The projected idea synthesizes multiple aims under a complex set of rules, that should be met with a minimum cost. The first aim explicitly committed was to use the full density allowed for the plot, with a number of 48 apartments of 57 sq. meters each, that should meet the standard requirements for social housing funded by the state within a total building budget of USD 41.600. Besides limiting the maximum density, gross area and building height to 4 stories within determined setbacks, the urban codes demanded one parking lot per housing unit, plus many other minor restrictions. The standards for the housing units included several rooms complying with minimum dimensions: a living, dining and kitchen room, a main bedroom, two secondary bedrooms, one for two beds and the other for one bed, and a bathroom. As the size of the units is small, the importance of extending the living premises to a community place increases. So, with no extra cost, we devised a central planted courtyard as a common living place shared by all private units, flanked by corridors that access the superposed duplex housing units, with staircases at both ends of these parallel blocks. But, a wrong interpretation of a rule by the state authority obliged us to give a direct entrance to each unit and to fill the empty space of the courtyard with many extra staircases. Then, the challenge of the project became to make those stairways as transparent, light and economic as possible.