Four couples who are friends agreed to be the developers and users of a block containing five dwellings and a sequence of spaces for communal use and interaction. This was the story behind the building that Thomas Lussi and Lola Domènech have raised on a very narrow plot in Barcelona, and which is remarkable in its carefully rendered details, its use of sustainable materials like wood and ceramic, and the way it saves energy passively, through a combination of solar protection strategies and natural ventilation.