Fire performance of Light-gauge Steel Frame (LSF) constructions is being extensively investigated recently, due to the critical behaviour of cold-formed steel structures at elevated temperatures. Among the many design parameters involved with LSF constructions, the effect of cavity insulation inside LSF walls at different ratios on the Fire Resistance Level (FRL) has not been addressed yet. Hence, Finite Element Models (FEMs) were developed for the LSF walls to simulate the full-scale fire tests conducted applying the standard fire temperatures, where the Finite Element Analyses (FEA) results were very well agreeing with the experimental results. Thereafter, the validated FEMs were extended to study the fire performance of the conventional and modular LSF wall systems with different cavity insulation ratios, where 0.4 cavity insulation ratio was found to be most efficient when structural FRL is of concern while producing satisfactory energy performance at reduced material costs. To calculate the structural FRLs of conventional and modular, single and double plasterboard layers sheathed LSF walls, 4 empirical models have been proposed where more than 97% accuracy was achieved. Moreover, incorporating back blocking panels and discontinuous insulation options, several novel conventional and modular LSF walls have been proposed with up-to 70% improvement in structural FRL.