Colusa County, CA Fence Regulations: Retaining Walls (2026)

The Colusa County Zoning Code (Chapter 44) contains no section regulating retaining-wall height, design, or location, and Article 44-0 (Definitions) does not define a retaining wall. Retaining walls in the unincorporated county are therefore controlled by the statewide California Residential Code (CRC), which the county adopts and enforces through its Building Code (County Code Chapter 5). Under CRC Section R105.2 (Work exempt from permit), a retaining wall is exempt from a building permit only if it is not over 4 feet in height measured from the bottom of the footing to the top of the wall, and provided it does not support a surcharge (such as a slope, driveway, or structure load) or impound Class I, II, or IIIA liquids. A retaining wall over 4 feet, or any wall supporting a surcharge, generally requires a building permit and engineered plans from the Colusa County Building Division. Retaining walls must also respect the setback requirements in Zoning Code Article 44-2 where they function as structures, and grading or drainage permits may apply on sloped or hillside parcels. Owners should confirm requirements with the Building Division before construction.