Tower cranes stretch above a construction site in downtown Vancouver. The city recently passed an ambitious law to reduce embodied carbon emissions by 40 percent for all new buildings. (Shutterstock / ArchonCodex)

Getting the carbon out of construction

Cities have made great strides lowering energy consumption in new buildings. Vancouver is taking the next step: reducing emissions from the building process itself.

Sidewalk Talk Features
Apr 22 · 9 min read

By Philip Preville

Five miles south of Vancouver’s downtown core, among the detached homes of the Sunset neighborhood, the finishing touches are currently being applied to the city’s first net-zero emissions building: Fire Hall 17. The design has been widely celebrated, with certifications already bestowed by Passive House and the Green Building Council. The building features a vast array of cutting-edge building technologies: rooftop solar panels, improved insulation, heat recovery ventilators, heat pumps, geoexchange heating systems, and more.

Once completed this summer, Fire Hall 17 will emit infinitesimal amounts of carbon into the atmosphere, contributing to declining greenhouse gases for decades to come. In this sense, it is a symbol of the fight against “operational” carbon emissions, or those produced through the everyday functions of a building. But before Fire Hall 17 ever opens its doors, its construction will have emitted more than 850 tons of carbon dioxide. Seen from that lens, the building is also an important symbol of the next phase of the urban climate fight: “embodied” emissions.

The global building sector is the single largest source of greenhouse gases in the world, accounting for roughly half of all global carbon emissions when including the manufacturing of building materials. Of those building-related emissions, the majority come from routine building operations: lighting and electricity, heating and cooling, waste management, and so on. Many cities around the world have mandated that new buildings reduce operational carbon, and industry has responded with a wave of new technologies. There are now 683 zero-energy buildings either completed or in development across North America, Fire Hall 17 among them.

But such measures don’t address the roughly 20 percent of global emissions caused by buildings’ construction. Fire Hall 17, like most other buildings, is made of concrete, steel, wood, insulation, glass, and countless other materials. Each of them has its own chain of greenhouse gas emissions: the extraction of raw materials, the manufacture of the product, its transport to the construction site, and their assembly into a building.

Vancouver, to its credit, last year joined a small but growing group of cities — including Budapest, Oslo, Mexico City, Los Angeles, and New York City — taking action on embodied carbon. Vancouver’s Climate Emergency Action Plan, approved by city council last November, requires all new buildings in the city to achieve a 40 percent reduction in embodied carbon from 2018 levels by 2030. The issue of embodied carbon is being discussed with increasing frequency and urgency by leaders in academia, government, and the development industry, because every minute of delay matters.

“We are at the point now where we really need to get emissions down by 2030, or we won’t be able to prevent substantial warming effects on the planet,” says Iain Macdonald, Director of the Tall Wood Design Institute in Portland, Oregon, and previously head of the Centre for Advanced Wood Products at Vancouver’s University of British Columbia. “If you build a Passive House with conventional materials, then over the next 25 or 50 or 75 years that building will have very low emissions, but you’ll have missed the opportunity to impact the decade we are in, which is the really critical period.”

The emerging science of embodied carbon

“Those emissions are like a big burp of greenhouse gases, a big chunk of carbon emissions before anyone sets foot in the building,” says Kate Simonen, a professor of architecture at the University of Washington and the Executive Director of the Carbon Leadership Forum, an organization dedicated to decarbonizing construction. “There’s no getting those emissions back. You can’t offset them with solar panels or a clean electrical grid.”

Broadly speaking, embodied emissions are those produced in the manufacture and transport of all the steel and concrete and glass and insulation and flooring and drywall and everything else that goes into buildings. Some of those materials are very carbon intensive to produce. Newly forged steel requires the mining of iron ore which is then heated in a blast furnace, powered by either coal or natural gas, to temperatures reaching 3,000 degrees. The cement used to make concrete requires similar mining practices and ultra-high temperatures. If the global concrete industry were its own country, it would be the third-largest emissions producer in the world, behind only China and the U.S.

There are two main ways to lower embodied emissions: change the way each of these building materials is manufactured, or use new building materials that aren’t as carbon intensive to produce. But you can’t pursue either approach unless you know how to calculate the embodied carbon in each component.

Consider Vancouver’s 40 percent reduction target as an example: 40 percent from what baseline? How can the city set a reduction target for embodied carbon in new buildings if it doesn’t have a reliable measurement for current buildings?

For most of the last decade, great efforts have gone into doing the math and cataloguing the results in the form of Life Cycle Assessments, or LCAs, which provide a standardized assessment of a material’s embodied carbon from its initial extraction to its eventual end-of-use disposal. “A decade ago, there was only one tool available for calculating and comparing LCAs,” says Simonen, a self-professed carbon-accounting geek. “Now there are lots of online tools, and the data is much more advanced.”

