Little research has been done into robustness of ‘green’ commercial building performance and the consequent risk to both environment and investor of a building/occupant mismatch. This project describes a due diligence analysis on a ‘green’-rated office building. The building was assumed to be a system consisting of envelope, services, occupants, economic and urban environment. A parametric differential sensitivity analysis tested the effects of short and long term changes. It was found that the ‘green’ building performance was most sensitive to occupant equipment load and changes in offices hours but was no less sensitive to changes than a hypothetical non- ‘green’ building.