ADU rules in Charleston

Since Ord. 2020-116 (9-8-2020), Sec. 54-214 lets the Zoning Administrator approve one ADU as an accessory use to a single-family dwelling in all base zoning districts, and the definition expressly covers a unit 'in an accessory building on the same lot', including garage apartments. Approval is a staff finding against objective conditions (site plan, covenant certification, recorded Declaration of Covenants and Restrictions), not a board hearing. Agricultural districts add the Sec. 54-1009 standards, and in agricultural conservation subdivisions Sec. 54-1039 allows only a 600 sq ft detached ADU on lots that do not abut an OCRM Critical Line.

The ADU definition covers a unit 'located in the same building as the principal dwelling unit', and the city's ADU page says an ADU can be located within the principal single-family building. The same Sec. 54-214 conditions apply as for a detached unit. In agricultural districts Sec. 54-1009 bars separate electrical meters for attached ADUs, while Sec. 54-214.d otherwise allows separate electric, gas and water meters.

Sec. 54-214.e caps an ADU at 850 square feet of conditioned floor area, and an ADU in an accessory building approved under the Sec. 54-506.f setback exception (building within 3 feet of interior side and rear lines, behind the house) is limited to a 600 square foot footprint; that exception also limits height to 1.5 stories and an 11 foot eave, or 2 stories and 24 feet where the house has two or more stories. Otherwise the accessory building follows the district's Table 3.1 setbacks, height and lot occupancy. In the AG-8 and AG-S agricultural districts Sec. 54-1009 allows up to 1,500 square feet of heated floor area but requires a lot at least 50 percent larger than the district minimum; conservation subdivision ADUs are capped at 600 square feet. Occupancy is limited to two adults (any number of children).

The recorded Declaration of Covenants and Restrictions must state that either the principal dwelling or the ADU is owner-occupied as the owner's primary dwelling; if neither unit is owner-occupied, the ADU may not be rented separately from the principal dwelling. In practice owner residence is an ongoing, recorded condition for renting the ADU as a separate unit, enforceable by the city including by revoking the certificate of occupancy; an absentee owner may only rent the two units together. South Carolina has no state law overriding this.

Sec. 54-214.f requires one off-street parking space for the ADU on the lot, in addition to the parking already required for existing uses (the city page notes two spaces for a single-family dwelling, so typically three in total). The ADU space may be in tandem with the other required spaces. There is no transit or peninsula exemption in the ADU section.

The city's 2020 page calls ADUs a 'conditional use', but the ordinance text makes it an administrative approval. The Zoning Administrator approves the ADU on a finding that the Sec. 54-214 conditions are met, with no board hearing. The process is a zoning application at the Permit Center with a site plan, a signed no-covenant statement and a draft DCR approved by Planning and Corporation Counsel, then a building permit; the certificate of completion waits on a recorded DCR. Within the Old and Historic District, new structures and visible exterior changes also need Board of Architectural Review approval under Sec. 54-232; that is design review, not use approval.

The ADU may be rented long-term when the owner lives in one of the two units; with no owner in residence it cannot be rented separately from the house. Subleases are prohibited, occupancy is capped at two adults, and the lot may never be converted to a horizontal property regime (no condo sale of the ADU). The DCR must bar short-term rental of both the ADU and the principal dwelling, and the city page states that lots with an ADU are not eligible for a short-term rental permit. Under the Secs. 54-208 to 54-208.3 STR regime, short-term rental is otherwise owner-operated, owner-resident and permit-based. An ADU built with a city housing subsidy that is rented must serve households at or below 80 percent of AMI for at least 30 years.