With such tools at its disposal, Vancouver began requiring new construction projects to provide a whole-building LCA assessment in 2017. A subsequent report commissioned by the city produced some noteworthy results. Specifically, it found that the more concrete and steel went into a building’s structure, the more its embodied emissions climbed — and that the more a building was made with wood, the more its embodied emissions declined.

A report commissioned by Vancouver found a clear relationship between structural material and global warming potential: rising in concrete and steel buildings and falling in mass timber. (Zera Solutions, 2019)

Timber: A natural alternative

Mass timber is a structural material manufactured, in effect, by sunshine and rainfall, making its LCA substantially lower than traditional building materials. Making mass timber building parts requires no superheated chemical transformation of the raw resource. It is harvested, milled, glued, and cut to specification at a fraction of the emissions required to manufacture concrete and steel, and if it is locally sourced, its transportation-related emissions can also be kept to a minimum. While mass timber is not a magic bullet solution to embodied carbon — its use still raises issues of sustainable forestry (more on that below) — it does provide clear advantages in the drive to reduce embodied carbon quickly.

Since the completion of Brock Commons in 2017, the Canadian Wood Council estimates that its construction avoided 748 tons of greenhouse gas emissions. Another study, by University of British Columbia researchers, compared Brock Commons to a conventionally-built student residence of similar height and dimension. They found that the use of mass timber products for Brock Commons’ structural elements resulted in a 36 percent reduction in global warming potential, the common unit of measure for embodied carbon.

More general studies of embodied carbon have come to similar conclusions. One study led by Simonen, which considered mass-timber alternatives to a typical concrete mid-rise office building, found that the timber designs reduced global warming potential by up to 26 percent. A 2020 study by researchers at Aalto University in Finland found more evidence that, in addition to having lower embodied carbon, timber also turns buildings into carbon storage units: trees take carbon out of the atmosphere, and the timber building sequesters it in place, resulting in an additional environmental benefit.

The tallest mass timber building in the world when completed, Brock Commons (shown here in 2016) avoided 748 tons of greenhouse gas emissions, according to one study. (Flickr / UBC Media Relations)

All of which helps explain the rising popularity of mass timber in cities worldwide. Regulators have adapted by updating construction codes to permit timber construction on an ever-larger scale. At the time it was built, the 190-foot Brock Commons was the tallest mass timber building in the world. It has since been surpassed by Mjøstårnet, a 280-foot-tall mass timber building in Brumunddal, Norway, which will itself soon be surpassed by Ascent, a 294-footer currently under construction in Milwaukee.

Mass timber’s light weight, relative to concrete and steel, gives it one more advantage over those structural materials: the ability to be manufactured much more efficiently. Factory production of timber building parts has the potential to unlock a whole new approach to sustainable development, accelerating the deployment of mass timber buildings at the very moment when their low-carbon footprint is needed most. It also creates an opportunity to measure the embodied carbon impact of a building, piece by piece, from conception to completion.

Urgency both now and later

The industrial sector is already working on its own reduced-carbon retooling. Concrete manufacturers are experimenting with different chemical compositions for cement that can substantially reduce its embodied carbon, though the changes often result in longer curing times, and thus extended project timelines. Scrap steel can be melted and refined using an electric-arc furnace, reducing embodied carbon compared to newly-minted steel. But “decarbonizing a steel mill takes time and energy and investment,” says Simonen. “These are not easy things to shift.”

Plus, she adds, “emissions that happen now are more impactful than emissions that happen in the future.”

One of structural timber’s advantages is that the technology is fully developed and the product is available now, during this crucial decade. Even so, a sudden shift towards reliance on timber could create its own set of forest-management complications. The construction of Brock Commons used more than 77,000 cubic feet of timber products; in the grand scheme of U.S. and Canadian forests, it takes only 6 minutes to grow that much wood. But if every building project were to suddenly abandon concrete and steel in favor of wood, the minutes would quickly turn into days, weeks, and months.

Both Macdonald and Simonen say that wood for mass timber construction must be sustainably harvested, and that it can be. “You have to grow as much as you harvest to get a stable system,” says Simonen. Canada and the United States together account for the majority of the planet’s certified forests, in which harvesting practices are verified by third parties for their commitments to sustainability and biodiversity. According to the North American Wood Products Council, both countries have roughly the same amount of forested land today as they did 100 years ago.

“A demand for wood products,” says Simonen, “is also a demand to manage forests well.”

Ideally, of course, developers would create buildings that had immediate and long-term benefits. Imagine a sustainably harvested highrise timber tower that combined the embodied carbon reductions of Brock Commons and the minuscule operational emissions of Fire Hall 17. It would burn the least amount of carbon to construct and emit the least amount of carbon once standing — a climate-fighting building both now and far into the future.

Philip Preville is an award-winning freelance writer and editor based in Toronto.

Sidewalk Talk features are reported works focusing on planning, design, or technology innovations that can help improve urban life. Follow Sidewalk Labs with our weekly newsletter and our podcasts.

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