Thermal performance of high-albedo envelope coatings in aging multi-family housing: a case study in Gimcheon City, South Korea

While cool roof technology is well-documented for single-family houses, empirical field evidence from multi-family housing remains limited despite this building type dominating Asian urban residential areas and housing heat-vulnerable populations. This study quantifies thermal performance and comfort improvements from high-albedo envelope coatings applied to aging public multi-family housing through comprehensive field measurements. A controlled field experiment compared two identical fifth-floor units at a 32-year-old public housing complex in Gimcheon, South Korea, during summer 2025. One unit received high-reflectance envelope coating while the control remained untreated. Continuous monitoring captured spatial temperature distributions under natural ventilation in a complex housing predominantly elderly and low-income residents. The high-albedo envelope coating application reduced ceiling temperatures by 3.05°C on average, wall temperatures by 2.92–3.07°C, and indoor air temperatures by 0.86°C. The Discomfort Index improved 0.44 points overall and 0.72 points during evening hours, reducing time spent in very uncomfortable conditions by 15%. Surface temperature variability decreased 50–70%. These field measurements demonstrate that high-albedo envelope coatings provide practical passive cooling for vulnerable populations in aging apartments, supporting implementation as a cost-effective climate adaptation strategy addressing thermal comfort and environmental justice.