How Many Bedrooms Can An ADU in California Have?

Peeking inside the bedroom of a spacious Abodu ADU.

Peeking inside the bedroom of a spacious Abodu One ADU.


December 16, 2023ADU Law

California has been relaxing Accessory Dwelling Unit (ADU) laws in response to the housing crisis since 2020. Relaxing the laws encourages property owners to create affordable housing options in existing neighborhoods, and ADU production in California is booming.

What is an ADU? ADUs, often called granny flats or in-law suites, are versatile living spaces attached or detached from a single-family home. Homeowners can convert existing space into an ADU or JADU (junior accessory dwelling unit). Your ADU can serve many functions, including a home office, art studio, guest house for visitors, long-term housing for family members, or rental housing to make monthly income.

California generally restricts rentals to 30 days or more, but certain local governments like San Rafael allow you to use ADUs as short-term rentals under 30 days. If you plan to build an ADU to make rental income, check your local laws so you can adhere to any adopted ordinances.

How Many Bedrooms Can Your California ADU Have? 

California state law allows accessory dwelling units up to 800 square feet, 16 feet high, with a 4-foot yard setback. A one-bedroom ADU can be up to 850 square feet, and an ADU with two or more bedrooms can be up to 1,000 square feet.

California building code requirements impose the following regulations for interior space in ADUs:

  • Bedrooms and living room should be at least 70 sq ft

  • The kitchen must be at least 50 sq ft

  • The main bathroom must be a minimum of 30 sq ft and have a toilet, sink, and a shower or bath

Local governments can adopt ADU ordinances with different regulations, and our experts at Abodu can help ensure your ADU plans meet these restrictions. California cannot legally restrict the minimum number of bedrooms in an ADU as it can be considered discriminatory.

ADU Size Limits 

California has state requirements for ADU size, but every municipality can adopt ordinances imposing different standards and zoning regulations, so laws vary throughout the country.

California ADU building code states the following size regulations for detached ADUs:

  • Detached ADUs can be up to 1200 sq ft

  • Detached ADUs with one bedroom or less can be 800 sq ft

  • Detached ADUs with two or more bedrooms can be up to 1000 sq ft

  • Detached ADUs can be up to 16 feet high unless a local ordinance says otherwise

  • Detached ADUs can be up to 18 feet if they are within one mile of a major transit stop or on a property with a multistory multifamily property

For the attached ADUs, California code states:

  • Attached ADUs can be no more than 50% of the main home’s square footage

  • Attached ADUs can be up to 25 feet or as high as the primary dwelling, whichever is lower

ADU conversions, like garage conversions, generally do not have maximum size limits because the structures already exist. If you’re converting space into a JADU, it cannot exceed 500 square feet and must have a separate entrance from the primary residence.

ADUs under 750 square feet are exempt from development limits, including minimum lot size requirements, lot coverage requirements, open space, and floor-area ratio (FAR) requirements. ADU designs under 750 feet are also exempt from impact fees.

ADU requirements in Los Angeles make it one of the best cities to build an ADU, while Walnut Creek’s requirements make it more challenging by limiting the maximum size to only 950 square feet.

How Much Does it Cost to Add a Bedroom to an ADU? 

Depending on your layout, a new prefab ADUs range from around $200,000 to over $400,000.

Adding a bedroom to a prefab ADU will depend on your existing unit. Contact Abodu for an idea of what it would cost. And review our pricing options to get an idea of what adding onto an ADU might cost.

Remember: Prefabricated units typically cost less than stick-built units because standardized designs save time and money on architectural and engineering planning. Prefab ADUs also avoid weather delays because construction happens in a dedicated climate-controlled environment.

Prices do not include sales tax or permit fees. Fees depend on your city’s regulations and vary quite a bit between towns. On average, you can expect to pay around $17,000 in taxes and permit fees for the ADU, but that fee might be different for adding onto an existing ADU.

Also, consider that an ADU will increase your property value and taxes. Taxes will not increase on your primary home but will increase based on the value your accessory structure adds.

Need Help Figuring Out the Perfect-Sized ADU? 

If you’re ready to get the ball rolling on your new ADU but don’t know where to start, Abodu’s team of experts can help determine the ideal-sized living unit for your property and intended use. At Abodu, we streamline the process from planning to ADU construction to installation. Schedule a call or showroom tour to start planning your perfect ADU.

Contact Abodu to help you build your ADU in California.

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