The provisions of this Section shall apply without requiring a building to comply with flood-resistant construction standards as established in paragraph (a) of Section 64-12 (Applicability).

In R5 through R10 Districts, and in Commercial and Manufacturing Districts, for all existing buildings, the regulations for permitted obstructions to height and setback regulations shall be modified to increase the permitted volume for elevator or stair bulkheads (including shafts, and vestibules not larger than 60 square feet in area providing access to a roof), roof water tanks and accessory mechanical equipment (including enclosures), other than solar or wind energy systems, as follows:

(a)        where the maximum building height is less than 120 feet, the maximum permitted height of such volume may be increased from 25 feet to 33 feet, provided that the lot coverage of all such obstructions does not exceed 20 percent of the lot coverage of the building; and

(b)        where the maximum building height is 120 feet or greater, the maximum permitted height of such volume may be increased from 40 feet to 55 feet, provided that the lot coverage of all such obstructions does not exceed 20 percent of the lot coverage of the building.