The aim of this study is to identify the most effective strategies to improve energy performance of an existing typical office building in the city of São Paulo/Brazil, by simulating the results of various retrofit interventions in EnergyPlus. Appropriate lighting levels were determined and the potential of natural light was simulated. Various air conditioning systems were simulated, comparing the performance of VRF (variable refrigerant flow) split systems with and the use of economizer. The building envelope was treated to reduce solar heat gain, specially through the glazing facades. The work dealt with different arrangements of external louvers, to achieve the ideal combination of horizontal and vertical shading devices. The conclusion shows an enormous potential for improvement on the performance of existing buildings in one of the biggest cities on the planet.