The residential building sector is a significant contributor to global energy use and emissions, with window design playing a crucial role in thermal performance. In Afghanistan, where most housing is informal and energy infrastructure is limited, the absence of climate-responsive design practices has led to inefficient heating and cooling. Despite the proven effectiveness of passive strategies such as window optimization, little empirical research exists within Afghanistan’s diverse climatic conditions. Therefore, this study investigates the combined impact of window-to-wall ratio (WWR), fa？ade orientation, and glazing type on the energy performance of residential buildings across five cities representing a distinct climate classification. Using BEoptTM simulation software integrated with EnergyPlusTM, a standardized single-zone model was evaluated under multiple configurations: WWRs (0% - 70%), sixteen orientations, and three glazing types (single, double, triple). Heating and cooling demands were analyzed across four major climatic zones—cold-dry, cold semi-arid, hot semi-arid, and hot desert. The results reveal that while heating and cooling patterns follow a consistent directional trend across climates, the magnitude of energy variation differs significantly. Larger WWRs increase cooling loads regardless of glazing performance or orientation, indicating that window openings cannot effectively reduce cooling demand. However, in cold regions, south-facing fa？ades (ENE to WSW) combined with moderate-to-high WWRs and high-performance glazing significantly reduce heating loads, offering up to 33% annual energy savings. In contrast, in hot regions like Kandahar and Farah, even high-performance glazing fails to compensate for the cooling penalties introduced by larger window areas, making minimal WWRs essential for energy-efficient design. This research contributes a data-driven foundation for climate-sensitive residential design in Afghanistan, providing localized guidance for architects and policymakers. It highlights the need for orientation-aware window optimization in cold climates and stringent WWR limitations in hot regions—an essential step toward developing national energy codes and advancing sustainable architecture in under-resourced contexts.
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