Embodied Carbon, I do not love you.

We all know we need to take the climate emergency seriously if we wish to continue as a species, or at least as a culture. People like Ronald Wright have been telling us this for decades. But, like gnats, our comprehension of consequences on vaster timescales than our own is elusive. I have been suspect of carbon-intensive architecture since my undergrad at Ryerson in the late 1980’s, when I received an “F” for submitting a wood-in-tension structure for my ‘Concrete Library’ assignment. I naively thought that a clever and principled, submission, supported by research from the Institute for Lightweight Structures in Stuttgart (where I later studied) in collaboration with the Technical University at Delft, would have landed me an ‘A’. My professor at the time, brutalist Canadian Architect Jack Shukla, commented that my failing grade was a result of an ‘unwillingness to follow instructions’ to detail a concrete building. Frankly, even now that I may be less naive, I would do little differently today. It had a concrete foundation after all.

In the intervening 30 years, architects worldwide have embraced tall wood and mass timber structures as alternatives to concrete and steel for superstructures, but as Rowan Moore points out in the Guardian: “The only snag, as the engineer Mark Skelly points out, is that there isn’t enough sustainably sourced timber in the world to make all buildings out of it”. These low-carbon solutions to concrete and steel towers – right down to midrise and low-rise construction, now dominate the global architectural media landscape. Meanwhile, the Amazon still burns even if it is no longer in the spotlight, while Canada’s forests waver between being a carbon sink and a carbon source. This wavering may be because Canada sees forestry data as a kind of political buffer, using selective interpretation of the data to manage their IPCC/Paris commitments. The green squiggle sneaking along the zero line at the bottom-left of this graph is Canada’s Forest’s contribution to carbon ‘sinking’

source: https://climateactiontracker.org/countries/canada/

It is neither going up or down. What this suggests is a relatively steady state. (November 2, 2020 update: it has become a source, no longer a sink, for a deep dive, read Barry Saxifrage’s article here). A big rush to mass timber buildings worldwide will likely drive that line above zero from a sink to a source of emissions.  If the mass illegal cutting of the Congolese forests are any indication, international pressure from countries like China on global timber resources is only gowing, and growing much faster than the forests of the world are growing. In fact Canada has been named by the World Resources Institute as disturbing its forest ecosystems at a higher rate than any other country on Earth, higher than Brazil in fact.

Canadian forest researcher Suzanne Simard digs in to the complex web of communication and material transport in her Ted Talk.

It will be interesting to see the updates to the Climate Action Tracker website after the pending fall 2020 update. 

While the ‘sustainability’ metrics (as distinct from ‘regenerative’ metrics) on specific carbon accounting from forestry and wood products may be reasonably accurate, our understanding of the rest of construction materials in the global economy is fuzzy at best. Even then, Jennifer Cutbill reminds me; “..we think we understand at the scale of the individual sticks, but since the CBA models don’t (and can’t) account for the holistic health (carbon sequestration + water filtration, biodiversity, medicine, other magic) of the forest, the math is totally wrong. Even on a purely carbon level, math is wrong. That article Barry Saxifrage wrote in the National Observer in June seems a good reference to underscore this cognitive dissonance”

We tend to focus on one element at the expense of everything else. The recent talk I did with architects Geoffrey Turnbull and David Constable from KPMB for the OAA virtual conference summarized that until there is accurate certification of PCR’s, embodied carbon data on a wider range of materials is not reliable, even if we can obtain some semblance of the big picture.

Image of a Sankey diagram from National Geographic’s recent deep dive into what a Circular Economy would mean. The staggering percentage of construction materials and energy use paint the predicament of today’s architect in stark relief.

Like the faces of people in a lucid dream, the data on embodied carbon seems to get blurrier the closer you look. So, at least for the moment, we need to step back from our hyperfocus and really try to see the wider view. In this light, we found the building form and massing discussion here compelling:

Building tall does not immediately mean an increase in density. Actually, the contrary is true; as buildings get taller, they must be set further apart and take up more land. Knowing this, it is not surprising that New York—with more than 250 completed buildings of 150+ meters—is still lower in density then Paris, Athens or Barcelona, according to CityLab. The main reason for this is age. European cities developed at a time when walkability was key and transit was, well, Medieval. A challenge in the 21st century is to adapt and create the best of both worlds—encouraging walkability and a vibrant street life, while still creating high-quality, dense urban environments.


