As of October 2026, one 2026 Georgia cost guide puts a mid-range 600 sq ft detached ADU in metro Atlanta at about $130,000 to $180,000, and national guides put garage or basement conversions at about $60,000 to $150,000. Plans, permit fees, utility connections and site work can push the total higher. The lot, the size and the finishes set the real price.
What do published guides say each type costs?
| ADU type | Published range, as of October 2026 | Source and scope |
|---|---|---|
| Detached ADU | About $130,000 to $180,000 for a mid-range 600 sq ft unit; about $95,000 basic to $255,000 high-end | costtobuildhouse.com, 2026 Georgia guide, metro Atlanta |
| Detached ADU | About $110,000 to $285,000 | Angi, national |
| Garage conversion | About $60,000 to $150,000 | Angi, national |
| Attached ADU | About $100,000 to $216,000 | Angi, national |
| Basement conversion | About $60,000 to $150,000 | Angi, national |
These are third-party estimates, not our prices. National ranges blend high- and low-cost regions, and the Georgia guide's own figures vary between its sections, so treat every number here as a starting point.
What is the cost per square foot?
Angi gives a national average of about $150 to $300 per square foot, with some ADUs above $600. Small units cost more per square foot than large ones, because a kitchen and a bathroom cost about the same whether the unit is 400 or 750 sq ft.
What gets added on top of construction?
- Design and engineering. Drawings, structural design and a site plan.
- Permits and fees. Set by each city; Georgia has no statewide ADU fee cap.
- Utilities. A sewer and water run to the back of the lot, and often a bigger electrical service.
- Site work. Grading, a retaining wall on a sloped lot, or tree removal and replacement where the tree ordinance applies.
- HOA review. Some associations charge for architectural review.
Why do two quotes for the same ADU differ so much?
It depends on what is inside each number. One builder may quote the structure alone; another may include design, permits, the utility runs and finish allowances. Before you compare, ask each one to spell out:
- which design, engineering and permit costs are included
- how far the utility work goes, and who pays for a service upgrade
- the allowance for cabinets, flooring, fixtures and appliances
- what happens when the city asks for changes
Our written, itemized quote lists each of those lines so you can compare like with like.
What makes an Atlanta ADU cost more or less?
- Type. Converting a sound garage usually costs less than building new.
- Size limits. In the City of Atlanta, the 750 sq ft detached cap keeps units small, which keeps totals down but raises cost per square foot.
- Slope and soil. Rolling intown lots and Georgia red clay can mean more foundation work.
- Trees. Protected trees can force a different footprint or add fees.
- Finishes. The widest swing of all.
How do I get a real number?
Send your address through the lot check form on this page. We confirm the zoning, visit the property, and then give you a written, itemized quote. Also see what an ADU can rent for in Atlanta.
Sources, as of October 2026:
- costtobuildhouse.com, "2026 Georgia ADU Cost Guide" (metro Atlanta figures).
- Angi, "How Much Do ADUs Cost?" (national ranges by type and per square foot).
- City of Atlanta Department of City Planning, ADU policy page (750 sq ft detached limit).