ADU Rules in DeKalb County, GA: What Homeowners Need to Know

A Complete 2026 Guide for DeKalb County Homeowners | Garages for Atlanta

DeKalb County is one of Metro Atlanta's most internally diverse jurisdictions — a county that contains the City of Decatur (with its own comprehensive ADU ordinance and the most progressive ADU framework in Metro Atlanta), Druid Hills (split between City of Atlanta and unincorporated DeKalb), Clarkston (with its own city planning board), Stone Mountain (with its own Historic Preservation Commission), and large sections of unincorporated county with their own UDO-governed ADU rules.

The challenge for DeKalb County homeowners is that 'DeKalb County ADU rules' is not one set of rules. It is multiple overlapping frameworks depending on whether your property is in unincorporated DeKalb County, within an incorporated city like Decatur or Stone Mountain, or in the portion of Druid Hills that was annexed into the City of Atlanta in 2018. This guide covers all of them.

Unincorporated DeKalb County: ADU Regulations Overview

DeKalb County's Unified Development Ordinance Section 4.2.3 permits accessory dwelling units in single-family residential zoning districts as attached structures, detached structures, or internal conversions (basements, wings, garages, attics). The property owner must reside in either the principal dwelling or the ADU and possess a homestead exemption. ADUs are capped at 800 square feet or 50 percent of the principal dwelling's heated floor area, whichever is less. Minimum lot size is 10,000 square feet. The ADU's appearance must be similar to the principal residence.

Unincorporated DeKalb County Requirement	Rule
ADU types permitted	Attached, detached, or internal conversion (basement, garage, wing, attic)
Maximum size	800 sq ft or 50% of principal dwelling heated floor area, whichever is less
Minimum size	300 sq ft (habitable space minimum per building code)
Minimum lot size	10,000 square feet
Owner occupancy	Required: owner must reside in primary dwelling or ADU and hold homestead exemption
Parking	One additional off-street parking space required for the ADU
Appearance	Must be similar to the principal residence in exterior materials and roofline
Eligible zones	R-85, R-75, R-60 single-family residential districts; confirm for specific parcel
Permit portal	DeKalb County epermits: epermits.dekalbcountyga.gov
Permit processing	3 to 5 weeks after complete application for residential accessory structures

Incorporated Cities in DeKalb County: Each Has Its Own Framework

DeKalb County contains multiple incorporated cities with entirely separate ADU frameworks. The City of Decatur has the most comprehensive and permissive ADU ordinance in Metro Atlanta, allowing ADUs in multiple residential zones with an 800 square foot cap (or 40 percent of the primary dwelling, whichever is less) and a mandatory owner-occupancy requirement. The City of Atlanta's rules govern properties in the Druid Hills area annexed in 2018. Stone Mountain has its own city planning process. Clarkston has its own Planning and Zoning Board. None of these cities use DeKalb County's UDO for zoning purposes.

City of Decatur: Metro Atlanta's Most Progressive ADU Framework

The City of Decatur has permitted ADUs since December 2012 and maintains the most detailed and permissive ADU ordinance in Metro Atlanta. Key rules:

• Size cap: 800 sq ft or 40% of the primary dwelling's size, whichever is smaller

• Owner occupancy: Owner must occupy primary home or ADU for at least 8 months per year

• Rear yard placement: Detached ADUs must be in rear yard; cannot occupy more than 30% of backyard area

• Lot coverage: Combined home + ADU cannot exceed 40% of total lot area

• Permit portal: communitycore.com; arborist pre-application at treepermits@decaturga.com if trees affected

• Historic districts: Clairemont, MAK, and Agnes Scott College districts carry additional design review

City of Atlanta (Druid Hills Annexation Area)

The portion of Druid Hills annexed into the City of Atlanta in 2018 follows Atlanta's ADU rules: permitted only in R-4, R-4A, and R-5 zones; 750 sq ft maximum; combined lot coverage not to exceed 55 percent; arborist meeting required (since June 2025, Ordinance 25-O-1341) before permit submission for projects affecting trees; Urban Design Commission review for historic district properties. Garages for Atlanta confirms whether a Druid Hills property falls in the Atlanta or unincorporated DeKalb jurisdiction at the first site evaluation.

