D.C. Mun. Regs. tit. 11, r. 11-636
A rear yard shall be provided for each residential building or structure.
When the residential use begins at or below grade, the minimum depth of rear yard shall be three inches per foot (3 in./ft.) of vertical distance from the mean finished grade at the middle of the rear of the structure to the highest point of the main roof, but not less than twelve feet (12 ft.).
When the residential use begins above grade, the minimum depth of rear yard shall be three inches per foot (3 in./ft.) of vertical distance from the horizontal plane upon which the residential use begins to the highest point of the main roof, but not less than twelve feet (12 ft.).
The rear yard referenced in § 636.3 shall be provided at and above the residential plane.
In the case of a through lot or a corner lot abutting three (3) or more streets, no rear yard shall be required for any building or structure.
For the purposes of this section, "residential building or structure" shall include dwellings, flats, multiple dwellings, rooming and boarding houses, hospitals, hotels, inns, and community-based residential facilities.
D.C. Mun. Regs. tit. 11, r. 11-636