This research investigates the impact on energy use of the different ways in which office spaces can be organised and used. It explores typical UK office layouts, utilisation densities and intensities on a good practice-base case shell. This is achieved using the TAS, Lightscape and Excel software packages. For the average occupancy of 50%, the analysis indicates that the variations in combined thermal and lighting loads are 19% and 51% during the UK peak winter and summer respectively. The respective per capita load variations are 80% and 16%. The analysis demonstrates that space planning and utilisation have significant impacts on energy use and are important in assessing energy performance.