Columbia County, GA Accessory Structures: ADU Rules (2026)

Code of Ordinances § 90-52 governs ancillary dwellings, the county's regulatory term for what many residents call a garage apartment, in-law suite, or accessory dwelling unit. An ancillary dwelling can only be built on a lot or tract containing at least 20,000 square feet, and on a tract of five acres or less, the county allows no more than one ancillary dwelling and caps it at 1,800 square feet of space under roof. The board of commissioners has discretion to approve a larger ancillary dwelling than the 1,800-square-foot cap by weighing the size of the lot, the size of the main house, the site's topography, how close the ancillary dwelling would sit to other structures, and any other factor affecting the aesthetics of its placement. On tracts larger than five acres, the board may also permit more than one ancillary dwelling and raise the size limits further, using the same list of factors.

The ordinance flatly excludes certain building types from qualifying as an ancillary dwelling: a manufactured or mobile home, or a tiny house, cannot serve as an ancillary dwelling no matter how it is sited. Zoning-wide, § 90-50's use table lists an ancillary dwelling as a limited (L) accessory use in every residential district, R-A through A-R10, meaning the use itself is allowed countywide once the § 90-52 lot-size, unit-count and size standards are met, and it is a separate concept from the leasing restriction in § 90-51 that limits how many unrelated occupants can rent rooms in the main house.