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

Yes. In Georgia, addition or structural alteration generally requires a permit, and Decatur 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. DeKalb County's own permitting office is the DeKalb County Planning and Sustainability, reachable on 404-371-2155 at https://dekalbcountyga.gov/departments/planning-and-sustainability/permits-plan-review-and-inspections. Its online permit portal is https://epermits.dekalbcountyga.gov/. 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. DeKalb 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. Decatur requires a pre-application meeting with the City Arborist before filing a building permit that proposes to remove trees or disturb the critical root zone of any protected tree; request it at treepermits@decaturga.com. Residential projects that change lot coverage must upload an as-built survey for approval, and a Certificate of Occupancy is issued only after all inspections, the as-built approval, and any High Performance Building Standards requirements are met. Construction must begin within 8 months of issuance, and a residential permit expires if the work is not completed within 12 months; renewals cost the original fee, or twice the fee for second and later renewals (UDO Sec. 10.1.1). Additions in a local historic district need a Certificate of Appropriateness from the Historic Preservation Commission.