Bay Area ADU Guide: Rules by City & County

Accessory dwelling units — ADUs, in-law units, granny flats, backyard cottages — are one of the most popular ways Bay Area homeowners add rental income, house family, and build long-term value. California has spent the last several years rewriting the rules to make them far easier to build, but the details still vary by city and county. This guide covers the statewide baseline, then points you to the specific ADU rules for your area.

This guide is general information, not legal or construction advice, and ADU law changes frequently. Always confirm the current rules with your local planning department before you design or build. We work with trusted ADU architects, designers, contractors, and land-use professionals across the Bay Area and are always happy to make an introduction — just ask.

ADU rules by area

Every city and county builds on California’s baseline a little differently. Find your area:

• ADUs in San Francisco — the city’s two ADU programs, no more neighbor notification, and multi-family rules.
• ADUs in Marin County — unincorporated county rules plus how the towns differ.
• ADUs in San Mateo County (Peninsula) — unincorporated county rules and how to find your city’s standards.
• ADUs in the East Bay — Alameda and Contra Costa counties, including Oakland and Berkeley.

ADU vs. JADU: the basics

• ADU (Accessory Dwelling Unit): A fully independent home — its own kitchen, bathroom, and entrance — attached to your house, converted from existing space like a garage, or detached in the yard.
• JADU (Junior ADU): Up to 500 sq ft created within the walls of the existing home, with its own entrance and a small kitchen. It may share a bathroom with the main house.

California state law: the baseline (and what’s new for 2026)

State law sets a floor that every California city and county must honor — local rules can be friendlier, but not more restrictive than the state minimums. The current baseline:

• Ministerial approval: Eligible ADUs are approved over the counter — no discretionary hearing or neighbor notification — within 60 days of a complete application.
• Setbacks: As little as 4 feet from side and rear property lines.
• Parking: No additional parking can be required within a half-mile of transit (and never for a JADU or garage conversion).
• Size: The state guarantees at least an 850 sq ft studio/1-bedroom ADU and 1,000 sq ft for 2+ bedrooms.
• Owner-occupancy: Not required for a standard ADU.

Recent legislation

• AB 1154 (Jan 1, 2026): A JADU only triggers an owner-occupancy requirement if it shares a bathroom with the main home.
• SB 543 (Jan 1, 2026): The city must determine whether your application is complete within 15 days, or it’s automatically deemed complete.
• AB 462 (Oct 10, 2025): Coastal Development Permits for ADUs must be acted on within 60 days, plus disaster-relief provisions for detached ADUs.
• SB 9 update (2026): JADU owner-occupancy is measured at permit approval, not in perpetuity.
• Pre-approved plans: Large cities (over 200,000 people, including San Francisco) must offer pre-approved ADU plan sets.
• Selling separately (AB 1033): ADUs may be sold individually as condominiums in jurisdictions that opt in — adoption is local, so confirm with your city.

What an ADU can do for your property

Done well, an ADU can generate steady rental income, give family a place of their own, and add real resale value. It can also be a smart piece of a downsizing plan — live in the smaller unit and rent the main house, or vice versa.

Thinking about an ADU?

We can help you weigh the cost, your city’s specific rules, and what an ADU would mean for your home’s value — and connect you with vetted designers and builders. Start with a free home valuation, call (415) 407-5324, or visit primaverarealty.com. — Beatrice Kopilenko, REALTOR® · DRE #01970797 · Primavera Realty