Numerical Investigation of the Effect of Fire-Resistant Overhanging Eaves on Vertical Fire Spread Along Building Facades

To investigate the influence of fire-resistant overhanging eave geometry (width and installation height) on vertical fire spread along building facades, a nine-story building model was developed using PyroSim (version 2023.2.0816), and simulations were conducted using Fire Dynamics Simulator. The results show that window-ejected flames form a buoyant spill plume that adheres to the facade due to the Coandă effect and air entrainment, resulting in a rapid temperature rise above window openings. Increasing both eave width (W) and installation height exhibited measurable but limited effectiveness in suppressing vertical fire spread. Specifically, increasing eave width significantly enhances flame deflection and reduces facade-attached plume intensity, whereas increasing installation height primarily alters plume impingement location with comparatively weaker suppression effects. A critical transition is observed at an eave width of approximately 0.4 m, beyond which lateral spill flames are induced due to flow obstruction. The relationship between eave geometry and flame behavior is further interpreted through dimensionless analysis based on characteristic fire diameter (D*), revealing that effective suppression occurs when W/D* exceeds a threshold value. These findings provide simulation-based insights into facade fire protection design, although further investigation is required to incorporate wind effects, complex facade geometries, and combustible materials.