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All ADU Regulations

Los Angeles County, California

The County of Los Angeles has updated its ADU ordinance to comply with new state laws. Below are the up-to-date requirements for permitting an ADU in unincorporated Los Angeles County, in places like Altadena.
Updated Sep 21, 2023

Los Angeles County - The ADU Capital of the State

Los Angeles County is a major hotspot for ADUs. The county received over 6,000 ADU permit applications in 2022, representing a 21% increase from the previous year. As ADUs become more and more popular amongst homeowners across Los Angeles County, here’s a rundown of ADU requirements to know for your project as of 2023.

General ADU requirements

All ADU types are permitted in Los Angeles County: detached, attached, conversion, and JADUs. The specific requirements for your project will depend on the ADU type. Standard ADUs must be equipped for independent living and have permanent facilities for:
  • Living
  • Eating
  • Sleeping
  • Sanitation
  • Cooking
  • Exterior access that is separate from the primary dwelling

ADU kitchens must also have:
  • A sink with running water
  • Countertops and cabinetry of a reasonable size
  • A refrigerator
  • A permanent range/cooktop that doesn’t need more than 120V or natural/propane gas JADUs may share bathroom/sanitation facilities with the primary dwelling, but they must have a separate entrance. Conversion ADUs must also have their own entrance.

Zoning

All properties zoned for single family and multifamily use may be eligible to build ADUs, unless the property is located in a Very High Fire Hazard Severity Zone (VHFHSZ) and does not have two means of access to a highway.

Fees

During the course of building your ADU project, you can expect to pay the following fees:
  • Building permit fee: This fee is based on the size and value of the ADU.
  • Plan check fee: This fee is paid to have the ADU plans reviewed by the county.
  • Impact fees: These fees are used to pay for the infrastructure improvements that are needed to support the new ADU.

Number of units

Lots zoned for single-family use that have an existing dwelling are permitted to add up to 1 detached ADU (new and/or conversion of accessory structure) and 1 Junior ADU (JADU). Lots zoned for multi-family use can add up to 1 ADU or 25% of total units (whichever is greater) converted from entirely within the MFR, and up to two detached ADUs (separate or connected to each other).

Building size

Maximum square footage is determined by your ADU type:
  • 500 sq. ft. for a Junior ADU (JADU)
  • 1,200 sq. ft. for a detached ADU
  • For attached ADUs, the maximum size is 50% of the existing SFR or 1200 sq. ft., whichever is less, provided at least an 800 sq. ft. ADU is allowed.
  • There is no maximum sqft for detached or attached ADUs that are contained entirely within the existing single family residence.

Building height

Detached ADUs and Attached ADUs are limited to 25 ft. or as specified by CSD/Specific Plan, whichever is less. ADUs within 200 ft. of a Scenic Highway may not exceed 18 ft. in height. For ADUs built on properties zoned for multi-family housing, the maximum height is 16 feet for detached ADUs accessory to one-story MFRs, and 18 feet for detached ADUs accessory to multi-story MFRs. Setbacks and height apply to new construction ADU portion only. A proposed ADU attached to the garage must comply with setbacks stated. If the garage is fully or partially converted to the ADU, existing setbacks are permitted as legally built.

Basements

You may convert a basement into an ADU in Los Angeles County.

Setbacks

Minimum setbacks of 4 feet from the side and rear lot lines, as well as 6 feet from any existing structures are required for detached ADUs.

Parking

One parking space is required for an ADU, unless the property meets any of the following exemptions:
  • The ADU is outside of a Very High Fire Hazard Severity Zone.
  • The ADU has no bedroom.
  • The ADU is detached from an existing SFR (single-family residence) and has a maximum floor area of 800 sq. ft and maximum height of 16 ft.
  • The ADU is detached from an existing MFR (multi-family residence) and has a maximum height of 16 ft. and minimum rear and side yard setbacks of 4 feet.
  • The ADU is entirely contained within an existing space of a primary residence or existing legal accessory structure (garage, guesthouse, rec room, etc.), and where no floor area expansion is proposed.
  • The ADU is located within ½ mile of public transit (i.e. bus stop, bike share station, train station).
  • The ADU is located within an architecturally and historically significant historic district.
  • On-street parking permits are required but not offered to the ADU occupant.
  • There is a car share vehicle located within one block (includes both sides of the street) of the ADU.

