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

UDO Subsec. 5.4.B, 'Accessory Apartments/Dwelling Units,' lets property owners in the AG district, every residential zoning district, and the MXU district add a second dwelling unit to a single-family lot without rezoning, subject to design limits meant to keep the property looking like a single-family home from the street. No more than one accessory dwelling unit is permitted per lot with a principal dwelling, and none is allowed on a lot that already carries a two-family or multi-family dwelling.

An ADU built within the principal building cannot exceed 25% of that building's heated floor area, and the section bars alterations, such as a second entranceway or a second mailbox, that would make the house read as multi-family from a public or private street; access to an in-house ADU must use an existing side or rear door unless the NC Building Code requires a new one, and no new doorway or stairway may be added facing the street. A detached ADU, whether a freestanding unit meeting the NC Building Code or a unit built into an accessory garage, must sit at least 10 feet from the principal building, meet every setback that applies to the principal building, have an approved sewage disposal connection, and stay within the zoning district's overall accessory-building coverage cap when its footprint is added to the lot's other accessory structures. Every ADU must be assigned a street address under the county's Street Name and Address Assignment Standards, and the minimum ADU size, attached or detached, is 250 square feet. Detached units built as mobile homes carry an added restriction: the principal dwelling must be a Class AA double-wide or a freestanding home meeting the NC Building Code before a mobile-home ADU can be sited on the lot.