Façades formed by double walls may suffer from condensation of water on the cold side of the insulation. This problem is difficult to solve when the aim is to preserve the water vapour diffusivity of the entire enclosure. The outer wall will hardly dissipate water vapour before it condenses. HArquitectes solved the problem in this house in Sant Cugat by means of regular microventilations, which escape from the traditional image of a cavity wall. Rainwater tightness is entrusted to the characteristics of the outer ceramic layer.