Midwest City, OK Environmental Rules: Grading & Drainage (2026)

Oklahoma County follows municipal grading regulations, primarily Oklahoma City Building Code §155-40 and Edmond Code §22-73, which require grading permits for excavation or fill exceeding 50 cubic yards, excavations over 4 feet deep, or fills over 4 feet high. Smaller thresholds apply near property lines or within drainage easements. Oklahoma common law follows the modified civil law rule for surface water drainage — property owners cannot redirect or concentrate water onto neighboring properties (Thompson v. Andrews, 1962 OK 79). Natural drainage patterns must be maintained or improved. Site grading must direct runoff away from structure foundations (minimum 5% slope for first 10 feet). Drainage swales, French drains, and area drains required where natural drainage is disrupted. Retaining walls over 4 feet from footing to top require building permits and engineered plans stamped by an Oklahoma-licensed professional engineer per OAC 245:15-13-5. Walls near property lines need setbacks. Oklahoma's red clay soil (Vernon-Kingfisher series) expands when wet and shrinks when dry, requiring proper moisture conditioning and 95% Standard Proctor compaction for structural fill. Frost depth minimum 18 inches for footings. Final grade inspections required before certificate of occupancy.