When choosing materials several factors have to be considered, and it is unlikely that absolute rules can be given for all situations. The first question is how environmental impact should be assessed. This can be thought of as factors determined by the material’s inherent qualities and as factors affected by the way materials are incorporated into a design.

Factors determined by a material’s qualities are, for example:

• energy required to produce the material;
• CO2 emissions resulting from the material’s manufacture;
• impact on the local environment resulting from the extraction of the material (e.g. quarry pit, wood taken from a forest, oil spills from an oil well, etc.);
• toxicity of the material;
• transportation of the material during its manufacture and delivery to site;
• degree of pollution resulting from the material at the end of its useful life.

Factors affected by material choice and design decisions include:

• location and detailing of an architectural element;
• maintenance required and the materials necessary for that maintenance;
• contribution that the material makes to reducing the building’s environmental impact (e.g., insulation);
• flexibility of a design to accommodate changing uses over time;
• lifetime of the material and its potential for reuse if the building is demolished.