New Castle County requires a building permit for retaining walls over 4 feet measured from bottom of footing to top of wall. Walls supporting surcharge loads require permits at any height. Engineered plans required over 4 feet.
New Castle County Department of Land Use requires a building permit for any retaining wall over 4 feet in height measured from the bottom of the footing to the top of the wall per the 2018 IRC (adopted with Delaware amendments). Walls supporting a surcharge — sloped backfill, driveway, structure, or swimming pool — require a permit regardless of height. Walls over 4 feet must be designed by a Delaware-licensed professional engineer with stamped drawings showing soil assumptions, drainage provisions, and reinforcement. Proper drainage with gravel backfill and weep holes or drain tile is required. Setbacks from property lines follow UDC accessory structure provisions (typically 3 feet minimum for walls). Wilmington has parallel provisions through its building code.
Unpermitted wall over 4 ft: stop-work order, double permit fees, required engineer review and retrofit or demolition if unsafe. Civil penalties $200 to $1,000. Failure to correct: Justice of the Peace Court citation.
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See how Wilmington's retaining walls rules stack up against other locations.
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