Homeowners in unincorporated Cobb County will be able to ask to build a small second home in the backyard. The Board of Commissioners voted 3-2 on Tuesday, Oct. 27, to add accessory dwelling units to the county's zoning code, with the three Democrats in favor and the two Republicans, including East Cobb's District 3 Commissioner JoAnn Birrell, voting no (via East Cobb News).
It's the county's second run at the idea. A similar ADU proposal in 2024 drew heavy pushback from neighborhood groups, and after the Cobb Planning Commission voted 5-0 to recommend denial, commissioners withdrew it on Nov. 12, 2024. East Cobb News reported that the language adopted this fall closely tracks that earlier version. This time it went through a Planning Commission hearing on Oct. 6 and commissioners' hearings on Oct. 13 and Oct. 27.
The ordinance text the county posted for those hearings spells out the rules a builder would design around:
The unit can't be larger than 850 square feet or half the gross square footage of the main house, and it's limited to one story, no taller than the primary home.
It has to sit in the rear yard and meet the same side and rear setbacks as the main house. The lot as a whole still has to stay under its zoning district's impervious surface limit, and the ADU has to follow the other accessory structure standards for that district.
It must run off the main house's utility meters rather than getting its own.
Only one ADU is allowed per single-family lot, and the property needs at least one off-street parking space for it.
The owner has to live on the property, in either the main house or the ADU, and the unit can't be used as a short-term rental. Owners also sign an affidavit stating the ADU doesn't conflict with any covenants, deed restrictions or HOA bylaws that apply to the lot.
The biggest catch is the approval path. ADUs aren't allowed by right. They were added to the county's list of uses that need a special land use permit, which means every single backyard unit goes to a public zoning hearing and a vote by commissioners.
Cobb's posted special land use permit application, still the 2025 form on the county's zoning forms page, lists a $1,000 application fee. Applicants must mail notice to every property owner within 1,000 feet, postmarked at least 30 days before the Planning Commission hearing, and post county notice signs on the property, with a $300 refundable deposit plus $15 per sign. If the lot is on septic, the Cobb County Health Department has to sign off before the application can even be filed. Applications are taken once a month, and under the county's own example, a case filed in early March reaches the Planning Commission and the Board of Commissioners in May.
Opposition hasn't gone away. At the hearing before the vote, Richard Grome of the East Cobb Civic Association told commissioners the group's concerns "remain unchanged," pointing to strain on water, sewer, stormwater and traffic in neighborhoods that weren't designed for extra homes. Marietta resident Donald Barth said he likes ADUs in general but doesn't think the county is "ready for it yet," arguing that what works on a quarter-acre lot in Marietta may not fit East Cobb's subdivisions.
Several Cobb cities, including Marietta, already allow ADUs under their own rules, and the county ordinance applies only in unincorporated areas. East Cobb News didn't report an effective date for the change, so anyone planning a project should confirm timing with the county's Zoning Division before filing.
Why it matters for Contractors
For small builders and remodelers in unincorporated Cobb, this opens a new kind of job, but it won't be a quick one. Every ADU is effectively a mini rezoning case, so the homeowner is looking at a monthly filing cycle, mailed notices, signs, a $1,000 fee and roughly two months or more before a vote, and only then the building permit. Neighbors get a formal chance to object, and in East Cobb they've shown they will.
The design limits are tight enough to plan around early. A one-story unit capped at 850 square feet (or half the house) that shares the main home's meters, sits within the house's setbacks and fits under the lot's impervious cap will rule out some lots and plenty of floor plans. Checking setbacks, coverage, utility capacity and any HOA covenants before you price the job will save you from bidding work that never gets approved. Shops that learn the special land use permit process and can hand clients a realistic timeline will have an edge as the first applications come through.