What's not (currently) legal
Detached accessory dwelling units are not allowed as-of-right on private residential properties in unincorporated Cobb County. A proposal — up to 850 sq ft or 50% of the main home, single-storey, owner-occupancy required, no short-term rentals, dedicated parking — was withdrawn in November 2024 after opposition and revived for October 2025 hearings. Until the amended county code is confirmed, treat 'we build ADUs in Cobb' marketing as a warning sign.
In-law suites in Cobb County: what is legal — the internal suite
Current code allows permitted home renovations such as in-law suites and converting basements into separate living units. The buildable products: a terrace-level suite with legal egress and bathroom, a main-level suite conversion, or a garage conversion — all covered on our in-law suites page, with basement finishing and garage conversion details.
City of Marietta addresses
Inside city limits, Marietta's own zoning governs; published summaries of a city ADU framework conflict with each other, so city parcels get a direct confirmation with Planning & Zoning before design. That five-minute check protects a six-figure project.
The three legal paths, compared honestly
- Terrace-level suite: uses space you already own, suits Cobb's sloped lots and daylight lower levels, and needs legal egress, a bathroom and permitted work — usually the fastest lawful route to a private suite with its own entry
- Main-level conversion: keeps a parent on the same floor as the kitchen and laundry, avoids stairs entirely, and gives up living space the household currently uses
- Garage conversion: adds a suite without an addition's foundation and roof costs, but removes parking and still cannot become a separate detached-style dwelling by the back door
The withdrawn-and-revived county proposal described above would have capped a detached unit at 850 square feet or 50% of the main home, single-storey, with the owner living on site, no short-term rentals, a dedicated off-street parking space and a shared utility meter. Read those parameters as a sketch of where county thinking has been — not as rules you can build to today. Until the amended code is confirmed, design the internal suite, keep the paperwork permitted, and let any future detached option be a bonus rather than the plan.