3111.1 Lowest Floor Height. The lowest floor (including basement or underground parking garage) of any new construction or substantial improvement of a mixed-use building located on a development site wholly or partially inside a flood hazard area shall either be at or above the DFE or be designed and constructed to be dry floodproofed during any flood up to the DFE.

3111.2 Residential Portion. The lowest floor of the residential portion of any new construction of, or substantial improvement to, a mixed-use building located on a development site wholly or partially inside a flood hazard area shall be at or above the DFE.

3111.3 Nonresidential Portion. The lowest floor of the nonresidential portion of any new construction or substantial improvement of a mixed-use building located on a development site wholly or partially inside a flood hazard area shall either be at or above the design flood elevation or be designed and constructed to be dry floodproofed during any flood up to the design flood elevation.

3111.4 Ancillary Residential Use Portion. The lowest floor of the ancillary residential use portion of any new construction or substantial improvement of a mixed-use building located on a development site wholly or partially inside a flood hazard area shall be at or above the DFE, except that the lowest floor of the ancillary residential use portion of any new construction or substantial improvement of a mixed-use building located entirely outside of flood hazard areas specified in § 3101.2(a), but wholly or partially inside flood hazard areas specified in §§ 3101.2(b), (c), or (d), shall be at or above the DFE or be designed and constructed to be dry floodproofed during any flood up to the height of the DFE.

3111.5 Mixed-Use Enclosures. For the new construction or substantial improvement of mixed-use structures wholly or partially inside flood hazard areas, the non-residential portions below the DFE must be dry floodproofed. All residential units, building systems and service equipment that serve residential units and ancillary areas used by residents, must be elevated above the DFE. When an enclosure is created by elevating the non-residential portions at or above the DFE, the space below the DFE shall only be used for parking of vehicles, building access, or incidental storage. These enclosed areas shall be adequately anchored and built using flood resistant building material. Any utilities or service facilities below the DFE shall be designed and/or located to prevent flood damage. The enclosure shall be designed and constructed in accordance with § 3108.8.

3111.6 Dry Floodproofing. Dry floodproofing of non-residential portions of mixed-use buildings is allowed if all residential units, building systems, and service equipment that serve residential units, and ancillary areas used by residents, are

elevated above the DFE. Dry floodproofed shared accesses, such as lobbies to residential and non-residential portions, must provide separate access to the elevated residential portions of the mixed-use structures. When the separate access to the residential portions of a mixed-use building is enclosed by walls and below an elevated building, the walls must comply with the requirements for enclosures in § 3108.8.

3111.7 Non-Conversion. For any new construction of or substantial improvement to a mixed-use 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, 6562 (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).