D.C. Mun. Regs. tit. 10-B, § 2713
2713.1 When alleys are provided, they shall be a not less than sixteen feet (16 ft.) in special purpose or residential zoning classifications and not less than twenty feet (20 ft.) in commercial or industrial zoning classifications.
SOURCE: Commissioners' Order 67-651(a), §3, effective May 16, 1967, 13 DCR 270 (June 19, 1967).