SB 9 lot splits and duplexes

SB 9 lets an owner in a single-family zone build up to two homes on one lot, or split the lot in two and build up to two homes on each. Cities must approve qualifying projects without a public hearing.

What SB 9 allows

• Up to two homes on one lot in a single-family zone.
• A split of one lot into two. Each new lot must be at least 1,200 square feet, and the smaller lot must be at least 40% of the original.
• With a lot split, up to four homes in total, two on each lot.
• Ministerial approval, with no public hearing. Since 2025 (SB 450), cities must act within 60 days and can't hold SB 9 homes to stricter design rules than other homes in the zone.

Who qualifies

• The lot must be in a single-family zone inside a city or an urbanized area.
• To split a lot, the owner signs an affidavit stating they intend to live in one of the homes for three years.
• SB 9 does not apply in historic districts, in Very High Fire Hazard Severity Zones unless the site meets fire mitigation rules, or where the work would demolish affordable, rent-controlled, or recently rented housing.
• SB 9 homes can't be rented for less than 30 days.

Local factors on the Peninsula and in the South Bay

• Parts of Woodside, Portola Valley, Los Altos Hills, Saratoga, and Los Gatos, and the hills around San Jose, sit in Very High Fire Hazard Severity Zones. Check the CAL FIRE map for the address first.
• Atherton, Woodside, Portola Valley, and Los Altos Hills have large minimum lot sizes. A split there can create two sizable lots, but slopes, septic systems, trees, and road access drive the budget.
• Bayside areas, including Foster City, Redwood Shores, and parts of East Palo Alto, Palo Alto, Mountain View, and Sunnyvale, include FEMA flood zones. That affects foundation design and insurance.
• Every city writes its own SB 9 ordinance on top of state law. Ask the planning department for a pre-application meeting before you hire a designer.

Bigger projects

SB 684 and SB 1123 allow small-lot subdivisions of up to 10 homes on some multifamily lots and on vacant single-family lots. These are separate from SB 9 and have their own rules.

Sources: California HCD: SB 9 fact sheet, CAL FIRE: Fire Hazard Severity Zones, FEMA Flood Map Service Center.

General information as of October 21, 2026, not legal or tax advice. Rules change and local ordinances differ. Confirm the details for your property with the agency named above, an attorney, or a tax advisor.