Once you start using and comparing data on embodied carbon and energy, it’s important to note the general order of magnitude of a given material by weight or volume. For ex. a 100% concrete structure has a similar carbon footprint to a steel building, even though a steel build has a lesser overall mass, because of the carbon and energy intensity is concentrated in the steel and cement (a small percentage of total concrete volume) whereas a wood building, OR a building with a broadly distributed versus tall massing can tend towards a much lower total EE/EC footprint. Some of this may relate to a function of what is sometimes called the ‘Galileo’ affect or the square-cube law: https://www.dinosaurtheory.com/scaling.html For every 3m in height (a typical floor-to-floor height) we determine stress at the base of the structure as ‘s’ which equals gDL where ‘g’ is acceleration due to gravity, ‘D’ is the density of the material and ‘L’ is our height increase, written as s=gDL. The higher you go, the increase in stress compounds in a non-arithmetic sequence.

The summary in this next article however reaches a number of conclusions around the effect of height on the carbon intensity of various conventional structures, but it is really more focused on the building form and not materiality: https://www.architectmagazine.com/design/with-housings-carbon-footprint-density-matters_o

I wanted to understand how this square-cube law influenced embodied carbon over a range of building sizes and heights, so to test the idea I built a wee web-app. There is a ‘Square-Cube’ coefficient in this carbon calculator, which is one attempt to present a big-picture overview of the formal decisions architects must make at the earliest stages of design in order to guide an architect’s material choices based on conventional cost:benefit analysis, with an added dimension of carbon accountability. This is a coarse calculation that is really about orders of magnitude and is not intended as a ‘by the kilogram’ approach to carbon accounting. The numbers are a best guess at this point and our ‘square-cube’ coefficient is a punitive placeholder value for now, until we get data from actual constructed buildings. If we could obtain a real-world coefficient of course our calculation would be more accurate, but the fact is most buildings are constructed for construction and labour efficiencies, and not primarily structural efficiencies, since labour in the North American market is more expensive than almost anywhere else. Construction labour is typically represented as 40% of total costs, Materials as 40% of total costs, and builder profit and overhead as 20% of total costs. The data on actual material volume use at the scale of a city is simply not available. Dr. Shoshanna Saxe of UofT’s Dept. of Civil Engineering is working to gather just that kind of data.

“…we need more information on these questions, which is the driver of my research. I just don’t think we can do it from structural first principles, as I think there is too much space between structural ideals and real buildings. Not to mention too much variability between buildings. You may find a paper we published recently interesting. It is very academic in its title but basically we argue that the heterogeneity in the built environment means we need to approach it differently than we have other types of human made products.  https://iopscience.iop.org/article/10.1088/1748-9326/ab85f8

from an email with Dr. Shoshanna Saxe, UofT Dept. of Civil Engineering

While wood is good, the blind faith in a shiny all wood future (ie. Sidewalk Labs Toronto Waterfront) misses a significant piece of the picture. That missing piece is the hundreds of years it takes for a healthy forest to recover from a clearcut, and the volumes of CO2e a healthy forest can sequester over a year, decades or hundreds of years. A tree plantation is not a forest. It is not as resilient, or efficient, at sequestering carbon or even surviving winds, fires, blights and pests, as a mature forest is.


I purchased a 50 acre woodlot in Quebec in 2010. I have studied it mostly by a kind of quiet, meditative, observational curiosity and compassionate reverence for weeks and years on end. I’ve observed the oak wilt, the blights, the emerald ash borers, the pine beetles and the much larger (and harder!) pine bugs. I see how winds over 100km/hr snap the young, compromised trees like pencils. I’ve watched how the humus builds in annual, thin layers over a mostly sandy soil and I’ve watched pioneer species slowly give way to poplar and the offspring of the few remaining elders on the site, the majestic White Pines, the Oaks, and a smattering of native Beech trees.


My elder neighbours explain how they have never seen winds, or fires that the past decade has brought to the region in the 80 years of living here and working in the bush. But this is the ‘new normal’ we are all supposed to get used to. Except it is not a static normal, it is a moving target and this is just the beginning of what some are calling the ‘forever crisis’. As I see it, the soil, the forest floor is like a giant brain, a brilliant sponge that communicates via roots and bacteria and rhizomes. When trees are attacked by invasive species or other parasites, in a healthy forest they communicate laterally to the other trees to fill their leaves with toxins or repellants or a million other strategies that help the forest survive. One tree on it’s own is doomed. Only a complete forest with a mature soil flora and fauna can develop this level of intelligence. The systems and relationships that developed over millions of years, the intelligence in the soil, the spongy brain that is the forest floor, is wiped out when a forest is clearcut, and needs to re-grow from scratch over literally hundreds of years.

