ASTM E1300 is the main US standard for determining the load resistance of glass in buildings. The safety concept is based on a “Failure Prediction Model”. Normally verification of glass is done against wind loads and for rectangular units only. In modern Curtain Walling facades irregular shapes and the additional impact of linear or concentrated loads on the glass units are demands not yet covered by FPM of ASTM E1300. For proper verification and evaluation of various influences use of an “Allowable Stress Design” is advisable. Relevant load case combinations are mentioned in IBC and ASCE. But just for typical loads within the building sector. The structural analysis of IGUs requires taking into account probable interaction of internal and external loads. This paper shows an approach how to combine loads with different load durations based on the safety concept of ASTM E 1300 and how to combine load types which are not explicitly mentioned in that standard. In conclusion the proposal of appropriate load cases combinations and relevant load durations leading to a reasonable “Allowable Stresses Design” is presented.