The Homeowner’s Essential Guide to ADU Housing Laws in The Bay Area

The Bay Area is known for its natural beauty and economic prowess which makes it an attractive place to live and work. However, its appeal comes with a hefty price tag. Real estate prices have soared over the years, making housing affordability a pressing issue for many residents. The need for alternative housing solutions is palpable, and this is where Accessory Dwelling Units (ADUs) come into play.

ADUs, often referred to as granny flats or in-law suites, are independent housing units on the same property as a single-family home. They can be either attached to the primary house or detached but share the same land parcel. ADUs provide a unique solution to the housing challenge, creating opportunities for affordable housing, while also allowing homeowners to generate additional income through rentals.

This guide is designed to navigate homeowners in the Bay Area through the legal landscape surrounding ADUs, both on a state and local level. As California, amidst housing shortages, has passed legislation to ease the development of ADUs, it’s crucial for homeowners to understand these laws and regulations, and how they specifically apply in the Bay Area.

The objective is to equip you with the knowledge and resources necessary to explore the feasibility of constructing an ADU on your property. By delving into the state-wide laws, local variations in the Bay Area, and practical considerations involved in ADU projects, this guide aims to be a comprehensive resource for homeowners considering this housing option.

Understanding ADUs

Accessory Dwelling Units, or ADUs, are self-contained residential units located on the same property as an existing single-family home. These units can be housed within the structure of the existing home, as a detached unit, or in a garage conversion. ADUs are typically complete with essential facilities like a kitchen, bathroom, and sleeping area, providing an independent living space.

Historically, the concept of ADUs has been around for many years in different forms. However, their significance has gained prominence in recent times due to evolving housing needs and changing legislations. California, being one of the states with high housing demand and escalating property prices, has recognized the potential of ADUs in addressing housing shortages and affordability issues.

The essence of ADUs lies in their versatility and ability to provide additional housing without the need for more land, new infrastructure, or further development. They present a win-win situation, where homeowners can generate extra income by renting them out, while also contributing to easing the housing shortage in their communities.

In California, the legal framework surrounding ADUs has evolved to facilitate their development, aimed at addressing the broader housing challenges. The state has set forth guidelines that standardize ADU development, ensuring they meet specific safety, design, and size requirements, while also granting local governments the autonomy to tailor these guidelines to their unique community needs.

Understanding the legal framework and the basic principles surrounding ADUs is the cornerstone for homeowners considering this option. It sets the stage for delving deeper into the specifics of ADU laws in California and the Bay Area, and understanding how these laws influence the feasibility and the process of adding an ADU to your property. This foundation is crucial in making informed decisions as you explore the possibility of constructing an ADU, aligning with both state and local regulations, and ultimately contributing to the solution for more affordable housing in the Bay Area.

adu kitchen the bay area

General ADU Laws in California

California has progressively amended its laws to encourage the development of Accessory Dwelling Units (ADUs) as a means to alleviate the housing crisis. Here are some notable laws and regulations as of 2023:

Statewide Legislation Overview

The state has enacted several bills to facilitate ADU construction and to make it a more attractive option both for homeowners and developers:

  • AB 2221 and SB 897: Effective from January 1, 2023, these bills bring significant changes to ADU laws in California. AB 2221 mandates all cities to allow a minimum height of 16 feet for ADUs, thus preventing cities from imposing lower height restrictions. This amendment fosters the construction of more 2-story ADUs. Additionally, local ordinances that do not align with the changes brought about by these bills will become null and void​1​.
  • AB 221: This legislation, effective from January 1, 2023, redefines height restrictions by requiring all cities to adjust their ADU size limits to at least 16 feet, promoting the development of 2-story ADUs​.
  • AB 345: Amendments to this bill now enable ADUs to be sold separately from the main property in certain cases, providing more flexibility to property owners and developers​.

Key Regulations Affecting Homeowners

Several regulations have been revised to simplify the process of ADU development and to reduce the hurdles homeowners might face:

Size and Design Regulations

  • Height Limitations: As mentioned, a minimum height of 16 feet must be allowed for ADUs, facilitating the development of 2-story units.

Zoning Regulations

  • Demolition Permits: Cities can no longer withhold demolition permits if the ADU permit is issued, making it more challenging for cities to block ADU development​1​.

Permitting Process

  • 60-Day Rule: Assembly Bill 2221 now mandates all agencies involved in reviewing ADU plans, including planning departments and utility companies, to respond within 60 days of submission, thus expediting the permitting process​4​.

These laws and regulations form a solid framework aimed at encouraging ADU development across California. By understanding these general laws, homeowners in the Bay Area and beyond can better navigate the process of developing an ADU on their property, aligning with the broader goal of addressing housing needs in the state.

