## 2 Methodology
### Artifacts Decay Processes  
Artifacts can be prone to three types of decay depending on the indoor conditions, i.e., biological, chemical, and/or mechanical decay. Each of these types of decay is assessed using a respective method that will be briefly described in this subchapter. More information concerning these topics can be found elsewhere [29]. Biological decay in materials will be assessed using the mold risk factor (MRF) [40], which will be calculated based on the isopleth method [41]. In order for mold to grow in organic materials, it is necessary that certain values of temperature and relative humidity are met, but it is also necessary that the substrate has the necessary nutrients for mold to grow [41]. For each timestep, the values of temperature and relative humidity are \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Measure** & **Insulation Material** & \multicolumn{2}{c}{**Thermal Conductivity**} & **Code** \\ \cline{3-4}  & PUR boards & 0.031 & W1 \\ \cline{2-4} Internal insulation wall & Mineral wool & 0.035 & W2 \\ \cline{2-4} (Thick. 2–10 * and 20 cm) & Perlite boards & 0.042 & W3 \\ \cline{2-4}  & Calcium silicate boards & 0.050 & W4 \\ \hline Thermal mortar (Thick. 1.5, 3, and 3 cm) & 0.045 & W5 \\ \hline Roof insulation & XPS & 0.030 & R1 \\ (Thick. 2–10 * cm) & EPS & 0.040 & R2 \\ \hline Ceiling insulation (Thick. & PUR foam & 0.025 & C1 \\ 2–10 * cm) & Mineral wool & 0.035 & C2 \\ \hline Windows replacement & \multicolumn{2}{c}{Double glazing with clear float (U\({}_{w}\) = 2.8 W/m\({}^{2}\).K)} & \multirow{2}{*}{Wd1} \\ \cline{2-4}  & Double glazing with low E glass (U\({}_{w}\) = 1.4 W/m\({}^{2}\).K)} & \\ \hline \hline \end{tabular} \(\leftarrow\)Thickness varies between 2 and 10 cm with an increase rate of 2 cm.  
\end{table} 
Table 1: Overview of the tested retrofit measures. Figure 2: Simulated and measured indoor temperature (**a**) and water-vapor pressure (**b**) variations for the St. Cristovano model (adapted from Ref. [16]). compared against the Lowest Isopleth for Mold (LIM) curve to determine if this value is overcome. In case LIM is overcome, then the spores become active fungi, and their respective time contribution is added to the overall mold risk factor (Ref. [41] shows how these time contributions are calculated). The spores became fully active fungi when MRF is 1.0 [40]. Chemical decay in materials will be assessed using the lifetime multiplier concept [42], more precisely, the equivalent lifetime multiplier concept. This latter concept manages to characterize the material's respawn to chemical decay under a single value [35]. Materials such as paper (activation energy of 100 kJ/mol [29]) and varnish (activation energy of 70 kJ/mol [29]) are prone to this type of decay. The lifetime multiplier concept is based on the Arrhenius equation, and it determines the time spans that material remains usable when compared to standard conditions, i.e., 20 \({}^{\circ}\)C and 50% RH. The equivalent lifetime multiplier (_eLM_, -), which is the average of the reciprocal of the lifetime multiplier values for the analyzed time period [42], is calculated using the following equation:  
\[eLM=1/\left(\frac{1}{n}\cdot\sum_{x=1}^{n}\left(\frac{1}{\left(\frac{50\ \%}{RH_{i}}\right)^{1.3}\cdot e^{\frac{E_{a}}{K}\left(\frac{1}{T_{i}+2\wedge 3 5}-\frac{1}{283.15}\right)}}\right)\right) \tag{1}\]  
where \(n\) is the number of data points in the selected period (-), \(RH_{i}\) is the surface relative humidity at instant \(i\) (%), \(E_{a}\) is the activation energy (J/mol), \(R\) is the gas constant (8.314 J/Kmol), and \(T_{i}\) is the temperature at instant \(i\) (\({}^{\circ}\)C). Mechanical decay is a crucial damaging process for hygroscopic materials, which is mainly governed by the variation of the relative humidity since it will cause the moisture content of these materials to vary. In turn, this moisture content variation will damage the materials due to the prompted shrink/swell cycles [29].