Missing Plans for Wood Retaining Walls (R404.4): Retaining walls that are not laterally supported at the top and that retain in excess of 48 inches of unbalanced fill, or retaining wall exceeding 24 inches in height that resist later loads in addition to soil, shall be designed in accordance with accepted engineering practice to ensure stability against overturning, sliding, excessive foundation pressure and water uplift. Retaining walls shall be designed for a safety factor of 1.5 against lateral sliding and overturning.