LCA shows preference for wood over concrete in construction

The cement industry has put lots of effort into trying to show that concrete manufacturing results in less CO2 per unit than almost all other construction materials, making it the sustainable construction material of choice. A new study by researchers in the School of Forestry and Environmental Studies at Yale University and the College of the Environment at the University of Washington in Seattle and published in the Journal of Sustainable Forestry finds that wood is a more sustainable construction material by a comfortable margin. GallonDaily suggests that this is by no means the last to be heard on this topic though the new research has a high degree of credibility on the topic.

In brief, the research identifies the significant value from a climate change perspective in using wood for durable (long life) products, to which construction is a significant contributor. The research identifies several pathways through which wood can potentially avoid emitting CO2 from FF (fossil fuels) to the atmosphere:

  • forest pathway (FP): sequestering CO2 in the standing forest;
  • storage pathway (SP): storing wood in the products so it does not rot or burn and produce CO2;
  • energy pathway (EP): displacing CO2 produced by burning FF with CO2 produced by burning energy;
  • avoidance pathway (AP): substituting wood for steel, concrete, and other products that use more energy in their manufacture, thus consuming less FF and emitting less CO2;
  • landfill pathway (LP): storing waste wood in landfills where it either does not decompose or decomposes and emits methane and other greenhouse gases.

In the case of construction, findings of the research include:

  • Avoided emissions (using wood in place of steel and concrete) contributes the most to CO2 and FF savings compared to the product and wood energy contributions. Burning parts of the harvested logs that are not used for products creates an additional CO2 and FF savings.
  • Globally, both enough extra wood can be harvested sustainably and enough infrastructure of buildings and bridges needs to be built to reduce annual CO2 emissions by 14 to 31% and FF consumption by 12 to 19% if part of this infrastructure were made of wood.
  • The greatest CO2 and FF savings from wood use are by avoiding the excess FF energy used to make steel and concrete structures (avoidance pathway). Wood products are more efficient than wood energy for CO2 and FF savings; however, up to 37 % of the world’s annual CO2 emissions and 27% of the FF use could be saved if all wood growth not used in construction were used for energy.
  • If catastrophic fires do not occur and forest regrowth after harvest is not considered, saving CO2 by not harvesting the forest growth is slightly more efficient than harvesting just for wood energy—but generally less efficient than harvesting for construction products. This efficiency of CO2 storage in unharvested forests also assumes none of the wood blows over or otherwise rots in the forest—an unrealistic assumption in most of the world.
  • When regrowth after harvest is considered, even wood harvested just for energy (energy pathway) can be more efficient for COsequestration than not harvesting the forest and using FF for energy.
  • It may be appropriate to adjust carbon sequestration incentives and building codes to reflect the value of wood use in saving COand FF. For example, REDD (Reducing Emissions from Deforestation and Forest Degradation, a mechanism under negotiation by the United Nations Framework Convention on Climate Change) and other incentives that seek to store CO2 in forests appear to be counterproductive if curtailing harvest meant steel and concrete were used in construction instead, with concomitant high rates of CO2 emissions and FF consumption.
The research clearly shows that wood is such a complex material that simplistic conclusions, such as ‘we need to save trees’ or ‘cutting of forests is bad’, may not be appropriate when viewed from a scientific perspective. Wood is a great way to sequester CO2 and long term storage of wood can be an effective way to sequester large quantities of carbon dioxide. Burning of wood or release of carbon dioxide from quick decay of short lived wood products, such as paper, may have a negative impact compared to fossil fuel based products but a more complete LCA is necessary to reach definitive conclusions.
 

 

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