Lake Forest, CA Fence Regulations: Retaining Walls (2026)

In Lake Forest, retaining walls are regulated on two levels. For zoning purposes, the definition of 'fences and walls' in Municipal Code Section 9.144.080.5 expressly includes retaining walls, so a retaining wall counts toward the same height limits as a fence: 3 1/2 feet within a required front setback and 6 feet within side and rear setbacks. A combination retaining-wall-plus-fence is measured as a unit against those limits, and exceeding them requires a site development permit under Section 9.184.010. For building safety, the City adopted the 2022 California Building Code through Municipal Code Chapter 8.02. Under California Building Code Section 105.2, retaining walls not over four (4) feet in height measured from the bottom of the footing to the top of the wall are exempt from a building permit, unless the wall supports a surcharge (such as a slope, driveway load, or another wall above it). Importantly, the four-foot threshold is measured from the bottom of the footing, not just the exposed face, so a wall with a deep footing or a back slope can require a permit even when only a few feet show above grade. The city also exempts certain excavations from a separate grading permit, but not excavations leaving an unsupported height greater than five feet after the structure is built. Always verify the measurement and engineering requirements with the Building Division.