On a Cool Coating for Roof Clay Tiles: Development of the Prototype and Thermal-energy Assessment

Clay tiles are the most common roof covering in Italian buildings, in particular in traditional residential buildings. Given the important role of the roof characteristics for building energy efficiency and indoor thermal comfort conditions, innovative solutions for improving the thermal-energy performance of such diffused roof element has become a key research issue. In this view, cool roof applications represent an effective solution to this aim. The present work deals with the analysis of innovative coatings for traditional clay tiles, aimed at increasing their “cooling” potential. Several pigments with the sodium silicate as binder are tested in terms of reflectance and emittance, which mainly determine the cool roof performance. Additionally, the year-round performance of the proposed tile is evaluated when applied to a single family residential building located in central Italy. The developed cool roof solution is characterized by the same visual appearance of traditional “natural brick” color tiles, while the solar reflectance is higher than natural terracotta tile by 13%. Therefore its thermal performance is optimized in order to reduce the roof overheating and the consequent energy requirement for cooling. Results of dynamic simulation of the case study building show how the proposed tile is able to decrease the number of hours when the indoor operative temperature of the attic is higher than 26 °C by 18%, while the same effect in lowering the indoor temperature below 20 °C in winter is less than 1%. Therefore, the proposed solution could be considered as an interesting strategy for new buildings or for traditional roof retrofitting, without producing any significant architectural impact, even in traditional or historic buildings, where more invasive solutions are too difficult to be implemented.