Abstract In the aftermath of catastrophic events, lightweight construction systems are often used to build temporary emergency architectures. However, if suitable environmental control systems are not present, as may occur in post-disaster scenarios, these buildings provide poor indoor thermal conditions, especially in hot climates, which may jeopardize the occupants’ physical and mental health in case of longer periods of occupations. In these contexts, passive cooling techniques are the preferred strategies to improve the indoor thermal environment. However, only a few papers evaluated the effectiveness of these measures on emergency buildings, also considering calibrated simulations, different climates, costs, and operational feasibility. In this work, the thermal performance of a novel emergency construction system, still not sufficiently studied in the literature and based on the assembly of 3D-reinforced EPS panels, is examined. First, a numerical model of an experimental unit is calibrated on experimental data. Then, the thermal performance in hot and temperate climates of a reference building, recently adopted in emergency scenarios, is numerically evaluated and improved through passive cooling measures, i.e. shading, thermal buffering, natural ventilation, and cooling materials. Results show high summer thermal discomfort in all climates. The efficacy of the different measures depends on climatic contexts, with natural ventilation, combined with cool roof materials or blinds (for temperate and hot climates, respectively), providing the best trade-off between thermal comfort, costs, and feasibility. However, the summer indoor thermal discomfort cannot be completely reduced. This study helps decision-makers and people to correctly improve the living conditions and sustainability of emergency architectures.