Do I need a permit for addition or structural alteration in Marietta?

Yes. In Georgia, addition or structural alteration generally requires a permit, and Marietta is no exception.

Additions and any change to load-bearing walls require a permit and reviewed plans in Georgia; removing or altering a bearing wall usually needs engineered details. Additions may trigger energy-code, zoning, and setback review, so confirm the full scope before starting. Cobb County's own permitting office is the Cobb County Development and Inspections, reachable on 770-528-1000 at https://www.cobbcounty.gov/community-development/building-development/permitting. Its online permit portal is https://cobbca.cobbcounty.gov/CitizenAccess/default.aspx. It issues permits for the unincorporated county. If your city does not run its own building department, and many smaller Georgia municipalities do not, this is the office that will handle the job. Cobb County sits inside the Metropolitan North Georgia Water Planning District, created by the Georgia General Assembly in 2001. Every local government in the District, cities included, has to adopt the District's model post-construction stormwater ordinance or an equivalent one at least as effective, so these rules follow you into any city in the county rather than stopping at the unincorporated line. An addition adds roof area, which counts as impervious surface, and a large one combined with new driveway or patio work can reach the local threshold. In practice the thresholds are aimed at larger development rather than ordinary homeowner work, so most single-family projects sit below them. Cobb County, for example, publishes its trigger as adding more than 5,000 square feet of impervious surface or disturbing more than an acre. Each local government sets its own figures, so check yours before assuming. Where it does apply, the current standard is to retain the first 1.0 inch of rainfall on the site to the maximum extent practicable, which usually means a detention or infiltration feature rather than just grading water to the street. Marietta's permit FAQ requires a site plan for any exterior work with land disturbance, and work within 10 feet of a property line may require a professional survey before construction starts. A design professional is required when an addition adds or subtracts loads on the existing structure, even though Georgia does not require stamped residential plans. The city will not run rough inspections until the structure is dried in with the roof and windows installed, and the general contractor schedules every inspection in SagesGov. An addition attached to the house counts as part of the principal building for setbacks under the district rules, such as Zoning Ordinance 708.04(F)(2) in R-4.