D.C. Mun. Regs. tit. 11, r. 11-G208
Except as provided elsewhere in this title, in any of the MU-1 through MU-15 zones, the minimum side yard shall be as set forth in this section.
In any of the MU-1 through MU-10 and MU-15 zones, no side yard is required for a building or structure other than a detached or semi-detached single household dwelling; however, if a side yard is provided, it shall be at least two inches (2 in.) wide for each one foot (1 ft.) of height of building, but no less than five feet (5 ft.).
In any of the MU-1 through MU-10 and MU-15 zones, a minimum side yard of eight feet (8 ft.) shall be provided for a detached or semi-detached single household dwelling.
In any of the MU-11 zones, for any building or structure located in whole or in part on land, the minimum width of each side yard shall be twelve feet (12 ft.).
In any of the MU-12, MU-13, and MU-14 zones, no side yard shall be required; however, if a side yard is provided, it shall be at least eight feet (8 ft.) in width.
Any portion of a building set back from the side lot line shall be considered a side yard and not a court.
D.C. Mun. Regs. tit. 11, r. 11-G208