D.C. Mun. Regs. app 12-A-G r. 12-A-G802
Lowest floor. The lowest floor (including basement or underground parking garage) of any new construction of, or substantial improvement to, a mixed- used building located on a development site wholly or partially within 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.
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 within a flood hazard area shall be at or above the design flood elevation.
Non-residential portion. The lowest floor of the non-residential portion of any new construction of, or substantial improvement to, a mixed- use building located on a development site wholly or partially within 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.
Ancillary residential use portion. The lowest floor of the ancillary residential use portion of any new construction of, or substantial improvement to, a mixed-use building located on a development site wholly or partially within a flood hazard area shall be at or above the design flood elevation.
D.C. Mun. Regs. app 12-A-G r. 12-A-G802