Raleigh, NC Accessory Structures: ADU Rules (2026)

Raleigh's Unified Development Ordinance treats the accessory dwelling unit (ADU) as its own "Additional Housing Pattern" under Sec. 3, layered on top of the base zoning district's use, dimensional and height rules. An ADU may sit on a lot with an existing Detached House or Tiny House (accessory to Single-unit Living), an existing Attached House, Townhouse or Tiny House (accessory to Two-unit Living), or an existing Townhouse in Multi-unit Living, in the R-1, R-2, R-4, R-6 or R-10 districts. Only one ADU is allowed per lot unless the property sits in a Frequent Transit Area shown on the city's Comprehensive Plan, where up to two are permitted -- though only one of the two may be attached to the principal dwelling, and townhouse lots are capped at one ADU regardless of location.

The ADU's gross floor area must stay below the principal dwelling's gross floor area, and the size cap itself steps down with lot size: 1,000 square feet on lots over 40,000 sf, and 800 square feet on lots between 10,000-40,000 sf and under 10,000 sf. Detached ADU setbacks likewise scale by lot size -- from the primary street the unit must sit at or behind the front wall of the house; from a side street, 15 feet on larger lots and 10 feet on lots under 10,000 sf; from side and rear lot lines, 10 feet on lots over 40,000 sf and 5 feet on smaller lots; and from an alley, 4 feet without parking access or 20 feet with it.

Overall height is capped at 26 feet regardless of lot size. An ADU must be affixed to a permanent foundation (manufactured homes qualify only if they meet specific roof-pitch, eave and skirting standards and stay under 600 sf), must be separated by at least 6 feet from any other building on the lot unless integrated into it, needs a lockable external entrance reachable from the driveway, street or alley, cannot be sold separately from the principal dwelling, and is barred entirely from Flag Lots.