Bay Area-Specific ADU Laws

The Bay Area, like the rest of California, has embraced the potential of Accessory Dwelling Units (ADUs) to address housing challenges. Here’s a closer look at the regulations pertaining to ADUs in the Bay Area:

Recent State Laws and Their Local Impact

Recent statewide laws like AB-881, AB-68, and SB-13 have significantly eased ADU construction, particularly beneficial for the dense urban settings of the Bay Area. These laws have removed certain lot restrictions, eliminated impact fees for ADUs under 750 square feet, and prevented Homeowners Associations from banning or unreasonably restricting ADUs​1​.

Property Designations and ADU Construction

Bay Area homeowners with historic properties or those located in “geohazard” or “landslide” zones have additional considerations. While ADUs are generally allowed, they must adhere to specific architectural or geologic requirements​1​.

Tax Implications

Constructing an ADU in the Bay Area will trigger a property reassessment, albeit a blended one where the ADU is assessed separately. Typically, property taxes are 1% of the property’s assessed market value, with a cap at 2% over time​.

adu dwelling above garage

Types of ADUs and Local Regulations

Attached ADUs

  • Can be built on any side of the house, except for properties with historic designations where they must be built in the rear yard. Front and side setback rules usually apply​.

Detached ADUs

  • Must be placed in the rear yard or 45 feet from the property line, with a minimum separation space of six feet from the main building. If a second story exists, it must be set back four feet from both the rear and side property lines​.

Junior ADUs (JADUs)

  • Smaller in size (typically less than 500 square feet) and must be converted within the existing square footage of a single-family home. In the Bay Area, homeowners can have either a JADU or a detached ADU, but not both​.

Size and Space Qualifications

Local governments in the Bay Area might have varying size allowances for ADUs, hence it’s essential to verify with them before beginning construction. Parking space, especially for converted garages, and driveway lengths are other local considerations​.

This section provides a glimpse into the Bay Area-specific ADU laws, enlightening homeowners on the legal landscape they need to navigate while considering ADU construction on their property.

Advantages and Challenges of ADU Development

The concept of Accessory Dwelling Units (ADUs) has gained traction as a viable solution to housing challenges. Whether it’s creating affordable housing or generating additional income, ADUs hold promise. However, like any development project, they come with their set of advantages and challenges that vary from region to region, especially in a place like the Bay Area with its unique housing landscape. Here’s a closer look at some of these aspects:


  1. Affordable Housing Solution:
    • ADUs provide a more affordable housing option in areas where real estate prices are soaring.
    • They are a step towards alleviating the housing crisis by adding more living spaces within existing residential properties.
  2. Income Generation:
    • Homeowners can earn a steady rental income by renting out ADUs.
    • This extra income can help homeowners offset mortgage payments or other expenses.
  3. Increased Property Value:
    • ADUs can significantly enhance the overall value of a property.
    • They add usable square footage and the potential for rental income, which are attractive to prospective buyers.
  4. Flexible Living Arrangements:
    • ADUs can house extended family members, providing a close but independent living arrangement.
    • They also provide downsizing options for homeowners or a space for caretakers.


  1. Cost of Construction:
    • The initial investment required for constructing an ADU can be substantial.
    • Financing the construction might require loans or other financial arrangements, which could be a barrier for some homeowners.
  2. Zoning and Permitting:
    • Navigating the local zoning laws and permitting processes can be complex and time-consuming.
    • Changes in local laws or opposition from neighborhood associations can also pose challenges.
  3. Space Limitations:
    • Limited lot size and space might constrain the size, design, and orientation of the ADU.
    • Some properties might not have sufficient space to meet the local setback requirements.
  4. Privacy Concerns:
    • Maintaining privacy can be a challenge due to close proximity between the main house and the ADU.
    • Soundproofing and adequate spacing can help, but privacy concerns might still persist, impacting the living experience.

The journey towards developing an ADU necessitates a balanced understanding of these advantages and challenges. Being well-informed enables homeowners to navigate through the process more smoothly and make decisions that align with their long-term goals.

How do I start the process of building an ADU in The Bay Area?

To initiate the process of building an ADU, begin by contacting an experienced addition contractor familiar with ADUs. They can elucidate the pertinent laws and regulations, and discuss your building options and the costs involved. Their expertise will provide a solid foundation for your project, ensuring compliance with local codes and successful navigation through the permitting process. This step will also help you understand the financial implications, thus allowing for well-informed budgeting and planning.

Learn More About ADU Dwellings

The allure of Accessory Dwelling Units (ADUs) lies in their potential to provide affordable housing, generate income, enhance property value, and offer flexible living arrangements. However, they come with challenges such as high construction costs, complex zoning and permitting processes, space limitations, and privacy concerns. The legal landscape governing ADUs in California and the Bay Area is evolving, aimed at fostering easier ADU development. Understanding both the general and local-specific laws, alongside the advantages and challenges of ADU development, equips homeowners to make informed decisions, aligning with their financial and living arrangement goals.

Spaces Home Remodeling is a home remodeling contractor in San Francisco that specializes in ADU construction. Contact us today to learn more about your ADU building options and to schedule a free consultation.

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