509.1 If a habitation is located on the ground floor of a residential building, the yard of the building which lies immediately outside the habitation shall be maintained clear of any obstruction to ventilation for a distance of at least three feet (3 ft.) from the exterior wall of the building, or such further distance as may be required by any other law or regulation.

509.2 A reasonable amount of trees or shrubbery shall not be considered to be a violation of this section.

SOURCE: The Housing Regulations of the District of Columbia, 5G DCRR § 2308, Commissioners' Order 55-1503, (August 11, 1955).