## 1 Introduction  
In 2020, buildings contributed to more than 30% of global energy-related greenhouse gas (GHG) emissions [1] and about 40% of the world's energy consumption, of which approximately 27% was attributed to the residential sector [2]. To deal with this problem, several directives were delivered by the European Union (EU) aiming to minimize heating/cooling and electricity demands, and thus reducing CO\({}_{2}\) emissions. Among the key policies for achieving these include the Energy Performance of Building Directive (EPBD), which was launched in 2010, and the Energy Efficiency Directive (EED), which was launched in 2012. With the application of these documents, the EU estimated a reduction of 8%, 12%, and 17% on the energy required for the heating/cooling of buildings in 2020, 2030, and 2050, respectively, compared to data for 2005. Nevertheless, these decreases cannot be achieved if only new construction and new buildings are considered, and a special look at the existing and even older built heritage needs to be performed, as these buildings represent most of the European-built patrimony. The use of proper insulation materials and design has already been proven as the best strategy to reducing energy losses and guaranteeing thermal comfort [3; 4]. Additionally, the reuse of construction building materials waste has also been promoted as a sustainable practice [5]. Thermal insulation systems can be applied using three different application techniques: to the exterior--exterior insulation; to the interior--interior insulation; and via injection--cavity insulation. External thermal insulation composite systems (ETICSs) are often applied on new constructions. However, when there is a need to insulate buildings in an urban context or even built heritage, the application of an ETICS is frequently not possible (for example, due to excessive narrowing of pedestrian walkways in narrow streets), and the application of interior insulation may be the only viable solution. The application of this technique comes with some disadvantages (such as reduction in room size) and problems, such as the development of thermal bridges [6], possible occurrence of interstitial condensation [7], frost damage [8], and decay on timber beam-ends [9], among others. It is known that air infiltration in many of the existing buildings can result in significant heat losses, with losses as high as 33% being noted in the UK [10]. As a result of these concerns about energy efficiency, along with society's desire to reduce its carbon footprint, buildings are now being designed to be increasingly airtight. This lack of unwanted ventilation can lead to dampness, moisture damage in buildings, and increased levels of indoor relative humidity. All these conditions strongly contribute to mold growth, along with several physical and environmental properties (e.g., water content, temperature, pH, and the type (i.e., organic and non-organic) and hygroscopic behavior of the materials [11; 12]). Previous research has shown that organic materials, with ample nutrients in their composition, are more prone to mold growth [13]. Furthermore, the development of new insulation materials, often multi-component in nature and comprising natural materials and/or wastes as part of the composition of their matrix, seriously increases the risk of biodeterioration [14; 15]. The need to evaluate the biodegradation risk of organic, inorganic, and composite insulation materials is therefore of utmost importance to enable a correct application and use of these materials in construction systems. According to [PERSON] et al. [16], the most common fungal genera found in indoor environments belong to the genera _Penicillium_, _Cladosporium_, _Aspergillus_, and _Stachybtorys_. The application of antifungal additives (e.g., sodium polyborate or dichloromethane) has been commonplace to avoid mold growth [17].