Ontario, CA Fence Regulations: Retaining Walls (2026)

Under the California Building Code as adopted by Ontario, a retaining wall is exempt from building permit requirements only when it is 4 feet or less in height measured from the bottom of the footing to the top of the wall AND it does not support a surcharge load. A surcharge includes any slope rising above the wall, driveway, vehicular load, pool deck, structure, or impounded water. Any retaining wall above 4 feet or carrying a surcharge requires a building permit with engineered plans from a licensed California civil or structural engineer showing footings, reinforcement, drainage, and lateral loads. Walls near property lines must also meet zoning setbacks and neighbor notification, and drainage cannot be directed onto neighboring parcels. Walls in hillside areas or near geologic hazards may require additional soils and grading review. Failure to permit a retaining wall creates substantial liability for failures, settlement, and drainage damage to neighbors, and Code Enforcement can require after-the-fact permits or removal.