Trinity County, CA Fence Regulations: Retaining Walls (2026)

Trinity County is entirely unincorporated, so the County Building Division handles retaining-wall permits. Trinity County Code Section 15.04.140, amended by Ordinance No. 1373 (June 3, 2025), lists permit-exempt work. Item 3 exempts 'Retaining walls that are not over 4 feet in height measured from the bottom of the footing to the top of the wall, unless supporting a surcharge.' Two points matter: the height is measured from the bottom of the footing, not from finished grade, so a wall that looks shorter above ground may still exceed 4 feet once the footing is included; and the surcharge exception means a wall of any height that retains a sloped backfill, a driveway, a structure, or other added load above it requires a building permit even if it is under 4 feet. Walls above 4 feet, or surcharged walls, typically need engineered plans submitted to the Building Division. Retaining walls must also respect the zoning district's required yards and, near County-maintained roads, may require an encroachment permit from the Department of Transportation. Owners planning terraced walls or grading should confirm whether a grading permit is also triggered, as the County regulates grading separately under its building and land development ordinances.