The process of converting old an building or structure to a new use different from its original function is known as 'adaptive reuse'.  Examples include adapting an abandoned factory for use as a condominium, or converting a church into a restaurant or library.  The key consideration in a building reuse project is maintaining as much of the existing structure as possible, while incorporating new materials and strategies to adapt the building to its new purpose (Evergreen).  This type of reuse is eligible for a credit under the LEED Green Building Rating System for New Construction. 

Preservation and restoration of existing structures has several important environmental advantages.  Traditional building construction puts a substantial strain on natural resources, consuming approximately 40% of materials nationally every year.  Further, building demolition and construction yields approximately 25% of landfill waste generated annually in the U.S.  Adaptive reuse has the potential to significantly reduce these figures (1). 

Adaptive reuse is also offers key cultural and economic benefits.  Older buildings offer a sense of culture, history and place.  While an older building may no longer be required for its original function, its cultural and historical significance can still be preserved for future generations.  This became an important consideration for the city of Toronto during the 1990s, when an economic recession resulted in the vacancy of numerous office buildings in the downtown core.  Rather than allowing these buildings to be demolished and replaced with parking lots capable of generating substantial revenue, the City chose to convert them into residential units, thereby preserving these historically significant buildings, revitalizing the downtown area, and the generating $1.6 million in housing taxes (2).

Sources:
¹ Vani Bahl, 2005.  Ethics of Adaptive Reuse.  Architecture Week No. 240.
² Canada's Historic Places Initiative, 2007.  Heritage Conservation Brief: Urban Revitalization.