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

Title 18 (Zoning) contains no retaining-wall standards, so retaining walls in unincorporated Modoc County are regulated through Title 15 (Building Regulations), which adopts the California Building Standards Code under §15.01.020 (2019 CBC and CRC editions). A retaining wall is a 'structure' (Modoc County Code §18.06.1000) and §15.01.030 requires a permit to construct any structure unless the adopted code exempts it. Under the state building code's permit-exemption list, low retaining walls are exempt only when they are not over the code-specified height (commonly stated as walls not more than 3 to 4 feet measured at the footing) AND do not support a surcharge or impound flammable liquids. Any retaining wall that supports a surcharge — such as a slope, driveway, or structure loading the wall — requires a building permit no matter its height. Because Modoc County is rural and includes sloped and flood-prone terrain (Title 18 also has Flood Hazard and Floodplain Management chapters, 18.70 and 18.71), engineered design may be required for taller or load-bearing walls. There is no separate county zoning approval for a retaining wall, but yard-setback rules in §18.110.050 still apply to where structures may sit. Confirm the current exemption height and any engineering requirement with Modoc County Building & Safety before construction.