Double-skin envelopes are an attractive design option for high-end buildings. They allow architects to combine completely transparent external facades with an internal skin, which can also be transparent, or partially opaque. Between both skins there is an air channel that is used to collect or evacuate the solar radiation absorbed by the facade. This design may be a solution for reducing thermal overheating, which is common in completely transparent facades in Mediterranean climates. A numerical code was developed to analyze and predict the thermal behaviour of these facades. This code was applied to the analysis of the 'standard' geometry of a double-skin facade. A parametric study was carried out for typical Mediterranean climates to determine the influence of different variables, such as the position of blinds, the introduction of solid-liquid phase-change materials (PCM) and the use of low-c glazing, etc. In order to characterize the thermal performance of the facades, two coefficients were defined that relate the indoor and enthalpic gains to the solar radiation. If they are designed carefully, ventilated facades will exhibit a significantly better passive behaviour than conventional glazed facades and also allow energy to be collected in the form of hot air to be used to reduce energy consumption in winter. (C) 2003 Elsevier Ltd. All rights reserved.