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March 29, 2018

Why we can’t reach our emissions goals without tracking embodied carbon

  • Net-zero buildings are great, but don’t forget all the carbon that’s emitted to build them in the first place.
    Skanska USA


    Most of us in the industry can rattle off certain accepted facts about the environmental impacts of the buildings and infrastructure we design and construct.

    For example, buildings generate more than 170 million tons of construction waste annually; buildings account for almost 14 percent of all potable water use; and buildings are responsible for almost 40 percent of carbon dioxide emissions.

    We are becoming fluent in the language of construction-waste management and energy- and water-use reduction, and as an industry we are equipped with the tools and knowledge to have deep impacts across those categories. Here in Seattle, Skanska consistently sees construction waste diversion above 80 percent. And when a project is pursuing a green-building certification, teams can design to effectively reduce water by 30-40 percent or to a targeted energy use intensity in the low 30s.

    But there is a metric missing from our daily conversations: embodied carbon.

    An overlooked issue

    A couple of years ago, I heard Ed Mazria of Architecture 2030 present on the Paris climate agreement and the commitment to a less than 2-degree Celsius temperature increase. To stay below that threshold, he said, we had to actively start reducing carbon emissions — not tomorrow, but today.

    Ed also explained how on the operational side of buildings, designers and builders understand how to get to net zero through energy use reductions and renewable energy production. It is not an insurmountable stretch to get to zero emissions by 2050 for building energy consumption.

    Ed then moved to embodied carbon, which encompasses the carbon emissions associated with the manufacture, transport and installation of all of the materials necessary to construct a building or infrastructure project, and how it is the missing piece of the emissions pie chart.

    I knew about this from work at Skanska, based on our internal embodied-carbon tracking for the projects we ourselves commercially develop and build. But I had not expanded my thinking past our small dataset of projects that were just helping us understand where embodied carbon emissions of a building came from.

    When you look at the two buckets of building emissions — operational vs. embodied — an interesting story begins to emerge. With such a focus on operational energy over the lifetime of a building, we have failed to give enough attention to the amount of carbon emissions we create in short periods to construct those buildings in the first place.

    We know there is an imperative of zero carbon by 2050 to keep things on this planet from going haywire, and it's simply not enough to get to zero on the operational side of the coin if the embodied carbon emissions haven't also been reduced or offset completely.

    Taking action

    Thinking about things this way was a shift for Skanska, and we moved forward quickly on finding a way to approach embodied carbon similarly to how we tackle operational energy consumption, and understanding the quantitative comparisons of the two. We needed to collect any and all building carbon footprints that we could get our hands on and utilize them to set benchmarks for embodied carbon per building type, so there was at least a dart on the dartboard of where to start and what to reduce against.

    We helped fund the first phase of research and data gathering for the creation of embodied carbon benchmarks across building types for the University of Washington's Carbon Leadership Forum. The outcome of this effort is open source and can be found at http://bit.ly/2pz6hFQ.

    The study showed that there were a great deal of variables associated with how embodied carbon calculations are currently being completed. There is a wide spectrum of reasons why teams tackle or don't tackle this quantification based on understanding, resources or client interest. And there is a glaring need for embodied carbon to be analyzed and benchmarked so it can be better understood and tracked by the building industry. Since the Embodied Carbon Benchmark Study effort, a lot of movement has occurred in a short time, including:

    • The Carbon Leadership Forum continues its work to create a life-cycle assessment practice guide as phase two of the grant.

    • A national Embodied Carbon Network has been established and is growing at a rapid pace, with over 200 members across eight task forces. Skanska and a handful of others are moving forward with the expansion of datasets by benchmarking our own projects more holistically, using building material quantity and site construction data already available to us on our projects.

    • Policymakers are beginning to understand materials emissions impacts, and proposing policy that would mandate that embodied carbon of materials be reported and reduced. Examples include state Rep. Beth Doglio’s Buy Clean Washington Act, which was proposed in the most recent legislative session.

    • And we are seeing actionable examples of what thinking about embodied carbon during the early phases of a project can equate to, both in real emissions and cost reduction, through case studies such as Skanska’s Interstate 5 corridor project. The project salvaged 52,569 square yards of demolished cement concrete for reuse on site as crushed surfacing base course, offsetting the emissions and cost associated with that amount of new material production, resulting in 960 fewer vehicle loads to the site.

    We are also seeing how presenting the data we already have is allowing informed clients to understand their potential embodied carbon and total carbon impact, and begin to set reduction targets that we can then help them work to accomplish. When owners see a metric that their building would need to operate for more than 200 years for the operational energy emissions to equal the embodied emissions of constructing the building in the first place, it’s hard not to want to do something.

    We currently have a project in early design that has committed to becoming a zero-carbon building through reductions and offsets, based on the client simply understanding the project’s embodied carbon impact. We expect more to follow.

    Stacy Smedley is sustainability director at Skanska USA, where she provides strategic guidance for local and national projects.

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