Upward flame spread behaviour of cladding materials on a medium-scale ventilated façade experimental setup with a single combustible wall

A parametric experimental study was performed to characterise the fire spread dynamics in a simplified ventilated façade using a medium-scale testing rig comprised of a non-combustible and a combustible cladding wall (1800 × 600 mm). Three different cavity widths and four different cladding materials were tested. Measurements of the flame height, the incident heat flux on the non-combustible cavity wall and oxygen consumption calorimetry were performed. A strong relationship between flame height and heat release rate was found for the growth phase of the fire. It has been shown that the time for encapsulation failure and subsequent cladding material core ignition decreased as the cavity width was reduced since the heat transfer to the walls was enhanced. The increase in the heat transfer to the opposite wall with all the materials could lead to external heat fluxes above the critical heat flux for ignition of a number of combustible cladding materials. This highlights the importance of considering the interaction of the products used in the façade and its geometry for the design of façade assemblies when accounting for the fire performance of the system. The results also show the need to understand the impact of the interaction between the design variables and the system performance, since the material performance observed at bench-scale may fail to capture the performance in heat transfer and flame spread scenarios observed at a system scale.