A numerical analysis of two-dimensional transient heat transfer through the ground floor slab of a modem commercial building is presented. A finite-element model of heat conduction is applied to the thermal performance of a concrete slab of normal weight. The relevant experimental data and material properties are also briefly described. The results show a very good correlation between numerically simulated and field-measured thermal responses. A practical approach for the determination of a representative initial temperature distribution is illustrated. A relatively versatile modelling approach appears necessary to accommodate the interaction of a number of different material types. Furthermore, the variation of climauc boundary conditions with time and space needs to be included correctly in the analysis. The work is viewed as a contribution to the overall validation of ground heat transfer models via the direct comparison of simulated results with high-quality in-situ experimental data.