SB 9 Lot Split Design-Build in the Bay Area
Short answer: SB 9 lets many owners of single-family lots in California split the lot once into two parcels and build up to two homes on each, through a ministerial (non-discretionary) approval. Type Five designs, permits, and builds new homes on lots created this way.
What SB 9 allows
Senate Bill 9 (2021) added Government Code sections 65852.21 and 66411.7. According to the California Department of Housing and Community Development (HCD), it requires cities to ministerially approve up to two primary units on a single-family-zoned lot, a split of that lot into two parcels, or both, which can mean up to four homes where one stood before.
- Lot size: the two new parcels must be roughly equal, neither smaller than 40% of the original lot, and generally at least 1,200 square feet each.
- Unit size: local objective standards cannot prevent two units of at least 800 square feet each.
- Owner occupancy: the applicant for a lot split signs an affidavit stating they intend to live in one of the units as their principal residence for at least three years.
- No short-term rentals: units created under SB 9 must be rented for terms longer than 30 days.
- Exclusions: SB 9 does not apply where the work would demolish or alter rent-restricted housing or housing occupied by a tenant in the last three years, on parcels withdrawn from the rental market under the Ellis Act in the last 15 years, or on many environmentally constrained or historic sites. A parcel can only be split once under SB 9.
Sources: HCD SB 9 Fact Sheet (https://www.hcd.ca.gov/sites/default/files/docs/planning-and-community/sb-9-fact-sheet.pdf) and HCD Housing Law Fact Sheet: Duplexes and Lot Splits (https://www.hcd.ca.gov/sites/default/files/docs/planning-and-community/lot-splits-and-duplexes-sb-9.pdf).
What we have learned building on split lots
Splitting a lot is only the first step. A new parcel still needs a design that works within the city's objective standards, utility connections, a building permit, financing, and construction. Two recent Type Five projects show how differently that can play out.
Saint James, Orinda: a newly created SB 9 parcel had proved difficult to sell as vacant land. We designed a two-story, three-bedroom, two-bath townhome of about 1,765 exterior square feet under Orinda's objective SB 9 standards, turning the lot into a finished home a buyer could purchase directly.
Lincoln, San Anselmo: the owners first explored SB 9, but a flood-zone condition at the rear of the property disqualified the ministerial path. We took the same infill idea through a conventional approval instead, keeping the existing house as a rental and building a one-story, three-bedroom home of about 1,175 exterior square feet for the family.
The lesson: check eligibility early. Flood zones, fire hazard areas, historic status, and tenancy history can each change the path, and a site review before design saves time and money.
Wondering if your lot qualifies?
Share your address and goals and we'll talk through whether SB 9, an ADU, or a conventional approval fits your property best.
SB 9 FAQs
Common questions from Bay Area homeowners.
Is SB 9 the same as building an ADU?
No. ADUs are accessory units on the same lot as a primary home and generally cannot be sold separately. SB 9 creates primary units and, with a lot split, a separate parcel that can be sold. Some owners combine both.
Do I have to live on the property?
For an urban lot split, state law requires the applicant to sign an affidavit of intent to occupy one of the units as a principal residence for at least three years, unless the applicant is a community land trust or qualified nonprofit.
What can disqualify a lot?
Common issues include recent tenancy, rent-restricted housing, Ellis Act withdrawals, historic designation, and site hazards such as flood zones or very high fire hazard severity zones. Our San Anselmo project moved to a conventional approval for exactly this reason.
Does Type Five handle the design, permits, and construction?
Yes. We are a design-build firm: we design the home, secure planning approval and the building permit, coordinate utilities, and build on site. A licensed surveyor or civil engineer typically prepares the parcel map for the split itself.
Can I rent out an SB 9 home on Airbnb?
No. Units created under SB 9 must be rented for terms longer than 30 days.