Light gauge steel frame (LSF) floor-ceiling systems are increasingly used in buildings without a full understanding of their thermal and fire resistance performance. Hence a numerical study was undertaken on the thermal performance of LSF floor-ceiling systems with varying configurations under standard fire conditions. The configurations included Lipped Channel and rivet fastened Rectangular Hollow Flange Channel section joists, gypsum plasterboard lining, steel sheathing, structural plywood and rockwool fibre insulation. The measured elevated temperature thermal property data of the above floor system components were included in the 3D thermal finite element models and the results were compared with fire test results. A good comparison showed that the developed finite element models can be used to simulate the thermal behaviour of LSF floor-ceiling systems with varying configurations. A parametric study was then undertaken to extend the thermal performance data in terms of time-temperature profiles for LSF floor-ceiling systems. Finite element analyses showed that the new LSF floor-ceiling system with the addition of thin steel sheathing performed significantly better than conventional systems. The use of thin steel sheathing on both sides of plasterboard showed further improvements. The use of cavity insulation was shown to be detrimental and thus improved floor-ceiling configurations were proposed.