Renovation of a 2400m2 building dating from1775 in Madrid’s historical quarter. The main functional decision was the construction of a second staircase nucleus, which permitted an optimal arrangement of apartments adjusted to the minimum size allowed by planning regulations. The apartments themselves are organized around a service nucleus (kitchen, bathroom and storage) which simultaneously separates and relates the served spaces, and around which the house evolves as an open, continuous space. In the attic, a continuous roof section was suppressed to create terraces, relieving the interior character usual in these spaces. The floor structure, in good state but insufficient in resistance, was reinforced with a 5cmthick light-concrete slab connected to the beams, offering an inexpensive and effective solution which allowed to keep the beams visible and gain ceiling height.