The promotion of energy efficiency (EES) and renewable energy. (RES) programs has a long history in developed countries; however, in the rest of the world such initiatives are incipient. Meanwhile, cities are the main recipients of this type of programs; therefore, the development of methodologies for the elaboration of prospective urban-energy studies is really important to efficiently use the available resources. Nevertheless, cities have substantial differences among themselves in terms of structure, conformation and growth, along different regions in the world. Hence, it is necessary that methodologies can respond to different realities that each case presents. In Argentina, as in many developing countries, cities are heterogeneous within their own urban structure, manifesting large socio-economic, morphological and infrastructure inequalities. This situation forces us to board the territory in a particular way and, therefore, to develop a proper methodology for the construction of prospective studies for our context. Thus, this paper proposes an innovative methodology that disaggregates the city in urban areas with similar internal behaviors [homogeneous areas (HA)]; which allows us to assess specific EES/RES measures for each of them, such as the application of regulations, programs or incentives for: the improvement of new and existing building's envelopes; the insertion of solar energy systems for space heating, sanitary hot water or PV; the replacement of energy-intensive appliances; among other options. This analysis considers socio-demographic, urban-morphology, building and energy consumption variables/indicators, which enable us to identify critical aspects in each homogenous area. This approach is unusual in most prospective urban-energy studies, where the study areas are addressed as a single element or, alternatively, a small urban sector is used as an example. In this context, this paper presents the methodology for the urban-energy diagnosis stage, obtaining as results the construction of the "base year" model into the LEAP software and the energy guidelines for each homogenous area. The continuation of this research, with the assessment of "alternative scenarios", will be presented in future publications.