D.C. Mun. Regs. tit. 11, r. 11-B306
In addition to the height limitations of the Zoning Regulations, all buildings are also subject to and shall conform to the limitations of the Height Act.
Where the maximum height permitted within a zone differs from the maximum height permitted by the Height Act, the more restrictive maximum height shall apply.
Zone height limits shall be stated in terms of feet.
The height limits in each zone apply to structures located in the public space included within the zone's boundary.
Architectural embellishments including, but not limited to, spires, towers, domes, minarets, and pinnacles may be erected to a greater height than any limit prescribed by these regulations or the Height Act, provided the architectural embellishment does not result in the appearance of a raised building height for more than thirty percent (30%) of each the wall on which the architectural embellishment is located.
A chimney, smokestack, or flagpole may be erected to a height in excess of that authorized in the district in which it is located when required by other municipal law or regulation.
Green roofs and their membranes shall not be included in the calculation of height.
The height of a penthouse or rooftop structure shall be as measured from the building roof upon which it sits to the top of the roof or parapet of the penthouse or rooftop structure, whichever is higher. Where the building roof is not a flat roof, the height of a penthouse or rooftop structure shall be measured from the midpoint of the base of the wall of the penthouse or rooftop structure at the lowest elevation to the highest point of the roof or parapet of the penthouse or rooftop structure.
Roof hatches and skylights shall be evaluated in a closed state for measuring height and setback requirements.
D.C. Mun. Regs. tit. 11, r. 11-B306