ADUs and the SB-9 Law in California: What Homeowners Need to Know
California’s housing laws have changed dramatically over the last few years. New legislation has made it easier for homeowners to add additional housing units to their property through Accessory Dwelling Units (ADUs) and the SB-9 lot split law.
For homeowners in the East Bay, these laws can create opportunities to add rental income, build housing for family members, or increase property value.
This guide explains what ADUs and SB-9 are, how they work, and how they may impact homeowners in California.
What Is an ADU?
An Accessory Dwelling Unit (ADU) is a secondary housing unit built on the same property as a primary home. These units are sometimes called:
Backyard homes
In-law units
Granny flats
Secondary dwellings
ADUs can be attached to the main house, detached in the backyard, or created by converting existing space like a garage or basement.
California has strongly encouraged ADU construction as a way to increase housing supply. These units are now allowed in most residential zones across the state.
Typical ADU features include:
A kitchen
Bathroom
Living area
Separate entrance
In many cases, homeowners build ADUs to create rental income, house family members, or add long-term flexibility to their property.
Key ADU Rules in California
California has gradually reduced restrictions on ADUs, making them easier to build. Some of the most important statewide rules include:
ADUs are allowed in most residential zones
Detached ADUs can be up to about 1,200 square feet
Smaller ADUs (around 800 square feet) must generally be approved by cities regardless of zoning restrictions
Detached ADUs typically must be at least four feet from property lines
These statewide rules override many local restrictions, which means cities must allow ADUs if projects meet state standards.
What Is California’s SB-9 Law?
Senate Bill 9 (SB-9) is a major housing reform law that took effect in 2022. The goal of the law is to allow more housing within existing residential neighborhoods.
Under SB-9, homeowners may be able to:
Build two primary housing units on a single-family lot
Split one residential lot into two separate parcels
This means a property that previously allowed only one house may now support multiple housing units.
How SB-9 Lot Splits Work
The most well-known part of SB-9 is the urban lot split provision.
Under this rule:
A single residential lot can be divided into two separate lots
Each lot can generally have up to two housing units
In some situations, this means a property could support up to four housing units total if the lot is split and each new parcel includes two homes.
However, SB-9 projects must meet certain requirements, including minimum lot sizes and other eligibility rules.
SB-9 vs ADUs: What’s the Difference?
While both laws allow additional housing, they work differently.
ADU
Built on the same lot as an existing home
Considered a secondary unit
Usually cannot be sold separately from the primary home
SB-9
Allows two primary housing units
Allows splitting a lot into two parcels
In some cases, units may be sold separately
Because of these differences, homeowners often evaluate whether an ADU, duplex, or lot split is the best option for their property.
Why California Passed These Laws
California has faced a severe housing shortage for many years. ADUs and SB-9 are intended to help increase housing availability while allowing development within existing neighborhoods.
These laws aim to:
Increase housing supply
Provide more affordable housing options
Allow multigenerational living
Create additional rental opportunities for homeowners
As a result, ADUs have become one of the fastest-growing housing types in California.
Is Your Property Eligible?
Not every property qualifies for an ADU or SB-9 project. Eligibility depends on factors such as:
Zoning
Lot size
Existing structures
Local planning requirements
Environmental restrictions
Some cities also have additional design guidelines or development standards that apply to these projects.
Because of these variables, it is important to review your property with a contractor, architect, or planning professional before beginning a project.
ADUs and SB-9 in the East Bay
Across the East Bay—including communities like Danville, Lafayette, Orinda, Walnut Creek, and San Ramon—many homeowners are exploring ADU construction and SB-9 opportunities.
Large residential lots, existing single-family neighborhoods, and strong rental demand make these projects especially attractive in this region.
Homeowners may use ADUs or additional housing units to:
Create rental income
House extended family
Increase long-term property value
Add flexible living space
Planning an ADU or SB-9 Project
Adding housing to an existing property requires careful planning and coordination. Projects often involve:
Architectural design
Site planning and feasibility analysis
Permitting and approvals
Structural engineering
Construction management
Working with an experienced contractor early in the process can help ensure the project meets local requirements and moves through approvals efficiently.
Start Planning Your ADU or Home Expansion
ADUs and SB-9 projects have created new opportunities for homeowners across California. Whether you are interested in building an ADU, converting existing space, or exploring lot-split development, understanding the rules is the first step.
If you are considering a construction project in the East Bay, working with an experienced builder can help you evaluate your options and bring your vision to life.