Durham, NC Accessory Structures: ADU Rules (2026)

Sec. 2, Accessory Dwellings, sets the UDO's baseline rule for standard residential ADUs: on a lot developed with one or two primary dwelling units, only one accessory dwelling is allowed. The unit can be attached to the primary structure or built as a separate detached structure. If the primary home is a single-family residence, the accessory building can even be a duplex, as long as both units together stay within a combined 1,200-heated-square-foot cap. For a standard single ADU, the heated floor area is capped at 1,000 square feet on a single story and 1,200 square feet total -- except in the RR District, where an ADU on a lot of four acres or larger can reach up to 50% of the primary dwelling's heated floor area, though it can never equal or exceed the primary structure's floor area outright.

No parking is required for an accessory dwelling. A travel trailer or recreational vehicle cannot serve as an ADU in a residential district, except during a temporary visit of two weeks or less. For height, a detached ADU follows the same limit that applies to accessory structures generally under Sec. 1, while an ADU added onto the primary structure follows that structure's own height limit instead; converting existing space within the primary structure into an ADU isn't subject to a separate height test at all.

A nonconforming accessory structure can be renovated or reconstructed into an ADU, though the ordinance's own commentary flags that, depending on the scope of the project, a special use permit under Sec. 4, Nonconforming Improvements and Structures, or a variance under Sec. 14, Variance, may still be required. Accessory dwellings are barred outright from Special Flood Hazard Areas and Future Conditions Flood Hazard Areas, wherever the lot sits.