Jefferson County, AL Accessory Structures: ADU Rules (2026)

Section 1207 of the Jefferson County Zoning Resolution, Accessory Dwelling Units, governs ADUs and garage apartments wherever they are allowed by right or by Special Use Permit in the unincorporated county. Only one ADU or guest house is permitted per lot, and it must be built on a lot that already carries a primary residence. The unit is tied to the main house administratively as well as physically: it must share utility services and meters with the primary structure rather than carrying its own separate account, and, if detached, must be sited in the rear yard.

Attached and detached ADUs alike must meet the same setback standards that apply to the principal structure, so an ADU cannot be pushed closer to a property line than the main house could be. The Resolution caps unit size two ways at once: an ADU cannot exceed 40% of the principal structure's square footage, and cannot be smaller than 400 square feet or 20% of the principal structure's square footage, whichever figure is more restrictive, forcing every ADU into a narrow size band tied to the house it accompanies.

Interior layout is capped too, no more than one kitchen, at least one bathroom, and no more than two bedrooms, and the unit's own footage does not count toward the minimum square footage required of the primary structure under the applicable zoning classification. Design must also match: the section requires the ADU to be of similar architectural style to the principal structure. 03's notice, misdemeanor and injunction process.