ABSTRACT: The case study, we talk about in our paper, is centred on "Cesarea ex-hospital", a XVII century building at present used as residence. There is a restoration project made by the Naples municipality on this ex- hospital and now it's being carried out. The present state of physical and typological degradation has caused the loss of the functional and aesthetic prestations of the building. Our analysis and proposals of architectural intervention is aim at a global building improvement. For example in our restoration project, we propose to return to the natural ventilation and sunning system today spoiled by dangerous and neglectful superfetations. A part of our communication will be devoted to the examination of the methodology we've studied to outline an appropriate refurbishment project. We believe that methodology is apt to define an item of praxis but the case study obliges to carry out a specific research on the building in object and the environment in which it is. So we recognise three phases of approach to the project: 1) the knowledge phases, based on the building subdivision in FUNCTIONAL SYSTEMS search and prestational valuations aiming at specific themes. 2) definition of objectives and architectural project. 3) examination of the justness of chosen solutions. Our paper describes the intervention hypothesis studied at good level of definition. This part concerns the collection and rescue of meteoric and gray waters to re-employ them for common uses by people living at Cesarea ex-hospital. BIO-FILTERS and BIO-PHITODEPURATION are the techniques utilized to clean used waters, first separated according to their different origin. KEYWORDS: ancient building, methodology, microclima control, prestational analysis, sustainable recovery project.