Investment & Rentals
How Many ADUs Can You Build on a Multifamily Property?
Wondering how many ADUs you can build on a multifamily property in California? We've reviewed the latest regulations under SB 1211 to provide clarity. More than a dozen of our ongoing or completed ADU projects feature multiple units. Check out our projects with multiple ADUs for inspiration.
If you own a multifamily property—whether it’s a duplex or a larger apartment building—you can build up to eight new detached ADUs, with the number of ADUs allowed matching the existing units. Additionally, you can convert non-habitable spaces, such as garages, into ADUs.
Recent changes to California law have made it easier to add an accessory dwelling unit (ADU), often referred to as a granny flat, casita, guest house, or mother-in-law suite, to most residential properties. Parking requirements have been reduced or eliminated, and many impact fees have been waived for ADU projects. Setbacks have been reduced to just 4 feet on side and rear yards, allowing smaller lots to accommodate ADUs. These laws apply to both single-family and multifamily residential properties.
Multifamily ADU Rules in Los Angeles: New Opportunities with SB 1211
The newly passed SB 1211, signed into law on September 19, 2024, and taking effect on January 1, 2025, introduces significant changes for multifamily ADUs in Los Angeles by providing property owners with more flexibility and reducing regulatory barriers. Whether you own a duplex or a larger multifamily property, these updates impact how ADUs can be developed.
How Many ADUs Can You Build on Multifamily Properties?
The number of ADUs allowed on multifamily properties in Los Angeles depends on the number of existing units.
New Detached ADUs for Multifamily Properties
Before SB 1211, most multifamily properties were limited to two new detached ADUs. Under the new regulations, property owners can now build up to 8 detached ADUs, as long as the total number of ADUs does not exceed the number of existing units.
Conversion ADUs for Multifamily Properties
In addition to detached ADUs, SB 1211 allows you to convert existing non-livable spaces, such as garages or storage rooms, into ADUs. The minimum number of conversions is one, with a maximum of 25% of the existing units. For example, on an eight-unit property, you could convert up to two non-habitable spaces into ADUs (8 units x 25%) in addition to the detached ADUs.
In Los Angeles, any non-habitable accessory structures, such as garages or sheds, can be converted into ADUs. These conversions are subject to local regulations and setbacks. However, if you have a non-conforming garage that encroaches on setbacks, you may convert or demolish it and rebuild an ADU in its place.
Restrictions on ADU Size
Zoning restrictions, such as floor area ratios (FAR), still apply to ADU construction in Los Angeles. However, state law requires cities to allow a single-story 800 sq. ft. ADU "by right" if it meets building codes, even if the property exceeds FAR or RFA limits. Unlike single-family properties, you cannot add a junior ADU (JADU) to a multifamily property.
Affordable ADU Bonus Program in Los Angeles
Los Angeles also offers an Affordable ADU Bonus Program. This program allows you to build one market-rate ADU for every affordable ADU you construct, subject to zoning regulations on floor area ratio and lot coverage. This means you could potentially build more ADUs than the existing units in certain areas. Learn more about the Affordable ADU Bonus Program in Los Angeles.
What Counts as a Multifamily Dwelling in Los Angeles?
A multifamily dwelling refers to any property with more than one housing unit, such as duplexes, triplexes, or apartment buildings. It's important to differentiate between the property's zoning and the actual structure. For an ADU project, multifamily units must be attached to be considered multifamily under California ADU laws.
Common examples of multifamily properties in Los Angeles include:
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Single-family dwellings on multifamily-zoned lots
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Duplexes and triplexes
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Multifamily apartment buildings (two or more attached units)
ADUs are generally allowed on properties that already have multifamily dwellings.
Can You Build an ADU on a Duplex in Los Angeles?
Yes, you can build up to two detached ADUs on a duplex in Los Angeles under SB 1211. This provides an excellent opportunity for property owners to expand living space and increase rental potential. In addition, non-habitable spaces like garages can also be converted into additional ADUs.
How to Fit Multiple ADUs on a Property
In some areas of Los Angeles, ADUs must be standalone structures with a minimum separation between them. In other cases, you have the option to attach ADUs side by side or stack them as two-story units, allowing even smaller lots to accommodate multiple units. Learn more about stacked ADUs and how they work in Los Angeles.
ADUs can be up to 1,200 sq. ft. in size in many parts of Los Angeles, providing ample room for larger units with up to three or four bedrooms. This makes ADUs an ideal option for renters or extended family members looking for flexible housing solutions.
How Much Does It Cost to Build Multiple ADUs?
