An energy audit for one department at the faculty of Engineering and Technology at the University of Jordan has been conducted as a way to apply the concept of green building to an existing structure. According to the Jordanian green building code, a classification for the green building has been carried out according to its saving in energy and water in addition to the other factors such as indoor quality and material. The heating and cooling loads were calculated and the results were compared with the values for the same building after amendments to the windows and walls. The insulation for external walls of the building has been introduced in addition the double glazing instead of the current single glass windows for the building. The electricity for the lighting consumption of this building was obtained and analyzed and the potential of utilizing a lighting sensor for different halls and rooms was studied and analyzed. The boiler performance has been studied and an estimation of efficiency enhancement was proposed. It has been found that choosing a larger window area facing south, east and west can save more energy in winter and decreasing the heating costs using a certain types of double glazing, while decreasing the glazing area facing north can save money and energy. Also, it has been found that the payback period for the annual saving in fuel and electricity bills is less than 3 years. The needed investment for obtaining the energy saving is shown in the paper. (C) 2014 Published by Elsevier Ltd.