Sustainability is a judgement of history.

Over-use of words like 'sustainability' reduces them to the lowest level of meaning, that is to say the level where politicians and marketing directors feel comfortable using them, safe in the knowledge that they can mean almost anything. The arrogant description of buildings, places and their architecture, as being 'sustainable' generally flies in the face of history. It is not given to architects to predict correctly those changes in social, political, economic and even climatic conditions which determine how long certain buildings are going to be useful. In Hong Kong it is a commonplace that office towers are expected to last not much longer than thirty years before being ripe for replacement by bigger or more up-to-date models. All that embodied energy kissed goodbye! In large parts of London, the idea of wholesale replacement is anathema (about 80 per cent of the borough of Westminster comprises designated conservation areas, for example). Across the world, communities based on coal-mining, or shipbuilding, or car-production, have had to come to terms with sudden geographical shifts in production, as a result of globalisation, which have rendered their economic base obsolete almost overnight. They are no longer 'sustainable', despite having been so for, sometimes, hundreds of years.

What history does tell us, however, is that buildings and developments with certain characteristics are more likely to last than others, all else being equal. By definition they will probably be robustly built; they will be capable of adaptation, and not just in relation to their initial use; they will be reasonably efficient (or easy to make so) from the point of view of energy consumption; often they will be bigger in volume if not area; they will sometimes be over-engineered in relation to their first use. That is why certain schools, churches and even power stations can survive from one century to another, examples of creative adaptation which put to shame the flotsam and jetsam which too often surrounds us.

A good question to ask of any design for a building is: if this were not a house/office/shop/warehouse--could it be capable of being anything else? And if the first use were no longer relevant, would demolition be inevitable? If the answers to these two questions are no and yes respectively, then we can be fairly sure that what is proposed isn't going to last very long; this might be taken into account in the way we think about financing and valuing construction assets. A former president of the Royal Institute of British Architects, Alex Gordon, commissioned a report on these matters in the 1970s, entitled 'Long Life, Loose Fit, Low Energy'. That might serve as a useful motto for those thinking about 'sustainable' buildings from single focus perspectives. In respect of our existing building stock, which produces a frightening proportion of carbon emissions, we can only hope that retrofit makes economic as well as environmental sense.