SB 9 (Atkins, 2021) ended single-family-only zoning in California. On a single-family-zoned lot in an urban area, an owner can do two things by right: build a duplex, and split the lot into two parcels and build up to two units on each. The theoretical maximum is four homes where one stood.
SB 9 analysis is not yet in the Parcy app. Today the app models ADUs and JADUs only. SB 9, SB 684, SB 1123, and SB 79 are next on the engine's roadmap, and this page explains the law in the meantime.
Lot split rules
- Each new parcel must be at least 40% of the original lot and no smaller than 1,200 square feet.
- The owner must sign an affidavit to live on one of the parcels for three years.
- The lot cannot have been split under SB 9 before, and adjacent lots owned by the same person cannot both be split.
- No demolition of rent-controlled or recently tenanted housing.
- Excluded: historic districts, very high fire severity zones without mitigation, wetlands, hazardous sites, and farmland.
Standards cities can apply
Objective standards only, and nothing that would prevent two units of at least 800 square feet each. Side and rear setbacks are capped at four feet. One parking space per unit, waived near transit. Approval is ministerial, with no CEQA and no hearing.
SB 9 versus ADUs
Many lots do better with ADUs than with SB 9. An ADU plan keeps one parcel, needs no owner-occupancy affidavit, and (under the two-ADU rule) gets you to three units. SB 9 shines when you want to sell the new homes individually: each split parcel is a separate fee-simple lot with its own address. And SB 9 and ADUs can combine; a city must allow at least one ADU on each parcel created by an SB 9 split in most configurations.
What the math looks like
A 7,500 square foot lot in a $1.4 million single-family market, split into two 3,750 square foot parcels with a new 1,600 square foot home on the rear lot: typical cost around $750,000 all-in for the new home, site work, and split; typical sale value of the rear parcel $1.1 million to $1.3 million, while the front house keeps most of its value. The return depends almost entirely on land value, which is why this works in coastal Southern California and the Bay Area and rarely inland.
Until SB 9 ships in the app, our team runs it by hand. Book a consult.
Frequently asked questions
Does SB 9 require owner-occupancy?
For a lot split, yes: the owner signs an affidavit to live on one of the resulting parcels for three years. A duplex without a split has no owner-occupancy requirement.
Can I do SB 9 and build an ADU?
Generally yes. Cities must allow at least one ADU on each parcel created by an SB 9 split, subject to the four-unit overall cap in some configurations.
Informational only. Not legal, architectural, or investment advice. Confirm current rules with your local planning department.