Colusa County, CA Accessory Structures: ADU Rules (2026)
ADU rules in Colusa County, CA, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- County code section
- Colusa County Code Sec. 44-4.10 (Accessory Units)
- County term
- 'Accessory unit'
- County max size
- 1,200 sq ft (up to 2,500 sq ft on ag classifications)
- County detached setbacks
- 3 ft side, 8 ft rear (Sec. 44-4.10.060(e))
- Controlling state law
- Cal. Gov. Code 66310-66342 (ministerial; preempts owner-occupancy)
- State-guaranteed ADU
- 800 sq ft, 16 ft, 4 ft setbacks; JADU up to 500 sq ft
Summary
Unincorporated Colusa County regulates ADUs as 'accessory units' in Section 44-4.10 of the Zoning Code (Chapter 44). The county caps a unit at 1,200 sq ft (up to 2,500 sq ft on agricultural classifications) and historically required owner occupancy and a recorded deed restriction, but current California law (Gov. Code 66310-66342) preempts those owner-occupancy rules and requires ministerial approval.
Maximum Unit Size. The floor area of the accessory unit shall not exceed one thousand two hundred square feet, except on agricultural classifications (F-A, E-A, U-C, U-T, and A-T) the floor area may be up to two thousand five hundred square feet.
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 850, passed April 7, 2026).
Full Breakdown
10. Only one accessory unit is allowed per legally created parcel, and it is not permitted on a parcel already containing two or more dwelling units (Sec. 010). The unit may be within, attached to, or detached from the primary dwelling and must have its own kitchen, bathroom, and separate entrance (Sec. 030). 060, the maximum floor area is 1,200 square feet, except on agricultural classifications (F-A, E-A, U-C, U-T, and A-T) where it may reach 2,500 square feet; the minimum is 150 square feet (or the state efficiency-unit size, whichever is greater).
Detached accessory units require a 3-foot side setback and 8-foot rear setback, with at least 10 feet between buildings. A one-story detached unit is limited to 16 feet and a two-story unit to 28 feet in height. 100 of the county code require the owner to occupy the primary or accessory unit and to record a deed restriction barring separate sale. However, current state ADU law - recodified into Government Code Sections 66310-66342 - preempts conflicting local rules: it bars owner-occupancy requirements for standard ADUs, requires ministerial (no-hearing) approval, guarantees at least an 800-square-foot unit at 16 feet with 4-foot side and rear setbacks, and allows a junior ADU up to 500 square feet within an existing single-family home. Where the county's older Ord. 765/788 text conflicts with that state law, state law controls. Confirm current requirements with Colusa County Planning & Building.
Violations & Fines
Building or occupying an accessory unit without the required building permit and zoning approval, or in violation of the Section 44-4.10 standards, is a violation of the Colusa County Zoning Code subject to code enforcement. Where county provisions (such as the owner-occupancy and deed-restriction requirements) conflict with California Government Code Sections 66310-66342, the qualifying ADU must still be approved ministerially under state law; unpermitted units are ineligible for that streamlined approval and may be abated as zoning and building-code violations.
Frequently Asked Questions
Can I build an ADU on my property in unincorporated Colusa County?
How big can my ADU be in Colusa County?
Does Colusa County still require me to live on the property?
Sources & Official References
Other rules in Colusa County
How Colusa County compares: Easiest Cities to Build an ADU·California rules heatmap·Compare Colusa County to another location·View the California accessory structures overview
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