## 6 Conclusions  
The primary aim of this study was to evaluate the effectiveness of various building facade retrofit strategies in reducing cooling energy consumption, with a focus on the hot climatic conditions of Saudi Arabia. The research was conducted on a student housing building located at KFUPM, Dhahran, and involved a comparative analysis using numerical \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Strategy Code** & **Strategy Description** & **Total Retrofit Cost** & \
\begin{tabular}{c} **Annual Cooling** \\ **Cost Reduction** \\ **[SAR]** \\ \end{tabular} &
\begin{tabular}{c} **Payback Period** \\ **[Year]** \\ \end{tabular} \\ \hline S1 & ETCIS, louvers, Argon & 334,469 & 21,370 & 15.7 \\ \hline S2 & ETCIS, louvers, low-e coating & 359,199 & 23,569 & 15.2 \\ \hline S3 & ETCIS, louvers, low-e coating, Argon & 361,179 & 24,397 & 14.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 12: Initial cost and payback period of the three combined retrofit strategies. modeling. The investigation assessed multiple individual and combined retrofit strategies for external walls, windows, and shading devices, considering the availability of materials and associated costs in the Saudi market. A base case model was developed and validated using DesignBuilder software, where the building's annual cooling electricity consumption was recorded at 477,074 kWh, translating into a significant yearly cost of approximately 152,663 SAR. In total, eight retrofit strategies for external walls, seven for windows, and four for shading devices were identified and thoroughly examined. The external wall retrofit strategies had a significant impact on reducing heat gains, achieving reductions between 47% and 75% compared to the base case. This reduction translated to a decrease in cooling energy consumption ranging from 11.1% to 18%. Among the strategies, the use of prefabricated wood as external insulation proved the most effective, while the ventilated facade with FC cladding showed the lowest reduction. However, when considering local prices in the Saudi market and factoring in the payback period, the ETICS strategy stood out, offering the shortest payback period of 15.4 years despite the lower cooling energy reduction it offered, which was 13% compared to the base case. Several window retrofit strategies were also evaluated, with reductions in glazing heat gains of up to 45% and cooling electricity reductions of up to 8%, particularly with the use of smart glazing filled with Argon gas. However, this strategy had the longest payback period of 11 years. In contrast, the triple glazing strategy, while achieving a smaller cooling energy reduction of 4.3%, offered the shortest payback period of 4.9 years. To enhance the effectiveness of these strategies, they were tested in combination, resulting in 224 different facade compositions, which were analyzed using the genetic algorithm optimization method. The study identified that the most efficient combination involved using ETCIS for the walls, louvers for the windows, and low-e coating with Argon gas for glazing. This combination achieved the highest cooling energy reduction of approximately 16% and the shortest payback period of 14.8 years. The study concluded with several recommendations for stakeholders involved in building retrofit projects in Saudi Arabia:  
* Design for Adaptability: In the context of sustainability, buildings must be designed with a high degree of adaptability, allowing for the periodic retrofitting of construction elements and control systems. Designing for adaptability reduces the demand for unnecessary new construction and minimizes the waste and emissions associated with it. * Economic Feasibility and Market Availability: It is recommended that retrofit strategies that offer the greatest financial benefits and the shortest payback periods be selected while considering both economic feasibility and the availability of materials in the market.