Embodied Carbon 101

Pie chart of global carbon emissions, with buildings as 26% of the total.

Data Source: IEA 2019

Getting to zero

If you're in the architecture, engineering, and construction industry, you've probably seen figures like this: carbon emissions from buildings represent about 26% of global emissions. As designers and builders, it is our responsibility to get this number to zero.

However, this only tells us about operational carbon, the emissions generated by running the heating, cooling, ventilation, and electrical systems when the building is in use.

And that's not the full picture of carbon emissions from buildings.

Seeing the full picture

Embodied carbon refers to the upfront emissions generated by the extraction, manufacture, and transport of building materials - essentially, the carbon footprint of a building or infrastructure project before it starts operation.

Many of the industries supplying building products - steel, cement, concrete, carpet, aluminum, insulation, to name some of the biggest contributors - rely on energy-intensive processes and long-distance transport of heavy materials.

When we consider those impacts, the buildings sector represents about 39% of global emissions.

Pie chart showing global carbon emissions by sector. The buildings portion is now at 39%, including emissions from the industry and transport sectors.

Data Source: IEA 2019.

Graph with years on the X axis and total emissions on the Y axis. A line starts at zero and steadily rises to illustrate an increase in total emissions every year.

This is just an illustration, but Architecture 2030 has some real numbers on embodied vs operational carbon over time.

Emissions over time

To look at it another way, imagine a new building that is completed in the year 2020. As it consumes fossil fuels for heating and electricity, its total emissions rise steadily year over year.

Let's see what happens if we change two things about this building's emissions.

First of all, we'll assume it's built to high energy efficiency standards, so it's generating fewer emissions year over year. Then, we'll add in the embodied carbon emissions generated during the manufacture and transport of all the steel, concrete, glass, and other materials used for construction.

The operational carbon becomes a much smaller share of the building's overall climate impact.

The same graph as above, showing zero operational emissions. The line is flat across the center of the graph, representing the total emissions not changing after construction.

Now imagine this building is all-electric, so it's not burning any fossil fuels on site for heating or cooking. And it has installed enough solar panels on site to meet its needs, or it gets electricity from a utility that uses carbon-free sources like hydro or nuclear power.

In this case, embodied carbon is the only source of emissions from the building.

In a Chicago context...

What would this hypothetical building look like in the City of Chicago? If it's built to current code, its operational energy consumption should be efficient.

And if the City meets the renewable energy goals it laid out in March 2019, emissions from the grid supplying this building will decline and eventually reach zero. The building's operational emissions will level out.

These are important goals, and accomplishing them by 2035 will positively impact the climate as well as Chicagoans' health and financial well-being. But the better we get at designing for energy efficiency, and the cleaner our electrical grid becomes, the more embodied carbon matters to the overall emissions from new construction.

The graph from above has been altered to illustrate the City of Chicago's climate goals. Total emissions increase steadily until 2025, then slow down, then level off at 2035. About two-thirds of the total emissions are the embodied carbon emissions.

Source for climate goals

Guiding principles

We know some basic principles that will help reduce the embodied carbon of our built environment:

Reduce: How many square feet of building do we need per person? Where can we make structures more efficient and eliminate unneeded space to reduce the total materials used?
Reuse: Structural material has some of the highest carbon impacts - it's often the physically largest portion of a building, and requires energy-intensive processes to manufacture. Are there existing structures that will meet our needs with a retrofit?
Recycle: Steel and aluminum take a lot of energy to manufacture from raw materials, but using recycled inputs can dramatically reduce their footprint.
Capture: Some products use atmospheric carbon as a building block, capturing it for use in materials. Plants grow by absorbing carbon from the air, so timber structures, straw-bale insulation, bamboo finishes, and other plant products can potentially have a massive impact on a building's carbon footprint. Cement and concrete manufacturers are adopting new technologies that use atmospheric carbon as a strengthening agent.
Optimize: When specifying construction materials, are we taking full advantage of lighter weight products? Locally sourced materials?

Challenges

Moving beyond those basics, there is a lot of room for our industry to grow into truly understanding, quantifying, and ultimately eliminating embodied carbon:

Benchmarking: What is the embodied carbon impact of a typical project? Can we set a baseline for comparing specific buildings?
Transparency: When we specify and purchase products, do we know the carbon impact across their life cycle? Can we easily compare similar product lines from different manufacturers?
Communication: Low-carbon and carbon-capture materials are out there, but coordination between the manufacturer, vendor, specifier, and builder is vital to ensure that the design team is aware of available products and the construction team follows through on the low-carbon design intent.
Budgeting: Which products and processes for reducing embodied carbon are worth the added cost, and which can lower the overall cost? How do we build the cost of carbon emissions into a project budget?
Advocacy: Building code approvals may be needed for alternate structural materials like timber. Our industry can also work to advance policies that promote building reuse or limit the embodied carbon of building and infrastructure projects.

CLF Chicago hosts the conversations and educational sessions that can make these solutions a reality in Chicago.