There is a great deal of misrepresentation on the web about the environmental and climate-related benefits of mass timber use for high-rise buildings. This backgrounder helps to set the record straight. Many of these articles fail to address serious risk factors associated with such structures or misrepresent their true environmental impacts.

They often extoll the supposed virtues of tall timber buildings, noting that structures built using cross-laminated timber are an “environmentally sustainable alternative to concrete and steel, which generate large quantities of greenhouse gases in their production.”

For those unfamiliar with the term, cross-laminated timber is a form of engineered wood where pieces of wood are glued together to create a panel that is stronger than an ordinary wooden beam. This is a relatively new building product, but it is gaining popularity in North America in large part due to intense lobbying efforts by proponents in the architectural community and in the wood products sector.

The use of mass timber for tall buildings is touted for its ability to mitigate climate change because it removes carbon from the atmosphere, a fundamentally false assertion.

A recent paper commissioned by Sierra Club California and authored by Global Efficiency Intelligence paints an inaccurate and intentionally misleading picture of the California cement industry. The paper’s sensational claims that the California cement industry is “failing the climate challenge” and is “substantially dirtier” than cement industries in other nations, including China, are absurd and incompatible with the facts, including many of those presented in the paper itself.

PNBRC – January 2, 2019 – It’s a process known to many in the construction sector, but not well understood. It’s called ‘carbonation’ and means that concrete and mortar exposed to the air absorb carbon dioxide (CO2) from the atmosphere. Determining how much CO2 is absorbed per unit volume of exposed concrete has been difficult, in part because concrete varies significantly depending on how and where it is used. Also, although many measurement approaches have been tried, a global consensus on how to measure carbonation remains elusive.

PNBRC, Americans recently received a sobering reminder that the world has changed forever. That fact has far-reaching implications for the industries that build our cities and towns, and the systems that sustain our way of life. The National Climate Assessment report sums it up clearly. “The nation’s economy, security, and culture all depend on the resilience of urban infrastructure systems.” The report explores many dimensions of the nation’s economy, society and the natural environment affected by climate change and clarifies that adaptation to new and harsher realities is unavoidable.

It’s a mantra repeated so often that it is accepted on faith as being true: wood sequesters carbon, and concrete production emits carbon. As in most things, the truth is often lost in translation. It is true, living trees sequester carbon. A long-lived, wood-based building product continues to sequester carbon, but only a small fraction of the carbon originally sequestered in a living tree. So too is the production of cement a carbon-intensive process that emits carbon into the atmosphere.

Reducing Greenhouse Gas (GHG) emissions associated with the built environment is now a major issue in efforts to alleviate the impacts of climate change. Promoting the construction of more energy-efficient and climate-resilient buildings has become a key public policy focus in many jurisdictions.

Slideshow PDF from a presentation delivered on February 16, 2018 by the US Resiliency Council.

While living trees store a great deal of carbon, the biggest carbon pool in the forest is below ground in the soils, accounting for nearly 50% of total ecosystem carbon. The merchantable portion of trees accounts for only about 10%.