A fire resistance rating (FRR) for a wall system applies in both directions unless specified as ‘one-way’. 

In a ‘two-way’ FRR wall, both the exposed and unexposed linings contribute to performance as shown in Figure 1(a). The exposed lining primarily protects the framing and acts as a radiation shield for the unexposed lining, while the unexposed lining delays integrity and insulation failures as cavity temperatures increase. 

In a ‘one-way’ FRR wall, the protective linings are installed only on the fire-exposed side, providing all three ratings in FRR. As shown in Figure 1(b), the cavity temperature rise on the unexposed face of the linings can be limited to approximately 300 °C, but at 90mm away the insulation criterion is met. 

Figure 1(a)                                                                                                            Figure 1(b) 

‘One-way’ systems are commonly used for external walls supporting a fire-rated floor/ceiling above. However, only a structural adequacy rating is often required unless the building is located sufficiently close to a property boundary or external vertical fire spread is of concern (See Figure 2). If an exterior wall is lined on the interior side only with GIB® plasterboard in accordance with a ‘two-way’ FRR wall specification, its structural adequacy rating is maintained when fire exposure is from the interior side. 

 
Figure 2 

For example, a loadbearing timber frame external wall requiring a 60/-/- FRR for fire exposure from the interior side can be lined with a single layer of 13mm GIB Fyreline® fixed in accordance with GBTL 60 on the interior side only. However, the mass of the lower unit wall lining also assists in achieving the required noise attenuation between levels and in minimising potential impact and airborne noise flanking via the structure. In this case, denser or thicker wall lining options are recommended. 

For further information, please contact the GIB® Helpline on 0800 100 442.