This Week in Metro Atlanta: Cobb Puts a Number on the Backyard Unit, and the Beltline Gets a January Deadline

Three things this week, and all three are governments putting a date on a decision rather than making one. Cobb commissioners saw the actual text of the code amendments that would legalize backyard units and write the county's first data center rules. In the city, council gave the mayor's office, MARTA and Atlanta Beltline Inc. four months to say how a $3.5 billion rail line gets paid for. None of it is law yet. All of it has a calendar entry, which is the part worth knowing.

Start in Cobb, because the backyard-unit question finally has numbers attached. I wrote two weeks ago that Cobb was one October vote away from allowing accessory dwelling units. This week the board got the proposal itself at a work session, and here is what it actually says. An ADU would be capped at 850 square feet or 50 percent of the main house, whichever is smaller. Single story only. It has to run off the main building's utility meter. It needs at least one off-street parking space. The owner has to live on the property. And it cannot be used as a short-term rental. That last pair of conditions is the whole ballgame, and it is the same language Cobb withdrew in late 2024 after neighborhood opposition, brought back with little changed.

So who does this actually help. If you own a Cobb house on a decent lot and want a place out back for a parent, an adult kid or a long-term tenant, this is a real option and it adds real value to the lot. If you were planning to buy a Cobb house, build an 850-square-foot unit and run it on Airbnb, the draft says no twice, once with owner-occupancy and once by naming short-term rentals outright. Investors buying to rent out the whole property land on the wrong side of that same line. I would not pay a premium today for a Cobb lot on the theory that an ADU is coming. I would, if you have been putting off a multigenerational plan, get a builder to price an 850-square-foot single-story unit now, so you know the number before the vote rather than after.

The same code package is where Cobb writes its data center rules, and this one matters more to landowners than to homeowners. The draft would require a data center site to sit on at least 5 acres and no more than 30, to draw its power from off-site generation rather than building its own, to use closed-loop water cooling with no wastewater discharge except for maintenance, and to meet noise limits on both the cooling systems and the backup generators, plus limits on site lighting and building height. Cobb has had a moratorium on new data center applications running through February 2027 while staff wrote this.

Read that 30-acre ceiling carefully if you own industrial-adjacent land in Cobb. It is the number that takes the giant single-campus deal off the table in unincorporated Cobb and leaves the mid-sized ones, so if you have been holding a large parcel hoping for one enormous offer, that offer is being legislated away and your realistic buyer pool changes shape. Next door, DeKalb went the other way and did nothing: commissioners rejected their own planning department's data center ordinance in June, which would have capped campuses at 1 million square feet of disturbed land and pushed residential buffers from 500 to 750 feet, then extended DeKalb's moratorium to March 30, 2027 so other departments could weigh in. Two counties, two moratoriums, one draft. Cobb's calendar is specific: the planning commission takes the zoning chapter October 6 at 9 a.m., the Board of Commissioners holds hearings October 13 at 9 a.m. and October 27 at 7 p.m., and the vote comes that night, all at 100 Cherokee Street in Marietta.

Third, the city. On Monday the Atlanta City Council adopted a resolution from District 2's Kelsea Bond calling on the mayor's administration, MARTA and Atlanta Beltline Inc. to deliver a funding and implementation plan for light rail on the full 22-mile Beltline loop. Urbanize Atlanta reports the vote at 14-0. Atlanta News First puts the deadline at January 26, 2027, when a coordinated report is due to the council's Transportation Committee. The $3.5 billion price tag comes from the three-and-a-half-year transportation study presented September 3. Councilmember Byron Amos amended the resolution to strip out language supporting the use of Beltline tax allocation district money, arguing the TAD should finish its work on the Westside and Southwest before it expires at the end of 2030.

Here is the honest read for anyone who owns near the corridor. The resolution does not fund anything, does not pick a first construction segment and does not set a phasing order, and it says so on its face. What it does is force a written answer by late January on where $3.5 billion would come from, which is the first time the city has put itself on a clock about it. If you are selling on the Eastside or Westside trail in the next six months, price the trail you can walk on today, not the train. If you are buying to hold ten years, January 26 tells you whether this is a plan or a wish. Watch what the report says about the TAD, because Amos just took the easiest funding source off the table.

One more Cobb item, since the same board had a busy week. Commissioners voted 5-0 to fund a $2.3 million rebuild of the Johnson Ferry and Shallowford intersection, adding two through lanes and two left-turn lanes on the westbound approach plus raised medians, new signals and pedestrian work. Design starts March 2027, construction September 2027, substantial completion September 2028. If you are buying in that pocket of East Cobb, that is a year of construction between contract and finished road. The board also approved $6.3 million in CobbLinc Go microtransit at $2.50 a rider, a two-year pilot around Acworth and Kennesaw and a one-year pilot in Mableton, funded mostly by state transit money. Two commissioners voted against it.

So the dates: October 27 if you own in Cobb and care about either backyard units or data centers. January 26 if you own along the Beltline. March 30, 2027 if you are waiting on DeKalb to decide anything at all. If you want to know whether any of this touches a specific address, send it to me and I will tell you straight.