Although the individual building system has been designed to meet the specific performance criteria, the way people will perceive and react to a total office environment is only known after it is in use and subjected to diagnostic. Evaluation of office space has gone beyond looking at a single building requirement. There exists the need to look at the interrelationship of performance mandates to provide healthy buildings for building occupants and most importantly, to reduce energy consumption during the construction and operation of buildings. This study aims to demonstrate the use of total building performance (TBP) evaluation and diagnostic to assess the performance of an existing office building in Singapore. Two floors of the evaluated high-rise commercial building have been evaluated by using the TBP paradigm. Objective measurements and observations (walkthrough) coupled with occupant survey (subjective measurement) has been conducted. The analysis demonstrates that there is concurrence between the objective and subjective measures, and that the holistic approach of TBP elicited the interrelationships between the performance's mandates and constitutes a sound basis for diagnostics and sustainability improvement. This study is significant because it provides an evaluation tool for ensuring sustainable buildings. DOI: 10.1061/(ASCE)EY.1943-7897.0000056. (C) 2012 American Society of Civil Engineers.