Simi Valley, CA Fence Regulations: Retaining Walls (2026)

Two separate sections govern retaining walls in Simi Valley, and a wall can clear one and still fail the other. 03(a)(5) of the Building Code exempts "retaining walls which are not over four (4) feet (1,219 mm) in height measured from the bottom of the footing to the top of the wall" from needing a building permit at all, "unless supporting a surcharge or impounding Class I, II or III-A Liquids," in which case the exemption does not apply regardless of height and an engineered permit is required.

" A wall over four feet anywhere on the lot needs a building permit with engineered plans regardless of zone, and a wall in the front or street-side setback is capped at 36 inches by zoning even where the Building Code would otherwise let a taller wall go up without a permit. 050(A)(2)(b) applies instead, capping fences and walls at six feet measured from the highest adjacent grade unless authorized by law. Excavation near a slope triggers a separate geotechnical review: the City's local amendment to California Building Code Appendix J, Section J106, requires a geotechnical report addressing slope stability whenever a retaining wall or similar structure encroaches into the projected plane of a 3:1 or steeper slope.