Reconsider could become the fourth R in the mantra Reduce, Reuse, and Recycle.
When designing a new structure, if architects reconsider concrete and steel materials and instead use sustainably harvested wood they reduce the amount of carbon dioxide associated with construction, stated a recent study published in the journal Carbon Management. The wooden structures themselves then become storehouses of carbon.
If builders use more wooden structures, the amount of carbon locked up in construction materials could be quadrupled within the next century, according to the results of the study.
“Every time you see a wood building, it’s a storehouse of carbon from the forest. When you see steel or concrete, you’re seeing the emissions of carbon dioxide that had to go into the atmosphere for those structures to go up,” said Bruce Lippke, professor emeritus of forests resources at the University of Washington, in a press release.
Lippke is lead author of the paper in Carbon Management that pulled together studies on the environmental impact of wood, concrete, steel, and other building materials.
In the paper, Lippke and co-authors from the University of Washington, Mid Sweden University, and the U.S. Forest Service consider the entire life-cycle of the building materials. That means they included things like the gas used to truck logs out of the forest and the energy used to fuel concrete factories. They also considered the amount of carbon dioxide sequestered, or stored, by the building materials.
“There’s really no way to make these comparisons – and get the right answer for carbon mitigation – without doing life cycle analysis,” Lippke said.
The production of steel and concrete needs tremendous amounts of energy and releases greenhouse gases. They cause a one-way flow of carbon dioxide. Lots of the gas gets released; none of it gets sucked back up.
Trees have a two-way flow of carbon dioxide. First, trees breathe in carbon dioxide during their metabolic cycle. They store much of that carbon in their trunks, leaves and roots. That carbon stays locked up in the tree until it burns or rots. Interrupting the flow and using the trees for construction locks up carbon dioxide in floor joists, plywood panels, and other structures.
For example, replacing steel floor joists with engineered wood joists reduced the carbon footprint by almost 10 tons of carbon dioxide for every ton of wood used. In another example, the use of wood flooring instead of concrete slab flooring reduced the carbon footprint by approximately 3.5 tons of carbon dioxide for every ton of wood used.
Lippke and his team also looked at ways to improve the efficiency of sustainable forestry. One recommendation was to harvest trees from the forest once their speed of growth peaks.
“While the carbon in the wood stored in forests is substantial, like any garden, forests have limited capacity to absorb carbon from the atmosphere as they age,” Lippke said. “And there’s always a chance a fire will sweep through a mature forest, immediately releasing the carbon dioxide in the trees back to the atmosphere,” he added.
“However, like harvesting a garden sustainably, we can use the wood grown in our forests for products and biofuels to displace the use of fossil-intensive products and fuels like steel, concrete, coal and oil,” said Lippke.
Lippke stresses they aren’t talking about clear-cutting old-growth forests, which have ecological value beyond the price of the wood they contain. The authors point to Sweden as model for using forests sustainably.
The amount of carbon dioxide stored by forests is tremendous. Another recent study published in Science Express found that the world’s forests store an average of about 2.4 gigatons of carbon per year.
“Our results imply that clearly, forests play a critical role in Earth’s terrestrial carbon balance, and exert considerable control over the evolution of atmospheric carbon dioxide,” said A. David McGuire, co-author Science Express study and professor of ecology at the University of Alaska Fairbanks Institute of Arctic Biology, in a press release.
IMAGE 1: A construction worker in New York City carries a wooden plank on the current top floor of 1 World Trade Center as the Empire State building and skyline of Midtown Manhattan loom behind him. Earlier this year the tower reached more than 50 floors, roughly halfway to its final height. Workers are adding nearly a floor a week to the building which will be the tallest in New York when it is completed in 2013. (Photo by Chris Hondros/Getty Images)
IMAGE 2: A Northwest state or private forest, harvested regularly for 100 years, helps keep carbon dioxide out of the atmosphere year after year by storing carbon in long-term wood products (blue) and by substituting wood for fossil-fuel-intensive products like steel and cement, thus avoids carbon dioxide emissions during their manufacture (orange). The chart also shows carbon that remains in a sustainably managed and harvested forest (green and black); and an “emissions” line (cranberry) at the bottom, representing the energy to harvest and process wood, which is partly counterbalanced by the “mill residual” line (yellow) that represents mill wastes burned for energy in place of fossil fuels. (Credit: E Oneil/University of Washington)
IMAGE 3: New, Second Growth Forest of Lodgepole Pine (Pinus Contorta) in the Foothills of Rocky Mountains Close to Hinton, Alberta, Canada. (Credit: Stan Navratil/All Canada Photos/Corbis)