## 3 Materials and Methods
### Selection and Cost Estimation of Retrofit Strategies
#### 3.3.1 Description of Facade Retrofit Strategies  
The study examined various strategies for retrofitting external walls, windows, and shading devices, both individually and in combination, to assess their impact on reducing cooling electricity consumption. This investigation utilized different materials available in the Saudi market. For the external walls, three primary retrofit strategies were initially explored: ventilated facade, External Thermal Insulation Composite System (ETICS), and prefabricated wood. The ventilated facade is a dynamic construction method that incorporates 5 cm of extruded polystyrene (XPS) insulation, a 2.5 cm air gap, and a finishing layer of 2.5-3 cm. Various cladding materials sourced from the Saudi market are used within the ventilated facade system, resulting in eight distinct retrofit strategies, as detailed in Table 2. The ETICS strategy involves applying an 8 cm layer of expanded polystyrene (EPS) insulation to the external walls, reinforced with a mesh, and finished with a 2 cm plaster layer. Meanwhile, the prefabricated wood option consists of modular panels featuring a timber frame structure filled with a layer of mineral wool, yielding a total thickness of 14 cm. Window retrofitting involves a variety of strategies, as detailed in Table 3. One approach included the use of smart glass, where the base window could be replaced with electrochromic glass. This double-glazing system features 6 mm glass panes separated by a 13 mm air gap, allowing the glass to change color and prevent solar gains from entering the space when the outside temperature reaches 24 \({}^{\circ}\)C. Another strategy involved applying a low-e coating to the base window. These thin, transparent coatings are typically applied to the surface of the glass and are designed to reflect and emit radiant heat, thereby reducing the amount of heat that passes through the window. A third strategy considered replacing the double glazing with triple glazing, maintaining the same specifications of 6 mm glass panes and 13 mm air gaps. Additionally, the study explored filling the air gap in the base window and all other strategies with Argon gas. The installation of shading devices was also examined as part of the facade retrofit. These devices help regulate sunlight and heat \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Strategy Code** & **Strategy Description** & **Thickness [m]** & **U-Value [W/m\({}^{2}\).K]** \\ \hline S-WA-1 & VF with ACP sheet cladding & 0.1 & 0.153 \\ \hline S-WA-2 & VF with FC & 0.1 & 0.124 \\ \hline S-WA-3 & ETICS & 0.1 & 0.16 \\ \hline S-WA-4 & Prefabricated wood & 0.3 & 0.14 \\ \hline S-WA-5 & VF with limestone cladding & 0.1 & 0.194 \\ \hline S-WA-6 & VF with sandstone cladding & 0.1 & 0.195 \\ \hline S-WA-7 & VF with AAC brick cladding & 0.12 & 0.192 \\ \hline S-WA-8 & VF with WPC cladding & 0.1 & 0.223 \\ \hline \hline \end{tabular}  
* AAC = Autoclavored Aerated Concrete, ACP = Aluminum Composite Panel, ETICS = External Thermal Insulation Composite Systems, FC = Fiber Cement Board, VF = Vertilated Facade, WPC = Wood Plastic Composite.  
\end{table} 
Table 2: U-value of the different wall retrofit strategies (compared to a U-value of 0.56 W/m\({}^{2}\).K in the base case). entering a building, ultimately reducing the need for excessive air conditioning. Three types of shading devices were investigated: internal smart aluminum blinds, external window louvers that cover the entire window at a tilt angle of 15 degrees, and overhangs made from either wood or steel, each with a depth of 1 m.  
Following the assessment of individual retrofitting strategies for external walls, windows, and shading devices, a series of combined strategies were evaluated through optimization. Three key performance indicators were established: reducing heat gains, minimizing cooling energy consumption, and enhancing financial efficiency. An optimization framework was implemented based on these indicators.