Stone Mountain, Clarkston, and Other DeKalb Cities

Stone Mountain requires a zoning review with the city planning department before any building permit can be submitted for footprint-expanding structures. Tree removal requires an arborist report on official letterhead with the arborist's license number, photographs, and a notarized owner affidavit. The Historic Preservation Commission has authority over designated historic district properties.

Clarkston has its own Planning and Zoning Board and a Historic Preservation Commission. Building permits submit through DeKalb County's epermits system, but City of Clarkston review may apply to certain project types. Garages for Atlanta screens for both layers at the first site consultation for every Clarkston ADU project.

Expert Insight: Why DeKalb County ADU Research Requires Jurisdiction Confirmation First

DeKalb County homeowners who search for 'DeKalb County ADU rules' online frequently find information that applies to either unincorporated DeKalb, the City of Atlanta, or the City of Decatur — but not necessarily to their specific property. A property in the Druid Hills CDP may fall under City of Atlanta ADU rules (750 sq ft cap, R-4/R-4A/R-5 zones only), unincorporated DeKalb rules (800 sq ft cap, owner occupancy required, homestead exemption required), or neither if the specific zoning district does not permit ADUs at all. Garages for Atlanta confirms jurisdiction using parcel-level data at the first site evaluation — before any design is proposed, any budget is discussed, or any permit research is done. The jurisdiction determination is the most important first step on any DeKalb County ADU project.

ADU Configuration Options in DeKalb County

DeKalb County's UDO explicitly lists the permitted ADU configurations for single-family residential parcels:

• Within the existing house: Renovations to basements, wings, or attics converted into a separate living unit

• Attached to the house: Addition connected to the existing structure with its own entrance

• Detached structure: Stand-alone new construction in the rear yard — most privacy, most design freedom

• Above the garage: Living space built above an existing or new garage bay — most popular in GFA's DeKalb service area

Garage conversions in DeKalb County are particularly practical because converting an existing structure to an ADU maintains the existing building footprint — no new lot coverage, no Accessory Building Location Plan required for new construction, and a simpler permit pathway than a new detached build. For DeKalb homeowners near the coverage limits common on smaller in-town lots, the conversion is often the only ADU configuration that works within the available margin.

Costs and Timelines for DeKalb County ADU Projects in 2026

ADU Configuration	2026 Cost Range	Timeline	DeKalb County Variable
ADU Above Garage (new garage + ADU)	$185,000 – $220,000+	24–36 Weeks	Structural engineering; fire separation; DeKalb County CO
ADU Above Garage (existing garage)	$130,000 – $185,000	18–26 Weeks	Structural assessment; fire-rated assembly; egress windows
Detached Backyard Cottage	$120,000 – $190,000	20–30 Weeks	10,000 sq ft min lot; owner occupancy; similar appearance required
Garage Conversion to ADU	$40,000 – $75,000	8–14 Weeks	Zero new footprint; change of use permit; fastest path
Decatur ADU (city-specific)	$150,000 – $200,000	22–32 Weeks	communitycore.com; arborist pre-app; 40% impervious limit

City-specific detail for the City of Decatur, Druid Hills, Stone Mountain, and Clarkston location pages covers each city's requirements in depth. The complete ADU guide for Georgia covers the statewide framework. Call 404-509-5526 or contact GFA online to schedule a no-cost site evaluation.

