The choice of building materials is as important as the site design or choice of construction methods. Designers have significant influence over the materials used through the specifications they make in design and planning. Many designersare not aware of the implications beyond cost and specific performance criteria of choosing one material over another. To be sure, site designers have fewer materials to choose from than do architects, but their awareness of the characteristics of site materials is just as important. As a matter of practice, materials should be selected in part because of their durability. The process of manufacturing materials is energy and material intensive, and durable materials usually require less maintenance over a longer service life. Materials that require less maintenance or whose maintenance has a lower environmental impact are also preferred. Materials that are heavily processed or manufactured have a higher embodied energy—that is, there are greater energy inputs required to manufacture the product. Locally produced products require less transportation energy and produce less pollution. Designers should seek a durable, locally produced, low-maintenance product with a low embodied energy. For example, local hardwoods are preferable to tropical woods, and local stone to imported stone.
The best choice for materials may be recycled materials. Using recycled materials reduces solid waste, reduces the energy needed for manufacturing, and reduces the impact on natural resources. Using fly ash in concrete, recycled plastic in site furniture, and ground tires in pavement are all possible ways of incorporating recycled materials in site work. Use of materials, such as pressuretreated lumber that contain toxins should be avoided by specifying alternatives such as recycled plastic lumber.
Determining whether a building material is green involves the consideration of the entire life cycle of the material: the manufacture of the material, the impacts of its use, its distribution and service life, and finally its disposal. Every stage of the material’s life involves energy use and environmental impacts. There are a variety of different life cycle assessment techniques, including the Building for Economic and Environmental Sustainability (BEES) model developed by the National Institute of Standards and Technology (NIST) with support from the Environmental Protection Agency (EPA) and the Department of Housing and Urban Development (HUD). The BEES model considers 10 potential environmental impacts of building materials:
1. Global warming
4. Natural resource depletion
5. Indoor air quality
6. Solid waste
8. Ecological toxicity
9. Human toxicity
10. Ozone depletion
Each of the calculations involves converting impacts to a known and given reference point provided in the BEES documentation. The program then calculates the environmental loading of the product to allow designers to compare alternative materials. BEES software is available from the National Institute of Standards and Technology (NIST) along with a manual that describes the use of the software, explains the algorithms, and provides examples of material and product data already evaluated using BEES. The American Society for Testing and Materials (ASTM) has developed the Standard Guide for Environmental Life Cycle Assessment of Building Materials/Products, E 1991–98. The standard guide describes a four-step process for conducting a life cycle assessment (LCA): a definition of goals, an analysis of inventory, an impact assessment, and an interpretation of findings. The LCA is broad based and comprehensive in scope and includes considerations of embodied energy, raw materials acquisition, and environmental impacts from cradle to grave, as well as performance considerations. Other more approachable methods have also emerged. There are public and private green building initiatives throughout the world. Many of these organizations have established standards or thresholds that products must meet to be listed as green.
Since site work involves fewer materials as a rule than building construction, most of the work has been done on materials used in buildings. Still materials used in site development are not without their environmental “signature” as it were. The general elements of green building materials are summarized in Table 1.7.
TABLE 1.7 Green Building Material Requirements
1. Products made from recycled or salvaged materials
2. Products made from wood harvested from Forest Stewardship Council Certified forests
3. Products made from materials that are renewable in the short term (10 years or less)
4. Products that do not contain toxics or environmentally damaging materials
5. Products (or methods) that reduce the material volume required
6. Products that reduce environmental impacts during the manufacturing process, construction,
renovation or demolition
7. Products (or methods) that are energy efficient or that reduce the heating and cooling loads
on a building
8. Products that are reusable or recyclable
9. Local products rather than products from far away