A horizontal assembly refers to roofs and floors. Floor and roof assemblies that are required to have a fire-resistance rating must comply with this section. All floor and roof assemblies must be made of materials allowed by the type of building construction and the fire-resistance rating of floor and roof assemblies cannot be less than that required by the building type of construction. But what if you have floor assemblies that separate mixed occupancies?In cases such as this, the assembly must have a fire-resistance rating of no less than the minimum required by code, based on the occupancies that are being separated.
If a floor assembly separates a single occupancy into different fire areas, the assembly must have a fire-resistance rating of no less than what was discussed earlier in this chapter. All floor assemblies that separate living spaces in the same building or sleeping units in occupancies in Group R-1, hotel occupancies, R-2, and I-1 must be a minimum of one-hour fire-resistance- rated construction. The only exception to this is dwelling and sleeping units that are used as separation in buildings of Type IIB, IIIB, and VB construction which must have a fire-resistance rating of no less than ½ hour in buildings that are equipped throughout with an automatic sprinkler system.