Martinez, CA Fence Regulations: Retaining Walls (2026)

Contra Costa County's building code (based on the California Building Code) exempts from permit requirements most retaining walls of 4 feet or less measured from the bottom of the footing to the top of the wall, provided there is no surcharge (no building, driveway, pool, or significant slope above that loads the wall). Walls over 4 feet or any wall with surcharge require a permit and typically an engineered design stamped by a licensed civil or structural engineer. In the hilly portions of Contra Costa — Alamo, Blackhawk, Kensington, El Sobrante, Orinda fringe, and the San Ramon-Danville foothills — expansive clay soils and landslide risk often push grading-permit thresholds lower and drive engineering requirements. Drainage must direct water away from neighbors and not create erosion onto adjacent parcels (grading ordinance). Walls in mapped landslide, fault, or Alquist-Priolo zones receive additional scrutiny. Adding a fence on top of a retaining wall is permitted, but combined height (retained earth + fence) is calculated for fence-permit thresholds and for sight-distance rules. Unpermitted walls that fail can create personal-injury liability and insurance issues; the county can require removal or retrofit of non-compliant walls.