# The Evaluation of Historic Building Energy Retrofit Projects through the Life Cycle Assessment
## 3 Thermal Insulation for Historic Buildings  
In energy retrofit projects of existing buildings, new insulation materials are used to isolate the building's walls by cooling and enhancing the liveability of internal spaces. According to [PERSON] et al. (2005), the increased awareness towards the environment and public health is leading to an integrated evaluation of insulation materials, and, whilst no one questions their positive energy balance, there is still significant potential for improving their overall performance, in terms of environmental impacts from cradle to grave ([PERSON] et al., 2018). The evaluation of the performance of insulation materials is a multicriteria problem, that has to be carried out with respect to:  
1. their physical properties,
2. their health and environmental properties,
3. their applicability in specific building elements and structural problems, and
4. their cost, as a function of the above-mentioned parameters ([PERSON] et al., 2018). The thermal insulation of historic buildings is the most significant problem because it delays the rate of heat flow by conduction, convection, and radiation. The selection of the appropriate insulation materials for the thermal insulation of buildings reduces not only the energy usage but also downsizes the heating, ventilation, and air-conditioning (HVAC). A simple and effective way to improve the energy efficiency of a building is by improving the thermal insulation of the envelope. In historic buildings, usually, the materials chosen for the thermal insulation are placed close to the inner surface of the building, to respect its aesthetic values. Additionally, the selection of thermal insulation thickness is strongly connected with the thermal conductivity and thermal inertia of the selected insulation material [22]. It happens very often that the increase in temperature and moisture content of the insulation material increases its thermal conductivity, thereby degrading its performance. In fact, studies have shown that water in the form of vapor or liquid has a detrimental effect on the material characteristics of slag-rock, wool, fibers, and fiberglass. The thermal insulation of materials is critical to global warming. The possible reason may be that different materials have different R-values that affect heat transfer and energy consumption in the building. Similarly, materials are critical to design and operate energy efficient systems, such as the cooling system and the heat exchanger [6, 7]. According to a study by [PERSON] et al. (2011), the most commonly used insulation building materials and solutions are classified in two clusters: traditional thermal insulation materials and innovative materials [23]. Regarding the conventional insulation materials, we can find mineral wool, expanded polystyrene (EPS) and extruded polystyrene (XPS), cellulose and cork, and polyurethane (PUR). Among the innovative materials, we can find vacuum insulation panels (VIP), gas-filled panels (GFP), aerogels, phase change materials (PCM), vacuum insulation materials (VIM) and gas insulation materials (GIM), nano insulation materials (NIM), dynamic insulation materials (DIM), nano-con, and bio-materials. Today, the use of expanded and extruded polystyrene is the most widely used thermal insulation technique. Expanded polystyrene (EPS) is made from small spheres of polystyrene (from crude oil) containing an expansion agent, i.e., pentane C\({}_{6}\)H\({}_{12}\), which expands by heating with water vapor. The expanding spheres are bound together at their contact areas ([PERSON] et al., 2011). It is produced from melted polystyrene (from crude oil) by adding an expansion gas, i.e., HFC, CO\({}_{2}\), or C\({}_{6}\)H\({}_{12}\)[23]. The thermal conductivity of XPS varies with temperature, moisture content, and mass density. As an example, the thermal conductivity of XPS may increase from 34 mW/(mK) to 44 mW/(mK) with increasing moisture content from 0 vol% to 10 vol%, respectively.