Glass facades, particularly in high-rise buildings, increase in energy consumption for heating, cooling and ventilation. This causes too high running cost of mechanical systems. Double skin glass facade is a system that decreases these disadvantages, by providing natural ventilation, preventing solar heat gain, controlling daylight, etc. This paper aims to investigate the appropriateness of double skin glass facades in moderate climate, such as Istanbul, in terms of the energy and cost efficiency when compared to single skin glass facades. For this purpose, an approach is proposed to determine the efficient alternatives. It comprises to generate standard facade alternatives by considering the objectives, constraints and performance criteria, and to evaluate their energy and cost efficiency for both single and double skin glass facades. In conclusion, the most energy efficient double skin glass facade is about 22.84% more efficient than the most energy efficient single skin glass facade is. Additionally, the most cost efficient single skin glass facade is about 24.68% more efficient than the most cost efficient double skin glass facade is. (c) 2004 Elsevier B.V. All rights reserved.