The structural fire resistance of light timber frame walls and floors has traditionally been determined by using standard fire resistance tests to provide a Fire Resistance Rating (FRR). The required FRR was prescribed by building codes and had little relation to likely fire severity. More recently, simple formulae have been used to determine an appropriate FRR given the ventilation parameters of a compartment, the likely fuel load and to a lesser extent the thermal properties of the compartment boundaries. The work described in this thesis determines the validity of these formulae for light timber frame walls and floors and other materials. It is shown that, computer modelling can be used to determine the thermal and structural performance of light timber frame walls and floors exposed to fire. The COMPF-2 program can be used with modification to model compartment fires. The thermal behaviour of cavity walls and floors exposed to fire can be modelled accurately using the TASEF program. The structural behaviour of light timber frame walls and floors exposed to fire can be modelled using a general purpose finite element program, such as ABAQUS. The temperature dependent thermal properties used in the thermal model and the temperature dependent mechanical properties used in the structural model may not be absolutely accurate values, but are effective values that are (modifications of known values within a reasonable range) determined in the calibration process. A simple temperature based failure criterion has been devised for the structural response of light timber frame walls and floors exposed to fires. This study shows that simple time equivalent formulae are not suitable for the prediction of such a complex and variable phenomenon as the response of structures to fire. For accurate prediction of structural response under fire exposure, a more rigorous computer based analysis can be used to give much more reliable results than a simple time equivalent method.