ADU rules in Aiken

Aiken's Zoning Ordinance calls an ADU an 'accessory apartment' and allows one per lot in an accessory building as a conditional use (C) in the RS-15, RS-10, RS-8, RS-6, RSH and RSS single-family districts. In Aiken a conditional use permit is issued by right by the Planning Director once the listed standards are met (§6.2.7), so it counts as allowed. The binding standards are a lot of at least 10,000 square feet and 75 feet wide, and owner occupancy. A second accessory building for an apartment needs a lot of at least half an acre. Converting an accessory building that got a reduced setback by variance or waiver needs a Board of Zoning Appeals special exception. The RSA, RSM, RML, RMH and RMP districts do not list the use, apart from an RML/RMH exception for lots holding only one detached house.

The same accessory apartment may be 'within the principal dwelling' (§3.4.1.A.2), on the same conditional-use, staff-issued permit in the same districts and with the same 10,000 square foot lot and 75 foot width minimums. An internal conversion inside the existing footprint is the by-right route. Enlarging the footprint of the house to create the apartment requires a Board of Zoning Appeals special exception (§3.4.1.A.6.a). Nonconforming buildings also need a special exception.

An apartment in an accessory building 'may not exceed 35 percent of the gross heated floor area of the principal dwelling' (§3.4.1.A.3, Ord. 01122009). Every accessory apartment must have at least 450 square feet (§3.4.1.A.3 and §4.2.2). Separately, all accessory buildings on a lot together may not exceed 50 percent of the principal building's heated gross floor area, and no accessory building may be taller than the principal building (§3.4.2.D, E). Those two limits do not apply in the Horse District, in RSS lots in the Historic Overlay District, or on RSS lots of one acre or more outside it (§3.4.2.A). An internal apartment has no stated size cap, but enlarging the house to create it requires a special exception.

'Either the principal dwelling or the accessory apartment must be occupied by the property owner' (§3.4.1.A.4). The text states this as a standing condition of the use, not a one-time application test, and it applies in every district where the use is allowed (nonresidential districts incorporate §3.4.1.A through §3.4.1.B). No state law affects this.

'One off-street parking space is required for each accessory apartment' (§3.4.1.A.7). The space for an apartment in an accessory building may not be in the front yard of the principal building. This is on top of the 2 spaces per dwelling unit that §4.5.1 requires for single-family use.

The use tables mark the accessory apartment 'C' (conditional use) in the single-family districts. §6.2.7 defines Aiken's conditional use permit as 'a permit issued by right for a use subject to listed conditions'. It goes through the building permit procedure, and the Planning Director approves or denies it within 15 working days, or approves the site plan where one is required. There is no public hearing. A Board of Zoning Appeals special exception (§6.2.18) is needed to enlarge a building's footprint, add a second floor to an accessory building, use a nonconforming building, convert a setback-waived accessory building, add a second apartment in RSS (one-acre lot), or build an apartment in the HD district.

The ordinance does not bar renting the accessory apartment long-term. The owner-occupancy rule means one of the two units must be the owner's home (§3.4.1.A.4). Household Living, which covers accessory apartments, means occupancy 'on a month-to-month or longer basis' and excludes 'lodging where unit is rented on a less-than-monthly basis' (§3.2.2.A). Stays under 30 days are Overnight Accommodations (§3.2.5.D), allowed in residential districts only as an owner-occupied Bed and Breakfast Home Stay by Board of Zoning Appeals special exception in RS-15, RSH, RSS, RML and RMH. The city's business licensing page says some districts do not allow short-term rentals and others need a special exception, and operators must remit the City accommodations tax. Aiken had no standalone short-term rental ordinance at extraction; council took up the topic again in an April 2026 work session, to be handled in the pending UDO.