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SB 9: up to four homes on a house lot
Build a second home on any single-family lot, or split the lot and build two homes on each half, with staff-level approval.
SB 9 lets you split one single-family lot into two and build up to two homes on each, for a total of four, with staff-level approval. Since SB 450 (2025), cities must decide within 60 days and can apply only the same objective standards they apply to everyone in the zone.
What it gets you
- Works on the most common lot in California: a single-family parcel with a house already on it.
- Keep the existing house as income or for sale while you build behind or beside it.
- The lot split creates two separately saleable parcels without a tentative map hearing.
- No more than one parking space per unit, and none within half a mile of high-quality transit.
- A denial must come with a written list of defects and how to fix them.
- Pairs with ADU law on lots that are not split, for a duplex plus ADUs.
The catches
- A lot split requires the applicant to sign an affidavit to live in one unit for three years. This makes SB 9 a better fit for owner-builders than for pure investors.
- Excluded: homes rented to tenants in the last three years, rent-controlled or deed-restricted units, and Ellis Act withdrawals in the last 15 years.
- Historic districts, very high fire hazard zones and some protected lands are excluded or limited.
- One split per lot, and the same owner cannot split adjacent lots.
- Cities may count ADUs toward a cap of two units on each split lot. Rentals must be longer than 30 days.
How we help
- Split-line studies that find the 60/40 line giving both lots access, utilities and a marketable home.
- Compact two- and three-bedroom plans that fit inside 4 ft setbacks and local height limits.
- Side-by-side yield comparison of SB 9 versus SB 1123 or ADUs on the same parcel.
Gov. Code §§ 65852.21, 66411.7
Questions we get about SB 9
How many homes can I build under SB 9?
Up to four from one original single-family lot: an urban lot split creates two lots, and each can hold two homes.
What is the minimum lot size for an SB 9 lot split?
Each new lot must be at least 1,200 sf and at least 40% of the original lot.
Can investors use SB 9?
An SB 9 lot split requires the applicant to sign an affidavit to live in one of the units for three years, so it suits owner-builders better than pure investors. Investors often look at SB 1123 for vacant lots or ADU law instead.
How long does SB 9 approval take?
Since SB 450 took effect Jan. 1, 2025, the city must decide within 60 days or the application is deemed approved. A denial must list the defects and how to fix them.
What setbacks and home sizes does SB 9 guarantee?
Side and rear setbacks are capped at 4 ft, and a city's standards cannot prevent homes of at least 800 sf.
Should I use SB 9 or SB 1123?
SB 9 works on lots that already have a house and yields up to four homes. SB 1123 requires a vacant lot but can yield up to ten. A lot already split under SB 9 cannot then use SB 1123. We compare both on the same parcel before you buy.
This page is general information, not legal advice. It summarizes California law as of October 2026. Cities adopt their own implementing ordinances, and eligibility depends on site-specific facts. Confirm with the local planning department and your land use counsel before acquiring a site.
Send us an address
Tell us where the site is and what you are hoping to build. We will tell you which of these laws applies and roughly how many homes it can hold.
info@s2arch.us