3110.1 Lowest Floor Height. For the new construction or substantial improvement of non-residential structures wholly or partially inside flood hazard areas, the lowest floor (including the basement) either shall be at least the height of the DFE or the entire structure shall be designed and constructed to be dry floodproofed during any flood up to the DFE height.

3110.2 Additions. For all lateral additions to an existing nonresidential structure that constitute a substantial improvement and are located wholly or partially inside the Flood Hazard Area, the lowest floor of the addition shall be at least the height of the DFE or designed and constructed to be dry floodproofed during any flood up to the height of the DFE for the additions to a non-residential structure.

3110.3 Nonresidential Enclosures. For the new construction or substantial improvement of non-residential structures wholly or partially inside flood hazard areas, any enclosures below the DFE shall only be used for parking of vehicles, building access, or incidental storage. Enclosed areas of non-residential structures that are below the lowest floor must be adequately anchored and built using flood resistant building material. Any utilities or service facilities located below the DFE must be designed and/or located to prevent flood damage. The enclosure shall be designed and constructed in accordance with § 3108.8.

3110.4 Non-Conversion. For any new construction of, or substantial improvement to, a nonresidential building located wholly or partially inside a flood hazard area, a non-residential space below the DFE shall not be converted to a residential use.

SOURCE: Final Rulemaking published at 32 DCR 6547, 6561 (November 15, 1985); as amended by Notice of Final Rulemaking published at 57 DCR 10781 (November 19, 2010); as amended by Final Rulemaking published at 72 DCR 006821 (June 20, 2025).