Tall Mass Timber Buildings and Climate Change

The following is an excerpt from the 2012 report, “THE CASE FOR Tall Wood BUILDINGS.” A feasibility study from the Canadian Wood Council illustrates how massive timber products and systems can provide viable and sustainable alternatives for the construction of 10 to 30-story buildings. Canadian Wood Council

As our understanding of anthropogenic climate change evolves we have come to understand that greenhouse gas emissions and in particular the dominant greenhouse gas of carbon dioxide has a direct impact on the greenhouse effect that is impacting overall global warming. The two ways the world can address climate change will be to: 1. Reduce carbon and other greenhouse gas emissions 2. Find ways to store carbon and other greenhouse gases. Wood can contribute to both of these critical tasks.

Emissions

The building industry represents approximately a third of greenhouse gas emissions worldwide. This is primarily due to fossil fuel consumption in building operations such as heating, cooling, and lighting and, to a lesser extent, the embodied energy consumption in materials and building construction and maintenance. Fundamentally the large carbon footprint of buildings must be reduced for the world to address climate change.

The effects of embodied energy in structures are significant, and they will command our attention more as buildings become increasingly energy efficient (thereby changing the operating versus embodied energy ratio). Numerous publications have highlighted the lighter embodied footprint of wood over other systems. For example, the 2004 Canadian Wood Council document, Energy and the Environment in Residential Construction, presented operating and embodied energy assessment results, based on life cycle assessment. These results were summarized into six categories: primary energy, greenhouse gas emissions, air pollution, water pollution, solid waste production and resource use. This study included assessment of the following building life cycle stages: product manufacturing, on-site construction, maintenance and replacement, and building end-of-life (demolition and final disposition of materials). While a study of single family housing at a much smaller scale to the Mass Timber typology proposed, the results are worth discussing here as base statistics:

“The steel and concrete designs embody 26% and 57% more energy relative to the wood design, emit 34% and 81% more greenhouse gases, release 24% and 47% more pollutants into the air, discharge 400% and 350% more water pollution, produce 8% and 23% more solid waste, and use 11% and 81% more resources (from a weighted resource use perspective).” (Canadian Wood Council 2004)

Carbon Sequestration

A growing forest removes carbon dioxide from the atmosphere and stores this carbon in vegetation and soil. Some of this carbon is released back into the atmosphere through decaying trees, forest fires, insect outbreaks, and forest management practices. A forest, if managed properly, is a large carbon reservoir. When a tree is manufactured into a lumber product, the carbon accumulated in the tree is stored within that product for its complete life cycle. Wood stores somewhere between 1 to 1.6 tonnes of carbon dioxide per cubic meter of wood depending on species, harvesting methods and secondary manufacturing methods. (FPInnovations 2011) A typical North American timber-frame home captures about 28 tonnes of carbon dioxide, the equivalent of seven years of driving a mid-size car or about 12,500 liters of gasoline. (BREAAM 2010, Naturally wood 2010) The success of carbon sequestration relies on sustainable forestry practices as well as strategies for management of wood products at a building’s end of life. If Mass Timber building systems were to become common in the building industry, the amount of carbon stored in buildings would significantly increase. Until recently there was simply no need to innovate a new structural solution for mid-rise and tall buildings. The impacts of climate change raise the need to look to better solutions than steel and concrete. Wood will be an important part of the solution. This is not to say that concrete and steel will be eliminated from construction. Indeed hybrid solutions of wood, steel and concrete will be necessary. Each has a purpose but in the end increasing wood use in large buildings is a viable approach to carbon-neutral building structures.

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