Moisture in a closed cavity double skin façade J. Laverge 1 , S. Schouwenaars 2 , M. Steeman 1 , A. Janssens 1 1 Ghent University, Belgium 2 Scheldebouw, The Netherlands Corresponding email: jelle.laverge@ugent.be SUMMARY Double skin façades are a popular feature in office buildings worldwide, because of their aesthetic, thermal and acoustical properties. This paper discusses a dynamic model that allows the designer of such a façade to assess the risk for condensation in the enclosed cavity between the panes of the façade. Prediction of this risk is crucial because of the associated need for cleaning and accessibility of the cavity. First, the assumptions made for the thermal, airflow and hygric behaviour within the cavity are discussed. Next, the results rendered by the model are compared to those obtained in a full scale test setup. The good agreement demonstrated when hygroscopic behaviour is included yields the conclusion that this model is a powerful tool to describe the hygro-thermal behaviour of the cavity in a double skin façade and stresses the importance of including non-isothermal moisture buffering behaviour in the such a model. INTRODUCTION For highrise office buildings, double skin façades offer a attractive alternative in building envelope conception. In office building architecture, glass envelopes have gained popularity since the rise of modernism, even in cold climates. Traditional glass facades however, have a number of implicit disadvantages. The most relevant in this context include poor thermal insulation properties for winter conditions and high overheating risks, even in extremely cold climates, in sunny conditions. In noisy environments, poor acoustic insulation can also be an important drawback. Double skin facades combine the aesthetic value of a fully glazed envelope with good thermal and acoustic performance. Furthermore, they protect shading devices, mounted in the cavity between exterior and interior glazing, from wind gusts. This allows to operate the shading even in windy conditions and thus protect the building better against overheating. Lots of possible configurations of doubles skin façades and their properties have been discussed in literature [1,2,3] along with models to simulate their behaviour. A distinction can be made according to the ventilation scheme of the cavity or according to the placing of the insulating glass unit (IGU). Each of the configurations has its own specific (dis)advantages. To prevent excessive heat gains towards the interior of the building, for example, the IGU is often placed at the interior side of the facade element. A recurrent problem in these double skin facade concepts with single outdoor and double indoor glazing is condensation on the cavity side of the single glass pane. This phenomenon is caused by under cooling of the outer single glass pane due to long wave radiation or the leakage of humid air from the indoor environment into the cavity. Permasteelisa Group developed an innovative concept, with a fully sealed cavity and a very modest dry air flow (“closed cavity façade”), aimed at preventing condensation within the