The Ventilated Façade (VF) supposes an improvement compared with a conventional façade –single layerin terms of thermal comfort, through the ventilation of the wall cavity, limited by an inner and an outer layer, usually of open joints. However, in buildings with VF the constructions characteristics in the wall cavity are often different from that considered in academic studies, performed by simulations or prototype measurements. The present work analyses the air movement in the VF wall cavity of existing buildings built in Barcelona city. In situ measurements were made in summer in 10 buildings, using a Testo405i thermal anemometer with management via a smartphone. The methodology consisted in the monitoring of the cases in periods of 30 minutes in the morning and 30 minutes in the afternoon. The data were recorded every two seconds, according to the sequence: 5 minutes outside, 20 minutes inside the wall cavity and 5 minutes outside. The extensible telescope (400mm long) of the anemometer was introduced by the open joints of the outer sheets, so that the sensor is perpendicular to the vertical air flow in the wall cavity. The results show two determining factors for the adequate performance of the air movement in the VF chamber: on the one hand, the increase in the incidence of solar radiation on the facade, and on the other hand, the increase of the entrance and exit apertures of air in the chamber. Besides, temperatures tend to increase in the wall cavity, that is to say that there are always gains of heat in the air chamber.