In this publication, we examine a new ‘sponge city’ concept known as the ‘hybrid roof’ and compare its cooling potential on hot summer days with that of a green roof. The hybrid roof combines high reflectivity (albedo) provided by light-coloured marble pebbles with evaporative cooling, resulting in significantly lower surface temperatures than those of a green roof. Hydrophilic rock wool was used beneath the marble pebbles for water storage; this material can store significantly more water than conventional green roof substrates. During a heatwave in September 2023, the hybrid roof therefore still had water stored for evaporative cooling, whilst the green roof module had dried out. The hybrid roof is therefore a promising adaptation measure for urban heat.
Faymonville, L., Heusinger, J., Weber, S., 2026. Combining shortwave reflectivity and evaporation in a novel rooftop solution for urban cooling. Urban Clim 67, 102956. https://doi.org/10.1016/J.UCLIM.2026.102956