With the exception of a building meeting the requirements of Subtitle I § 525.2, the maximum permitted building height, not including the penthouse or rooftop structure, in the D-4 zone shall be ninety feet (90 ft.), unless the building does not have frontage on a street with a right-of-way width of at least ninety feet (90 ft.), in which case the maximum permitted building height, not including the penthouse or rooftop structure, shall be the width of the street right-of-way, plus twenty feet (20 ft.).
If a building in the D-4 zone fronts on a designated tertiary street segment noted in Subtitle I, Chapter 6 and illustrated in Subtitle I § 603.1, or if the Zoning Commission, pursuant Subtitle I, Chapter 7, permits the building's height to exceed ninety feet (90 ft.), the building shall be subject to the following regulations:
The maximum permitted building height, not including the penthouse or rooftop structure, in the D-4 zone shall be limited to ninety feet (90 ft.) on the portion of the site occupied by a historic landmark or a contributing building within a historic district.
No building that abuts or is across an alley from an R zone lot, or that abuts or is across an alley from an MU zone lot west of the centerline of 20th Street, N.W., shall project above a plane at a forty-five degree (45°) angle from a line that is directly above the zone boundary line between the D zone lot and the R zone lot, at the matter-of-right height permitted for the R zone lot.
The maximum permitted height of a penthouse or rooftop structure shall be twenty feet (20 ft.). The maximum permitted number of stories for penthouse habitable space shall be one (1) plus a mezzanine, except a second story shall be permitted for penthouse mechanical space.
D.C. Mun. Regs. tit. 11, r. 11-I525