ADU Rules in the City of Decatur
Verified against Decatur Unified Development Ordinance §6.8.2 and §6.8.3.A · August 2026
Decatur has permitted accessory dwelling units since 2015 and treats them as part of its "missing middle" housing strategy. The rules are clear and workable, but there several caveats, including an owner-occupancy requirement with real teeth.
Can I build one on my lot?
ADUs are allowed in the R-50, R-60, R-85, RS-17, RM-18, RM-22, RM-43 and PO districts. One ADU per lot of record. No exceptions. The unit may be developed within, adjacent to, or detached from either an existing or a new principal dwelling. Decatur is more flexible than the City of Atlanta here, which permits detached units only.
How big can it be?
This is where most people go wrong, because there are two separate caps.
The ADU itself: minimum 300 sq ft, maximum 800 sq ft of floor area, excluding any related garage area or ancillary storage. It also cannot exceed 40% of the floor area of the principal dwelling, whichever limit binds first.
The building it sits in: if your ADU is part of an accessory building, such as a garage with living space above, that whole structure is capped at 1,000 sq ft total, inclusive of dwelling, garage and storage. So a garage-plus-ADU building can be 1,000 sq ft overall, of which no more than 800 can be living space. Two bedrooms maximum. On a modest bungalow, the 40% rule will often bite before the 800 sq ft cap does.
How tall, and how many buildings?
Accessory buildings cannot exceed 25 feet in height, and you may have no more than two accessory buildings per lot, excluding structures under 100 sq ft. Twenty-five feet is generous compared with Atlanta's 20, and it is what makes a genuine two-story garage-and-ADU structure workable in Decatur.
Do I have to live on the property?
Yes, and you'll sign for it. The property owner must occupy either the principal dwelling or the ADU as their permanent residence for at least eight months of each year, and may receive no rent on the unit they occupy. At building permit application you must submit a sworn, notarized statement to the Zoning Administrator confirming this. If your plan is to rent both units as an investment, Decatur is not the jurisdiction for it.
Utilities, parking and permits
An ADU may share utility services and meters with the main building, or have its own. Decatur permits either. Parking is governed by UDO §7.1. Be aware that Decatur treats certain equipment as prima facie evidence that a space is a separate dwelling unit: separate utility services or meters, a separate mailbox, or kitchen equipment such as a sink, stove, oven or cabinets. Installing those in an accessory building not permitted as an ADU can create a compliance problem.
What else will hold up your permit
Decatur caps impervious surface across the lot, so driveway, house, patio and new structure all count against the same ceiling. There is also a mandatory arborist pre-application meeting before any permit involving tree disturbance. And if your property sits in a local historic district, the Historic Preservation Commission reviews the design.
Frequently asked questions
How big can an ADU be in Decatur?
Between 300 and 800 sq ft, excluding garage space, and no more than 40% of the principal dwelling's floor area. Maximum two bedrooms.
Can I build a garage with an apartment above it in Decatur?
Yes. The accessory building is capped at 1,000 sq ft total including the garage, of which the living space can be up to 800.
Do I have to live there in Decatur?
Yes. Owner-occupancy of one unit for at least eight months a year, confirmed by notarized affidavit at permit application.
Can I rent out my Decatur ADU?
You can rent the unit you don't occupy. You cannot rent both.
How many ADUs can I have?
One per lot of record.
Considering an ADU in Decatur?
We'll check your zoning district, run the 40% calculation against your existing house, and confirm what fits within the impervious surface limit. Call 404-509-5526.
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