This paper describes how the use of BIM / simulation integrated within the design process for a new corporate office of 30,470sqm NIA for 3,200 people that is designed to BCO 2010 A grade standards (British Council for Offices, 2009), and incorporates a number of innovative low energy features including earth tubes for supply of tempered air, double skin facade; atrium and biofuel CHP, has influenced the design process when working to a very tight programme. Simulation was used to evaluate the building orientation, the performance of the double skin facade, potential for natural ventilation, optimisation of shading, predicted energy consumption, performance of the earth tubes, chilled beams, impact of exposed fabric, structural design, lift traffic analysis and heat recovery efficiency.