effective January 1, 2022, allows property owners in single-family zones to split their lot and/or build up to two primary dwelling units per parcel. SB 9 works in conjunction with ADU law to significantly increase density on single-family lots.
Urban Lot Split — Diagram
Two-Unit Development (§ 65852.21)
Standard
Requirement
Notes
Units Allowed
2 primary units per lot
Plus ADUs and JADUs per standard ADU law
Maximum Unit Size
No state maximum
Subject to local zoning (FAR, lot coverage, height)
Setbacks
4 ft side and rear
No front setback reduction
Height
Per underlying zone
Typically 28–35 ft in single-family zones
Parking
1 space per unit required
Waived within ½ mile of transit
Design Standards
Objective standards only
No subjective architectural review allowed
Owner-Occupancy
Required for 3 years post-approval
Applicant must intend to occupy one unit
Demolition Limits
Cannot demolish more than 25% of existing exterior walls
Protects against whole-lot teardowns via SB 9
Tenant Protections
No eviction of existing tenants within prior 3 years
Cannot subdivide if tenant-occupied in past 3 years
Urban Lot Split (§ 66411.7)
Standard
Requirement
Split Ratio
60/40 minimum — larger parcel ≥ 60% of original
Minimum Lot Size (each parcel)
1,200 sq ft
Units per Parcel After Split
2 primary units + up to 2 ADUs + 1 JADU = up to 6 total units
Passageway Required
Yes — access to public ROW from each parcel
Map Type
Parcel Map or Tentative Parcel Map
Timing
Ministerial approval within 60 days
Successive Splits
Not permitted — each original parcel may only be split once under SB 9
Eligibility — Disqualifying Conditions
Condition
Effect
Historic District or Landmark
SB 9 rights do not apply
High Fire Hazard Severity Zone (VHFHSZ)
City may deny; case-by-case review
Earthquake Fault Zone
May require geotechnical study; limits apply
Flood Zone (FEMA AE/VE)
Subject to additional state and local restrictions
Prime Agricultural Land
Exempt from SB 9
Environmental Sensitive Area (ESA)
Coastal Commission, wetlands, ESHA — may not qualify
Density Stacking: Maximum Units Per Original Parcel
Mechanism
Units Added
Total Running Count
Original single-family lot
1
1
SB 9 Two-Unit Development
+1
2
JADU (within existing structure)
+1
3
ADU (detached or attached)
+1
4
SB 9 Lot Split → repeat above on 2nd parcel
up to +4
Up to 8
Disclaimer: SB 9 is subject to ongoing litigation and local interpretation. This guide reflects the law as of early 2026. Consult a licensed architect or land use attorney for specific project advice.
