Union County, NC Accessory Structures: ADU Rules (2026)

030 of the Union County Unified Development Ordinance allows accessory dwelling units in every residential zoning district, but only on a lot already occupied by a single principal dwelling unit, and no more than one ADU is allowed per parcel. The accessory unit cannot be larger than 50 percent of the size of the principal dwelling. An ADU can be created five ways: converting existing living space such as an attic or basement, adding floor area to the existing house, building a new detached unit that must meet the North Carolina Building Code, converting space inside an existing detached accessory building, or constructing a new dwelling that already includes an internal or detached ADU.

A lot combining a detached house and an ADU still has to meet the minimum lot size required for a single-family dwelling in that zoning district; the ADU does not let a lot go smaller than the district's normal minimum. Apart from these ADU-specific rules, the unit is otherwise subject to every regulation of the zoning district where it sits, including any applicable setbacks and permit requirements under Article 35.