California ADU Laws: Guide to 2025 Rules & Regulations, and download the free California ADU Handbook

As Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) emerge as essential components in addressing California's housing needs, understanding the current state laws is crucial for homeowners. The California Department of Housing and Community Development (HCD) continuously updates its guidance to reflect the evolving legal framework, aiming for clarity and consistency.

What are ADUs and JADUs?

An ADU is an attached or detached residential dwelling unit providing complete, independent living facilities for one or more persons on a lot with a proposed or existing primary residence. It must include permanent provisions for living, sleeping, eating, cooking, and sanitation. ADUs can take many forms, including efficiency units and manufactured homes.

A JADU, on the other hand, is a smaller unit, no more than 500 square feet, that is contained entirely within a single-family residence. A JADU can have separate sanitation facilities or share them with the existing structure. Only one JADU is permitted per lot zoned for single-family residences.

The Benefits of Building an ADU in California

ADUs offer a wide range of advantages for California homeowners and the state's housing supply:

• Affordability: ADUs are an affordable type of home to construct because they do not require paying for land, major new infrastructure, structured parking, or elevators. They are often built with cost-effective wood frame construction, which is significantly less costly than new multifamily infill buildings.

• Income Potential: ADUs can serve as a valuable source of income for homeowners through rent.

• Family Proximity and Aging in Place: These units allow extended families to live near one another while maintaining privacy. They also give homeowners the flexibility to share independent living areas with family members and others, facilitating older adults' ability to age in place.

• Housing Supply: ADUs are making a difference in the housing crisis. Between 2016 and 2023, the number of ADUs permitted annually in California grew 20-fold, from 1,336 to 26,924. In 2023, ADUs made up over 21% of all homes permitted statewide.

Key Regulatory Standards for ADUs

Understanding the rules governing ADU development is essential to a smooth permitting process.

Permitting and Timing

ADUs that are subject to State ADU Law must be reviewed, approved, or denied ministerially—meaning without discretionary review or a hearing. The review is based on objective standards that involve no personal or subjective judgment.

A permitting agency generally has 60 days to approve or deny a complete ADU or JADU application if an existing dwelling is on the lot. If the agency fails to act within 60 days of receiving a completed application, the permit is "deemed approved".

Owner-Occupancy and Rental Terms

A local agency cannot impose an owner-occupancy requirement on any ADU. However, local agencies can require that ADUs be used for rentals with terms longer than 30 days. For JADUs, the owner must reside in either the remaining portion of the primary residence or in the newly created JADU, with limited exceptions.

Size and Height Limitations

While local agencies may set maximum unit sizes by ordinance, they must allow an ADU of at least 850 square feet, or 1,000 square feet for ADUs with more than one bedroom. Also, conversion ADUs—created from existing space within a primary dwelling or accessory structure—are not subject to these unit size requirements.

A local agency may impose height limits, but they may not be less than:

• Detached ADUs: 16 feet on a lot with a proposed or existing single-family or multifamily dwelling unit. This increases to 18 feet if the lot is within a half-mile walking distance of a major transit stop or a high-quality transit corridor.

• Attached ADUs: 25 feet, or the height limitation that applies to the primary dwelling in the local zoning ordinance, whichever is lower.

Setbacks and Parking

For an attached or detached ADU, a setback of no more than four feet from the side and rear lot lines can be required. Importantly, no setback is required for an ADU or JADU created within an existing living area or accessory structure, or an ADU created in a new structure in the same location and to the same dimensions as an existing structure.

Local agencies are prohibited from imposing parking standards on ADUs in a number of specific circumstances, including ADUs located within a half-mile walking distance of public transit, or ADUs that are part of the proposed or existing primary residence or an accessory structure. In general, parking requirements cannot exceed one space per unit or bedroom, whichever is less. Furthermore, if a garage or carport is demolished or converted for an ADU, the local agency shall not require that those off-street parking spaces for the primary unit be replaced.

Overcoming Homeowners Association (HOA) Restrictions

Covenants, conditions, and restrictions (CC&Rs) and operating rules that effectively prohibit or unreasonably restrict the construction or use of an ADU or JADU on lots zoned for single-family residential uses are void and unenforceable under the Civil Code. HOAs may impose limited objective standards on an ADU or JADU, such as requiring specific materials or architectural styles, but these standards cannot unreasonably increase the cost to build or effectively prohibit construction. HOAs may not influence a local agency's ministerial approval of an ADU or JADU.

Unpermitted Structures Built Before 2020

A local agency is precluded from denying a permit for an unpermitted ADU or JADU constructed before January 1, 2020, because the unit violates building standards, State ADU Law, or a local ordinance. Denial is only permitted if correcting the violation is necessary to protect public health and safety, or if the building is deemed substandard. Homeowners applying for a permit for a previously unpermitted ADU or JADU constructed before January 1, 2020, may also be exempt from impact fees or connection/capacity charges if they provide written evidence that their household income does not exceed the definition of a low- or moderate-income household.

Start Your ADU Journey with Confidence

The process of building an ADU can seem complex, but by understanding the State's ADU laws and leveraging expert resources, California homeowners can successfully navigate the process. HCD provides resources and technical assistance on these matters through its online ADU Portal.

As you prepare to unlock your property’s potential, remember that having the right tools and information is key. We offer specialized resources to simplify the complex journey from concept to completion:

• California ADU Handbook: This free official handbook provides comprehensive guidance directly from the California Department of Housing and Community Development (HCD).

• ADU Ebook: Your Complete Guide to California ADUs: This comprehensive guide dives deeper into the regulatory details, design options, and local considerations to ensure you start your project fully informed.

