buildings, perhaps originally built as banks that are now restaurants, perhaps industrial mills that are now loft apartments, or even railway stations that have become art galleries. In each case the collective memory of the shape and character of the city is generally held to be more desirable than the possibility of a new building on the same site, although clearly economic forces apply. It is also possible to speculate that there might well be further new interiors for these structures in future years, but for each alteration the technical and technological expertise of the era will determine the extent to which the building is modified in its building life cycle. Certain structure's interiors remain unaltered over time due to historic preservation, unchanged use, or financial limitations. Nevertheless, most buildings have only three possible long-range internal futures: First, designated significantly important to maintain visually unchanged, only accommodating unseen modern utilities, access, and structural stabilization, and restoration needs. Second, demolished to make way for a new building on the same site, or abandoned, becoming ruins. Finally, redesigned and altered to accommodate new uses. There are many different degrees of alteration – a minor one to enable the building to conform to new legal codes is likely to prolong the first (or indeed later) iteration of interior space, but a major alteration, such as the retention of only the facade, is to all intents and purposes a new building. All possibilities within and between the two extremes are the domain of the interior architect. If the practice of architecture is concerned with the art and science of new building, then the practice of Interior architecture is concerned with the alteration of existing buildings for new uses. Sustainability A critical part in the evolution of interior architecture and design is the central theme of sustainability and consciously thinking of the environment and the materials being sourced- energy use, site selection, water usage, and material selection (Leigh Bacon). This sub-category of Interior Architecture focuses on finding creative and holistic ways of building new or retro fitting existing structures that have little to no impact on the environment. The eco-friendly movement became an important issue around the 1970s when the major energy crisis struck, making individuals aware of their contributions and what can be done to help lighten the impacts (BStone). Sustainability in Interior Architecture has really taken off in the last few decades with