Field investigation on air permeability of ventilated pitched roofs

A common aim of energy policies is to carry out plans to reduce energy demand for air conditioning and to obtain high standards of indoor comfort. In view of this, the implementation of passive strategies, such as the exploitation of natural ventilation, has been recently encouraged to improve the performance of the building envelope. This study investigates the thermal and fluid-dynamic behaviour of two ventilated roofs equipped with a new tile shape in comparison with a standard Portoguese tile. The novel tile shape was designed to improve the air permeability of coverings, thus producing a further Above Sheathing Ventilation enhancement as proposed in the ongoing LIFE HEROTILE European project, in which original roof tiles with innovative sidelock and headlock patterns have been designed, produced and are now under testing with real operating conditions. The heat and mass transfer in the different roof layers has been experimentally analysed by means of a dedicated real scale mock-up. The results of the preliminary testing period are presented in this paper, they are referred to a first period with open eaves and to a second one in which eaves were closed to observe the only effect of tile air permeability. The data analysis shows that the ASV is strictly linked to the external wind conditions and grants better performances in HEROTILE roof. Moreover, the new tile design produces a significant increase of the ASV, so that better thermal performances are achievable in reducing solar heat gain during hot periods. As a consequence, the mock-up with HEROTILE ventilated roofs need less energy for air conditioning and allows high energy saving when compared with the Standard one.