Evaluation of High Reflective Products in Flat Roofs Rehabilitation – Experimental Study

Flat roofs are particularly unfavourable to the thermal performance of single family houses and apartments of the the upper floor of multifamily buildings. Often these housing typologies are too hot during summer, when incident solar radiation affects the roof more than any other element of the building envelope.Recent developments have given rise to many high reflectance products. However, thermal performance of these products has not yet been thoroughly quantified, when applied to flat roofs under real weather conditions. Performance assessment of innovative solutions must consist in the evaluation under real exposure conditions and analytical modelling.Two full-scale experimental cells under weathering conditions, located in Laboratório Nacional de Engenharia Civil (LNEC) campus, were used in this study. The experimental cells have identical dimensions, constructive characteristics and thermal behaviour.Initially, the two cells (C5 and C6) presented the same APP modified bitumen waterproofing solution, finished on the top layer with natural slate granules (XN). Subsequently, simulating a rehabilitation intervention, it was introduced in C5 an improved reflectance APP modified bitumen membrane surfaced with thermally coloured white slate granules (XB).After a coexistence period of solutions XB (C5) and XN (C6), it was applied over C6 XN a high reflectance white paint (XN/PB).The characterization of the thermal performance under real weather of each tested solution was based on the analysis of the values of the following parameters recorded under free-floating operation and controlled regime: temperature of the flat roof’s upper and lower surfaces, indoor temperature and electric consumption under controlled regime.