# The Evaluation of Historic Building Energy Retrofit Projects through the Life Cycle Assessment
## 2 State-of-the-Art Review of Innovative Materials and Solutions in Building Retrofitting  
It is well known that the preservation of cultural heritage is an indispensable action for its transmission to future generations. Therefore, for historic buildings, an appropriate design approach is required to ensure its functioning and preservation, avoiding the creation of damage and reducing energy use and environmental impact without compromising its cultural value. We processed an analysis of the state of art through the use of a VOSviewer software, to identify the best design solutions to adopt for the energy retrofit of existing buildings. VOSviewer is a software for constructing and visualizing bibliometric networks, which elaborates data about a specific research topic. The construction of a \"data network\" was created through the research works collected in the Web of Science, Scopus, Dimensions, and PubMed databases [5]. Therefore, we used the Web of Science, and the key words entered in the search box were: \"energy retrofit for existing buildings\", \"new materials for energy retrofit design project\", and \"bio-based materials\". This scientific database identified around 390 studies (filtered from 2017 to 2021), identifying all relevant research questions in the form of \"keywords\". Figure 1 shows the \"visualization map of the scientific landscape\" elaborated with VOSviewer. There are two clusters (red and green) with 84 items. The \"size of the circle\" identifies the weight of the relevant questions and the colors identify the clusters (categories) in which the researchers promote their studies. The distance between the entries in the visualization identifies the relationships in terms of citations in the scientific literature (Figure 1). In the 390 papers identified, it emerges that the energy and renovation problems of existing buildings is a consolidated research topic. In the green circle are included more than 72 documents that discuss energy retrofit solutions for the renovation of the built environment sector, through the experimentation of an innovative methodology/approach and design solutions. In the map, there is an evident link between the city pollution and the built environment. Moreover, it appears that life cycle assessment is the evaluation tool most suitable to evaluate the environmental impacts of the retrofit projects. To the red circles, approximately 318 papers correspond to the study/use of innovative materials (bio-materials) for the renovation of historic buildings. It emerges that the use of bio-based materials in refurbishment is important because of their negative or low global warming potential (GWP), their low primary energy (PEI) need for production, their cost-effective benefits, and their recycling/reuse potential [21]. According to a study by [PERSON] et al. (2020), there is a large number of products available in the market for the insulation of internal facades, including natural materials (e.g., cellulose, cork), conventional materials (e.g., mineral wool, glass wool, polyurethane, expanded polystyrene, insulating plaster), and other advanced materials (e.g., calcium silicate, aerated concrete) [22]. Through the analysis of these documents, it appears that the \"internal insulation\" is a consolidated renovation solution for historic buildings. The external thermal insulation is often not suitable because of the need for preserving the facades along with their aesthetical, heritage, and cultural values [23]. Figure 1: VosViewer map of the scientific landscape. Today, the design solutions' beauty problem is of relevant interest. In this regard, [PERSON] et al. (2018), in a literature review analysis, identified 73 scientific studies that discuss the most suitable aesthetic design solutions for the energy retrofit of existing buildings ([PERSON] et al., 2018). Moreover, they underlined that there has been an increasing number of European programs that have financed projects of energy renovation of historic buildings with specific beauty standards.