Retaining walls in San Mateo under 4 feet in height (measured from bottom of footing) are generally exempt from building permits under the California Building Code. Walls over 4 feet require a building permit and may need engineered plans. San Mateo's hillside terrain makes retaining walls common.
Retaining walls in San Mateo are regulated under the California Building Code as adopted in Title 23. Walls not retaining a slope and under 4 feet from the bottom of the footing are generally exempt from building permit requirements. Walls exceeding 4 feet require a building permit and typically require engineered plans from a licensed civil engineer. Surcharges (driveways, structures, or slopes above the wall) may require engineering regardless of height. San Mateo's hilly western neighborhoods have extensive use of retaining walls, and proper drainage behind walls is critical to prevent hydrostatic pressure and failure. Retaining walls near property lines may need to comply with both retaining wall and fence regulations. The Building Division processes retaining wall permits at 650-522-7200.
Retaining walls over 4 feet without permits are code violations. Failing walls creating safety hazards may be declared nuisances. Property owners are liable for damage to neighboring properties from retaining wall failures.
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See how San Mateo's retaining walls rules stack up against other locations.
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