D.C. Mun. Regs. tit. 11, r. 11-K303
The buildings to be erected within the USN zone will be supported by two (2) platforms erected above the existing railroad tracks and separated by H Street, N.E. (the platform or platforms).
The platforms will be generally horizontal structures that provide support for the new surface area, above the railroad tracks, on which development will be built.
In addition to providing structural support, the platforms may house mechanical equipment, parking and loading areas, and non-residential, residential, retail, and arts uses permitted by Subtitle K § 313, as well as utilities and rail-related uses.
Structures below the grade of the railroad tracks and generally vertical, above-grade columns and structures will support the Platforms (collectively foundation systems). The term "platform" or "platforms", when used in this chapter, does not include foundation systems or any station and rail-related functions or facilities that are constructed below the platforms on the subjacent lots.
Although portions of a platform may extend below the volume of an air rights lot, any provision of this chapter pertaining to the platform shall apply to the entire platform.
D.C. Mun. Regs. tit. 11, r. 11-K303