46 16 Match Use Span What if we made materials do more by using them longer? In Making the Modern World , Vaclav Smil proposed that “design for durability is perhaps the most obvious option.” 1 Durability, however, would require a reformulation of the building economy, which currently makes buildings obsolescent far before buildings and infrastructures reach the end of their use cycles. It may be useful to think about matching the durability of materials to the projected use span of a building. Will a building be in use for 200 years, forty years, twenty years, or two months? Do the amount of materials used and their expected service life make sense? A building’s projected use span should affect the materials it uses and how they are assembled. In some cases, projects can and should be designed for longevity and use durable materials that also ensure the maintenance needed to keep them operational can be carried out. It is also important to understand how user needs will change over time and whether these needs will generate new or different demands. For some functions, adaptability can be built- in, allowing a structure to perform beyond the lifespan of its given use. For others, a project can be built with the intention of growth so that additional space and material is only used if and when it is called for and when the inhabitants are able to pay for the expansion. 1 Vaclav Smil, Making the Modern World: Materials and Dematerialization (Chichester, UK: John Wiley, 2014).