Can Wood Help Us Sequester Carbon Emissions?
Materials developed and used (steel, iron, cement) in the construction industry emit roughly 11% of global greenhouse gas emissions. Another 20 or so come from building operations — the energy required to produce, transport and utilize the materials on site. Is it possible that a far more sustainable solution exists? One that is not only renewable but also sequesters carbon in the process?
Cross Laminated Timber is a building material made of soft woods — primarily spruce, fir and pine — that when bonded together in alternating directions are found to be more flame resistant, structurally more stable and emit less Green House Gases than steel. In fact, when comparing wood and steel, steel production emits about 21x as much carbon as an equal weight of framing lumber. CLT is incredibly strong, weighing just one fifth of reinforced concrete, and requires less water, energy and fossil fuels to produce than that of concrete and steel. A team at the University of Washington attempted a full, soup-to-nuts lifecycle analysis comparing a “hybrid, mid-rise, cross-laminated timber (CLT) commercial building” to “a reinforced concrete building with similar functional characteristics.” After tallying up all the many factors, they concluded that the CLT building represented a “26.5% reduction in global warming potential.”
Yet another benefit is the average size of a CLT board is approximately 10’0” x 40’0”. This size capability allows for the pre-manufacturing of custom sizes off site, minimizing waste and eliminating added labor time on site — both of which arguably save money. Technically, if given accurate and detailed drawings, factories can fabricate walls with proper cut outs for doors and windows, eliminating on site waste all together. According to the softwood lumber industry, “Mass timber buildings are roughly 25% faster to construct than concrete buildings and require 90% less construction traffic.”
Despite what appear to be obvious benefits, there are those who feel the logging industry is not the answer. Poorly managed forests continue to decimate the natural biomes, and are in large part the cause of wild fires on the West Coast of the US. Truthfully, we have neither shown we are capable nor prepared to take the necessary steps to do manage them sustainably. A 2014 study in the Journal of Sustainable Forestry looked into the question of the carbon effects of large-scale substitution of wood products for alternatives and concluded: “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 biggest drop in CO2 emissions came, it said, from “avoiding the excess [fossil fuel] energy used to make steel and concrete structures.”
While both sides argue in favor of their research, one thing is certain, the housing shortage isn’t going away. In 2050 we’re projected to have 2.3 billion new urban dwellers. The ultimate goal needs to be in collecting enough data to safely say whether or not CLT’s are sequestering and off-setting as much as the initial tests assume. Until then, those forests who abide by the Forest Stewardship Council should and will continue to provide wood to those brave enough to push forward with this new structure type.
