D.C. Code § 9-203.05

Any area between the property line and the building restriction line shall be considered as private property set aside and treated as public space under the care and maintenance of the property owner. The use of this area shall be controlled by the District of Columbia police regulations with respect to the use of public space and the projection of buildings beyond the building line. The District shall have a right-of-way through this area for sewers and water mains free of charge. The Mayor may build sidewalks on this area if in the judgment of the Mayor the space between the street lines is not sufficient to permit the construction of sidewalks within the street lines.