The 'Ironclad Rule of Carbon' Means We Have to Change How We Think About Design

As we electrify everything, upfront carbon emissions dominate.

Building with straw and thatch makes sense again.


I try to distill many of the thoughts discussed on Treehugger into coherent lectures when teaching Sustainable Design at Toronto Metropolitan University's School of Interior Design and The Creative School. The theme of my teaching in 2022 is the importance of upfront carbon emissions—a subject I talk about often on Treehugger and a term that was actually developed on this site in a 2019 post titled "Let's Rename Embodied Carbon" to "Upfront Carbon Emissions." More recently, I wrote a post in which I developed what I called the "ironclad rule of carbon."

What is the Ironclad Rule of Carbon?

As our buildings become more efficient and we decarbonize the electricity supply, emissions from embodied carbon will increasingly dominate and approach 100% of emissions.

This does not just apply to buildings, but to everything from cars to computers. I am increasingly convinced it is an issue that needs more attention, so here is the story again in a series of graphs.

operating vs embodied
1996: Embodied vs. Operating Energy.

Building Science Corporation

Twenty-five years ago we talked about energy, not carbon. And embodied energy, if it was talked about at all, was not considered very important. As engineer John Straube noted in Building Science Digests, the operating energy was far more important. Buildings were leaky, and the energy supply was dirty.

Straube wrote in 2010: "The on-going consumption of energy to operate, condition, and light a building, as well as the energy embodied in on-going maintenance, is the largest single source of environmental damage and resource consumption due to buildings."

He continued: "Scientific life-cycle energy analyses have repeatedly found that the energy used in the operation and maintenance of buildings dwarf the so-called 'embodied' energy of the materials. Cole and Kernan (1996) and Reepe and Blanchard (1998), for example, found that the energy of operation was between 83 to 94% of the 50-year life cycle energy use."

energy use in buildings over time

John Ochsendorf / MIT

But a funny thing happened when buildings got more efficient because of tighter building codes and the growth of building certification systems such as LEED or Passivhaus: the cumulative operating energy took much longer to overtake the embodied energy. It was such an obscure issue in 2009 that it had to be explained in MIT's article on embodied energy:

"As the world struggles to reduce energy consumption and greenhouse gas (GHG) emissions, much attention is focusing on making buildings—both existing and new—operate more efficiently. But John Ochsendorf, associate professor of building technology, thinks mostly about another, less-recognized aspect of the built environment: the “embodied energy” of buildings, that is, the energy consumed in construction, including the entire life cycle of the materials used, from the extraction of raw materials to the manufacture, transportation, and installation of products at the building site."

John Ochsendorf also questioned the 50 and even 100-year life cycle energy use. “Conventional wisdom says that the operating energy is far more important than the embodied energy because buildings have a long life—maybe a hundred years,” Ochsendorf told MIT. “But we have office buildings in Boston that are torn down after only 20 years.”

While others may view buildings as essentially permanent, he views them as “waste in transit.”

Carbon Curve

Robbie Andrew / IPCC

As the Intergovernmental Panel on Climate Change (IPCC) rolled out its reports, many people started talking about carbon emissions instead of energy consumption. The IPCC came up with hard carbon budgets that we had to stay under to keep the global average temperature rise below 1.5 or 2 degrees Celsius. It determined we had to cut carbon emissions almost in half by 2030 and to almost zero by 2050. It became immediately obvious that talking about 50-year life cycles made no sense.

In 2019, I wrote "Forget About Life-Cycle Analyses, We Don't Have Time," where I concluded, "We have to concentrate our minds on reducing our carbon dioxide output by half in the next dozen years. That is our life cycle."

Magwood foam drawing

Chris Magwood

Also around 2018, Chris Magwood, a green builder in Ontario, released some research he had done on "embodied carbon," the term many people were beginning to use instead of embodied energy since they were finally realizing that carbon is a bigger problem than energy. It was counterintuitive and jaw-dropping.

Because so much greenhouse gas was emitted in the making of foam insulation, even on a life cycle analysis of 30 years, the high-performance building with over twice the insulation had greater emissions than the crappy house built to the conventional building code. As a builder in Boston noted in an article about Magwood: “It was like a light turning on. We’ve been doing everything wrong.” 

