Green roof yearly performance: A case study in a highly insulated building under temperate climate

The research deals with the experimental assessment of the yearly thermal performance of a green roof compared to other passive cooling technologies under temperate climate. All roofs are installed on highly insulated slabs (U-value <0.25 W/m(2) K), in order to understand whether in summer the passive cooling effects are inhibited by the low thermal transmittance recently introduced in many southern Europe countries to meet the demands of the energy saving regulations for the winter heating season. Even though many studies have focused on the performance of green roofs, there is little knowledge regarding their potential in highly insulated roofs. Most of the studies derived from analytical simulations, but the thermal behaviour of a green roof is a complex phenomenon and involves combined heat and mass transfer exchanges difficult to assess with analytical models, while more experimental data are necessary. Optical properties of the roofs covering materials were experimentally measured, and the thermal transmittance of the roofs was experimentally evaluated. Field measurements show how in winter the green roof is able to guarantee further insulation even in saturation conditions. In summer, the green roof mitigates incoming heat fluxes and ceiling temperatures. Its performance is however partially hindered by high insulation. (C) 2012 Elsevier B.V. All rights reserved.