Fungal and phototroph growth on fiber cement roofs and its influence on solar reflectance in a tropical climate

The materials used on roofs are mainly responsible for the reflection of the incident sunlight and absorption of heat at these surfaces. We investigated the occurrence of fungi and phototrophs, as well as determining the change in color (as L*), solar reflectance and thermal emittance of fiber cement exposed for 5 years in Pirassununga, a rural town in tropical Brazil. Considerable discoloration on the upper, exposed surface was shown to be related to high phototroph (especially cyanobacterial) colonization and reduction in reflectance. The large numbers of fungi detected on the lower, protected surface produced little color change and no reduction in reflectance. Thermal emittance was slightly, though significantly, reduced on the upper surface. The results indicate that, under conditions at this site, after 5 years exposure, phototrophs are more important than fungi in the reduction of reflectance at the exposed surface of fiber cement. This has important implications for cool roofing technology.