Section 27-239. Classification of buildings

Every building hereafter erected
  or  altered  under  the  provisions of section 27-115 of article four of
  subchapter one of this chapter shall, for the purposes of this code,  be
  classified  in one of the occupancy groups listed in table 3-1 according
  to the main use or dominant occupancy of the building. However,  at  the
  option  of  the  applicant, subject to the approval of the commissioner,
  buildings may be classified in any other occupancy group, provided  such
  occupancy  group  has  a higher fire index, as listed in table 3-1, than
  the fire index of the occupancy group classification of the main use  or
  dominant occupant.