The first objective of the proposal is the restoration, extension and conditioning of an existing equipment for its use as a public library, work of Marcià Codinachs on the Via Favencia, in an adapted urban stretch over the roof of the "Rondas" (peripheral city road) of Barcelona. The second part of the project consists of the development of the adjacent spaces, in particular the area between the existing buildings, where the main entrance is located, which turns this space into a great outdoor hall open to the city. This equipment is a neighborhood library which consists of a public area at street level where the children's area, computer rooms, daily press and formation and educational lessons are taught. The program is divided between the existing building and the new adjacent extension, connected by a transition space conceived as an exhibition area: spacious with a grand stepped ramp which connects the different levels. On the bottom floor, taking advantage of the slope of the "Rondas", a conference hall with an independent access and a working and administration area are located. The structural plan, affected by the delicate situation of its location (over the roof of the city motorway), is resolved by a steel structure working as a bridge, over three bedplates which rest on the existing built structure, with 15 meter distances between pillars. This structural principle allows open and spacious spaces with natural light which give the building a great atmospheric quality. In the existing building, long skylights looking North give a constant uniform light and also support the photovoltaic panels. The general exterior image pretends to be aggressive and monolithic, with a blunt and clear geometry, in contrast to a warm atmosphere with a high acoustic and visual comfort on the inside. This effect is achieved with the treatment of the used materials, boosting their characteristics and expression: "corten" steel on the outside and clear birch wood on the inside. The adjacent extension is a rectangular volume lined with "corten" steel which is hung and separated from the actual building. This new space opens to the East with a great two storey window and a sloping ceiling which emphasizes the perspective effect and focuses vision towards the city panorama, while it remains completely closed to the noise from the side roads. The main façade, made of a "corten" perforated sheet, allows to play with variable light gradients depending on the day and night hours, transforming into a transparent filter or an absolutely opaque screen. The library has turned into a meeting point and a reference for the neighborhood due to its strong geometry and easy lecture of its exterior and a clear organization of spaces and routes on the inside, where the used materials and the human scale provide a warm and welcoming atmosphere.