What can we do about embodied carbon?

Embodied carbon explained

“Embodied carbon” is an imperfect term. The word “embodied” sounds like we’re talking about carbon encapsulated in a material. Instead, it’s shorthand for all the lifetime indirect greenhouse gas (GHG) emissions due to a building—in other words, everything other than emissions from building operations. For example, the GHGs emitted from diesel combustion in transporting a product to the building site are part of the embodied carbon in the product.

Embodied carbon is also known as value chain emissions, upstream/downstream emissions, or Scope 3 emissions. The complete carbon footprint of a building includes all of these GHG emissions. A true zero-carbon building would account for and offset its operational carbon as well as its embodied carbon.

Most embodied carbon emissions are upstream or “upfront” of building occupancy—they are primarily related to the manufacturing of materials. This includes the extraction of raw resources, manufacturing of building products, and transportation of those products.

GHG emissions due to material manufacturing, use and disposal are more significant than many people realize. First, these emissions are a big upfront GHG pulse in the life of a building, which makes them a good near-term target for climate change mitigation. Second, as buildings approach net-zero carbon operation, embodied impacts will make up most of the carbon footprint in the built environment.

Embodied carbon has a lot of buzz lately, and that’s inspiring to some design professionals. Kevin Welsh, Senior Sustainability Advisor at Integral Group, is one of them: “It’s great to see the accelerating interest in embodied carbon. It’s the next evolution of our industry’s enthusiasm and dedication towards reducing the impacts of projects.”

How to measure embodied carbon

Embodied carbon reduction begins with data. Without data, we’re just guessing about where to look for improvements, and what decisions are actually beneficial. To bring in data, we need life-cycle assessment (LCA).

LCA is a holistic environmental impact assessment method. A cradle-to-grave LCA for a building accounts for all the lifetime flows between the building and nature, and then estimates the impact of those flows on the planet. An LCA provides multiple results having to do with damage to air, land and water.

Embodied carbon is one of these results—the global warming potential (GWP), expressed in equivalent tonnes of CO2. To calculate embodied carbon requires a full LCA study, although only one result from the study—the GWP—will be used.

Assessing embodied carbon impacts of design and material decisions is always a case-by-case situation involving cradle-to-grave LCA in the context of the whole building. There is no shortcut for this. And whole-building LCA is tricky. But two well-respected North American software tools make it easier for design teams: the Athena Impact Estimator for Buildings (a free standalone tool, produced by the Canada-based non-profit research group that I head) and Tally (a Revit plugin, developed by architecture firm Kieran Timberlake).

One word of caution: embodied carbon calculations are estimates, not absolutes. While LCA is a well-established, rigorous science guided by international standards, it is inexact. There are many variables and assumptions in LCA, and some data gaps and methodology question marks. The uncertainty in results increases with long-lived and complicated products like buildings.

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published on www.canadianarchitect.com by Jennifer O’Connor

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