Columbia permits accessory dwelling units (ADUs) under the Unified Development Ordinance (UDO), Chapter 17 Sec. 17-4.3(c) of the Columbia Code of Ordinances. An ADU requires a zoning permit and a building permit, with construction subject to the 2021 International Residential Code as adopted by the South Carolina Building Codes Council. ADUs may be attached, internal (basement or upstairs), or detached, and floor area is capped at the lesser of 1,000 square feet or 50% of the principal dwelling's floor area.
The Columbia Unified Development Ordinance (UDO), adopted August 20, 2019 and amended periodically, regulates accessory dwelling units as accessory uses to single-family dwellings under Sec. 17-4.3(c). An ADU may be attached, internal to the principal dwelling (such as an upstairs or basement apartment), or a detached structure (for example, an apartment above a garage). The UDO caps ADU floor area at the lesser of 1,000 square feet or 50% of the floor area of the principal dwelling, excluding carports and garages. Only one ADU is allowed per lot. Detached ADUs must be set back at least three feet from any side or rear property line and at least five feet from any other main building (unless open on all sides). Applicants submit a zoning permit demonstrating compliance with use, lot coverage, setback, and height limits, followed by a building permit through Columbia Planning and Development. Construction follows the 2021 IRC and 2021 IBC as adopted by the South Carolina Building Codes Council under SC Code Title 6, Chapter 9. ADUs in designated historic districts or on landmarked properties also require Design/Development Review Commission approval.
Building an ADU without a zoning permit or building permit triggers a stop-work order and code-enforcement action under Chapter 17 of the Columbia Code of Ordinances. Unpermitted work in a designated historic district may require Design/Development Review Commission after-the-fact review and possible restoration. Confirm current penalty amounts with Columbia Planning and Development.
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See how Columbia's adu permits rules stack up against other locations.
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