Splitting a property under SB 9 vs building an ADU

Most owners who ask about SB 9 want one of two things: more homes on the property, or a second property that stands on its own. An ADU answers the first need for most single-family properties, with fewer conditions. SB 9 can answer both, but it asks more of the owner and of the property. This guide sets the two side by side, using state law as read on November 12, 2026.

What SB 9 allows

SB 9 (Chapter 162, Statutes of 2021) applies to properties in a single-family zone. HCD's fact sheet describes three ways to use it:

• Two homes, no split. Build up to two primary homes on the property.
• A split into two. Divide the property into two of roughly equal size.
• Both. Split the property and build up to two homes on each new property.

The city reviews an SB 9 application ministerially: staff check it against written, objective standards, with no hearing. The city can still apply its own objective rules on height, front setbacks and design, but only if they do not prevent two homes of at least 800 sq ft each. A city cannot require more than 4 ft at the side and back of the property, and it cannot require a setback for an existing building kept in place. Under HCD's April 2026 fact sheet, local rules also cannot prevent two new properties of 1,200 sq ft each.

Parking is limited too. The city can require up to one space per home, and none if the property is within half a mile walking of a high-quality transit corridor or a major transit stop, or within a block of a car share vehicle.

SB 9 also comes with conditions an ADU does not have:

• Owner occupancy for a split. The applicant signs an affidavit to live in one of the homes as their main residence for at least three years from approval, unless the applicant is a community land trust or a nonprofit.
• One split only. A property created by an SB 9 split cannot be split again, and the city does not have to approve a split next to one the same owner already made.
• No short-term rentals. Homes created under SB 9 must rent for more than 30 days.

What an ADU allows

An ADU adds a home without dividing the property. State law sets these limits (ADUCheck rules, sections 2 to 7):

• Size. A detached ADU can be up to 1,200 sq ft. A city must always allow at least 800 sq ft at 16 ft tall with 4 ft at the side and back of the property. Since January 1, 2026, size means interior livable space.
• Combining. On a single-family property, a conversion ADU, a junior ADU and a detached ADU can all be built together.
• Owner occupancy. None for an ADU. A junior ADU needs the owner to live on the property only if it shares a bathroom with the main home.
• Fees. No development impact fees on an ADU of 750 sq ft or less, and no school fees on one of 500 sq ft or less.
• Timing. The city has 15 business days to say whether the application is complete and 60 days from a complete application to decide.

An ADU stays part of the property it sits on. ADUCheck does not treat an ADU as something that can be sold apart from the main home. If that matters to your plans, ask a real estate attorney before you design anything.

How the two paths compare

Question	ADU	SB 9
Zones	Residential and mixed-use zones	Single-family zones only
Homes added	A conversion, a junior ADU and a detached ADU together on a single-family property	Up to two homes, or two on each new property after a split
Owner must live there	No (a junior ADU with a shared bathroom: yes)	Yes for a split, for three years, with exceptions
Side and back of the property	Up to 4 ft	Up to 4 ft
Decision	60 days from a complete application	60 days from receipt of a complete application
Rentals	More than 30 days for junior and conversion ADUs	More than 30 days

The counting rules differ. After a split, HCD says ADUs and junior ADUs count toward the two homes allowed on each new property, so the most you reach across both is four. Without a split, the property can have up to two homes under SB 9 plus ADUs under ADU law. HCD's 2024 fact sheet adds that SB 9 never requires a city to allow more than four homes on one property, in any mix. How a city counts them can vary, so confirm with its planning office.

Where SB 9 does not apply

SB 9 has more exclusions than ADU law. HCD lists these:

• Properties outside a single-family zone, even where a single-family home is allowed.
• Fire hazard areas, wetlands, prime farmland, flood risk areas, earthquake hazard areas and other protected land listed in state law, with some exceptions.
• Historic districts, properties on the State Historic Resources Inventory, and city or county landmarks.
• Work that would demolish or alter rent-restricted housing, rent-controlled housing, or housing a tenant has lived in during the last three years.
• A property where homes were taken off the rental market under the Ellis Act in the last 15 years.

ADUs face fewer of these limits. A detached ADU is allowed in most fire and historic areas, though the City of Los Angeles adds its own limits in hillside areas and very high fire hazard severity zones, and design review may apply in historic areas. The property report shows these as "Check with LADBS" until the city rule is confirmed.

Cities also adopt their own SB 9 rules within these limits. ADUCheck gives full reports for the City of Los Angeles and the City of San Diego. Every other city gets a report under the state rules, so check that city's SB 9 page or planning counter for its local standards.

Which path fits which goal

An ADU usually fits when you want one or two more homes, plan to keep the whole property, and would rather not commit to living on site for three years. It is the simpler path, it combines with a junior ADU and a conversion, and it avoids most of the SB 9 exclusions.

SB 9 may fit when the property is large enough for two new properties, you plan to live in one of the homes, and you want each new property to stand on its own parcel. A split involves a parcel map, a survey, easements for utilities and access, and questions for your lender and title company. Talk to a real estate attorney and a licensed surveyor or civil engineer before you commit. Nothing in this guide is legal or tax advice.

Multifamily properties have other paths. SB 1211 allows up to 8 detached ADUs on a property with an existing multifamily building, never more than the number of homes already there, and SB 684 allows up to 10 homes on a multifamily-zoned property of 5 acres or less. Both are covered on the rules page for more than one home.

A property may qualify; a review decides

No automated check can say a property qualifies for SB 9. The zone, the fire map, historic status, tenant history and the size and shape of the property all matter, and some of these are not in any public map. When the report sees room for more than one home, it shows "Room for more than one home: may qualify" and a button to talk to Vivienda. Vivienda reviews properties with room for more homes and tells you which path, if any, is worth pursuing.

To start, run the free property report for your address. It shows the zone, which ADUs fit, where a detached ADU can go and whether the property may have room for more than one home, with every fact sourced and dated. For what the ADU path costs and how long it takes, see how much an ADU costs in Los Angeles and how long an ADU permit takes.

A guide is a starting point, not a permit. Confirm the current rules with your city's planning office before you apply.