D.C. Mun. Regs. tit. 11, § 2906
2906
ROOFTOP PENTHOUSES
2906.1 Rooftop penthouses not intended for human occupation, such as penthouses over mechanical equipment, a stairway, or an elevator shaft shall be erected or enlarged pursuant to § 770.6 through 770.8.
2906.2 Such a penthouse shall not exceed eighteen feet, six inches (18 ft., 6 in.), in height above the roof upon which it is located. Mechanical equipment shall not extend above the permitted eighteen foot, six inch (18 ft., 6 in.), height of the housing.
2906.3 A penthouse not intended for human occupancy may be erected to a height in excess of that authorized in the USN District subject to the provisions of the Height Act.
2906.4 Spires, towers, domes, pinnacles, or minarets serving as architectural embellishments, ventilator shafts, antennas, chimneys, smokestacks, or fire sprinkler tanks may be erected to a height in excess of that which this section otherwise authorizes.
SOURCE: Notice of Final Rulemaking published at 58 DCR 4788, 4797 (June 3, 2011).