The off-the-shelf price of a building component represents only the manufacturing and transportation costs, not the social or environmental costs. A material is only considered a sustainable resource if it can be grown at a rate that meets or exceeds the rate of human consumption. The embodied energy of a material refers to the total energy required to produce that material, including collection of raw materials. When low-embodied-energy natural materials are incorporated into building products, the products become more sustainable. Materials that are easily installed with common tools also reduce overall waste from trimming and fitting. The key consideration is the material´s appropriateness for the intended function.
A cradle to grave analysis of building products from the gathering of raw materials to their ultimate disposal, provides a better understanding of the long term costs of the materials. The material´s life cycle can be organized into three phases: pre building, building and post-building.
- The Pre-Building Phase describes the production and delivery process of a material up to, but not including, the point of installation.
- The Building Phase refers to a building material´s useful life. This phase begins at the point of the material´s assembly into a structure, includes the maintenance and repair of the material, and extends throughout the life of the material within or as a part of the building.
- The Post Building Phase refers to the building materials when their usefulness in a building has been expired. At this point, a material may be used in its entirety, have its components recycled back into other products or be discarded.
Limestone is perhaps the most prevalent building material obtained through mining. It is used as a cladding material and plays an important role in the production of a wide range of building products. Limestone which is primarily calcium carbonate is coverted into quicklime or calcium oxide through prolonged exposure to high heat. The quicklime is then crushed and screened and before it can be used in plaster or cement, it must be mixed with water and then dried.
Steel requires the mining of iron ore, limestone, magnesium and other trace elements. Steel is produced by controlling the amount of carbon through smelting. Limestone and magnesium are added to remove oxygen and make the steel stronger. A maximum carbon content of 2% is desired.
Aluminum should be used only where its light weight and anti-corrosion characteristics cannot be matched by another material. It can be recycled for 10-20% of the energy required to transform raw ore into finished goods. Aluminum, derived from bauxite ore, requires a large amount of raw material to produce a small amount of final product. Bauxite is generally strip mined in tropical rainforests, a process that requires removing vegetation and top soil from large areas of land.
Jute is a renewable crop material, with very little energy required in the growth and manufacturing process. It bio degrades upon disposal and can be recycled. The material has a higher density and longer life than comparable synthetics.
The building industry is highly dependent on materials derived from petroleum and natural gas. These are used in a wide range of products including plastics, adhesives for plywood, particleboard, laminated countertops, insulation, carpeting and paints.
