The main function of building facades, which often consists of glazing windows, is to provide protection to the occupants and contents of the building from external hazards. In a blast event, the facade component of a building may become the weakest link of the structure, whereby its breach may lead to blast pressure ingress and hazardous projectiles into a structure. This paper reports part of a study to establish the performance of glass windows under blast pressures. Two modelling techniques were used to simulate the response of a façade panel. They are the Single Degree of Freedom (SDOF) modelling technique and the Finite Element (FE) modelling technique. Although the SDOF approach can be used with a reasonable degree of accuracy, the limitations of its basic assumption lead to loss of details in the idealisation process. This paper presents an attempt to establish performance indices of a façade panel, and to identify the discrepancies between simplified approach and the detailed numerical modelling approach analysis.