Grading and drainage in New Castle County are regulated through NCC Code building permits (IRC/IBC grading provisions) and the Delaware Sediment and Stormwater Program (7 Del.C. Chapter 40). Grading exceeding 100 cubic yards or creating significant cuts or fills requires permit. Drainage cannot be redirected onto neighboring property. Retaining walls over 4 feet require engineered design.
Grading and drainage in New Castle County is governed by several overlapping authorities: the NCC building code under Chapter 6 (which adopts the International Building Code and International Residential Code with Delaware amendments), the Delaware Sediment and Stormwater Program (7 Del.C. Chapter 40) administered through the New Castle Conservation District, and UDC Article 40 for site-plan-level review. Grading permits are required for earth-moving activities exceeding specified thresholds, typically 100 cubic yards of excavation or fill, or any grading that changes drainage patterns affecting off-site conditions. Delaware common law recognizes the Modified Civil Law Rule for surface water drainage: upper landowners may discharge natural drainage to lower properties, but they cannot artificially concentrate, accelerate, or redirect water onto neighbors in ways that cause damage. Diverting drainage onto a neighbor can result in injunction and damages. Retaining walls over 4 feet (measured from bottom of footing) require engineered plans sealed by a Delaware-licensed engineer and a separate permit. Walls must not impede natural drainage and must provide adequate weep holes or subsurface drainage. Site grading must direct drainage away from primary structures (minimum 5% slope for 10 feet per IRC Section R401.3) and into approved conveyance systems, not onto neighbors. Compaction testing required for structural fill. Floodplain rules (NCC floodplain ordinance consistent with FEMA NFIP) impose additional controls on fill in floodways.
Unpermitted grading: stop-work order, fines $250 to $2,500 under NCC Code. Redirecting drainage onto neighbors: civil claim plus corrective action order. Grading in floodway without approval: $500 to $10,000+ plus restoration. Retaining wall without engineering: stop-work, correction required.
Wilmington, DE
Residential swimming pools in Wilmington require a building permit from the Department of Licenses and Inspections and must comply with the Delaware State Bu...
Wilmington, DE
Delaware does not preempt local tiny-home rules, and Wilmington's City Code Chapter 48 (Zoning) treats dwellings under the standard residential district bulk...
Wilmington, DE
Carports in Wilmington are accessory structures regulated under City Code Chapter 48 (Zoning) and require a building permit from the Department of Licenses a...
Wilmington, DE
Wilmington follows Delaware HB 80 (2017) informal sanctuary protections. The Wilmington Police Department limits civil immigration cooperation with ICE; crim...
Wilmington, DE
Delaware's Healthy Delaware Families Act (DE 19 §3702A) created statewide paid family and medical leave, fully effective 2026. Wilmington cannot create a sep...
Wilmington, DE
Delaware preempts local minimum-wage rules. The state minimum wage rose from $13.25 (2025) to $15.00 effective 2026 under DE Title 19 §902, applying uniforml...
See how Wilmington's grading & drainage rules stack up against other locations.
Help us keep this page accurate. If you notice an error or outdated information, let us know.