How Many ADUs Can You Have on Your Property in California?

New California ADU Laws for 2025

California’s Accessory Dwelling Unit landscape will see significant changes in 2025, driven by new laws designed to expand housing opportunities and simplify the approval process.

Key updates include:

• More ADUs Allowed: Senate Bill 1211 increases allowable detached ADUs on multifamily properties from two to up to eight, matching the number of existing residential units. This expansion encourages property owners to create extra income while supporting California’s housing needs.
• Faster Approvals: Once deemed complete, local agencies have 60 days to finalize ADU permit applications. Some cities also provide optional pre-approved ADU plans that may shorten the review time to as little as 30 days. Still, this accelerated timeline is not mandated statewide and varies by locality.
• Flexible Parking Rules: Updated requirements for ADUs relax previous parking restrictions, allowing for more efficient use of available space, provided units adhere to compliance with building codes, yard setbacks, and local zoning laws.
• Owner-Occupancy Removed (for ADUs Only): Under current state law, you do not have to live on the property if you build a new Accessory Dwelling Unit. However, Junior ADUs (JADUs) do require the owner to occupy either the JADU or the main home.

While these new provisions broaden ADU possibilities, homeowners must still comply with local zoning laws, including limits on yard setbacks and maximum square feet in size. Additionally, this expansion specifically applies to multifamily lots; single-family ADU rules from earlier legislation remain the same. If you are looking to build large-scale developments for multi-family units on your property, make sure to consult the Planning and Development Department to understand these new regulations and building standards.

Stay current on the latest legislative changes to effectively plan and permit your ADUs.

Understanding California’s ADU Regulations

The state of California dictates that there may be up to 3 dwellings on a single-family residential lot. These dwellings can include 1 single-family residence, 1 accessory unit, and 1 junior accessory unit.

Traditional accessory buildings can be as large as 1200 square feet, though many municipalities have lower maximum limits than this. When it comes to junior accessory dwellings, the maximum size is 500 square feet.

Start your ADU project with a feasibility study to understand local size limits, setbacks, and utility connections—early planning prevents costly surprises later.

Standard ADU Vs. Junior ADU Comparison

When it comes to ADUs vs JADUS, most people think that “junior” simply implies that the unit is smaller, and though this can be the case, size is not actually what defines a JADU.

An ADU is an independent living structure built on the same lot as an existing home. It can be attached to the main home, creating an attached ADU, or it can be a completely detached, separate unit. In either case, it is new construction and can be as small 150-220 square feet or as large as 1200.

Junior Accessory Dwelling Units reallocate existing space within the home to create a separate living space So, while the exterior footprint of the house does not change, it has still been transformed into a multifamily home.

Other key differences between an ADU and a JADU include:

How Many ADUs Can You Build on a Single Property?

Assembly Bill 68 was created to increase affordable housing options and says that a single property can contain up to 3 independent dwelling units.

These 3 separate units include:

• The primary structure, which is oftentimes the lot’s original single-family home
• An ADU, which can either be a detached or attached unit
• A JADU, or junior accessory unit

Note: The new SB 1211 legislation mainly applies to multifamily lots, so the single-family 3-dwelling limit remains the same.

Review state and local rules early to confirm how many additional units you can legally add.

Key Regulations for Building Both an ADU and JADU

Along with individual city building codes, you also need to understand the regulation differences when it comes to building multiple ADUs on a single-family residential property as opposed to a multi-family structure.

Accurate, detailed plans are essential for seamless approval of ADU and JADU permits—work with experienced designers to streamline the process.

Single-Family Residential Properties

Here are key regulations to consider if you are the owner of a single-family residence looking to add multiple ADUs to your property.

Number of Units

On single-family lots, you can build 1 ADU and 1 JADU in addition to the main dwelling.

JADU Location

A JADU must be within the primary residence. This could involve converting an existing part of the house, such as a spare bedroom and a garage, into a separate living space, so long as it does not exceed 500 sq ft.

ADU Location

The ADU can be detached or attached and is allowed to be up to 1,200 sqft. If the ADU is attached, it cannot exceed 50% of the size of the primary dwelling.

