Experimental and numerical hygrothermal analysis of a refurbished double-skin flat roof

In order to mitigate the consequences of climate change, and in the view of increasingly stringent energy performance requirements, energy-efficient refurbishment of building constructions is extremely important. Double-skin roof constructions have been analysed in the case of pitched roofs or flat roofs without refurbishment in the past; thus, we examined a refurbished structure of a panel building. The ventilated air layer of the flat roof was partially loose-filled with glass wool thermal insulation, and the layer boundaries were equipped with temperature and relative humidity sensors at four measurement places. The monitoring measurement was conducted for more than a year. Laboratory tests analysed the density-dependent thermal conductivity and moisture storage function of the applied thermal insulation, and the refurbishment was modelled with dynamic hygrothermal simulation. As a result, we found that the ventilation continued to work, and no condensation occurred in the measured layers, and the external concrete skin can reduce solar radiation by up to 85%. Respectively, we determined the thermal transmittance of the structure under dynamic hygrothermal conditions, which was 35% higher in the heating season than the dry steady-state design value.

Automated summary

This study investigated a refurbished roof structure, finding that the ventilated air layer filled with glass wool insulation performed well, with no condensation observed, and the external concrete skin effectively reduced solar radiation. Under dynamic hygrothermal conditions, the thermal transmittance of the structure was found to be 35% higher than the dry steady-state design value.