The existing built heritage is excessively energy intensive compared to the standards required by European policies that promote zero- or near-zero-energy buildings. Hence the need to promote a radical energy requalification of the existing stock through ad hoc solutions. In the modelling of buildings undergoing redevelopment, the boundary conditions considered by the designer are often underestimated, resulting in a digital model that does not perfectly adhere to reality, due to a lack of historical and documentary knowledge. The present work—which concerns the Santa Maria Micaela residential complex built in Valencia by architect Santiago Artal Ríos, a representative work of Spanish Modernism—aims to overcome this vulnus with modelling that also takes into account historical and archive information. The housing complex was studied using a multidisciplinary approach with historical–archival analyses and site surveys that allowed BIM modelling and localisation in a WEB-GIS platform. The modelling took into account the peculiarities of the original design (exposure, windiness, and shading) and data from historical research (stratigraphy of building elements, dimensions, types of materials). The energy simulation, on the other hand, referred to a representative dwelling unit of the complex, and using SolidWorks software the ventilation flows were evaluated, which made it possible to create a model that was more in keeping with reality and to more correctly identify the performance upgrading proposal. The energy improvement was then evaluated according to the hypothesised interventions using two different analysis methodologies, TerMus and CE3X, for direct comparison. The transposition into WebGIS then made it possible to assess the potential of a digital platform to enhance information sharing.