N.Y.C. Admin. Code § 27-239: § 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.