ADU rules in New Castle County, DE — also called accessory dwelling unit regulations or granny flat ordinances — cover setbacks, owner-occupancy, parking, and permit requirements.
Accessory dwelling units (ADUs) in New Castle County require both zoning and building permits. Attached ADUs and some garage conversions may be permissible in residential zones under UDC Chapter 40.
New Castle County's UDC Chapter 40 addresses ADUs as accessory uses. Residential additions (including attached ADUs) require permits from the Dept. of Land Use. Freestanding accessory structures may not be used for human habitation (except on lots 2 acres or larger with a guest house). Attached ADUs and garage conversions to living space require both a zoning review and building permit. The county has been updating its rules to facilitate more infill housing options.
Unpermitted habitation of accessory structures violates Ch. 40 and building codes.
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See how New Castle County's adu rules rules stack up against other locations.
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