Two homes on a single-family lot, or split it in two

The rule

• Only in single-family zones.
• Closed if anyone rented the house at any time in the last 3 years, or if it is rent-controlled.
• The City has to allow two homes of at least 800 sq ft each, with side and rear setbacks of no more than 4 ft.
• Approved with a permit and no hearing. The City has 60 days.

The numbers

What you can build

• Build a second house, attached or detached, or convert part of the one you have.
• Rent both homes, for terms longer than 30 days. The two-home route has no owner-occupancy rule.
• Skip parking within a half-mile walk of a major transit stop; elsewhere the City can ask for 1 space per home at most.
• Split one lot into two. Each new lot must be at least 40% of the old one and at least 1,200 sq ft, so the smallest lot you can split is 2,400 sq ft.
• Put up to two homes on each new lot, which usually means 4 homes where there was 1.
• Split without street dedications or off-site improvements. The City can't require them.

What it doesn’t allow

• Split the lot unless you sign an affidavit that you'll live in one of the homes for 3 years. That rules out most investors.
• Use it after an Ellis Act withdrawal in the last 15 years.
• Split a lot that came from an earlier SB 9 split, or one next to a lot you already split under SB 9.
• Use it on a landmark, or on a contributing building in a historic district.
• Build in a Very High fire zone unless the City accepts fire-hardening measures, or in a FEMA flood zone or an earthquake fault zone unless the project meets those rules.

Two bills called SB 9

• This page is the 2021 law, the one about second homes and lot splits. A 2025 bill with the same number deals with ADU ordinances.