By Duane Schantz
For many building designers, the choice of wood as a structural material is driven by price. Wood is cost effective—in terms of materials, speed of construction and design flexibility—while meeting code requirements for safety and performance in a wide range of building types. However, as green building has evolved beyond its initial emphasis on operational energy efficiency, it has become increasingly clear that, in addition to cost, there are compelling environmental reasons to choose wood.
Lighter Carbon Footprint
As trees grow, they absorb carbon dioxide; they then release the oxygen and incorporate the carbon into their wood, leaves or needles, roots and surrounding soil. When trees are harvested and manufactured into products, much of this carbon remains stored in the wood, while the regenerating forest once again begins absorbing carbon dioxide. In the case of wood buildings, the carbon is stored for the life of the structure—or longer if the wood is reclaimed and used in other buildings. Using wood instead of materials that require large amounts of fossil fuels to manufacture also avoids greenhouse gases that would have otherwise been emitted during production.
Reduced Life Cycle Impacts
As illustrated in the latest proposals for LEED v4, there is a growing trend toward the use of life cycle assessment as an objective way to evaluate materials over the course of their entire lives, from resource extraction through end-of-life disposal or recycling. When viewed over its life cycle, an inherent advantage of wood is that it grows naturally and requires very little fossil-based energy to manufacture into products. Wood buildings are responsible for less greenhouse gas emissions, air pollution and water pollution, and require less energy across their life cycles than buildings made from other materials.
Adaptability and Reuse
Although there are examples of wood buildings that remain structurally sound after hundreds of years, North American buildings often have a service life of less than 50 years because of changing needs or increasing land values as opposed to performance issues. When one considers the embodied energy in these structures and the implications of material disposal, it’s easy to understand why one of the tenets of sustainable design is that buildings should last 100 years or more. However, the foremost requirement is in fact the use of materials such as wood that can adapt to changing needs, either through renovation or deconstruction and reuse.
Evidence suggests that the use of natural materials can contribute to an individual’s sense of well-being, productivity and even health. For example, a study at the University of British Columbia and FPInnovations found that the presence of visual wood surfaces in a room lowered activation of the sympathetic nervous system (SNS). The SNS is responsible for physiological stress responses in the human body such as increased blood pressure and heart rate while inhibiting the system responsible for digestion, recovery and repair functions.
Renewable and Sustainable
Wood is the only major building material that grows naturally and is renewable. In North America, forest management is strongly regulated to ensure that forests are legally harvested and managed for long-term sustainability. According to the 2007 State of America’s Forests report, “less than 2% of the standing tree inventory is harvested each year while net tree growth is close to 3%.” The USDA Forest Service’s 2010 National Report on Sustainable Forests 2010 speaks to the continuation of this trend, confirming that “the area of timber land in the United States has been very stable during the past 50 years.”
Wood is also the only building material with third-party certification programs in place to verify that products originate from a sustainably managed resource. Sustainable forest certification allows forest companies to demonstrate the effectiveness of their practices by having them independently assessed against a stringent standard that considers environmental, economic and social values. North America has more certified forests than any other part of the world.
The push for more sustainable buildings, combined with advances in wood technology and building systems, is generating interest in wood as the “material of the future.” There is even a trend toward taller wood buildings—including high-rises, thanks to the strength and dimensional stability of engineered products such as cross laminated timber. Right now, the tallest modern wood building is eight stories of wood over one story of concrete, but a 10-story wood building recently broke ground in Australia. Given a recent study suggesting that 30-story wood buildings are possible, there is every reason to believe that wood use in the future will be growing.
Duane Schantz is regional director of WoodWorks in the central US. WoodWorks is an initiative of the Wood Products Council, established to provide free education and technical support to design and building professionals using wood in non-residential and multi-family buildings. Email firstname.lastname@example.org or visit www.woodworks.org. See All Tags