These carbon emissions, the big orange bar, all happen at the beginning, upfront. And while "embodied energy" made some sense because the energy was going into making the thing, "embodied carbon" made no sense because the carbon was going out into the atmosphere. This is why a Twitter discussion among architects Elrond Burrell, Jorge Chapa, and myself came up with "upfront carbon emissions."

embodied carbon

World Green Building Council

By 2020, a lot of people were talking about different materials and their upfront carbon emissions. Stephanie Carlisle of Kieran Timberlake wrote for Fast Company:

"We’ve come to recognize that it is not enough for architects and engineers to focus solely on operational carbon.... When we look at new buildings anticipated to be built between now and 2050, embodied carbon, also known as “upfront carbon” because it is released before a building is even occupied, is projected to account for nearly half of total new construction emissions. For practicing architects, engineers, policymakers, and anyone who cares about climate strategy, this should give us pause."
Embodied Emissions as total


In fact, many people thought that Carlisle is way low at half of the carbon emissions. The Architects Climate Action Network in the United Kingdom did a study, "The Climate Footprint of Construction," and concluded that "the embodied carbon of a building can be up to 75% of its total emissions over a typical 60-year lifetime." 

I read this report and had trouble believing it at first, but the logic was inescapable: As operating energy demand is reduced, the upfront carbon increases as a proportion of the total. In my beloved Passivhaus buildings that sip energy, they are almost all upfront carbon.

I also realized it is not just our buildings that are changing, but also our energy supply. Our electricity is decarbonizing as we get more renewables, and the prices of wind and solar keep dropping. Then there is the heat pump revolution, where we can pull heat out of the air or ground and run on rooftop solar. Our storage of renewables is getting better and cheaper. And I had an epiphany, writing in February 2021:

"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."

A few months later, while writing about the importance of measuring the embodied carbon in everything, I concluded the issue was even bigger: "As more of our stuff, from cars to tools, run on electricity, as our electrical grids get cleaner, as our building efficiencies get better, then the issues of embodied or upfront carbon become more important. This appears to be a fundamental principle that applies to everything, which I will pretentiously call the 'ironclad rule of carbon.'"

I kind of buried the lede in that story because I did think calling this an ironclad rule was pretentious, and, at the time, I thought I might be overstating the case for dramatic effect. But I am more convinced than ever that this rule applies—not just to buildings, but to everything.

Ironclad Rule of Carbon

Lloyd Alter

So forgive the crappy drawing I did last night to make the point, but if you run your house on gas, the operating carbon is significant. If you run your heat pump on dirty electricity, it will eventually catch up. But if you live in a well-insulated house in hydro-powered Montreal or Seattle and have a heat pump, you have almost no operating emissions. Your home is 100% upfront carbon.

The Ironclad Rule Applies to Everything

Apple iPhone 11 life cycle chart
The life cycle of an Apple iPhone 11.


Buildings are a major source of upfront carbon emissions, but they are not the only source and some things are already approaching 100% upfront. Take my iPhone: Apple publishes the life cycle data and calculates the source materials and make to be 83% and the transport to be 3%, both of which I consider to be upfront carbon. They list the use (the energy consumed to run it) at 12% of the 80 kilograms of carbon emissions. But, according to their footnotes, "Geographic differences in the power grid mix have been accounted for."

They are probably using the average American carbon estimate for the grid, which according to the U.S. Energy Information Administration, is 0.85 pounds of carbon dioxide per kilowatt-hour. But again, if you live in Seattle or Montreal, the upfront carbon approaches 100%. This is why I am not lining up for a new iPhone 14—I want to avoid those upfront carbon emissions.

Development stages

World Green Building Council

This is why the ironclad rule of carbon affects our design thinking. We have been focused for so long on designing to reduce demand and operating emissions, but the more we reduce demand, the more upfront emissions dominate the carbon emissions picture. We can't ignore them.

We also cannot forget that all that clean energy supply has to come from somewhere, and there are the costs and upfront carbon emissions that come from decarbonizing the grid, which is why we have to continue working to reduce demand.

If we haven't ignored upfront carbon emissions, we have certainly just paid lip service to the issue. And as Gilberth and Holderith noted, we need transparency. We need to know what the upfront carbon emissions are for our toasters and our Teslas to make intelligent decisions about them, and to encourage the manufacturers to reduce them.

This is why, as the World Green Building Council noted in words that apply to everything, we have to:

  • Question whether we need this at all.
  • Reduce and Optimize to "minimize the quantity of new material required to deliver the desired function." This includes "prioritize materials which are low or zero carbon."
  • Plan for the Future, designing for disassembly and deconstruction.

As one of my students noted in a paper, "As designers, we need to approach design efficiently and simply, with carbon in mind from the beginning. This means using less of everything; tools, space, and materials."

And as I have noted many times, we need to think about sufficiencysimplicity, and efficiency.

Correction—September 25, 2022: This article has been revised to clarify that efficiency matters and the role of reducing demand.