By Joseph Pomponi, Email: jpp5251@vt.edu
Sustainability in building materials is a concept of using more biodegradable materials for construction projects. Sustainable development is described as enhancing quality of life and allowing people to live in a healthy environment and improve conditions for present and future generations (Ortiz, Castells, and Sonnemann 2009). “The improving social, economic and environmental indicators of sustainable development are drawing attention to the construction industry, which is a globally emerging sector, and a highly active industry in both developed and developing countries” (Ortiz, Castells, and Sonnemann 2009). To illustrate these concepts, the life cycle assessment helps evaluate the environmental load of products and processes. “The life cycle inventory (LCI) involves collecting data for each unit process regarding all relevant inputs and outputs of energy and mass flow, as well as data on emissions to air, water and land. This phase includes calculating both the material and the energy input and output of a building system. The life cycle impact assessment (LCIA) phase evaluates potential environmental impacts and estimates the resources used in the modeled system” (Ortiz, Castells, and Sonnemann 2009). Essentially, these analyses help with the life cycles of certain building materials and how these materials can impact the environment during their life in use and after they are able to be used for their purpose. The idea is to promote the use of more sustainable building materials such as wood, and engineered wood products as opposed to products such as steel and titanium. The wood materials tend to be more friendly to the environment, and helps towards reducing energy consumption. Carbon emissions are important to consider when deciding the sustainability of a building materials, as well as the life cycle of the certain material.
“Wood has many positive characteristics, including low embodied energy, low carbon impact, and sustainability. These characteristics are important because in the United States, slightly more than half of the wood harvested in the forest is used in construction” (Falk 2009). There is a difference in energy consumption when mining for materials needed to make products such as steel and other metals. Wood is seen to be easier to harvest and takes less energy to construct projects. The energy consumed in the construction of a steel-framed house in Minneapolis was around 17 percent greater than for a wood-framed house (Lippke et al. 2004). Below is a table discussing the designs of houses in Atlanta and Minneapolis and the difference of energy consumption between steel-framed and wooden-framed.
Table 1. Environmental Performance Indices for Above-Grade Wall Designs in Residential Construction (Lippke et al. 2004)
| Wood frame | Steel frame | Difference | Change (%)b | |
| Minneapolis Design | ||||
| Embodied design (GJ) | 250 | 296 | 46 | +18 |
| Global warming potential (CO2 kg) | 13,009 | 17,262 | 4,253 | +33 |
| Air emission index (index scale) | 3,820 | 4,222 | 402 | +11 |
| Water emission index (index scale) | 3 | 29 | 26 | +867 |
| Solid waste (total kg) | 3,496 | 3,181 | -315 | -0.9 |
| Atlanta Design | ||||
| Embodied design (GJ) | 168 | 231 | 63 | +38 |
| Global warming potential (CO2 kg) | 8,345 | 14,982 | 6,637 | +80 |
| Air emission index (index scale) | 2,313 | 3,373 | 1,060 | +46 |
| Water emission index (index scale) | 2 | 2 | 0 | 0 |
| Solid waste (total kg) | 2,325 | 6,152 | 3,827 | +164 |
b % change = [(Steel frame – Wood frame)/(Wood frame)] X 100
Carbon plays a huge role in the earth’s ecosystem and in climate change as well. It is viewed as a negative impact on ecosystem sustainability. Forests play a huge role in balancing the Earth’s carbon cycle. Essentially, forests and other vegetation removes the carbon in the atmosphere through the carbon cycle. The process converts carbon dioxide and water into sugars for needed for the tree growth as well as releasing oxygen into the atmosphere. Approximately 26 billion metric tonnes of carbon is sequestered within standing trees, forest litter, and other woody debris in domestic forests and another 28.7 billion tonnes in forest soils (Birdsey and Lewis 2002). Different materials have different carbon emissions, table two shows carbon emissions of common building materials and materials used in construction.
Table 2. Net Carbon Emissions in Producing a Tonne of Various Materials (Falk 2009)
| Material | Net carbon emissions (kg C/t)a,b | Near-term net carbon emissions including carbon storage within material (kg C/t)c,d |
| Framing material | 33 | -457 |
| Medium-density fiberboard (virgin fiber) | 60 | -382 |
| Brick | 88 | 88 |
| Glass | 154 | 154 |
| Recycled steel (100% from scrap) | 220 | 330 |
| Concrete | 265 | 265 |
| Concretee | 291 | 291 |
| Recycled aluminum (100% recycled content) | 309 | 309 |
| Steel (virgin) | 694 | 694 |
| Plastic | 2,502 | 2,502 |
| Aluminum (virgin) | 4,532 | 4,532 |
a Values are based on life-cycle assessment and include gathering and processing of raw materials, primary and secondary processing, and transportation. b Source: EPA 2006. c From Bowyer et al. 2008; a carbon content of 49% is assumed for wood. d The carbon stored within wood will eventually be emitted back to the atmosphere at the end of the useful life of the wood product. e Derived based on EPA value for concrete and consideration of additional steps involved in making blocks.
From the table it can be seen that the carbon emissions of traditional building materials such as concrete, steel, and aluminum are greater than wooden framing material and medium-density fiberboard. The wooden materials also have a negative value of the near-term carbon emissions meaning the materials are more beneficial to the environment in terms of carbon emissions. Wood products have a low level of embodied energy compared to other building products and because wood is one-half carbon by weight, wood products can be carbon negative (Bowyer et al. 2008). Wooden building materials have a place for use in the construction industry. Wood materials in the end help with issues such as “green-building” and being more sustainable. These materials also have lower carbon emissions and in turn can potentially help reduce energy consumption of a building. Of course, fossil fuel-based products and metals are not renewable whereas in the forest resource is renewable. It is important for the wood products and forestry industry to have proper management of the forests to have sustainable harvesting for materials needed in the construction industry.
Works Cited
- Birdsey, R. and G. Lewis. 2002. Carbon in U.S. Forests and Wood Products, 1987–1997: State by State Estimates. USDA Forest Service, General Technical Report GTR-NE-310
- Bowyer, J., S. Bratkovich, A. Lindberg, and K. Fernholz. 2008. Wood Products and Carbon Protocols: Carbon Storage and Low Energy Intensity Should be Considered. Report of the Dovetail Partners, Inc. www.dovetailinc.org.
- Falk, B. 2009. Wood as a sustainable building material. For. Prod. J., 59(9), 6–12.
- Lippke, B., J. Wilson, J. Perez-Garcia, J. Bowyer, and J. Meil. 2004. CORRIM: Life-Cycle Environmental Performance of Renewable Building Materials. Forest Prod. J. 54(6): 8-19
- Ortiz, O., Castells, F., Sonnemann, G., 2009a. Sustainability in the construction industry: a review of recent developments based on LCA. Construction and Building Materials 23 (1), 28–39