The City of Decatur has permitted ADUs since December 2012. As of October 2026, its ADU page allows one per primary dwelling in the R-85, R-60, R-50, RM-18, RM-22 and RM-43 districts, up to 800 sq ft and no more than 40% of the main house, with at most two bedrooms. The owner must live in one of the two units at least eight months a year.
Can a Decatur ADU be attached?
Yes. The city's page says an ADU may be attached, for example on the lower level of the house, or detached. That makes Decatur one of the few cities near Atlanta where a basement or lower-level suite can be a legal unit. A detached ADU has to be in the rear yard, with a footprint no larger than 30% of that yard.
What if I combine it with a garage?
Decatur allows a total of up to 1,000 sq ft when the ADU is combined with a garage, per the city's ADU page. That opens up a garage-plus-unit design that would not fit under the 800 sq ft cap alone.
How does lot coverage work?
The city lists two caps: the main house and the ADU together should not exceed 40% of the lot area in floor area, and all impervious surfaces, including driveways and patios, should not exceed 40% of the lot. On smaller lots, coverage is often what limits the unit, not the 800 sq ft cap.
What does owner occupancy mean in practice?
You must live in either the main house or the ADU for at least eight months each year and sign an affidavit confirming it. A 2024 city text amendment memo also notes that the owner cannot collect rent on the unit they occupy. If you plan to move out and rent both, Decatur's rules will not fit, and that should shape your plans before you build.
What usually matters on a Decatur lot?
- Small, mature lots. Coverage and the rear-yard footprint cap decide the size.
- Older houses. Electrical service and sewer laterals often need attention when a unit is added.
- Historic districts. Parts of Decatur are in local historic districts, where design review can apply.
Who reviews ADUs in Decatur?
Decatur's own planning and building staff review the zoning and building permit. Decatur sits in DeKalb County, but county ADU rules do not apply inside city limits.