In the R-3/GT zone, two (2) side yards, each a minimum of five feet (5 ft.) in width, shall be provided for all detached buildings.
In the case of a building with a non-conforming side yard, an extension or addition may be made to the building; provided, that the width of the existing side yard shall not be decreased; and provided further, that the width of the side yard adjacent to the extension or addition shall be a minimum of five feet (5 ft.) in the R-1B/GT zone and a minimum of three feet (3 ft.) in the R-3/GT zone.
D.C. Mun. Regs. tit. 11, r. 11-D1104