3.6.4.2.

(1) A horizontal service space that penetrates a required vertical fire separation shall be separated from the remainder of the building it serves in conformance with Sentence (2).

(2) If a horizontal service space or other concealed space is located above a required vertical fire separation other than a vertical shaft, this space need not be divided at the fire separation as required by Article 3.1.8.3. provided the construction between this space and the space below is a fire separation with a fire-resistance rating equivalent to that required for the vertical fire separation, except that the fire-resistance rating is permitted to be not less than 30 min if the vertical fire separation is not required to have a fire-resistance rating more than 45 min.