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California Rules and Regulations for ADU Construction

Introduction - Regulations for ADU Construction

In response to the housing crisis and the need for affordable housing options, California has implemented a set of rules and regulations governing the construction of Accessory Dwelling Units (ADUs) on single-family dwellings. ADUs, also known as granny flats or in-law units, offer homeowners the opportunity to increase property value and generate rental income while contributing to the state's housing goals. Understanding the specific guidelines set by the California government is crucial for homeowners considering ADU construction. This blog will explore the key rules and regulations governing ADU construction in the Golden State.

A hand drawing of an ADU
ADUs, also known as granny flats or in-law units, offer homeowners the opportunity to increase property value.

1. Statewide ADU Legislation

In 2017, California passed Senate Bill 1069, followed by Assembly Bill 2299 and Senate Bill 13 in 2018. These legislative changes aimed to streamline the ADU approval process and remove barriers to construction. As a result, many local jurisdictions have updated their zoning codes and building regulations to comply with the new state laws.

2. Zoning Requirements

Each city or county in California has its own zoning regulations, which dictate land use and building requirements. Homeowners looking to build an ADU must adhere to these zoning codes, which often specify factors such as minimum lot size, setback requirements, and allowable building height. It's essential to check with the local planning department to ensure compliance with these regulations.

3. ADU Size and Design

The state legislation provides guidelines on the size and design of ADUs, ensuring they are proportional to the primary dwelling and the overall neighborhood. For example, California allows both attached and detached ADUs, with maximum sizes varying based on factors like lot size and whether the unit is attached or detached. These guidelines help maintain the character of existing neighborhoods while providing flexibility for homeowners.

4. Parking Requirements

Parking regulations for ADUs can vary based on the location and the proximity to public transportation. State laws generally limit local jurisdictions from imposing parking requirements for ADUs located within a half-mile of public transit or in historic districts. However, it's crucial to verify the specific parking regulations in the local jurisdiction where the property is located.

5. Impact Fees

Some cities and counties may impose impact fees on ADU construction to fund infrastructure improvements in the community. However, state laws limit the imposition of certain fees for ADUs under specified conditions. Homeowners should be aware of any potential impact fees and understand the criteria that must be met to qualify for fee exemptions or reductions.

6. Junior ADUs (JADUs)

In addition to traditional ADUs, California allows for the creation of Junior ADUs (JADUs). JADUs are smaller units created within the existing footprint of a single-family home, such as converting a garage or adding an extension. These units have specific size limitations and are subject to their own set of regulations, providing homeowners with additional options for expanding their living space.


California's rules and regulations for ADU construction on single-family dwellings have evolved to encourage the development of affordable housing options and address the state's housing crisis. Homeowners interested in building ADUs should thoroughly research and understand the specific requirements outlined by both state legislation and local zoning codes. By doing so, they can navigate the regulatory landscape successfully and contribute to the state's ongoing efforts to increase housing availability.


1. California State Legislature. (2017). Senate Bill No. 1069 - Accessory dwelling units: standards. (

2. California State Legislature. (2018). Assembly Bill No. 2299 - Accessory dwelling units: land use. (

3. California State Legislature. (2019). Senate Bill No. 13 - Accessory dwelling units: incentives. (

4. California Department of Housing and Community Development. (2022). Accessory Dwelling Units (ADUs).

5. California Department of Housing and Community Development. (2022). ADU Resources.

6. California Planning & Development Report. (2019). What Cities Should Know About ADU Impact Fees.

**Please note that regulations and laws may be subject to change, and it's advisable to check with local planning departments or legal professionals for the most up-to-date information.

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