Buildings use about 40% of the national energy consumption, and approximately 25-30% of this energy is wasted due to inefficient windows. Installation of energy efficient glazing allows significant reduction of cooling load. While increase of hat consumption can be observed in heating period due to significant reduction of solar heat gains. On the basis of computer simulations there were found dependences between overall energy efficiency of the building and such parameters as its orientation, urbanization, and the types of glazing. Building energy modelling (BEM) allows to predict the energy consumption of the building, to find and correct the weak spots in terms of energy consumption and to find the most effective way to use energy saving technologies. The IDA-ICE, chosen as the BEM in the research, is a whole-year detailed and dynamic multi-zone simulation application for study of thermal indoor climate and the entire building energy consumption. The main advantage of the software package is a detailed report for each of the building zones and for the whole building, which includes calculation of heat flows and inflows, maintained temperatures, sources of heat losses and energy costs to maintain a comfort temperature. The variable data are the type of glazing (different window types chosen, with special emphasis on g-value of glass and coefficient of shading) and building's orientation to the world sides. The research demonstrates the effectiveness of using particular glazing types depending on the building conditions. The developed recommendations allow to reduce energy consumption in existing buildings and to reduce construction costs of new office buildings at the design stage.