A detached accessory dwelling unit (ADU) under 600 square feet is fully legal in the City of Decatur, Georgia. Local zoning allows one ADU per residential lot, and the maximum size for a detached unit is currently 800 sq ft, so this 599 sq ft project is comfortably within code. Because it is detached and less than the main house, it will be classified as an accessory structure rather than a duplex, simplifying both planning and long-term property taxes.
The floor plan fits two bedrooms, one bathroom and an open living-kitchen area into a compact rectangle. A single exterior entrance at the front satisfies the building department’s life-safety rules, while at least one egress window in each bedroom meets emergency-escape requirements set by the International Residential Code, which Georgia follows. Keeping the kitchen along one wall limits plumbing runs and preserves floor space—a common strategy in sub-600 sq ft ADUs.
Decatur follows Georgia’s residential energy code, so the shell must reach minimum R-values (R-13 or better in walls and R-30 or better in the ceiling) and use high-efficiency windows. Most builders meet the heating and cooling load with a ductless mini-split heat pump, an option that avoids bulky ductwork and keeps utility bills predictable in Atlanta’s hot, humid summers.
Permitting time in the Atlanta metro varies, but four to six months is a realistic range for a by-right detached ADU if plans are complete and no variances are needed. Construction for a wood-frame unit of this size commonly runs three to five months once ground is broken. Recent projects around Metro Atlanta suggest all-in costs often fall between $100 k and $175 k, depending on finishes, foundation type, and site conditions.
For homeowners, a 2-bedroom ADU offers several clear benefits. It can serve as a long-term rental, multigenerational housing, or a future downsizing option while the main house is rented out. In many Atlanta-area neighborhoods, adding a legal ADU also increases resale appeal and overall property value, especially as more buyers look for flexible housing or supplemental income potential.
If you’re considering an ADU in Decatur, start with a zoning check to confirm setbacks, height limits and tree-protection rules. Engage a designer or architect familiar with local plan-review expectations, submit a complete package that includes site plan, structural details and energy-code compliance, and retain licensed contractors who understand Georgia building codes. By following these steps, a 599 sq ft detached ADU can become a high-value asset that meets today’s housing needs and tomorrow’s market demand.
Explore your ADU possibilities with Gather. We provide ADU planning, design, permitting, and construction management services in California, Georgia, Washington, Oregon and beyond!