Owner Occupancy

For properties with a JADU, the homeowner is required to live on-site, either in the main residence or the JADU.
Parking Requirements

Parking spaces are not required for ADUs under certain conditions, such as proximity to public transit. JADUs don’t require additional parking.

What is a Multi-Family Property?

Multi-family structures—such as apartment buildings, condos, townhomes, and triplexes—present strong potential for ADU plans. While local jurisdictions do impose reasonable restrictions on adding accessory units, converting existing non-habitable space can help address California’s housing shortage by creating additional living areas. Because multi-family properties follow different rules than single-family residences, carefully review local guidelines to ensure your plans meet all regulations and maximize your property’s potential.

Confirm your property’s status as multifamily to access higher ADU counts under state and local guidelines.

How Many ADUs Can You Build on Multifamily Properties?

Under SB 1211, you can typically build up to eight detached ADUs on a multifamily property, provided the number of new ADUs does not exceed the number of existing units. Additionally, you may convert non-habitable spaces (e.g., detached garages, basements, storage rooms, separate structures) into ADUs—up to 25% of your existing unit count.

Bonus ADUs

Certain local jurisdictions—such as the City of San Diego—offer “bonus ADU” programs in Transit Priority Areas (TPAs) or comparable zones. Under these local programs, property owners who dedicate some or all of their accessory units as affordable housing may exceed normal ADU caps, effectively allowing unlimited ADUs in certain circumstances. However, this is not a statewide policy; whether bonus ADUs are permitted and to what extent depends on each city’s regulations. If you’re interested in building bonus ADUs, be sure to consult your local planning department to confirm current requirements and incentives.

New Detached ADUs for Multifamily

SB 1211 has dramatically increased allowable detached ADUs. Previously capped at two, multifamily property owners can now build up to eight detached ADUs—one for each existing residential unit. However, this limit depends on how many units already exist on the property.

Thus, a property owner with a 6-unit apartment building that features ample backyard space could add 6 detached ADUs, effectively doubling the property’s rentable units and substantially boosting cash flow without purchasing additional land.

Conversion ADU for Multifamily

Alongside detached units, SB 1211 encourages property owners to convert existing non-habitable areas within multifamily buildings into ADUs. These non-habitable areas often include storage spaces, boiler rooms, garages, parking structures, or unused retail areas. Regulations generally limit conversions to 25% of existing residential units.

For instance, an 8-unit complex could repurpose two vacant storage rooms into attractive rental units, turning underutilized spaces into immediate sources of additional revenue. Such conversions help revitalize older buildings and address housing demands efficiently, especially in densely populated urban areas.

What Counts as a Multi-family Dwelling in California ADU Development?

When planning an ADU project, understanding what California considers a multifamily dwelling is essential. In general, multifamily dwellings are residential properties with two or more units, such as duplexes, triplexes, apartment buildings, condominiums, or townhomes. These properties have distinct ADU rules and allowances that differ significantly from single-family residences.

Correctly identifying multifamily status can grant you broader building rights and multiple ADU conversions.

City of San Diego Multifamily Dwelling Exceptions

San Diego uniquely defines multifamily dwellings not only by the current property use but also by zoning designations. Specifically, properties zoned as multifamily—even if currently containing only one single-family home—can often qualify under multifamily ADU regulations, allowing additional development opportunities.

For example, a single-family homeowner in North Park, living on a lot zoned for multifamily use, could leverage this zoning to build up to two detached ADUs, despite having just one primary residence. This exception creates lucrative opportunities, significantly increasing the property’s income potential without the need to purchase new land or undergo extensive rezoning processes.

Research city-specific exemptions to expand ADU potential in multifamily zones and boost rental income.

Can You Build an ADU on a Duplex in California?

Yes, California explicitly allows ADU development on duplex properties. The updated San Diego city code requirements uniquely define multifamily dwellings by the current property use and zoning designations. Specifically, properties zoned as multifamily—even if currently containing only one single-family home—can often qualify under multifamily ADU regulations.

For example, a single-family homeowner in North Park, living on a lot zoned for multifamily use, could leverage this zoning to build up to two detached ADUs, despite having just one primary residence.

Duplex owners can often double their rental potential by leveraging new ADU allowances for multifamily structures.

