Architects Climate Action Network Calls for Regulation of Embodied Carbon

The majority of a building's carbon emissions happen before it's even opened.


Finbar Charleson / ACAN

The clever frontispiece (shown above) of the report "The Climate Footprint of Construction" says it all: above the line is the finished building, while below the line are the power plants, freighters, transport trucks, cranes, factories, and mines that make all the stuff that goes into a building. All of those industries and processes emit carbon dioxide and equivalent gases, and added together are known as embodied carbon. It's unseen and has been mostly ignored, but according to the report's authors, the Architects Climate Action Network (ACAN), can total more than 75% of a building's lifetime carbon emissions.

Embodied energy
credit: John Ochsendorf/MIT

Embodied carbon is controversial because some materials that are pretty standard in the construction industry have a lot of it, most notably steel and concrete, which together pump out about 12% of the world's CO2 while being made. It was also not considered that important until recently; as John Ochsendorf's famous graph shows, in a low-efficiency building like everyone used to build, operating energy and emissions dominate within a couple of years. In a more modern, normal efficiency building, operating energy still dominates over the life of a building. But if you take a high-efficiency modern building, it could take the entire lifetime of the building before operating emissions are greater than the embodied emissions. And we have been showing that graph for a decade.

ACAN Carbon Emissions
Carbon emissions throughout the lifecycle of a building.

'Finbar Charleson / ACAN

ACAN shows it differently, with the big burp of carbon upfront. (Which is why I preferred to call them Upfront Carbon Emissions, because they are not embodied in the building, they are in the atmosphere, and they are upfront; but that horse is out of the barn.) There are also continued embodied emissions as the building is repaired and maintained, and then at the end, another big chunk from demolition and disposal. This totals up to an extraordinary number.

Embodied Emissions as total

'Finbar Charleson / ACAN with information from Sturgis Carbon Profile

According to the report, "the embodied carbon of a building can be up to 75% of its total emissions over a typical 60-year lifetime." I thought that this was high, but one of the report writers, Joe Giddings (who along with co-writer Rachael Owens was kind enough to meet over Zoom) tells Treehugger:

"We had quite a lot of discussion about that figure, and at one point we were actually considering putting it higher. But two British organizations (RICS and RIBA) quoted 76% based on Simon Sturgis's work ... since that figure was announced we found another report based on an analysis of 650 carbon assessments."

Simon Sturgis is a recognized expert in the field and has "has spent the last 10 years working on practical assessments of resource-efficient, circular economy, and low carbon design for a wide variety of projects, for both new and existing buildings." We are also talking about modern, energy-efficient buildings made with modern materials, many of which (like concrete, steel, and plastic foam) have very high levels of embodied carbon.

modified graph with totals

'Finbar Charleson / ACAN modified by Lloyd Alter

This issue troubled me so much that I actually measured all the little gray bars of operating carbon on the ACAN graph and piled them up to see which ended up higher; in this example, the total embodied carbon just barely exceeded the operational carbon. However, after reading the RICS report "Redefining Zero" by Sturgis Associates, it becomes clear that in a few years, as codes aim towards net-zero, the embodied carbon could be north of 95%!

It's obvious: if the building has no operating emissions, then everything is embodied. That's why when you look at what is being built now, and where codes are going in terms of energy efficiency, dealing with embodied carbon becomes critically important; it will dominate the carbon footprint of our buildings. And the 75% number used in the ACAN report looks not only plausible but conservative.

The exercise also reinforced the point that the operating emissions are spread out over the life of the building, while the vast majority of the embodied emissions are happening upfront; they are significant, and they are eating into the global carbon budget that we have to keep under to hold the global temperature rise to under 1.5 degrees. That means we have to stop doing this not by 2050 or 2030 but now.

How Do We Reduce the Embodied Carbon in the Building Sector?

building with wood dalston lanes
credit: Waugh Thistleton Architects/ Photo Daniel Shearing

The authors of the report start this section with our favorite photo, Daniel Shearing's shot of the guy checking out the cross-laminated timber (CLT) at Waugh Thistleton's Dalston Lane project in London. CLT is the miracle material made from gluing wood together into big panels but is only one of many made from natural materials that have far lower carbon footprints than the more traditional steel and concrete. The report notes that "These remove carbon from the atmosphere as they grow and so could be used to ‘lock' carbon into the building for the duration of its lifespan and beyond."

"Providing they are sustainably sourced, the overall balanced benefits associated with bio-based materials and their use in construction are many and well known, ranging from health and well-being to adequate resource management (as opposed to natural resource depletion) and ecological protection."

But just building with natural materials isn't enough; it still has a carbon footprint, and it has to be harvested sustainably. It is just one part of a larger strategy that is outlined by ACAN in the report:

  1. Reuse existing buildings: Pursuing a strategy of retrofit, refurbishment, extension, and reuse over demolition and new build.
  2. Build using less material: Designing more efficient and lightweight structures and designing out waste.
  3. Build using low carbon materials: Use materials that have low or close to zero embodied carbon emissions.
  4. Build using certified recycled material: Moving towards a circular economy and reusing building materials and products derived from low-carbon recycling processes that can be repeated almost perpetually without quality loss.
  5. Build using long-lasting and durable materials, designed for easy disassembly: Avoid products that require frequent maintenance or replacement but that can be dismantled for reuse.
  6. Build flexibly and for future adaptability to allow for the re-purposing of buildings.

It is important to stress that the issue of building with wood is only one point out of six. A look back at that first graph showed the end of life embodied carbon to be almost a quarter of the total, carbon that could be avoided if the structure had been designed for disassembly and reuse. We have to look at the whole picture.

Put It In the Codes

ACAN is calling for changes in planning policy with "whole life-cycle carbon assessments to be completed at the early design stages, to be submitted as part of pre-application enquiries and full planning submissions for all developments." They also want building regulations changed to include limits on embodied carbon.

"Currently, only a building’s operational energy is regulated, but through introducing strict limit values on embodied carbon, all schemes will be required to consider and reduce these. Achieving net-zero or low embodied carbon targets would require offsetting through verified schemes as a final step, which could provide significant financial investments into green technology and initiatives. Similar to offsetting for operational energy emissions, it should be of a similar quantum to disincentivize reliance on them."

The authors also point to many other good suggestions for driving reductions in embodied carbon, and look at legislation in Finland, France, and the Netherlands, and conclude:

"The UK construction industry is ready for embodied carbon regulation and we can learn from the steps taken in other countries to introduce legislation. We must act now to regulate embodied carbon in line with our commitments to tackle the climate crisis, requiring all projects to report whole life carbon emissions."

Read and download more at the Architects Climate Action Network.

It's Not Just How We Build, It's What We Build

Tulip from the air
The Tulip is not dead yet.

Foster + Partners

Joe Giddings, Rachael Owens, my Ryerson student Sabrina Thomason and I continued with a discussion about how zoning, density, and planning regulations affect the type of built form. The issue goes deeper than just how we build but raises questions of what we build; Norman Foster's silly restaurant on a stick in London is the poster child for a pointless building with a vast carbon footprint, the kind of thing we wouldn't even consider if we were serious about carbon. Embodied carbon is also not just an issue for buildings, but for infrastructure and transportation as well. I discuss it, electric cars, concrete tunnels, and more in What Happens When You Plan or Design With Upfront Carbon Emissions in Mind? Here is also a roundup of Treehugger's recent posts about the issue of embodied carbon.