Frequently Asked Questions

1. Are ADUs allowed in DeKalb County, GA?

Answer: Yes. Unincorporated DeKalb County's UDO Section 4.2.3 permits ADUs in single-family residential districts as attached, detached, or internal conversion structures. Incorporated cities within DeKalb — including Decatur, Stone Mountain, and Clarkston — each have their own frameworks. The City of Atlanta's rules govern properties in the Druid Hills area annexed in 2018.

2. How large can an ADU be in DeKalb County?

Answer: In unincorporated DeKalb County, ADUs are capped at 800 square feet or 50 percent of the principal dwelling's heated floor area, whichever is less. The minimum size is 300 square feet per building code habitability requirements. The City of Decatur caps at 800 square feet or 40 percent of the primary dwelling. The City of Atlanta caps at 750 square feet.

3. Does DeKalb County require owner occupancy for ADUs?

Answer: Yes. Unincorporated DeKalb County requires the property owner to reside in either the primary dwelling or the ADU and must possess a homestead exemption. The City of Decatur requires the owner to occupy either the primary home or the ADU for at least 8 months per year. Confirm the specific owner occupancy requirement for your jurisdiction before building with rental income as the primary goal.

4. What is the minimum lot size for an ADU in DeKalb County?

Answer: Unincorporated DeKalb County requires a minimum lot size of 10,000 square feet for ADU construction. Incorporated cities within DeKalb set their own minimum lot requirements. Confirm the applicable minimum for your specific jurisdiction and zoning district.

5. Can I convert my garage to an ADU in DeKalb County?

Answer: Yes. Garage conversions to ADUs are explicitly permitted in DeKalb County's UDO as an internal conversion of an existing structure. The conversion requires a building permit for change of use, electrical, plumbing, and mechanical permits, and must pass all required inspections to receive a certificate of occupancy. Conversions add no new impervious coverage, making them the most practical ADU option for smaller in-town lots.

6. What is different about ADU rules in the City of Decatur vs unincorporated DeKalb?

Answer: The City of Decatur has a more detailed and permissive ADU framework than unincorporated DeKalb County. Decatur permits ADUs in multiple residential zones, has a 40% impervious surface limit that constrains footprints on smaller lots, requires a pre-application arborist meeting (treepermits@decaturga.com) before any permit involving tree disturbance, and requires owner occupancy for at least 8 months per year. Unincorporated DeKalb requires owner occupancy and a homestead exemption but has a 10,000 sq ft minimum lot size rather than an impervious surface limit.

7. How does the Druid Hills split jurisdiction affect ADU rules?

Answer: Druid Hills straddles the City of Atlanta and unincorporated DeKalb County. The Atlanta portion (including the area annexed from DeKalb County in 2018) follows City of Atlanta ADU rules: R-4/R-4A/R-5 zones only, 750 sq ft maximum, arborist meeting required for projects affecting trees. The unincorporated DeKalb portion follows the county's UDO. Garages for Atlanta confirms which jurisdiction applies to every Druid Hills property at the first site evaluation.

8. What permits are required for an ADU in DeKalb County?

Answer: ADU construction in unincorporated DeKalb County requires a building permit submitted through epermits.dekalbcountyga.gov, plus separate electrical, plumbing, and mechanical permits. A certificate of occupancy must be issued before the ADU can be legally occupied or rented. Incorporated city projects also require the city's review in addition to or instead of the county permit.

9. How much does it cost to build an ADU in DeKalb County?

Answer: Garage conversions run $40,000 to $75,000. ADUs above existing garages run $130,000 to $185,000. New garage plus ADU builds run $185,000 to $220,000. Detached backyard cottages run $120,000 to $190,000. City of Decatur projects carry additional permitting complexity from the arborist pre-application and impervious surface requirements.

10. How do I start an ADU project in DeKalb County?

Answer: Start with a no-cost site evaluation from Garages for Atlanta that confirms your jurisdiction, calculates lot coverage, identifies applicable size limits and setbacks, and screens for any historic district or overlay requirements. Contact Garages for Atlanta at 404-509-5526.