Section 27-306. Measurement

In  applying  the  provisions  of  this  code
  governing height limits, the following appurtenant structures shall  not
  be  included  in the height of the building unless the aggregate area of
  all such structures exceeds thirty-three and one-third  percent  of  the
  area of the roof of the building upon which they are erected:
    (a) Roof tanks and their supports.
    (b)  Ventilating,  air  conditioning,  and  similar  building  service
  equipment.
    (c) Roof structures, bulkheads, and penthouses.
    (d) Chimneys.
    (e) Parapet walls four feet or less in height.