Effects of conventional, extensive and semi-intensive green roofs on building conductive heat fluxes and surface temperatures in winter in Paris

International audienceThis study investigated the impacts of extensive and semi-intensive green roofs on both building insulation and surface urban heat island effect under winter conditions. To this aim we compared measurements of surface andbuilding envelope temperatures as well as conductive heat fluxes reaching the external building envelope with those measured on a conventional bituminous roof under identical climatic conditions. The main effect of greenroofs was to decrease daily fluctuations of external building envelope temperatures and as a consequence to reduce fluctuations of conductive heat fluxes reaching the building envelope. This effect is all the more importantthat the substrate is deep, in link with its heat capacity and thermal inertia. Yet, no significant effect of the green roofs on surface urban heat island has been observed on average despite a surface cooling during daytime. It isconcluded that the green roofs can be suitable urban greening solutions since they do not have negative effect on surface urban heat island during winter, provide cooling during summer, and contribute to building insulationinducing therefore building energy savings