The Ultimate Guide: California ADU Laws in 2025

Accessory Dwelling Units (ADUs) have become a cornerstone of California’s strategy to address its housing crisis – and for good reason.

In addition to boosting the housing supply, ADUs offer valuable space for offices, hobbies, guests, boomerang kids, and aging parents. They can also provide rental income and significantly increase your home’s value when it comes time to sell.

A rendering of a one-bedroom ADU design by Urban Building Workshop.

Homes with ADUs in California appraise for about 49% more than comparable homes without them, according to a 2023 analysis by the Federal Housing Finance Agency.

With sweeping legislative changes taking effect in 2025, understanding the latest ADU regulations is essential for homeowners, investors, and design professionals.

This guide covers everything you need to know about building, legalizing, and maximizing ADUs in California. We've also included a special focus on San Francisco and Los Angeles.

What is an ADU?

Defined by the California Department of Housing and Community Development, an ADU is a self-contained residential unit located on the same lot as a primary home.

ADUs can be detached, attached, or converted from existing space (such as a garage or basement). Junior ADUs (JADUs) are smaller units-up to 500 square feet-created within the footprint of a single-family home.

A rendering of the interior of a one-bedroom ADU design by Urban Building Workshop.

Why are ADUs important in California?

• Housing supply: ADUs are a fast, flexible way to increase the housing supply without large-scale development.

• Affordability: They offer more affordable rental options and can provide homeowners with supplemental income.

• Multigenerational living: ADUs support families by allowing aging parents, adult children, or caregivers to live nearby.

• Sustainability: ADUs make better use of existing infrastructure and land.

Major California ADU laws in 2025

California’s ADU laws have evolved rapidly, and 2025 brings some of the most significant changes yet:

Streamlined Permitting & Pre-Approved Plans

• Faster approvals: Assembly Bill 1332 mandates cities and counties to process ADU applications within 60 days. If you use a pre-approved ADU plan, review time drops to just 30 days.

• Clear denials: If an application is denied, cities must provide a detailed explanation and suggestions for compliance.

Expanded Building Rights

• State-exempt ADUs: Under Senate Bill 1211, every homeowner can build at least one 800-square-foot, 16-foot-tall ADU, regardless of lot size, lot coverage, or neighborhood standards, provided it meets 4-foot side and rear setbacks.

• Multifamily properties: The law also allows up to eight detached ADUs on multifamily lots, dramatically expanding development potential.

• Height limits: Detached ADUs can be up to 16 feet tall. If your property is within half a mile of public transit, you can build up to 18 feet tall. Attached ADUs can be as tall as the main house, up to 25 feet, depending on local zoning rules.

Owner-Occupancy and Condo Conversion

• No owner-occupancy requirement: AB 976 mandates that owners are no longer required to live in either the main home or the ADU (except for JADUs).

• ADUs as condos: AB 1033 allows local jurisdictions to decided whether ADUs can be sold separately as condominiums. This offers new opportunities for homeownership and investment.

Legalizing Unpermitted ADUs

• AB 2533: Owners of unpermitted ADUs or garage conversions built before Jan. 1, 2020, can now bring these units into compliance without penalties or impact fees, provided they meet health and safety standards.

Fees & Financial Relief

• Impact fees: ADUs under 750 sq. ft. are exempt from impact fees. This exemption now extends to previously unpermitted units built before 2020.

• Grants: State and local grant programs may offer up to $40,000 to help with ADU construction costs.

HOA and Local Restrictions

• HOA restrictions curtailed: Under Civil Code section 4751, homeowners associations (HOAs) can no longer enforce rules that unreasonably restrict ADU development.

• Local control: Cities can set their own ADU standards but cannot be more restrictive than state law.

A rendering of a two-bedroom ADU design by Urban Building Workshop.

Regional Spotlight – ADUs in San Francisco

San Francisco has been a pioneer in ADU policy, incrementally adjusting its approach since 2013 to become one of the most progressive cities for ADU development in California.

Early reforms focused on legalizing existing, often unpermitted, units and streamlining the approval process. As a result, ADU production jumped from just 3 units in 2013 to over 200 per quarter by 2017.

The city’s ADU program is notable for its flexibility:

• Two approval tracks: One track is for straightforward, code-compliant projects, while the other is for those seeking waivers from density, open space, or parking requirements.

• Affordability and workforce housing: San Francisco actively promotes ADUs as a way to provide lower-cost housing for essential workers, including teachers, service staff, and first responders.

• Cost efficiency: Building an ADU in San Francisco typically costs less than $150,000, compared to $500,000 per unit for new multi-family developments.

In 2025, San Francisco is considering legislation to allow ADUs to be sold as condominiums, which could make ADU construction more financially appealing to homeowners and create new entry-level homeownership opportunities.

Regional Spotlight – ADUs in Los Angeles

Los Angeles has experienced one of the most dramatic ADU booms in the country.

After years of restrictive local policies, state law reforms in 2016 forced the city to adopt more permissive ADU rules, triggering exponential growth in permits and construction.

• Permit surge: ADU permits skyrocketed from just 80 in 2016 to over 7,160 in 2022 – an increase of 8,850%. By 2022, LA had permitted at least 26,862 ADUs, and one in every three new homes permitted in the city was an ADU.

• Neighborhood impact: The ADU boom has reached even the city’s most exclusive and traditionally low-density neighborhoods, providing new housing options where large-scale development is often resisted.

• Regulatory framework: Los Angeles has tailored its own ADU regulations within the broader state mandates, including local development standards and a streamlined ministerial review process.

• Market effects: ADUs are now seen as a vital tool for stabilizing LA’s housing market, increasing rental supply, and offering flexible solutions for multi-generational living or rental income.

Ready to Build an ADU? Here’s Why Good Design Is So Important

A well-designed ADU blends seamlessly with the rest of your property, while a poorly designed one can feel out of place. The difference lies in the skill of your architect.

• Scale and proportion: Architects design ADUs that complement your main home and property, ensuring the right size and a comfortable fit.

• Smart layouts: They maximize every inch with efficient floor plans, clever storage, and multi-use spaces.

• Natural light and ventilation: Architects use windows, skylights, and smart placement to make small spaces feel bright, open, and energy-efficient.

• Personalization and aesthetics: They tailor the ADU’s look and feel to your style and needs, while ensuring quality and durability.

• Navigating codes and permits: Architects handle local regulations and permitting, making sure your ADU is legal and up to code.

• Sustainability and efficiency: They can include eco-friendly features and energy-saving materials to lower costs and reduce your environmental footprint.

• Project management: Architects coordinate the entire process, keeping your ADU project on track and within budget.

Looking for an architect who has experience designing ADUs? Let’s talk. Urban Building Workshop brings 25 years of experience in architecture, construction, and real estate development. We serve residential and commercial clients in the San Francisco Bay Area and across California.