Evaluation of a green roof structure in the Central Europe climate during winter.

The green roof is an example of increasing the water retention in the urban areas and reduction of urban heat islands. The impact of green roofs and its influence on the thermal resistance or its change during the winter is often not taken into account in the contrary to the summer benefits. The surface of a highly insulated flat roof is overcooled during the night by the long wave sky radiation. This radiative cooling increases the thermal losses. This is reduced by the existence of additional green roof layers. Also, these green roof composition layers have their thermal resistance, which is usually not included within the calculation of thermal resistance using the EN ISO 6946. The thermal conductance of these layers is influenced by the water content, which is mostly higher than design values and hard to obtain. Also, the presence of snow in various forms on the roof can increase the resistance. In this paper, temperature courses during the winter season of the green roof, flat roof with gravel and the regular flat roof, based on the experimental measurement are analyzed. In this case, the use of green roof kept the temperature of the membrane almost constant near 0 °C during winter without correlation to the outdoor air temperature. [ABSTRACT FROM AUTHOR]