Domestically constructed factory buildings have narrow spacing between structures, which makes them vulnerable to fires spreading to adjacent buildings. Additionally, these buildings often use temporary construction materials that are easy to install, leading to significant loss of life and property damage during fire spreading. When responding to a fire in a factory building, firefighters focus on extinguishing the fire at its source while implementing defensive water-supply measures to prevent its spread to adjacent buildings. In this study, we confirmed the effectiveness of a water-barrier system installed on the exterior walls of factory buildings as a replacement for firefighters’ defensive water-supply systems in the event of a fire. Under conditions simulating a factory fire, the radiant heat and core temperatures of sandwich panels on the exterior walls of factory buildings were measured while varying the nozzle types and separation distances of the water curtain systems. The results of the experiments showed that despite differences depending on the type of nozzle, the radiant heat decreased from 24.83 kW/m₂ to 33.09 kW/m₂, and the core temperature of the panels decreased from approximately 2.2 °C to 13 °C. Among these, nozzle B, which used approximately one-fourth of the water compared with the existing drencher nozzle, was found to be suitable for on-site applications. Based on these results, further studies will be conducted to develop the most suitable nozzle for water-film systems.