The design of tensioned membrane structures is not yet addressed by standards like the Eurocodes. Currently, in cooperation with the TensiNet Association, Working Group 5 of CEN TC250, is working on a general standardised design approach for membrane structures, consistent with the partial factor framework used in the Eurocodes (as specified in EN1990). To achieve such a design approach, research focusing on developing a methodology to verify the reliability of a membrane structure is needed. The structural behaviour of a tensioned membrane can be represented by a tensioned cable-net. This article starts from the investigation of a cable-net structure, as such structures are addressed in EN1993-1-11, followed by applying the established method to a membrane structure. This article evaluates the influence of the partial factor for pretension. If the cable-net and membrane structure are dimensioned according to a partial factor 1.0, the obtained reliability index is lower than the considered target reliability index. If the structures are dimensioned according to a partial factor 1.35 the obtained reliability index is higher than the considered target reliability index and therefore meet the safety requirements. The study shows that the influence of the structurally non-dominant direction plays an important role in the reliability analysis.