Full-scale natural fire tests on gypsum lined structural insulated panel (SIP) and engineered floor joist assemblies

SIPS are formed from the lamination of two oriented strand board (OSB) facing plates and a highly insulating polymer-based foam such as expanded polystyrene (EPS) or polyurethane (PUR). The resulting lightweight panels are typically used as primary load-bearing compression elements for buildings such as domestic dwellings, apartment blocks, schools and hotels. The regulatory fire performance of SIPS, like many systems, is assessed via a standard fire test. However, it is widely accepted that this is merely a comparative method for determining the relative performance of one product when compared to another; hence, it gives little indication of a component's likely behaviour in a real fire. With this in mind BRE Global, with support from the UK Department for Communities and Local Government (CLG), have undertaken a research programme to determine the performance of SIPS subject to realistic fire conditions. The research programme exposed four two storey SIP buildings to natural fire scenarios using timber cribs. Two buildings were constructed with EPS core SIPS. The other two were constructed with PUR core SIPS. Each material set was subdivided by passive fire protection specification (PFP). These were specified on the basis of 30 and 60-min fire resistance. The experiments highlighted a number of weaknesses in the system performance of SIP structures with engineered floors. Firstly, where PFP is under specified or poorly installed, collapses of the engineered floor plate are very likely. Mechanisms for fire spread were also identified where fitting details were not appropriately sealed. In addition, there appeared to be little appreciable difference in the behaviour of buildings formed with EPS or PUR core SIPS. Finally, a number of system redundancies and alternative load paths were identified, which prevented total collapse of any of the test buildings.