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

Section 4.2.33 sets ten numbered standards for accessory dwelling units. Item 1 restricts them to the ESA-1, ESA-2, ESA-3, A-1, A-2, A-3, RR, RSF-1, RSF-2, RSF/MH-1, RSF/MH-2, PRD (only on lots of one-half acre or more), and PRRD zoning districts, so an ADU is not permitted countywide by right. Item 2 requires the unit to be clearly incidental to, and connected with, a principal dwelling; a lot cannot carry an accessory dwelling unit without a primary house on it. Item 4 sets the size band: a minimum of 350 square feet, and a maximum of whichever is less between 75 percent of the principal dwelling's habitable floor area or 800 square feet outright, preventing an ADU from becoming as large as or larger than the main house.

Item 6 caps the county at one accessory dwelling unit per lot of record, so a property cannot add a second one later. Item 7 bars selling the accessory dwelling unit separately from the principal dwelling unit and the lot of record it sits on, tying the unit permanently to the main property rather than letting it become its own saleable parcel. The remaining numbered standards in Section 4.2.33 require the unit to meet the county's baseline housing standards, share utilities with the principal dwelling, and otherwise comply with every rule of the zoning district it sits in, with Section 4.2.33 controlling over any conflicting provision elsewhere in the Land Development Regulations.