• How To Finance an ADU Ebook: Navigate the financial landscape with our expert breakdown of loans, grants, and strategic financing options to make your ADU investment a reality.

• Pre-Approved ADU Plans for Sale: Save time and avoid costly revisions by starting with code-compliant, thoughtfully designed ADU plans engineered for California's unique requirements.

Empower your project with the clarity and expertise you need to build with confidence.

Understanding California's Title 24 Requirements for Accessory Dwelling Units

Accessory Dwelling Units, or ADUs, are becoming an increasingly popular way to add living space and housing options to existing residential properties. In California, ADUs are subject to a number of regulations and requirements, including Title 24 of the California Code of Regulations. Title 24 sets standards for energy efficiency, lighting, and other aspects of building design and construction. In this blog post, we will explore California's Title 24 requirements for ADUs and explain what homeowners and builders need to know to ensure compliance.

Promoting Energy Efficiency

One of the main purposes of Title 24 is to promote energy efficiency and reduce the environmental impact of buildings. California has set ambitious goals for reducing greenhouse gas emissions and promoting sustainable building practices, and Title 24 is a key tool in achieving these goals. The regulations apply to all new construction and remodeling projects in the state, including new construction ADUs.

Insulation, Systems, and Construction Considerations

For ADUs, Title 24 requires compliance with specific energy efficiency standards. This includes requirements for insulation, air sealing, heating and cooling systems, and more. For example, ADUs must have insulation that meets minimum R-value requirements, and they must be designed to minimize air leakage. HVAC systems must also meet certain efficiency standards to reduce energy consumption and emissions. We typically recommend that ADUs have insulated wall cavities in addition to continuous rigid insulation around the entire outside of the home. We also recommend ductless mini-split systems as an efficient way to provide heating and cooling.

Lighting Considerations

In addition to energy efficiency requirements, Title 24 also sets standards for lighting in ADUs. These requirements are designed to promote energy efficiency and ensure that ADUs are well-lit and safe for occupants. This includes requirements for the type and placement of light fixtures, as well as the use of lighting controls such as timers and motion sensors. To meet lighting requirements and reduce energy consumption we recommend LED light fixtures throughout all ADU projects.

Accessible Design

Another important aspect of Title 24 for ADUs is the requirement for accessible design. California law requires that all new construction and remodels meet accessibility standards under the Americans with Disabilities Act (ADA). This includes ADUs, which must be designed to be accessible for individuals with disabilities. This may include features such as wider doorways, lower countertops, and accessible bathroom facilities.

Solar Energy Requirements

An important aspect of Title 24 is the requirement to add solar energy systems that will offset the energy use of new construction residential projects. This includes ADUs. It is important to consider this requirement when budgeting for your project as well as locating the ADU on your property. Making sure the roof pitch is best oriented towards the sun will help you get the maximum benefits of a PV system. Along with solar energy production, you could also consider solar hot water systems and a way to further reduce your energy consumption and make your ADU more sustainable.

How To Comply

Most jurisdictions in California require a Title 24 report that analyzes your ADU design and does that calculations to show it complies with the code requirements. There are many companies that can provide these reports in only a few days time and typically for a few hundred dollars. They will provide the documentation and/or drawings needed to submit to your building department as part of the permit review process.

Overall, California's Title 24 requirements for ADUs are designed to promote energy efficiency, safety, and accessibility. While complying with these requirements can add some additional costs to a project, it is important to ensure that ADUs are built to the highest standards of quality and sustainability. By following these requirements, homeowners and builders can create ADUs that are comfortable, safe, and environmentally friendly, and that will provide long-lasting benefits for years to come.

Typically Title 24 reports are performed once the design of the ADU is completed but prior to submitting to permit. You can use our pre-designed ADU drawing sets to send to a company that provides Title 24 Reports and typically you can get the report in a few days.

Rooftop solar panels.
Photo by Mischa Frank

Why ADUs are Great For California

ADUs (accessory dwelling units) are becoming an increasingly popular housing option in California, and for good reason. There are many benefits to ADUs in California, both for property owners and for the state as a whole. Here are just a few:

1. California ADUs can provide affordable housing options.

   California has a well-documented housing crisis, with high housing costs and a shortage of available units. ADUs can provide a more affordable housing option for individuals and families who are struggling to find affordable housing. Because they are typically smaller than traditional homes, ADUs can be less expensive to build and maintain, making them a more accessible option for many people.

2. ADUs can increase the supply of California housing.

   By adding additional living space to existing properties, ADUs can help increase the overall supply of housing in California. This can help alleviate the pressure on the housing market and make it easier for people to find a place to live.

3. ADUs can provide additional rental income for California property owners.

   By adding an ADU to their property, property owners can rent out the space to generate additional income.

4. ADUs can provide additional living space for family members or guests.

   This can be especially useful for aging parents or adult children who may need a place to live but can’t afford market rate rents. By providing a separate living space, ADUs can offer a level of independence and privacy for these individuals while still allowing them to be close to the rest of the family.

5. ADUs can be a sustainable housing option.

   By making use of existing resources and infrastructure, ADUs can be a more sustainable housing option than building new, standalone homes. In addition, ADUs can be built to be energy-efficient, which can help reduce the environmental impact of housing and save money on utility bills.

Overall, ADUs can provide a range of benefits to California, including increasing the supply of affordable housing, providing additional rental income for property owners, and offering additional living space for family members and guests. In addition, ADUs can be a more sustainable housing option, which can help California meet its goal of reducing greenhouse gas emissions and promoting sustainable development.