D.C. Mun. Regs. tit. 11, r. 11-1728
In the event that the Council of the District of Columbia accepts a dedication of land for public alley purposes within DD/MVT that would have been required to be a rear yard pursuant to § 774.7, and the land dedicated is adjacent to a public alley and extends the entire length of the lot, the rear yard requirements for the portion of the structure above the horizontal plane described in § 774.7(a) shall be reduced by five (5) feet for every ten (10) foot depth of land dedicated.
For the purposes of § 1728.1, the depth of the land dedicated shall be measured perpendicular to the alignment of the adjacent public alley.
In the event that the Council of the District of Columbia accepts a dedication of land for public alley purposes within DD/MVT that would have been required to be a side yard pursuant to §§ 775.4 and 775.5, and the land dedicated is at least eight (8) feet deep, is adjacent to a public alley, and extends the entire length of the lot, the side yard requirement shall be eliminated for that portion of the structure below a horizontal plane twenty (20) feet above the mean finished grade measured at the middle of the side of the structure.
D.C. Mun. Regs. tit. 11, r. 11-1728