D.C. Mun. Regs. tit. 12, r. 12-B2603
Strike Sections P2603.5 and P2603.5.1 in the International Residential Code in their entirety and insert new Sections P2603.5 and P2603.5.1 in the Residential Code in their place to read as follows:
Freezing. A water, soil or waste pipe shall not be installed outside of a building, in exterior walls, in attics or crawl spaces, or in any other place subjected to freezing temperature unless adequate provision is made to protect it from freezing by insulation or heat or both. Water service pipe shall be installed not less than 36 inches (915 mm) deep.
Sewer depth.Building sewers that connect to private sewage disposal systems shall be a not less than 30 inches (762 mm) below finished grade at the point of septic tank connection. Building sewers shall be not less than 30 inches (762 mm) below grade.
D.C. Mun. Regs. tit. 12, r. 12-B2603