The systems in which energy is most intensely used in airport terminal buildings are HVAC systems. More efficient heating and cooling systems and the performance of the building envelope can provide significant reductions in energy consumption without compromising comfort conditions in terminal buildings. In this study, the exterior walls of the International Hasan Polatkan Airport were examined using a thermal camera, and it was observed that heat losses were due to the lack of thermal insulation. The optimum insulation thicknesses for different thermal insulation materials (EPS, XPS, glass wool and stone wool) were determined by the life cycle cost (LCC) method. The effect of the application of the calculated insulation thicknesses on energy performance and the economic payback periods were determined. As a result, optimum insulation thicknesses have been found as 0.05 m, 0.033 m, 0.078 m and 0.973 m for EPS, XPS, glass wool and stone wool in respective order. It was observed from the results of analysis that the economic payback period changed between 4.85 and 7.7 years if optimum insulation thicknesses are applied.