Accessory Structures in Sonoma County, CA (2026)
7 county-level rules, plus city-specific rules for 2 cities in Sonoma County, California.
Verified from official government sources
ADU Rules
Unincorporated Sonoma County permits ADUs ministerially under County Code Sec. 26-88-060, implementing California ADU law (Gov. Code 66310+). Detached ADUs are generally allowed up to 1,200 sq ft with 4-foot side/rear setbacks. No zoning permit is required, but building and any related septic/water permits are.
Sonoma County Accessory Dwelling Unit (ADU) Rules
Some RestrictionsSonoma County Ordinance No. 6222, Exhibit A (amending Sonoma County Code § 26-88-060, Accessory Dwelling Units)
Except as otherwise provided by this section, accessory dwelling units shall be ministerially permitted only in compliance with the requirements of this section, and all other requirements of the applicable zoning district in the following agricultural and residential zoning districts: LIA (Land Intensive Agriculture), LEA (Land Extensive Agriculture), DA (Diverse Agriculture), RRD (Rural Resou...
ADU Impact Fees
Sonoma County charges ADU development fees proportionally by square footage compared to the primary residence, and waives them entirely for ADUs under 750 square feet, per County Code § 26-88-060(f).
Sonoma County ADU Impact Fee Rule
Some RestrictionsSonoma County Code § 26-88-060(f)
Applicable development fees shall be charged proportionately by the square footage of the ADU in relation to the square footage of the primary residence. On a lot that contains a multifamily dwelling, the proportionality shall be based on the average square footage of the units within the multifamily dwelling structure. No fees shall be charged for ADUs of less than seventy hundred fifty (750) ...
ADU Owner Occupancy
Sonoma County requires the owner of a lot with a junior accessory dwelling unit to live in either the JADU or the main house, unless the JADU has its own bathroom or the owner is a government agency, land trust, or housing organization. The rule sits in Zoning Code § 26-24-150(C), which replaced the repealed § 26-88-061.
Sonoma County JADU Owner Occupancy Rules
Significant RestrictionsSonoma County Code § 26-24-150(C)
C. Use Restrictions. 1. Ownership. a. A JADU may be rented but shall not be sold separately from the single-family residence. b. The owner of the property must reside in either the JADU or the remaining portion of the single-family dwelling, unless either: (1) The JADU includes sanitation facilities that are separate from the single-family dwelling; or (2) The owner is a governmental agency, la...
ADU Rental Restrictions
Sonoma County lets owners rent an accessory dwelling unit but bars selling it apart from the main house: an ADU cannot be sold or conveyed separately from the primary residence unless State law provides otherwise, and no ADU can be rented for thirty days or less. The rule sits in Zoning Code § 26-24-020(C) after Ordinance No. 6544, adopted December 9, 2025, repealed the old § 26-88-060.
Sonoma County ADU Rental and Sale Restrictions
Some RestrictionsSonoma County Code § 26-24-020(C), (G)
Use Restrictions. 1. Ownership and Rental. ADUs may be rented but shall not be sold or otherwise conveyed separately from the primary residence, except as specifically provided for by State law. 2. Duration of Tenancy. ADUs shall not be rented for periods of thirty (30) days or less. ... Ministerial review. A complete permit application for an ADU meeting the standards described in this section...
Shed & Carport Rules
In unincorporated Sonoma County, detached residential accessory structures such as sheds need a building permit at 120 square feet or larger, per Permit Sonoma's policy. Sheds generally observe minimum side and rear setbacks and height limits, and must comply with the underlying zoning district's standards.
Sonoma County Shed and Detached Accessory Structure Rules
Some RestrictionsPermit Sonoma Administrative Policy 1-4-6 (Detached Residential Accessory Structures)
Accessory structure is a structure not greater than 3,000 square feet (sq. ft.) in floor area, and not over two stories in height, the use of which is customarily accessory to and incidental to that of the dwelling(s) and which is located on the same lot.
Garage Conversions
Converting a garage into living space in unincorporated Sonoma County is most commonly done as an ADU or Junior ADU under County Code Secs. 26-88-060 and 26-88-061. A building permit is required to change the use from a garage to habitable space, and an existing-structure conversion ADU is allowed ministerially.
Sonoma County Garage Conversion Rules
Some RestrictionsPermit Sonoma Administrative Policy 1-4-6 (Detached Residential Accessory Structures), Section 5(a)
Any accessory structure with a kitchen, as defined in Policy 1-4-5, is considered a dwelling unit and must either be classified as a second unit limited to 840 sq. ft. in size or meet the allowable density under zoning for another dwelling.
Tiny Homes
A permanently sited tiny home on a foundation is typically permitted in unincorporated Sonoma County as an ADU under County Code Sec. 26-88-060 (max generally 1,200 sq ft), processed ministerially. Movable tiny homes on wheels and RVs are not treated as permanent dwellings and face separate restrictions.
Sonoma County Tiny Homes Rules
Some RestrictionsPermit Sonoma, Tiny Houses; Policy 8-1-1; Sonoma County Code Sec. 26-88-010(P)
According to the 2018 International Residential Code (IRC), a tiny house is a dwelling that is 400 square feet or less in floor area excluding lofts. Stick-built/traditional/site-constructed homes: A small home constructed entirely at the building site. Manufactured houses (commonly referred to as mobile homes): Homes built in a factory mounted on a non-removable steel chassis or frame. Factory...
Accessory Structures by City in Sonoma County
2 cities in Sonoma County have their own accessory structures rules. Each link goes to that city's dedicated page with code citations.
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