Accessory Structures in Alameda County, CA (2026)

5 county-level rules, plus city-specific rules for 6 cities in Alameda County, California.

Verified from official government sources

Note: These county rules apply to unincorporated areas of Alameda County. If you live within an incorporated city, that city's own rules apply: see the city list below.

ADU Rules

ADUs and junior ADUs in unincorporated Alameda County can be built simultaneously with or after the main house, but every application needs county building inspection sign-off, plus environmental health approval on septic lots.

ADU Permit Process in Alameda County

Some Restrictions

Alameda County Code § 17.55.100

Accessory dwelling units and junior accessory dwelling units shall be allowed to be established either simultaneously with or after the construction of a primary dwelling unit that is located on the same lot of record and under one common ownership. Applications for accessory dwelling units and junior accessory dwelling units shall be subject to applicable building codes and require approval of...

Full ordinance details →Official source ↗

ADU Impact Fees

Unincorporated Alameda County waives park dedication impact fees for accessory dwelling units under 750 sq ft, and never charges them for junior accessory dwelling units, under Chapter 17.55.

ADU Impact Fee Waiver in Alameda County

Few Restrictions

Alameda County Code § 17.55.140

No park dedication impact fees are required for accessory dwelling units measuring less than seven hundred fifty (750) square feet in interior livable space and no park dedication impact fees shall be required for junior accessory dwelling units.

Full ordinance details →Official source ↗

Shed & Carport Rules

In unincorporated Alameda County's R districts, a detached shed or accessory building must sit at least six feet from any other building, stay one story, and stay under fifteen feet tall under the county zoning code.

Shed Setback Rules in Alameda County

Some Restrictions

Alameda County Code § 17.52.260

Every accessory building attached to a main building shall be subject to all the requirements of this title applicable to the main building. No detached accessory building in an R district shall be located within six feet of any other building on the same lot, or have more than one story or a height in excess of fifteen (15) feet.

Full ordinance details →Official source ↗

Garage Conversions

Unincorporated Alameda County bans converting a garage into living space in residential zones unless seven conditions are met, including one-to-one replacement parking.

Garage Conversion Rules in Alameda County

Significant Restrictions

Alameda County Code § 17.52.955

Within all residentially zoned districts and Planned Development (PD) districts with residential uses, garage conversions to non-garage uses shall not be permitted, except when all of the following conditions are met: A. When no other conforming building space is available on the property for conversion or addition into a non-garage space... D. When other conforming on-site parking space(s) is ...

Full ordinance details →Official source ↗

Tiny Homes

Unincorporated Alameda County has formally adopted the state residential code's tiny house appendix, so a compliant tiny house is a recognized dwelling type here.

Tiny House Rules in Alameda County

Light Restrictions

Alameda County Code § 15.08.330 (CRC § R101.2.1)

The following CRC appendix chapters are adopted and amended, as noted, by the County: 1. Appendix BF, Patio Covers — Adopted. 2. Appendix CI, Swimming Pool Safety Act — Adopted. 3. Appendix BB, Tiny Houses - Adopted. 4. Appendix CJ, Emergency Housing — Adopted. R102.6 Existing structures [BID][CDA]. The legal occupancy of any structure existing on the date of adoption of this cod...

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