Abstract Recent high-profile fires involving combustible façades have exposed significant gaps in both the understanding and regulation of external wall systems. Modern façade designs frequently employ polymers as insulation and/or laminated composite materials that, while improving energy efficiency, can inadvertently create pathways for vertical fire spread. Thus, there is a need to establish fundamental principles for evaluating the fire spread performance of these systems. Drawing on notable incidents, it is shown how uncontrolled flame spread can defeat compartmentation strategies, compromise occupant egress, and overwhelm firefighting efforts. Extending on previous studies, a performance-based approach to fire spread is proposed, examining four levels of relevance: material properties, product characteristics, assembly configuration, and overall building context. Key factors include combustibility, ventilation effects, and real-world variables (e.g., building characteristics). Case studies of testing methods illustrate both utility and limitations in capturing metrics relevant to façade design. Ultimately, it is advocated that there is an urgent need for rigorous, tailored assessment protocols supported by professional competence, thereby ensuring that complex external wall systems can be designed and managed to balance fire safety with sustainability and safety objectives.
Lucherini et al. (Mon,) studied this question.