Embodied Carbon Part 1

Written By George Kontaroudis

There are many numbers, percentages and figures associated with climate change. In his new book, “How to avoid a climate disaster”, Bill Gates begins with perhaps the most important of all: 51 billion and zero. Fifty-one billion is the amount of metric tons of greenhouse gas that humanity currently emits each year and zero is the amount we should be emitting by 2050 in order to avoid the worst effects of climate change. This will require a whole-of-humanity effort, but my focus is on the role of architecture and construction.

Buildings currently contribute by 39% to global CO2 emissions. Out of that, 28% is attributed to building operations and 11% to building materials and construction including new construction and renovations. For a new building 75% of its emissions for a lifespan of 60 years will come from embodied carbon. Embodied carbon is the sum of all the energy required to produce a product extrapolated to tons of CO2 released in the atmosphere. That energy includes efforts from extraction, manufacture and fabrication, transportation and installation.

This means that in tandem with reducing the energy consumption of buildings, the construction industry must focus on reducing the amount of energy required to produce the materials for our buildings. It is simply not possible to decarbonize by 2050 without addressing embodied carbon.

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This won’t be an easy task, but performing a Life Cycle Assessment (LCA) is a good place to start. LCA is the methodology for assessing the environmental impacts associated with all of the stages of life of a product. And fortunately, this process is becoming easier and more effective. The same technology and analytics that go into building energy modeling is being repurposed to LCAs. As an introduction, there are some simple rules of thumb:

  • reuse the existing buildings or components

  • maximize material efficiency

  • reduce the amount of concrete, or cement in the concrete

  • use timber instead of concrete or steel where possible

  • design for deconstruction

Incidentally, the Pritzker Prize was just awarded to Anne Lacaton and Jean-Philippe Vassal, whose architectural approach embraces many of these principles.

To help categorize building materials based on the amount of their embodied carbon, the Centre for Industrialized Architecture at the Royal Danish Academy developed a graphic pyramid that compares them.

Source: CINARK

Source: CINARK

Cement and concrete are big culprits here. The production of Portland cement, an essential component of concrete, is alone responsible for a staggering 8% of global CO2 emissions, and the production of 1,000kg of cement emits 927kg of CO2 into the atmosphere. Of course it is not currently possible to completely eliminate concrete from construction. And replacing it with steel does not necessarily solve the issue of embodied carbon (though it would be a comparatively better option).

Mass timber and cross laminated timber, however, do offer us a good alternative for the above ground structure of a building up to a certain height. While Carbon12 is the tallest CLT building in the US, with 8 floors, the technology was used to inform the 2021 Building Code which allow CLT structures up to 18 stories. CLT technology was developed in Austria where the current CLT building with the most floors is built, with 24 floors, the HoHo tower, while the current world’s tallest is the Mjøstårnet in Norway at 18 floors.

Lastly, I’ll be attending (or, due to COVID, “attending”) the International Mass Timber Conference at the end of the month where a series of educational events, as well as virtual building tours, are being organized. I will report what I further learn about the technology.

George Kontaroudis
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