Brentwood, CA Fence Regulations: Retaining Walls (2026)

Retaining wall requirements in Brentwood follow the California Building Code as adopted under BMC Title 15 (Building & Construction). Walls up to 4 feet tall (measured from bottom of footing to top of wall) that do not support a surcharge (sloped backfill, driveway, or other load above the wall) can generally be built without a building permit, though they still must comply with zoning setbacks and drainage rules. Walls over 4 feet, or any wall supporting a surcharge regardless of height, require a building permit and engineered drawings stamped by a California-licensed civil or structural engineer. Drainage must be provided behind the wall (weep holes or drain rock with perforated pipe) to prevent hydrostatic buildup. On hillside lots in Brentwood Hills or the eastern foothills, grading permits may also be required for earthwork exceeding 50 cubic yards. Walls affecting a neighboring property's drainage or lateral support are subject to additional engineering review and potentially easements. Non-permitted walls discovered during a property sale inspection can become costly correction items.