Every acre of forest sequesters or sucks up about 1 ton of carbon dioxide every year. This can be as high as 3 tons in a healthy deciduous forest, which is why it is so critically important to never clearcut, but selectively harvest. While the latter is much more labour intensive, one can argue that is creates more and longer-term, and less automated jobs, right? So, for anyone that claims wood buildings are ‘carbon negative’ – please show us the 300 year-old forest that wood came from – it won’t be there for another 300 years. Did you know that a typical 2,500sf house framed in wood represents about 25 Metric Tons of embodied CO2? That means for a single family stick-framed house, you’d need at least one acre to grow for at least 25 years to replace or offset the carbon-absorbing capacity of the actual forest. To say that your house is ‘sequestering carbon’ is erroneous because you just removed the carbon absorbing capacity of the former forest for next 25 to 100 years – depending on the amount of carbon your are claiming to have sequestered. In other words, you’d need approximately 25 acres of mature growing forest for a solid year to replace that much carbon sequestering capacity. That’s just for one house. This idea of ‘carbon sequestration’ is, as I see it, little more than a convenient environmental sophistry.

Global real estate is set to double in total area by the year 2060 (per: IEA Global Status Report 2017). Assuming a fair proportion of this will require wood buildings, this begs the question, do we even have that much wood in every forest on Earth? If one were to place the sequestering carbon of forests on balance with the embodied carbon of the proposed doubling of buildings worldwide, we’d likely need at least a few additional Earths to plant them on, the Wuppertal Institute in the late 1980’s put our rate of consumption at 10 additional Earth sized planets. Little has changed.

I dragged wind-fallen cedars out of a swamp, and milled them into boards. I selectively spaced out red pine logs and milled them on site for my joists. I seasoned them all for a year to let them balance to 14% humidity and made sure there were no bugs in them. So no kiln needed, just patience. I even buried the stumps so as they rotted the CO2 would release more slowly or stay underground. 50 acres can build a few houses for sure, but not hundreds.

So while the professionals and software engineers and foresters and ecologists and marketing hacks all clamber over one another to demonstrate how product x or product y does the least harm and has a GWP or Global Warming Potential of w or z, all we can really do is stop and look at the stupendous damage we have already done, and wonder just how the Earth can possibly take any more of these assaults. So, I developed a thingy using some javascript that shows that taller buildings are actually worse than short fat ones in terms of embodied carbon. And yes, mass-timber and tall wood buildings emit less carbon than steel or concrete buildings by orders of magnitude, you can try it out here: https://www.thomsonarchitecture.ca/embodied-carbon-calculator/

What this calculator won’t tell you is how we can replace what we take. This is the fundamental error of Western-European ‘white-man’ thinking – that there is no limit to what we can take or exploit. That needs to end. So while I can calculate and crunch numbers and find algorithms to condense and present data, what I cannot do with the usual sustainability approaches is help my forest recover. All I can do is watch, and wait, and try not to wreck it. We have a 10% chance: https://www.nature.com/articles/s41598-020-63657-6

Calculations show that, maintaining the actual rate of population growth and resource consumption, in particular forest consumption, we have a few decades left before an irreversible collapse of our civilisation (see Fig. 5).

Deforestation and world population sustainability: a quantitative analysis. Nature.com: Authors: Mauro Bologna & 
Gerardo Aquino

As Jen Cutbill further reminds me;

The Sustainability Mindset: minimize harm to finite  resources (where harm and scarcity are deemed necessary, and losers = the majority of people and species).

The Regenerative Mindset: design projects to help natural processes flourish (flips from scarcity-based to abundance-based, and from cost-reduction to value-generation). Regenerative Development seeks to design projects to help build capacity of nested living systems of inhabitants to mutually flourish in exponential value-generating abundance.

“How do we refill the empty bowl?…Something beyond gratitude is asked of us. The berries trust that we will hold up our end of the bargain and disperse their seeds to new places to grow, which is good for berries and good for [people]. They remind us that all flourishing is mutual. We need the berries and the berries need us. Their gifts multiply by our care for them, and dwindle with our neglect. We are [all] bound in a covenant of reciprocity, a pact of mutual responsibility to sustain those who sustain us. [This is how] the empty bowl is filled.”

Robin Wall-Kimmerer

In closing, there are a few rules architects could observe if they are aiming to be better stewards of the Earth;

  1. Regenerate whatever materials you have drawn or plan to draw from the environment in actual fact, and not with wishful thinking. This is the essence of aiming for a true circular economy.
  2. Source wood only from selectively logged, and preferably privately owned lands, where owners have ‘skin in the game’ and understand the forests as living systems.
  3. Aim for low and mid-rise construction, as the density goals of future cities can be met with Paris and Barcelona-sized city blocks, and 5-storey limits allow sufficient roof space for the PV required to offset energy needs locally.
  4. Take some time and interest to study, support, and protect the forests nearest you, the same way that they selflessly commit their life-force to providing us with beauty, oxygen, and materials.
  5. Take time to learn from Indigenous and Traditional Knowledge Keepers, whether from Druidic origins or right here on Turtle Island.
  6. Do everything you can to limit concrete to substructures, and not superstructures

In short, do not take what you cannot replace.

PS – Forests of the world, I still love you. Stay strong, we’ll get through this together, maybe.


Indigenous Forestry Resources:



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