Gaithersburg, MD Environmental Rules: Flood Elevation Requirements (2026)

Section 10-34 sets the elevation standard for new residential structures, residential portions of mixed-use buildings, and substantial improvements or repairs of substantial damage to existing homes in a special flood hazard area: the lowest floor, including any basement, must be elevated at least one foot above the base flood elevation established for that lot under Section 10-5. In zone AO areas of shallow flooding, the lowest floor instead must sit above the highest adjacent natural grade by the depth number printed on the FIRM plus two feet, or at least four feet if no depth number is shown.

Chapter 10's definitions section fixes the separate 'flood protection elevation' used for nonresidential buildings and floodproofing at the base flood elevation plus two feet of freeboard, an added safety margin the code says compensates for wave action, ice jams, and the hydrologic effect of urbanization on a watershed. Any enclosure built below the lowest floor, for parking or storage only, must be built of flood damage-resistant materials and carry at least two flood openings sized to one square inch of net open area per square foot of enclosed space, with the bottom of each opening no higher than one foot above the interior floor or exterior grade.

Fill used to reach the required elevation must be earthen soil or rock, sloped no steeper than one vertical to two horizontal, and protected from erosion. Applicants must sign an agreement to submit an elevation certificate, prepared by a licensed engineer or surveyor, both after the lowest floor is placed and again before the certificate of occupancy is issued.