To truly consider the use of green materials it is necessary to think about where materials come from, how they are used, and where they go when their useful life is over. Materials come from the earth or the biosphere. They need to be mined or harvested, transported to a manufacturing location where they are produced, and then transported to a distribution point before being transported to the point of use. All of these processes require energy use and have a waste stream associated with them. At the point of use, the product needs to be installed, which also requires energy and produces a waste stream. During use the product will need maintenance to extend its life, and at the end of its useable life span the product will become part of the waste stream unless it is recyclable (Freed 2008, 76–80). It would be ideal if perfect information about product lifecycle was available for all products. This is generally not the case but the situation is improving.
One way to approach the material choice situation is to consider the following concerns. Can a reclaimed material be used? An example would be flooring materials reclaimed from another building. Is there recycled content in the material? An example would be tiles made with recycled glass. Recycled content can come from the waste stream of a manufacturing process or from recycled consumer products. Is the material sustainably harvested? The best example of this is wood from forests taken in a manner that maintains the forest for future production. Is the material rapidly renewable? A good example of this is bamboo, which is a rapidly growing grass. Is the material durable? A longer usable life reduces the waste stream. Is the material recyclable? Materials are easier to recycle if they are one material not a composite of multiple materials. It is also better if the material can be recycled as the same material. As an example, steel can be recycled as steel. Is the material biodegradable? Most materials made from ecosystem entities, wood, paper, bamboo, will biodegrade if they end up in the waste stream in a landfill (Freed 2008, 84–86). Another consideration is low outgasing of volatile organic compounds (VOCs). New car smell or new carpet smell is an example of VOCs coming off the new material. Many products can now be purchased with very low VOC outgasing. Finally there is the concept that smaller is better. Living in an appropriately sized house for one’s needs saves materials and energy (Bradley 2010, 10–14).
Houses in the U.S. are mostly constructed with a wood frame. The wood should be specified as certified by the Forest Stewardship Council (FSC), which ensures that it was produced in an ecofriendly way. It is important to seal all the openings left between the rough frame openings and the finished doors and windows. It is also important to seal the top and bottom plates. Insulation can be placed between the vertical wall studs, and an insulation board sheathing can be applied to the outside underneath the exterior finish material to minimize thermal bridging through the wood framing. Light gauge steel can be used to frame a house. The construction process is very similar to wood framing with sheet metal screws replacing nails. Steel doesn’t require cutting down trees and it is recyclable as steel. Steel’s main drawback is that it conducts heat very well, so it is very important to sheath the building with insulation boards to reduce thermal bridging.