Paula Melton writes an important article, and raises some serious questions about our beloved mass timber construction.
We have said before that we should be thinking about embodied carbon in everything that we build or buy. Over at BuildingGreen, Paula Melton writes an important post about The Urgency of Embodied Carbon and What You Can Do about It.
Melton defines embodied carbon as the carbon dioxide greenhouse gases released when we construct our buildings in the first place, noting that the manufacture of building materials makes up 11% of total global greenhouse gas emissions.
That 11% might sound small compared with the impact of operational energy (28%), but for new construction, embodied carbon matters just as much as energy efficiency and renewables. That’s because the emissions we produce between now and 2050 will determine whether we meet the goals of the 2015 Paris climate accord and prevent the worst effects of climate change.
Embodied carbon used to be almost not worth talking about, because it was swamped by the operating energy. But as buildings get more efficient, its impact becomes bigger and bigger in proportion.
Melton looks at the embodied carbon of different materials, including concrete, steel, and wood construction. She notes that "by weight, steel has a much higher embodied carbon footprint than concrete does" but that is not relevant since steel structures are so much lighter. She does make some smart recommendations about using less of both materials by thinking about design and engineering, for instance with concrete: "Avoid over-engineering without good reason: work with the structural engineer to ensure you’re using only as much concrete as you really need." And steel: "Consider a braced frame rather than a moment frame, and work with the structural engineer to manage the architectural impacts."
Is wood really so wonderful?
She also questions whether wood is as good as we TreeHuggers keep saying it is.
But a few scientists are asking everyone to slow down, contending that LCAs have grossly overestimated the benefits of wood. “Wood is very tricky right now,” said Stephanie Carlisle, principal at KieranTimberlake and the lead developer of the Tally whole-building LCA software tool. “There is a big debate happening.” And that’s frustrating for designers who want guidance they can use. “The more we’ve dug, the more [the numbers] seem to be all over the place,” said Arup’s Yang. “There is so much uncertainty carried with them.”
Melton references studies that show that forests are being cut too soon, that different woods sequester different amounts of carbon, that kiln-drying takes a lot of energy.
“For those of us in the building industry, it gets really complicated,” sums up Kate Simonen, associate professor of architecture at the University of Washington, adding that people tend to have emotional rather than scientific responses to the available data. “I have not found anybody who has made a fully rigorous connection that satisfies both of the extreme sides of the story, which makes it really difficult to interpret.”
Melton concludes with much the same advice that she did for concrete and steel: use it responsibly.
The upshot? Wood can be beneficial for its reduced footprint, but don’t use wood as a get-out-of-carbon-jail-free card. Consider which materials and systems make the most sense for the project, and optimize how you use them, preferably with whole-building life-cycle assessment as a guide.
Whatever you use, use it responsibly.There's lots more in this important article, but the big takeaway is that we have to think more about what we build, as well as what we build it out of. The most important question is the first: can we fix what we've got? "The very first question to ask for any project is whether new construction is needed. By avoiding the use of new materials, we avoid their impacts altogether."
Reading that made me smile, given that she illustrates her article with an image of the new Mexico City Airport designed by Fernando Romero Enterprise and Foster + Partners. It had a full life-cycle assessment to calculate its embodied carbon, which doesn't include the fact that flying is responsible for almost as much greenhouse gas emissions as concrete. Surely the question about whether this is needed starts there.
This is what we have called Radical Sufficiency -- "What do we actually need? What is the least that will do the job? What is enough?"
The next is to design things properly to use as little of those materials as possible, whatever they are. This is what we have learned from Nick Grant and his Radical Simplicity.
And it goes without saying that every building should be designed to use as little energy as possible, for Radical Efficiency.
Important stuff on BuildingGreen from Paula Melton.