Green and cool roofs’ urban heat island mitigation potential in European climates for office buildings under free floating conditions

•Green and cool roofs are studied versus their urban heat mitigation potential.•Insulation level and thermal mass of cool roofs are examined.•Irrigation rate and vegetation type of green roofs are analyzed.•Free floating conditions for various climatic regions are used.

Heat island which is the most documented phenomenon of climatic change is related to the increase of urban temperatures compared to the suburban. Among the various urban heat island mitigation techniques, green and cool roofs are the most promising since they simultaneously contribute to buildings’ energy efficiency. The aim of the present paper is to study the mitigation potential of green and cool roofs by performing a comparative analysis under diverse boundary conditions defining their climatic, optical, thermal and hydrological conditions. The impact of cool roof’s thermal mass, insulation level and solar reflectance as well as the effect of green roofs’ irrigation rate and vegetation are examined. The parametric study is based on detailed simulation techniques coupled with a comparative presentation of the released integrated sensible heat for both technologies versus a conventional roof under various climatic conditions.