Charleston County, SC Accessory Structures: ADU Rules (2026)

Unincorporated Charleston County regulates ADUs under ZLDR Section 6.5.9, Accessory Dwelling Units, as most recently amended by Ordinance No. 2375 (effective January 27, 2026). The rule has six standards: (A) in the Rural Area, the lot must have a minimum area at least 50 percent larger than the minimum required for a principal structure, and the heated gross floor area of the ADU shall not exceed 1,500 square feet; (B) only one ADU is permitted per lot; (C) ADUs must comply with all dimensional standards of the applicable zoning district in Chapter 4 (setbacks, buffers, building coverage, impervious surface coverage, height, and waterfront standards), except that ADUs in Residential and Residential Office (RO) districts in the Urban/Suburban Area follow the setback requirements of Section 6.5.8.B.3 and are not required to be located wholly to the rear of the principal structure; (D) ADUs on parcels that contain or abut an OCRM Critical Line must comply with Article 4.24.2 (Minimum Lot Standards for ADUs on Parcels Which Contain or Abut an OCRM Critical Line); (E) separate electrical meters are not allowed for attached ADUs; and (F) separate electrical meters are required for detached ADUs. The county does not impose an owner-occupancy requirement in Sec. 6.5.9 itself, and Section 6.5.8.B.1 explicitly allows ADUs (including those within garage structures) to be located in front of the principal structure. South Carolina has not enacted statewide ADU preemption (H.3469 remains pending), so Charleston County's ZLDR controls in unincorporated areas. Properties inside the City of Charleston, North Charleston, Mount Pleasant, or other municipalities are governed by the city's separate ADU ordinance, not Section 6.5.9.