In statistics, the ability of a certain technique to deliver accurate results, although its assumptions are violated, is called the robustness of that technique. Analogously, the robustness of an (office) building or an HVAC system can be defined as the measure by which the building or the system lives up to its design purpose in a real life situation. Lack of robustness can be caused by hypersensitivity to aberration from the design assumptions, unfeasible maintenance demands, integration of heating and ventilation, regulating supply air volumes and lack of transparency to occupants and buildings management. The robustness hypothesis helps explain the results of field studies and mitigation investigations and has enough scientific credibility to warrant further research. It turns out that source control may be viewed as a special case of robustness. The concept of robustness has important ramifications for design practice and is totally in sync with recent developments in indoor environmental research. (C) 2005 Published by Elsevier B.V.