In addition to the floor area exemption for accessory off-street loading berths set forth in Section 12-10 (DEFINITIONS), for buildings with a total floor area in excess of 100,000 square feet, up to 300 square feet of floor space may be exempted from the definition of floor area where such buildings allocate a permanent space for dumpster storage, and such storage space has a minimum dimension of 12 feet by 25 feet. Such dumpster storage space shall be adjacent to a building’s loading berth.