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