The housing stock in Italy comprises over 12.5 million buildings, of which 63.8% (7.2 million) were built before 1971. Among the 35.5 million housing units, approximately 90% fall into the civil (A/2), economic (A/3), and public (A/4) categories, with 93% being individually owned. 

An annual report by Enea, based on the Energy Performance Certificates (EPCs) issued since 2020, reveals that 75.4% of the certificates relate to buildings in E, F, and G Energy Classes (G accounting for 35.3%). In particular, the residential sector exhibits a higher prevalence of the most energy-consuming categories. 

According to a study by CRESME assessing the cost-effectiveness of thermal insulation in dwellings, the building sector consumes 38% of the national energy budget. Moreover, Europe's Air Quality Status 2023 confirms that the Po Valley -including cities like Cremona, Bergamo, Piacenza, Brescia, and Venice- is listed as one of the most polluted areas in Western Europe, with the highest concentration of particulate matter and ozone levels 5 times higher than the WHO limits. Therefore, retrofitting an apartment according to the EnerPHit standard may showcase the benefits of energy efficiency, besides excellent indoor air quality.

The proposed case study is part of a building constructed in 1963, located in the eastern area of Bergamo and close to the historical centre. The apartment block is characterised by a rectangular floor plan with an east-west orientation, the main structure is in reinforced concrete, and it comprises 54 units distributed over six above-ground floors. The apartment is located on the second floor and has a total floor area (TFA) of approximately 100 m2, an internal height of 3 m, and two balconies. The retrofit was completed in 2023.

The design strategy comprises the following key objectives:

• Implementing a pilot EnerPHit certification for single apartments (component method) with the aim to maximise the energy performance and indoor air quality of the dwelling, taking into account the cost-effectiveness and feasibility of the intervention;
• Promoting bottom-up regeneration actions within the Italian real estate stock, aiming at the development of sustainable communities and the improvement of the critical environmental situation of the Po Valley, in line with the 2050 objectives of the European Green Deal;
• Supporting short construction supply chains: engagement of local manufacturers and workers in order to minimise the overall carbon footprint of the process, stimulate the sustainable development of the construction sector, and lay the foundations for new energy-efficiency oriented opportunities;
• Creating a replicable model that offers economic feasibility and design scalability: a framework of guidelines, strategies, and specific measures to be analysed and tested; a comprehensive monitoring of the dwelling performance as an effective tool to demonstrate the absence of the so-called performance gap while providing evidence for the implementation of energy efficiency measures;
• Investigating innovative and specific retrofit solutions that are compatible with various intervention limitations (e.g., environmental restrictions), preserving the historical integrity of buildings, considering sustainable construction materials and methods in line with environmental goals, and ensuring compliance with local authorities and environmental