The aim of this paper is to present a detailed methodology for the three-dimensional finite element analysis of asymmetric slim floor beams under fire conditions. A fully controlled solution process is suggested through a detailed step-by-step presentation of the simulation parameters incorporated into the model. Work has been carried out so that any asymmetric slim floor beam can be assessed using the same consistent method, which is validated against two reported fire tests. Time-temperature and time-vertical displacement curves are calculated for the appropriate comparisons with experimental results, which show that the proposed methodology can accurately predict the thermal and structural behaviour of such beams.