D.C. Mun. Regs. tit. 14, r. 14-404
Any room with more than fifty percent (50%) of any exterior wall area from floor to ceiling below ground level (using average level along each exterior wall) shall not be used as a habitable room, except as otherwise provided in this section.
In a building in existence prior to June 9, 1960, where there is an existing open well or areaway which is three feet (3 ft.) or more in width immediately adjacent to any exterior wall, that wall shall be considered above ground level for the length and depth of the open well or areaway.
Whenever any building in existence prior to the effective date of this amendment (June 9, 1960) is altered to conform to the requirements of this section, the newly constructed court or areaway immediately adjacent to any exterior wall shall be four feet (4 ft.) or more in width and of a depth necessary so that one-half (1/2) the height of all portions of any exterior wall of the room, measured from floor to ceiling, shall be above the ground immediately adjacent to the newly constructed court or areaway.
Whenever any existing building is altered to conform to the requirements of this section, a permit shall be obtained from the Director, and all alterations must conform in other respects to the applicable requirements of the Building Code of the District of Columbia (Title 12, DCMR).
Areaways constructed on buildings erected after the effective date of this amendment (June 9, 1960) shall comply fully with the applicable requirements of the Building Code (Title 12, DCMR) and the Zoning Regulations (Title 11, DCMR).
D.C. Mun. Regs. tit. 14, r. 14-404