Green roof evaluation and comparison during summer in Central Europe climate

Abstract

Greening structures, such as roofs or facades, attract the worldwide attention because of their multi-disciplinary benefits. Green roofs are considered to be one of the best ways to eliminate summer overheating, mitigate the climate change or reduce the urban heat island effect. Since 2020, experimental fragments of different green roofs are evaluated on the roof of one building in the university campus. Temperatures are measured within the roof and also in the additional green layers. Also the water retention is measured. In this paper, results of temperature measurements of three different types of protective layer on the single ply flat roof are presented. One is bare, unprotected PVC membrane, the other one is gravel and the third one is an extensive green roof. During the summer season and sunny days the daily amplitudes are reduced from approximately 56°C for the unprotected PVC membrane and 35 °C for the gravel to the 16 °C for the green roof. The gravel slightly reduced the maximum temperatures, but it has an accumulation capacity, which decelerates cooling of the surface and the heat emitted back to surroundings is higher. Water retention is also another benefit, which increases the reduction, but in this analysis the worst scenario with lack of any rainfall for more days was taken into account.