The greenness of a material is a complex issue. The problem can be broken down into a series of questions but even those questions can create questions. As an example consider the question. Is it hazardous? The question is when it might be hazardous. Is it hazardous installed, or during installation, or during mining, manufacturing, or transportation, and was there a hazardous substance used or discarded into the environment? Using local materials reduces transportation energy use. What happens if most of the material is local but some of it is not? Using recycled materials is a good thing, but what if the recycling facility is far away, or a toxic glue is used to bind the recycled material together. The question of energy intensity is simple, but what energy source is used? Coal puts far more carbon dioxide into the air than natural gas. After use, is a product capable of being recycled? There are levels of recycling. Steel can be recycled as steel. Concrete cannot be recycled as concrete. Concrete gets down-cycled to rubble. Green is a fuzzy term, but that does not mean that we should not push the concept (Spiegel and Meadows 2006, 33).