Decisions about the openings of the buildings play crucial role for improvements in recent and future energy and environmental performance characteristics. Therefore, the effects of window to wall ratio and window orientation on building annual heating, cooling energy consumptions and operational CO 2 emissions are investigated regarding recent (2018) and future weather conditions (2050s and 2080s) of İzmir. The simulation model of a typical office building is created, and several scenarios are

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... generated, including four facade orientations and different window to wall ratios, simultaneously. Then, the impacts of retrofits in window characteristics on building performance under climate change are examined for İzmir and Ankara. Finally, the results are evaluated in terms of different weather conditions to reach the most efficient opening design alternative. Considering the average life time of buildings, the outcomes of this study can be used as additional data for understanding the relation between transparent surface design and energy, environmental performance of buildings.