Life Cycle Assessment Receives Increasing Attention
By Dwight Yochim
According to a recent study, wood's primary advantages from an environmental standpoint are either undervalued or ignored in most green building rating systems, especially in North America. Light House Sustainable Building Centre in Vancouver, Canada, analyzed 18 of the most commonly used rating systems worldwide and how they relate to wood. The study, however, also uncovered evidence that rating systems may be changing as wood's environmental advantages—its carbon benefits in particular—are becoming more recognized and appreciated.
Wood products help reduce greenhouse gases in the atmosphere in two important ways. First, as a tree grows, it absorbs carbon dioxide (CO2) and releases oxygen (O2). The absorbed carbon (C) is incorporated into the tree's wood, leaves, and surrounding soil—and the products made from that tree, including lumber, continue to store much of the carbon indefinitely. In North America, where forests are managed sustainably*, the cycle is ongoing because the harvested area is regenerated with young trees that once again begin absorbing CO2.
Life Cycle Assessment
There is currently no rating system that gives credit for the carbon sequestered in sustainably managed forests or stored in wood products. However, there is a growing trend toward the inclusion of life cycle assessment (LCA), which considers embodied energy and greenhouse gas emissions (among other things), and demonstrates wood's lower impact compared to materials that require large amounts of fossil fuels to manufacture.
With a recognized methodology defined by the International Organization for Standardization (ISO 14040), LCA is a scientifically based approach to comparing products, materials, assemblies, and buildings over the course of their entire lives—from resource extraction through manufacturing, transportation, installation, use, maintenance, and disposal or re-use.
LCA's focus on quantifiable data is in contrast to the prescriptive (or assumption-based) approach that has historically been at the core of green rating systems. Recycled materials are a good example. For years, it was generally accepted that recycled products are always the best choice, and this is reflected in most systems. But what if the choice is wood from a sustainably managed forest, which requires minimal energy to produce and transport and is endlessly renewable, or recycled steel, which requires large amounts of fossil fuel-based energy to produce and transport and isn't renewable? LCA will give you an unbiased assessment of the real environmental impacts—and it's going to favor the wood.
According to the Light House study, only six of the rating systems incorporate LCA to date, despite the fact that embodied energy and other life cycle impacts are critical to the design of environmentally responsible buildings. But the news gets better. In North America, LCA is rewarded in the Green Globes rating system and is part of the new American National Standard based on Green Globes, ANSI/GBI 01-2010: Green Building Protocol for Commercial Buildings. It is also included as a pilot credit in the Leadership in Energy and Environmental Design (LEED) system, though a decision has not been made as to whether it will be incorporated fully into the next major revision. The state of California also recently included LCA as a voluntary measure in its draft Green Building Standards Code.
The Consortium for Research on Renewable Industrial Materials (CORRIM) is one of the leading LCA organizations in North America and has conducted numerous studies on the subject. One study used LCA to compare homes framed with wood vs. steel in Minneapolis and homes framed with wood vs. concrete in Atlanta (the framing types most common in each city). In both cases, the wood-frame homes performed substantially better than their non-wood counterparts. According to the report, the homes framed in steel and concrete required 17 and 16 percent more energy, respectively, from extraction through maintenance than the wood-frame homes. Likewise, the carbon footprint was 26 percent higher for the steel-frame home and 31 percent higher for the concrete-frame home than the homes framed in wood.
According to CORRIM's report, "producing building materials such as steel, cement, and glass requires temperatures of up to 3,500 degrees Fahrenheit," while wood products are made using energy from the sun, and "no more carbon is emitted in the production and whole life cycle of a wood product than is absorbed from the atmosphere while a tree is growing."
|Minneapolis Design||Wood||Steel||Difference||(% Change)|
|Embodied Energy (GJ)||651||764||113||17%|
|Carbon Footprint (CO2 kg)||37,047||46,826||9,779||26%|
|Atlanta Design||Wood||Concrete||Difference||(% Change)|
|Embodied Energy (GJ)||398||461||63||16%|
|Carbon Footprint (CO2 kg)||21,367||28,004||6,637||31%|
The multi-family and non-residential construction markets have a particular opportunity to reduce greenhouse gas emissions through increased wood use. For example, at eight stories of wood over one story of concrete, the Stadthaus building in London is the world's tallest mixed-use wood building. Other than the ground floor, this building is constructed entirely in cross-laminated timber (CLT). Between the emissions avoided by not using steel or concrete and the fact that wood continues to store carbon, the architect, Andrew Waugh, estimates that the savings are equivalent to about 300 tons of carbon—equal to the amount of CO2 emissions from 30,892 gallons of gasoline**. This is the amount the building was projected to emit over 21 years of operation.
New Resources Now Available
The Light House study points out, however, that there are challenges to calculating life cycle impacts—including the fact that LCA data, beyond helping to inform material selection, doesn't hold a lot of value to the building industry, given its lack of inclusion in green building policies or rating systems.
Once again, though, the news is positive, as the LCA tools available to building designers who want to make more informed environmental choices are becoming more widely available and easier to use. For example, the ATHENA EcoCalculator for Assemblies is a free online tool (www.athenasmi.org) that includes ready-to-use LCA data for hundreds of common building assemblies. Information is based on its more robust parent tool, the ATHENA Impact Estimator for Buildings, which can be brought into the equation should a more detailed assessment be desired.
Internationally, policies and regulations encouraging the use of more wood reflect an increased understanding of its environmental benefits. For example:
In the UK, changes to building regulations allowed the construction of the nine-story Stadthaus. Although the developers were impressed by the building's lower cost, it was the projected carbon footprint that convinced local authorities to approve the project.
In France, the government is encouraging building designers to increase the use of timber tenfold by 2020.
In Canada, the British Columbia government has a "Wood First" policy for all new public buildings, and the BC building code has also been changed to allow six-story, multi-family wood buildings, up from the previous four.
It's surprising, given wood's green credentials, that it doesn't play a bigger role in green rating systems. In addition to its carbon benefits, wood is the only major building material that's renewable and sustainable—and the only one with independent certification programs in place to verify that materials have come from a sustainably managed source. Why do other materials have no such level of accountability? Wood also contributes to a building's energy efficiency and indoor air quality. And yet, in the systems studied, an average of just 20 percent of credits relate to wood, and commercial building rating systems actually make it easier to gain points by using other materials.
At the same time, there is growing awareness of how buildings impact carbon emissions in particular—and of wood's ability to play an extremely positive role in this regard. The industry is beginning to take note that, as LCA has demonstrated time and time again, compared to the alternatives, wood buildings produce less greenhouse gases, air pollution, and water pollution, and require less energy across their life cycles. As rating systems continue to evolve, it is reasonable to believe that they will place greater emphasis on the use of wood as a low-carbon alternative to other materials.
Dwight Yochim is the national director of WoodWorks, 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 buildings.
*The United States and Canada have approximately the same amount of forested land now as they did 100 years ago. Source: State of the World's Forests reports, 1997 through 2009, United Nations Food and Agriculture Organization (FAO).
**Source: The Environmental Protection Agency Green House Gas