The fire-resistance level (FRL) required for building elements varies, depending on the expected fire load. This load is measured in the BCA by the building classification. With these differing FRLs, it is important that a fire in one classification does not cause the failure of building elements in any other classification.

There are two options to stop a fire spreading from one classification to another classification on the same storey:

• use the highest of the two fire-resistance levels (FRLs) required for each building element in that storey (see C3D9(1)(a)); or
• place a fire wall between the two different classifications (see C3D9(1)(b) and (4)). In a building of mixed classification C3D9(1)(b) clarifies that for Type A and Type B construction the FRL is the higher of that specified in Table S5C11d or S5C21d but for Type C construction it is the FRL specified in Table S5C21d in Specification 5. This is because the FRL for firewalls in Type C construction is the same for all classes.

Figure C3D9a illustrates some examples of fire walls separating different classifications within the same storey of a building. In the first diagram, the public corridor must be fire-separated from the Class 6 part (as shown) or the Class 5 part to achieve total fire-separation between the different classifications. If a doorway is located in the fire wall, it must comply with C4D6.

The diagrams in Figure C3D9b illustrate examples of fire walls separating different classifications within the same storey of a multi-storey building and floors separating different classifications.

Figure C3D9a: Examples of fire wall separating different classifications in a building of Type A construction

Figure C3D9b: Examples of fire walls and floors separating different classifications in a building of Type A construction