The aim of this paper is to stress the methodology for the regeneration of an open public space by preserving the cultural heritage and by addition of some new elements to achieve quality and urbanity. The paper is dealing with the regeneration of the Piazza de' Ciompi in Florence and the design of a green terrace. Therefore, the aspiration for a sustainable place-making is mostly the preservation of the existing, the revitalisation of the old square and the adaptation of the green terrace as a new structure. Finally, the adopted design principles run together with the attitude to obtain the best performance of the new intervention.In this contribution, it is outlined that one of the main design key principles on which to base the proposed project of a green terrace is the understanding of the context throughout the analysis of synchronic and diachronic evolution of the existing urban blocks and historic gardens to suggest permeability. Additionally, it is underlined how the re-interpretation of the urban pattern related to the historical character of the site can determine the key masterplan issues