Extension (4000 m2) of the Central University Library of Cluj, historic building dating from the beginning of the XXth century. The program included the extension of the existing reserve of books, new spaces of reading, an auditorium and a cafeteria. We imagined this extension as a " tower of books " connected with the existing library by footbridges through a big glazed atrium. The transparece is the central theme of this project; all the building is a big glass vessel where the light filter through shading panels of brick strips which remind the facade of the former library. These electric commanded panels are placed in a double glass skin, which contributes to the thermal comfort of the building.