Aging, soiling, and cleaning effects on cool roof performance: Experimental insights on aerogel-based and conventional reflective coatings in Mediterranean climate

Cool roofs are increasingly recognized as an effective strategy for reducing building cooling loads and mitigating urban heat islands. However, their long-term performance is strongly influenced by environmental aging and dust accumulation, which can degrade solar reflectance and thermal efficiency. This study presents a comprehensive three-year experimental campaign conducted in Benevento, Southern Italy, comparing a traditional bituminous membrane, a commercial ceramic reflective paint, and an innovative aerogel-based coating under real climatic conditions. Continuous monitoring of surface temperature, solar reflectance, and heat fluxes was performed, complemented by a post-washing analysis to evaluate maintenance effects. Results reveal that aging and soiling reduced solar reflectance by 42 % for ceramic coatings and 28 % for aerogel coatings after two years, leading to peak summer surface temperatures of 63.5 °C and 58.7 °C, respectively. Aerogel consistently outperformed ceramic in retaining higher reflectance, limiting thermal stress, and reducing heat flux into the building envelope. Post-washing significantly restored performance, with reflectance improvements of up to 21 % for ceramic and 13 % for aerogel. These findings highlight the importance of maintenance strategies in sustaining cool roof efficiency and demonstrate the superior durability of aerogel-based coatings in Mediterranean climates. The study provides in-field evidence that can inform design choices, energy simulations, and urban-scale policies promoting reflective materials for climate resilience. • Aerogel and ceramic cool paints are compared by means of experiments in Mediterranean climate. • 2 years aging and dirtying reduce in-field solar reflectance of 42 % for Ceramic and 28 % for Aerogel. • After 2 years, peak surface temperature passes from 52 °C to 63.5 °C for Ceramic and from 49.1 °C to 58.7 °C for Aerogel. • The washing reduces the difference with initial reflectance to 21 % for Ceramic and 13 % for Aerogel. • Peak surface temperature difference between Bitumen and Aerogel increases from 11°C to 14°C thanks to the cleaning.