Fire safety

Los Angeles County Fire Department requires the automatic sprinkler system when the combined floor area of an ADU and an attached garage exceeds 1,200 sf.
An attached ADU requires a fire separation with a 1-hour fire-resistance rating.

Owner-occupancy

Owner occupancy is not a requirement for permitting an ADU from January 1, 2020 until January 1, 2025. This is a great opportunity for rental property owners to increase their yields in a cost-effective way. However, as per state law, owner occupancy is required for JADUs.

Rental

While long-term rentals are permitted for ADUs, short-term rentals (e.g. Airbnb for less than 30 days) are not permitted in Los Angeles County.

Watch-outs

Do you have a utility easement over your property? Are you in a FEMA flood zone? Reach out to us and we’ll help you build a custom ADU to fit your unique property characteristics and local regulations!

FAQs

How close to my house can I build an ADU in Los Angeles County?

When building a detached ADU, it should be at least 6 ft away from your primary residence. You cannot build a detached ADU in front of a single-family primary residence or within the front setback area of a multi-family home. It is a good idea to check such requirements with local authorities before starting your project.

Can I convert my garage into an ADU?

Yes, if you own a single-family home in a residential-zoned area, you may convert your garage into an ADU. Depending on the condition that your garage is in, the project may take under 9 months to complete and cost less than building a detached ADU.

What is the smallest ADU I can build in Los Angeles County?

Across California, the smallest ADU you may build is 150 sq. ft., regardless of type.

Does an ADU need a kitchen in Los Angeles County?

Yes! ADUs must accommodate permanent and independent living, and be equipped with a fully functional kitchen.

Can I build 2 ADUs on my property in Los Angeles County?

If your property is zoned for single-family living, then you may be eligible to build one detached ADU and one JADU. Multi-family properties may house up to two detached ADUs in addition to one ADU within the multi-family property, but this may vary based on the number of dwelling units already on the property.

What is the difference between an ADU and a JADU?

ADUs may either be attached to or detached from the primary dwelling, while JADUs are contained entirely within the primary dwelling. ADUs must be equipped with permanent facilities for independent living, but JADUs need only have an “efficiency” kitchen and may share some facilities with the primary dwelling. The maximum size allowed for a JADU is 500 sq. ft., while two-bedroom ADUs may be up to 1,200 sq. ft.

How much does an ADU increase property taxes in Los Angeles County?

You can expect the value of your property to increase after you build your ADU. Since property taxes are often based on property values, this can increase your property taxes. However, any increases will only be based on the value of the ADU itself. Building an ADU will not trigger a reassessment of the value of your main home.

How many bedrooms can an ADU have in Los Angeles County?

There’s no explicit limit to the number of bedrooms for an ADU in Los Angeles, however at the maximum allowable size of 1,200 sq. ft., you’d generally be able to fit 2 nicely sized bedrooms or 3 smaller ones if you get creative.

How long does it take to build an ADU in Los Angeles County?

The entire process, from start to finish, would depend on the type of ADU you’re building, the scope of your project, and the area you’re building in. New ADU projects may take 4-6 months to design and permit, and an additional 4-6 months to build.

Can I rent my ADU in Los Angeles County?

Yes, renting out your ADU can be a great way to earn an additional income. While short-term rentals of less than 30 days are not allowed, you may rent out your ADU for a minimum period of 31 days at a time.

How many square feet can an ADU be in Los Angeles County?

Depending on zoning conditions, setbacks and the number of bedrooms you are hoping to include, you may be allowed to build an ADU that has a maximum area of 1,200 sq. ft.

Can you build a 2 story ADU in Los Angeles County?

Yes, you can build a 2 story ADU in Los Angeles County, though height maximums for ADUs on multi-family properties would make it difficult to build a 2 story ADU.

Want to learn more about ADU regulations in your area?

Book a free consultation and estimate with a Cottage ADU Expert to find out what’s possible on your property!