Alpharetta, GA Environmental Rules: Flood Elevation Requirements (2026)

Section 3.4.5.B.1 requires that, once a residential project meets the no-rise and encroachment standards of Sections 3.4.4.C, 3.4.4.D, and 3.4.4.E, its lowest floor, including any basement, be elevated no lower than three feet above the base flood elevation or one foot above the future-conditions flood elevation, whichever is higher. This same three-foot freeboard applies to substantial improvements of existing residential structures and to new manufactured homes under Sections 3.4.5.B.1.b and 3.4.5.B.5. Non-residential structures get a one-foot freeboard standard instead under Section 3.4.5.B.2, with an option to floodproof to that same level rather than elevate, certified by a licensed professional engineer or architect using the FEMA Floodproofing Certificate.

Where solid foundation perimeter walls are used to reach the required elevation, Section 3.4.5.A.5 requires flood vents sized to provide at least one square inch of opening for every square foot of enclosed area below the lowest floor, with the bottom of each opening no higher than one foot above grade. Buildings located adjacent to, rather than inside, the future-conditions floodplain still face the same three-foot residential and one-foot non-residential freeboard under Section 3.4.5.C. The Directors of Community Development and Public Works record the actual elevation of every new and substantially improved structure and can require an as-built Elevation Certificate before occupancy.