The term ‘sustainability’ is often used as a woolly term for everything that is good and desirable. Besides, ‘sustainability’ is a subjective area, which can be difficult to quantify. Any construction project has a wide range of environmental impacts, each of which may have been measured in a different way. Energy may have been measured in terms of carbon dioxide emissions, whereas wood or mineral extraction is generally measured volumetrically, making comparisons between environmental impacts difficult to determine. Various methodologies seek to standardise impacts for comparative purposes and the guiding principle for any environmental assessment is a comparison to the existing building stock, and a result is invariably in terms of a building's relative sustainability. However, to some it is not a matter of being ‘more’ or ‘less’ sustainable. You either are or you are not, therefore relative sustainability is not a valid concept. The discussion of sustainability in this paper is not a debate on the semantics of the term, but ultimately the purist's view does lead to the question whether there can ever be such a thing as a sustainable building and indeed what the role of architecture in the context of sustainability is.