ADU rules in Spartanburg

Only the Downtown Code allows a second dwelling on a house lot: its use table lists 'Dwelling-Secondary' as permitted in D-T4 (General Urban) and permitted subject to supplemental standards in D-T5 (Urban Center), and not in D-T3 or D-T6. In the ordinary residential districts (R-15, R-12, R-8 SFD, R-8 General, R-6) the Zoning Ordinance has no accessory dwelling use, Section 501.1 prohibits unlisted uses and Section 501.2 allows no more than one principal residential building per lot, and planning staff told the Board of Zoning Appeals in September 2026 that a new ADU or a garage conversion is not permitted in those districts. ADUs that predate the 1999 ordinance survive as nonconforming uses.

The Downtown Code defines a secondary dwelling as 'either detached or non-detached', so an attached unit is allowed in D-T4 and D-T5 on the same terms as a detached one (rear yard, one per lot). Elsewhere there is no accessory unit, but the R-12, R-8 General and R-6 districts allow two-family dwellings by right, so a house there can become a duplex if it meets the two-family lot area, yard and two-spaces-per-unit parking rules; R-15 and R-8 SFD allow single-family dwellings only (plus boarders or lodgers without a separate unit).

Section 3.2.3(c) says the secondary dwelling 'may not be larger than twenty-five (25) percent of the gross floor area of the principal structure with a minimum habitable area of not less than 500 square feet', and the definition describes a unit 'designed for occupancy by one or two persons, not exceeding 750 square feet of gross floorspace'. Read together, a house needs about 2,000 square feet of floor area before a 500 square foot unit fits the 25 percent cap. A unit over a detached garage is limited to two stories and may not exceed the principal structure's height; Downtown accessory buildings also sit in the rear yard with 5 ft rear and 0, 3 or 6 ft side setbacks by district. Outside the downtown districts no size rule applies because no ADU is allowed.

Neither Section 3.2.3 nor the 'Dwelling - Secondary' definition requires the owner to live on the lot; the unit must only be subordinate to the primary living quarters and sit on a lot with an existing single-family dwelling. The Zoning Ordinance attaches owner residency only to unrelated uses (bed and breakfast inns under §302.3.B.3 must be operated by a resident owner).

Section 3.2.3(d) requires 'at least one (1) parking space ... per unit', located in the rear or side yard of the principal dwelling or on-street in front of it, so on-street frontage can satisfy the requirement. A duplex conversion in the R-12, R-8 General or R-6 districts instead falls under the Zoning Ordinance parking index, which requires two spaces per unit for a two-family dwelling.

Where allowed, the secondary dwelling is a by-right use ('P' in D-T4, 'PS', permitted subject to supplemental use standards, in D-T5), checked by staff against Section 3.2.3; the Design Review Board does not make final determinations on detached single-family homes in D-T4 or on accessory structures in the third layer, though exterior changes visible from the street can still need design review. In the ordinary residential districts there is no permit route at all: staff denied a garage conversion in R-15 in 2026 and recommended the Board of Zoning Appeals deny the appeal, and S.C. Code §6-29-800(A)(2)(d)(i) bars a board from granting a variance that would establish a use not otherwise permitted in the district.

The Downtown Code puts no rental, owner-occupancy or separate-sale condition on a secondary dwelling, so long-term rental is not restricted beyond the one-or-two-person occupancy the definition describes. A full-text search of the Municode Code of Ordinances (Supp. No. 3, through Ord. 2026-003) found no short-term or vacation rental provision, and the city's CivicClerk records show none since 2024; the closest rules are the roominghouse business license (Chapter 8, Article XII, for space let to three or more unrelated persons, with stays under 30 days classed as transient and commercial) and the home occupation allowance for lodging up to three resident guests. State and local accommodations taxes and a business license still apply to short stays.