Historic, listed, or unlisted, buildings account for 30% of the European building stock. Since they are complex systems of cultural, architectural, and identity value, they need particular attention to ensure that they are preserved, used, and managed over time in a sustainable way. This implies a demand for retrofit solutions able to improve indoor thermal conditions while reducing the use of energy sources and preserving the heritage significance. Often, however, the choice and implementation of retrofit solutions in historic buildings is limited by socio-technical barriers (regulations, lack of knowledge on the hygrothermal behaviour of built heritage, economic viability, etc.). This paper presents the approach devised in the IEA-SHC Task 59 project (Renovating Historic Buildings Towards Zero Energy) to support decision makers in selecting retrofit solutions, in accordance with the provision of the EN 16883:2017 standard. In particular, the method followed by the project partners to gather and assess compatible solutions for historic buildings retrofitting is presented. It focuses on best practices for walls, windows, HVAC systems, and solar technologies. This work demonstrates that well-balanced retrofit solutions can exist and can be evaluated case-by-case through detailed assessment criteria. As a main result, the paper encourages decision makers to opt for tailored energy retrofit to solve the conflict between conservation and energy performance requirements.

Purpose: Improving the energy performance of historic buildings has the potential to reduce carbon emissions while protecting built heritage through its continued use. However, implementing energy retrofits in these buildings faces social, economic, and technical barriers. The purpose of this conceptual paper is to present the approach of IEA-SHC Task 59 to address some of these barriers. Design/methodology/approach: Task 59 aims to achieve the lowest possible energy demand for historic buildings. This paper proposes a definition for this concept and identifies three key socio-technical barriers to achieving this goal: the decision-makers’ lack of engagement in the renovation of historic buildings, a lack of support during the design process and limited access to proven retrofit solutions. Two methods – dissemination of best-practice and guidelines – are discussed in this paper as critical approaches for addressing the first two barriers. Findings: An assessment of existing databases indicates a lack of best-practice examples focused specifically on historic buildings and the need for tailored information describing these case studies. Similarly, an initial evaluation of guidelines highlighted the need for process-oriented guidance and its evaluation in practice. Originality/value: This paper provides a novel definition of lowest possible energy demand for historic buildings that is broadly applicable in both practice and research. Both best-practices and guidelines are intended to be widely disseminated throughout the field.

Buildings of heritage significance due to their historical, architectural, or cultural value, here called historic buildings, constitute a large proportion of the building stock in many countries around the world. Improving the performance of such buildings is necessary to lower the carbon emissions of the stock, which generates around 40% of the overall emissions worldwide. In historic buildings, it is estimated that heat loss through external walls contributes significantly to the overall energy consumption, and is associated with poor thermal comfort and indoor air quality. Measures to improve the performance of walls of historic buildings require a balance between energy performance, indoor environmental quality, heritage significance, and technical compatibility. Appropriate wall measures are available, but the correct selection and implementation require an integrated process throughout assessment (planning), design, construction, and use. Despite the available knowledge, decision-makers often have limited access to robust information on tested retrofit measures, hindering the implementation of deep renovation. This paper provides an evidence-based approach on the steps required during assessment, design, and construction, and after retrofitting through a literature review. Moreover, it provides a review of possible measures for wall retrofit within the deep renovation of historic buildings, including their advantages and disadvantages and the required considerations based on context.

Historic buildings are fragile systems to be managed and protected during time: in the task of heritage restoration, efficiency improvement interventions should enable a more sustainable building conservation and use. Such measures might be defined within the combination of building survey and energy performance simulation. A good knowledge of materials and physics characteristics is fundamental to weigh correctly any improvement intervention. This can be supported also by documentary research and diagnostics, to detect existing resources and conservation issues. However, how to match all collected qualitative and quantitative data with a building energy model is still an open question. Energy simulation alone gives a partial vision of heritage needs, excluding information which do not affect the thermal performance of the model; on the contrary, a whole building approach is necessary for defining restoration interventions. With the aim of suggesting a methodology to combine both fields of investigation, a case study has been chosen to our purpose: Giuseppe Terragni’s Casa del Fascio (1936). A multidisciplinary process with the combination of building survey, monitoring campaign, on-site investigation and energy modelling has been functional to the understanding of the real building needs and the definition of interventions. Furthermore, the analysis has given to the rediscover of Terragni’s microclimatic control system (not more existing), leading to the choice of reinventing - in a modern way – the existing devices (as curtains), well-balanced on building needs.

The paper aims to present a study carried out within the Regional Operational Program - European Regional Development Fund 2014/2020 financing project for the efficiency improvement of 106 public heritage, owned by the Sicily Region. 38 case studies of this stock have been selected, having different uses (museum, library, office, etc.), typology and construction period, shifting from XI to XX century buildings. The sample heterogeneity gives in fact a large-scale overview on the Mediterranean heritage, allowing to assess the efficacy of energy policies (at Regional level) and to suggest feasible retrofit solutions for historic public buildings. Weak and strength points of each case are highlighted as from both an energy audit (based on bills and simulated energy performance data) and an on-field survey in a comparison. The inclusion of stakeholders’ interviews in the walk-through investigation has clarified the efficacy of building and plants management. Finally, as tangible results, it is suggested to consider retrofit low-impact interventions accordingly to the building microclimate, as well as objects and users’ needs, as a win-win strategy.