Twain Harte, CA Fence Regulations: Retaining Walls (2026)

Tuolumne County adopts the 2022 California Building Code under Title 15, and the permit rules for retaining walls come from that code rather than the Title 17 zoning ordinance. California Building Code Section 105.2 exempts from a building permit 'Retaining walls that are not over 4 feet (1219 mm) in height measured from the bottom of the footing to the top of the wall, unless supporting a surcharge or impounding Class I, II or IIIA liquids.' A 'surcharge' means an added load such as a slope, driveway, or structure above the wall. So a wall over 4 feet, or any wall (even shorter) carrying a surcharge, requires a building permit and typically an engineered design. The four-foot measurement is taken from the bottom of the footing, not from finished grade, so a wall that looks under four feet at the surface can still exceed the threshold. Retaining walls must also respect the county's setback and easement provisions in Chapter 17.22.030: structures (including walls treated as appurtenances) must not obstruct public easements or rights-of-way, and grading near septic systems is limited. Tiered walls and walls near property lines or roadways may have additional engineering and drainage requirements through Building and Safety.