SB 9 Lot Splits & Two-Unit Homes: A California Homeowner’s Guide

One single-family lot can become two parcels — and up to four homes — under California’s SB 9.

Senate Bill 9 (SB 9), a California housing law in effect since 2022, changed the rules for many homeowners. It gives owners of single-family lots two new options: build a second home on the lot you already own, or split the lot into two separate parcels — each of which can hold up to two homes. Your city reviews SB 9 projects ministerially, through a streamlined process with no public hearings and no neighbor votes. Local rules still shape the minimum lot size and what you can build, and not every property qualifies — lot shape, access, and utilities all matter — so a careful review comes first.

The Two Paths SB 9 Opens

Who Qualifies

• Single-family zoning, urban area. The lot must be zoned for single-family residential use and sit inside an urbanized area or urban cluster — most California neighborhoods qualify.
• Big enough to split (lot splits only). Each new parcel must be at least 1,200 square feet, and the smaller parcel must be at least 40% of the original lot — the split can be no more lopsided than roughly 60/40.
• One split per property. A parcel created by an SB 9 split cannot be split again, and you cannot use SB 9 to split two adjacent lots you own at the same time.
• The owner applies. For a lot split, the owner signs the three-year owner-occupancy affidavit (community land trusts and qualified nonprofit housing organizations are exempt).

The Rules That Shape Your Project

• 800-square-foot protection. A city cannot impose standards that would prevent two homes of at least 800 square feet each. If local zoning already allows more, you can build bigger.
• Modest setbacks. For new SB 9 construction, a city can require no more than 4-foot side and rear setbacks; front setbacks follow the underlying zone. An existing home keeps its footprint — the city cannot force you to make it “conforming” as a condition of a split.
• Limited parking. At most one off-street parking space per unit — and none at all if the property is within a half-mile of a major transit stop or high-quality transit corridor, or within one block of a car-share vehicle.
• No short-term rentals. SB 9 homes are housing, not vacation rentals: rentals must be for terms of 30 days or longer.
• No exactions on splits. For a lot split, a city cannot require right-of-way dedications or offsite improvements as a condition of approval — though utility easements and street access for each parcel can be required.

What Can Disqualify a Property

• Historic property. The site is a designated historic landmark or lies within a historic district.
• Protected land. Prime farmland, wetlands, habitat for protected species, or land under a conservation easement.
• Hazard zones with conditions. Very high fire hazard severity zones, earthquake fault zones, and flood hazard areas are not automatic disqualifiers, but the project must meet specific state safety standards.
• Tenant protections. SB 9 cannot be used to demolish or change housing that is rent-controlled, deed-restricted as affordable, or occupied by a tenant within the last three years. A property where rental units were withdrawn under the Ellis Act within the previous 15 years is also excluded.
• Almost nothing else. A city can deny a qualifying SB 9 project only if its building official finds a specific adverse impact on public health, safety, or the physical environment that cannot be mitigated — a deliberately high bar.

How SB 9 Combines With ADUs

SB 9 and California’s ADU laws stack. On a single lot, a two-unit development can be paired with the state ADU rules many homeowners already know. After a lot split, each parcel is its own property: each can hold its own home and, in many cases, an additional dwelling unit as well — the combination that turns one house into as many as four homes. And because split parcels are separate legal lots, one can be sold on its own — something an ADU on the same lot can never do.

Why Families Do It

This page is a plain-language summary of California SB 9 (Government Code §§ 65852.21 and 66411.7 and the California Department of Housing and Community Development’s SB 9 guidance) for homeowners. It is not legal advice; your city’s objective standards and your parcel’s conditions control what can actually be built.

Work With ADU Cities

Splitting a Lot? You Need a Contractor Who Builds, Too

An SB 9 project lives or dies on execution — plans, permits, and up to four homes built in the right order. ADU Cities is a design-build ADU contractor that carries SB 9 projects from feasibility through final inspection.