Light steel frame (LSF) building systems are becoming more prevalent in commercial, industrial and residential construction in New Zealand. Tested fire resistance ratings are generally available for non-loadbearing LSF drywall systems lined with gypsum plasterboard. No test information exists for loadbearing systems. Current solutions are based on limiting steel temperature. This study investigates the parameters which affect the performance of loadbearing LSF drywall systems exposed to fire. Structural design codes for cold-formed steel members are compared. Methods are presented for calculating the reduction of steel strength and stiffness at elevated temperatures, and for predicting the deformations resulting from temperature gradients and P-∆ effects. Heat transfer modelling by computer is used to predict steel framing temperatures for systems exposed to the standard ISO834 time-temperature curve and real fires. Three full-scale furnace tests were carried out to evaluate analytical predictions. A model is proposed for predicting the performance of loadbearing LSF systems exposed to fire. Results are within 80-90% of test results. The current practice of designing to a limiting steel temperature results in unduly conservative predictions, particularly for systems with low applied axial loads. It was also found that fire tests may give non-conservative results for systems with low stud loads due to frictional restraints.