Restrictions on Size

While the quantity allowances have grown, specific size restrictions remain. Typically, detached ADUs are capped at 1,200 square feet, though local jurisdictions may enforce additional limits based on the primary building’s size specifications, zoning regulations, current setback requisites, maximum height, or other municipal codes. Converted spaces must meet local building and safety standards, ensuring a balance between development flexibility, liveability, and compliance.

Tailor your ADU’s design to local size caps, ensuring an efficient layout that meets code requirements.

ADU Affordability Bonus Program in City of San Diego

San Diego further incentivizes ADU construction through its ADU Affordability Bonus Program, allowing property owners to exceed standard density limits by dedicating a portion of their ADUs to affordable housing. For each affordable ADU provided, property owners can build additional market-rate ADUs beyond state-mandated limits. The program offers a streamlined permitting process, reduced parking requirements, and quicker project approval timelines.

In March 2025, the San Diego City Council voted to amend the ADU Affordability Bonus Program by limiting its scope to lower-density areas. Specifically, they repealed a controversial zoning footnote that had reduced minimum lot sizes in Encanto, reinstating larger lot size requirements (above 10,000 square feet).

The council also directed city staff to propose additional restrictions, potentially removing neighborhoods with larger lots from the Bonus Program altogether. Multifamily property owners, particularly those in low-density neighborhoods like Encanto, should monitor these evolving regulations closely, as future changes could impact the viability of larger-scale ADU developments. Also, remember that local programs, like San Diego’s Bonus ADU initiative, can apply additional requirements or incentives beyond what state law permits.

Providing affordable units can unlock bonus ADUs, allowing you to exceed standard limits and maximize returns.

How Do You Fit Multiple ADUs Onto a Property?

Adding multiple ADUs to a property requires thoughtful planning and adherence to zoning rules and building codes. With California’s SB 1211, multifamily properties can now construct up to eight detached ADUs—limited by the total number of existing units. Effective strategies include utilizing underused spaces such as large backyards, communal spaces, parking areas, or vacant portions of the lot. For example, an apartment complex with six existing units and extra outdoor space could build up to six detached ADUs, substantially boosting rental income without acquiring more land. Proper site layout ensures comfortable, private living spaces while meeting setback and size requirements.

Comparison Chart: Number of ADUs Allowed in Greater San Diego

What is the SB9 Rule in California?

The SB9 rule allows owners of single-family properties to split their lot to allow for more units to be built on the property. However, there are limits on who can implement SB9. Homes located in a San Diego county historic district, for example, cannot split their lot.

If you are curious about whether SB9 applies to your home, contact your building department.

SB9 lot splits can turn underutilized properties into housing solutions—consult a professional to explore opportunities without disrupting neighborhood aesthetics.

How to Maximize ADU Potential on Your Property

You don’t need to have a huge lot to maximize your property’s ADU potential. We encourage homeowners to consider unused spaces within their home, like guest bedrooms, secondary living spaces, or basements, as potential JADUs, so long as they can accommodate a separate entrance.

When it comes to traditional ADUs, garage conversions are often a cost-effective build, while 2-story ADUs will maximize your total square footage while minimizing the footprint on your property.

Don’t overlook vertical space—adding a second story to an ADU can significantly increase usable square footage while maintaining a smaller footprint.

Financial and Legal Considerations

The financial implications of building multiple ADUs on your property extend beyond construction costs and the payments associated with financing options. You also have to consider your property taxes and how adding rental units or in-law suites might impact that.

In terms of logistical and legal considerations, you must consider your local zoning regulations, rental laws, and restrictions placed by your homeowners association.

An experienced ADU builder can walk you through all these considerations before submitting your ADU permit application so you can feel prepared and confident about moving forward.

Before breaking ground, budget for construction, taxes, and future maintenance—thorough financial planning ensures your ADU remains a profitable investment.

Ready to Build Your ADU?

Whether you are looking to build one ADU or multiple ADUs on your property, Better Place Design & Build can help. Our free consultation will not only walk you through the potential costs and construction process but also help you pinpoint areas of your home that could be repurposed into an ADU or JADU, showing you possibilities you didn’t even know where there.