The Faculty of Mathematics of the Catholic University of Santiago occupied two neutral and schematic structures of the 1970s and needed a new building for its administration department and for the faculty, without a predetermined location. The project took as point of departure the decision to join those two structures inserting a new piece between them, generating a single building that fulfills three conditions to guarantee good performance. In the first place, it maintains the existing path between the buildings, an established diagonal shortcut that it was better to keep; secondly, to address the misadjustments that could arise after joining two separate elements; and, lastly, to eliminate the front-back duality of the facades, marked by a portico along the north facade of the existing pavilions. For its part, the structure – regular, symmetric, and arranged along the perimeter – is designed to comply with the seismic codes, while the enclosures reflect a greater compositive freedom. The concrete of the building contrasts with other facade materials like glass, wood, and copper. This type of metal was chosen because its appearance improves with the passage of time, with a dark and noble oxidation process.