Double skin façades: externally and naturally ventilated small and big cavities: a case study in Milan

Double-skin façades aim to improve the thermal, acoustic and daylight performances of the building envelope, contributing substantially to the indoor comfort and reducing solar heat gains in summer. To evaluate the performances of a double-skin façade, various analytical and CFD modelling methods (Computational Fluid Dynamics) are used to assist designers and key-role makers in defining architectural and technical characteristics. Double skin façade systems are basically divided in natural and mechanically ventilated ones. Technical solutions for a natural ventilated double skin system range among single vertical channel, dual channels or single ventilated façade unit. These different configurations may significantly modify the thermal, acoustic and daylight response of a building. Coupling a double-skin façade to a natural ventilation system is also challenging for the correct design of width and height of the cavity between the two skins. Furthermore, outer skins have also a specific architectural function, considering irregular or non-planar glass panes or cladding panels, that characterize today rounded, twisted façade free forms. The paper presents the case study of a double skin façade of an office building in Milan, highlighting technical advantages and disadvantages of natural ventilation in relation with depth and height of the interspace cavity.