Scientific community and government institutions have acknowledged energyretrofitting solutions for historic buildings as strategic within the EU "20-20-20" target, provided that they should be developed from the assessment of the local environment. Geographic-climatic conditions of site, historic-morphological development of settlement, typological-architectural configuration of buildings and construction-technical characteristics of components feature that environment, which shapes the domain, where expected performances of requalification products and processes might be defined. The final goal is the challenging and desirable balance among conservation of original material and formal identity, enhancement of present and potential relationships between indoor space and outdoor environment, technological improvement of construction systems. The paper is going to discuss an assessment methodology, applied to the historic sea towns in the Province of Bari, South Italy. Specifically, the methodology focuses on the investigation of all the above-mentioned aspects, also by means of analytical simulations, onsite measurements and thematic maps, in order to develop reliable energy models for historic buildings. The models should support the analysis of the relationships between performances of building sub-systems and efficiency of building system, always taking into account the transformation boundaries of the envelope, towards efficient, compatible and convenient energy-retrofitting solutions.