The Complete Bay Area ADU Requirements Guide
If you’re thinking of building an accessory dwelling unit (ADU) in the Bay Area, knowing the requirements is a crucial first step in the construction process.
An ADU is a self-contained living space that shares a lot with a primary home. It can be attached, detached, or created by converting existing space. Thanks to a series of statewide ADU laws, ADUs are now allowed in nearly every residential area in the Bay Area, and cities and counties must follow consistent statewide rules. They’ve become a key part of regional housing production, comprising 13.4% of the Bay Area’s building permits in 2020.
Keep reading to learn the current regulations and how Samara can help you get it done.
Bay Area ADU regulations at a glance
Cities and counties across California are required to review complete applications within 60 days, and most ADU permits are approved in three to four months. ADUs are allowed on any lot with an existing or proposed home in a residential or mixed-use zone. Local zoning codes still apply, but state law requires cities and counties to approve qualifying ADUs even if local rules would otherwise restrict them.
Size and lot requirements
The minimum size for an ADU is 150 square feet. The maximum size depends on the type:
- Detached ADUs must be allowed up to 800 square feet by right. Many cities and counties—like San Jose, Oakland, Alameda County, and Redwood City—permit up to 1,200 square feet, but others cap ADUs at 850 or 1,000 square feet depending on lot size or unit type. Detached ADUs must also be allowed to reach 16 feet in height at minimum, and up to 18-20 feet if near transit or on a multifamily lot and the roof pitch matches the main home.
- Attached ADUs can also be up to 1,200 square feet, though many jurisdictions limit them to 50% of the main home’s floor area. State law overrides that limit if it would prevent an attached ADU of at least 850 or 1,000 square feet. Attached ADUs may be built up to 25 feet tall or match the main home’s zoning height limit.
- Junior ADUs (JADUs) must be created entirely within the existing footprint of a single-family home and are limited to 500 square feet.
All new ADUs must maintain 4-foot side and rear setbacks. Detached ADUs typically need at least 6 feet of separation from other structures. Setbacks do not apply when converting existing interior space or rebuilding on the same footprint. Additional height is allowed in flood zones to meet elevation requirements.
Meet the KurodasDesign requirements
Not all Bay Area jurisdictions have design requirements, but when they do, the standards must be objective. In most cases:
- Detached ADUs must use similar rooflines, exterior materials, and colors as the main residence—especially if visible from the street.
- Attached ADUs must generally match the appearance of the home and cannot alter the street-facing façade.
Additional requirements may apply in historic districts, but ADUs are still permitted.
Parking requirements
Most ADUs in the Bay Area do not require a dedicated parking space. No parking is required if an ADU is within one-half mile of a transit stop, part of an existing home or accessory structure, in a historic district, near a car-share location, or on a lot with restricted permit parking. If a garage or carport is converted to an ADU, replacement parking is not required. If you choose to add a parking space, it can be located in tandem or setback areas.
Zoning eligibility
ADUs are permitted on any lot zoned for residential or mixed-use use in all nine Bay Area counties, including single-family and multi-family zones. They are also allowed in areas with fire, flood, or coastal overlays, but additional safety or design requirements may apply. A primary home must already exist or be proposed on the lot.
Number of ADUs allowed
On single-family lots, you can build one detached or attached ADU, plus one JADU created within the existing home.
On multifamily lots, you can build up to eight detached ADUs—so long as the total number does not exceed the number of existing units—and up to 25% of the existing unit count as interior conversion ADUs.
You could keep reading about ADUs.
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Streamline your ADU project in the Bay Area
If you’re looking to build an ADU, Samara makes it easy. We handle everything from permits to installation and even offer our own financing. Call us at 650-420-2607 to schedule a 15-minute consultation and discover how simple adding a Backyard ADU can be.
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