Building a second ADU generally costs around 80-85% of the first. Although shared mobilization and project management offer savings, additional units still require high-cost elements like kitchens and bathrooms. Therefore, building multiple ADUs is less cost-effective than expanding the size of a single unit.
While you save on mobilizing construction crews and streamlining the process, there are still significant costs involved. For instance, fire-rated construction between units and dedicated HVAC and electrical systems for each ADU add expenses. As a result, the cost per square foot doesn't decrease as sharply as it would for a single ADU.
To learn more about ADU costs and important considerations such as utilities and sitework, explore our detailed resources.
What are the Requirements for Renting Out ADUs?
ADUs can be rented out for periods longer than 30 days. The owner occupancy requirement has been waived for ADUs built through 2024, with an expected extension to 2030. This means that multifamily property owners can build and rent out an ADU without needing to sign an agreement to live on the premises, a requirement that was in place before recent legislation changes. Learn more about owner occupancy requirements and renting ADUs on our blog.
Read SB 1211 – Updated ADU Multifamily Rules for California
Interested in diving into the multifamily ADU code and understanding how SB 1211 changed key state regulations? We’ve made it easy to follow: red text shows removed wording, green indicates changes, and we’ve highlighted key areas in underline. You’ll also find the entire piece of legislation listed in order, with our commentary at the top of each section.
Parking Spots Need Not be Replaced
In Los Angeles, ADUs built by replacing existing structures like carports or driveways no longer require replacement parking. According to California law:
66314 (d) (11) When a garage, carport, or covered parking structure structure, or uncovered parking space is demolished in conjunction with the construction of an accessory dwelling unit or converted to an accessory dwelling unit, the local agency shall not require that those offstreet parking spaces be replaced.
Conversions of Existing Space
For the conversion of non-habitable spaces (e.g., garages, basements), you can build at least one ADU, with a maximum number of ADU conversions equaling up to 25% of the number of existing multifamily units.
66323 (a) (3) (A) Multiple accessory dwelling units within the portions of existing multifamily dwelling structures that are not used as livable space, including, but not limited to, storage rooms, boiler rooms, passageways, attics, basements, or garages, if each unit complies with state building standards for dwellings.
(B) A local agency shall allow at least one accessory dwelling unit within an existing multifamily dwelling and shall allow up to 25 percent of the existing multifamily dwelling units.
Height Restrictions
The height restriction for detached ADUs in Los Angeles varies from 16 to 20 feet depending on specific conditions. In many cases, taller ADUs are allowed if they comply with local zoning regulations.
66323 (a) (4) (A) Not (i) more than two accessory dwelling units Multiple accessory dwelling units, not to exceed the number specified in clause (ii) or (iii), as applicable, that are located on a lot that has an existing or proposed multifamily dwelling, but are detached from that multifamily dwelling and are subject to a height limitation in subparagraph (A), (B), or (C) of paragraph (4) of subdivision (b) of Section 66321, as applicable, and rear yard and side setbacks of no more than four feet.
Section 66321 (b) (4) (A-C) for easy reference
(A) A height of 16 feet for a detached accessory dwelling unit on a lot with an existing or proposed single family or multifamily dwelling unit.
(B) A height of 18 feet for a detached accessory dwelling unit on a lot with an existing or proposed single family or multifamily dwelling unit that is within one-half of one mile walking distance of a major transit stop or a high-quality transit corridor, as those terms are defined in Section 21155 of the Public Resources Code. A local agency shall also allow an additional two feet in height to accommodate a roof pitch on the accessory dwelling unit that is aligned with the roof pitch of the primary dwelling unit.
(C) A height of 18 feet for a detached accessory dwelling unit on a lot with an existing or proposed multifamily, multistory dwelling.
Number of ADUs
On multifamily properties, the number of ADUs you can build depends on the existing units. You may build as many detached ADUs as the number of existing units, up to a maximum of eight.
66323 (a) (4) (A) (ii) On a lot with an existing multifamily dwelling, not more than eight detached accessory dwelling units. However, the number of accessory dwelling units allowable pursuant to this clause shall not exceed the number of existing units on the lot.
(iii) On a lot with a proposed multifamily dwelling, not more than two detached accessory dwelling units.
Key Takeaways
All information in this blog is based on our experience with design, permitting, and building ADUs in Los Angeles, as well as our understanding of current local and state regulations. Our goal is to help clients anticipate likely scenarios and budget considerations, so there are no surprises—except how smoothly things go and how amazing the finished ADU looks!