Embodied carbon: a hidden climate challenge


The Rocky Mountain Institute (RMI) notes in a new report that “solutions to combat the carbon incorporated in buildings have not been widely studied in the United States, which leaves a significant gap in the knowledge of engineers, architects , contractors, decision-makers and building owners. “This is one of the report’s many euphemisms, titled“ Reduce Embedded Carbon in Buildings. ”Embedded carbon is pretty much ignored in North America; it’s the building industry’s blind spot. This report can help change that.

“Embedded carbon” is the terrible name for carbon emissions which I have described as “the CO2 emitted during the construction of a building, the carbon burp that comes from the manufacture of the materials that go into a building, from their construction. transport and assembly. ”A few years ago, I suggested that they be renamed“ Upfront Carbon Emissions ”because they are not incorporated; they are in the atmosphere and they now count when every gram of carbon counts towards the carbon budget. The term has been accepted in the UK (where much of the work on embedded carbon is ongoing) and is used for all emissions at the product stage and at the stage of the construction process, up to the point where the building begins to be used. .


The report demonstrates that it is surprisingly simple and affordable to reduce the intrinsic carbon of concrete construction by optimizing the concrete mix and using recycled content in rebar. He actually claims that “concrete and steel offer the greatest reduction opportunities” and that we can “reduce embodied carbon from 24% to 46% at less than 1% overcost”.

The report’s authors – Matt Jungclaus, Rebecca Esau, Victor Olgyay and Audrey Rempher – describe the problems of structural materials like cement, “one of the biggest contributors to US emissions at 68.3 million metric tons (MMT) of CO2 equivalent per year. , and steel, “responsible for 104.6 MMT of CO2 emissions per year”. They aren’t as excited about solid wood as many others, even wondering if it really stores carbon, writing:

“Viewing wood as a carbon sequestering material is a point of contention among industry experts, with much of the debate revolving around different forestry and harvesting practices and their effects on emissions. Nevertheless, wood is generally regarded as a low carbon alternative to steel and concrete. when used as a structural material. ”

It’s a bit overwhelming with slight praise there for those of us who think concrete and steel should be replaced with sustainably harvested mass timber as soon as possible; but it is probably a bridge too far for RMI, even in times of climate crisis. They make solid wood sound like a bad thing, instead of the only material that even has a chance of being carbon neutral. It’s not perfect, but really, such negativity:

“As the demand for wood products increases, it will be crucial to ensure that this demand is met through sustainable forest management practices. Otherwise, the wider use of wood as a construction product could result in higher carbon emissions and less ecological diversity. ”

Original issues, British style.

World Green Building Council

RMI takes a different approach to initial carbon emissions than is typically done in the UK or Canada: “Initial embodied carbon includes emissions related to extraction, transportation (from the extraction site to the manufacturing site). ) and the manufacture of materials. But it does not include “emissions related to transport to the site, construction or use phases, or end-of-life considerations.”

But transportation to the jobsite and the construction itself are important parts of the initial emissions, which usually include everything up to the use phase. Later in the report, they note:

“The transport of materials within or across geographic regions can have a significant impact on the embodied carbon of a product. Although the manufacturing stage typically emits the highest levels of carbon in the life cycle of a given product, transport emissions can be substantial, especially when a large amount of material is transported over long distances. .

But obviously, it’s too hard to do. “The information is not readily available through tools like EC3. Additionally, it requires a lateral calculation for each material depending on its source.”

We need more than that.

It’s wonderful that the RMI is tackling embedded carbon and trying to bring a big conservative industry on board, but this report is deeply unsatisfying and at times confusing. These are the times when we need to get people’s attention.

The report mentions in blue boxes that “the initial decisions that affect the fundamental design of a building to reduce embodied carbon while meeting the functional requirements of the project”. Yet when they do an entire section on case studies on the economics of low carbon embodied buildings, they note that “this study does not include any change in whole building design strategy.” This is obviously too difficult because the EC3 tool they use “does not have the capacity to inform design changes of the whole building”. But if you are doing case studies, these are fundamental. Frances Gannon of Make is quoted in our previous article on the form of construction:

“The main design elements at the start of the project will make the biggest difference: reuse existing buildings wherever possible, keep new building shapes simple and efficient, ensure structural efficiency, keep structural grids small and consider how. the facade interacts with the frame are key contributors to the general principle of using less. Then, as the conversation turns to materials, we will have the best chance of meeting ambitious embodied carbon targets. ”

The RMI report mentions most of them casually in the blue boxes, but it is a huge failure not to run the numbers in the case studies after optimizing the form. People in the industry were perhaps even more impressed with the cost savings.

More critically, the report seems determined to downplay the urgency, by explaining how easy it is to do and won’t cost that much money. They mention the time value of carbon and refer to Architecture 2030 and do not even mention the Intergovernmental Panel on Climate Change (IPCC) until the conclusion. You have no idea the crisis or the magnitude of the problem that you see among architects and engineers in other countries, like where Steve Yates of Webb Yates Engineers says things like:

“It is absolutely scandalous that an architect goes to buy locally grown tomatoes at the supermarket, gets on his bike to [go to] work, and think they are an environmentally conscious person when designing a concrete or steel building. It’s the architects and engineers who make the decisions, so why don’t they get involved? ”

It looks like RMI is trying to walk a fine line, saying, “Hey, you can lower your embodied carbon and it won’t hurt, and you can do it on the cheap!” instead of saying we need to drastically cut carbon emissions now. Maybe they don’t want to sound extreme and seem to tip the boat over, but the boat needs to be rocked. Buried in the conclusion, the RMI finally expresses a certain sense of urgency:

“Reducing embodied carbon is an urgent and critical issue as the trajectory of embodied carbon emissions is currently not aligned with global climate goals … It is imperative that practitioners employ the strategies and solutions available today. to accelerate the adoption of These changes are necessary to implement the unprecedented actions required to achieve the goal of the Paris Climate Agreement and limit global warming to 1.5 ° C.

But all of this is too little, too late.

Read Frances Gannon of Make Architects in the UK to find out what her firm does; look at the positions of the Architects Climate Action Network. This is serious.

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