As a result of the type of buildings we currently construct in New Zealand, a scenario that has become more common is when an external wall is fire rated only for the purposes of supporting a mid-floor above. In this case the wall is required to provide a structural adequacy rating for the required time of fire-resistance and the framing needs to be protected accordingly. A structural adequacy rating is represented by the first number in the fire resistance rating (FRR) sequence, e.g. 60/-/- for an external wall required to provide structural support only. 

Commonly the internal plasterboard linings will be specified as a 1-way system e.g., GBUW 60 which uses 2/13mm GIB Fyreline®. Whist this is still the correct way to specify a 60/60/60 FRR for the external wall, it can affect jamb detailing around joinery. An alternative approach is to specify a 2-way fire rated system with linings on the inside and outside of the frame. This works well if you already plan on incorporating a rigid air barrier such as GIB Weatherline®.  

However, when only a structural adequacy rating is required, we have added a more equitable solution on page 12 of our latest literature ‘GIB® Fire Rated Systems, 2024’, which is supported by BRANZ Appraisal No.289[2024].  

The section states that: 

“… if the external wall is not serving as a boundary fire separation wall, such walls may only be required to achieve a structural adequacy rating against fire exposure from inside the building. The lining on the exterior side helps delay the integrity and insulation failure times but is not essential to achieve the structural adequacy rating. If an exterior wall is lined on the interior side only with GIB® plasterboard in accordance with a two-way FRR wall specification, the structural adequacy rating of that wall is maintained when fire exposure is from the GIB® plasterboard lining side.” 

Consult your fire designer before finalising the appropriate specification. The structural adequacy only condition applies to external walls sufficiently far away from a relevant boundary. If the external wall is in proximity to a boundary, a full 2-way fire-rated specification may be required.