Embodied carbon the new frontier

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Incentives for the private sector to reward projects with lower embodied carbon or density bonuses could reduce emissions from the building sector

BUILDING MATERIALS Plenty of work has gone into making buildings more energy efficient and encouraging the switch from fossil fuels to renewables, but much less attention has been given to reducing the carbon in the materials they are made from. Experts are now examining how best to cut these “embodied emissions”

REDUCE, REUSE & RECYCLE Only using the amount of steel or concrete required for structural stability and reusing and recycling materials or even whole parts of existing buildings is key to emissions reduction in the construction business

KEY QUOTE A building should have a carbon budget just as it has a financial budget

Work to make buildings more climate-friendly tends to focus on operational emissions produced by the energy used for heating, cooling, cooking and other activities. But increasingly attention is turning to so-called embodied carbon, emissions released during the making, transport, assembly, installation, demolition and decomposition of buildings and construction materials. “You follow the brick all the way back to the quarry and you [also] figure out what is going to happen to it in 100 or 2000 years,” is how architectural historian Kiel Moe explains the concept. A building’s fuel efficiency may be important, but it is missing the big picture, he says.

As much as 11% of global emissions are represented by embodied carbon, says the non-profit World Green Building Council (WorldGBC). As operational emissions have decreased with increased renewables and energy efficiency measures, embodied carbon, which until now has remained hidden further down the supply chain, has become the biggest climate problem from buildings. Bringing Carbon Upfront, a report published in September 2019 by WorldGBC, engineering company Ramboll and NGO C40 Cities sets the goal of reducing embodied carbon in new and renovated projects by 40% within a decade and to net zero by 2050.

It is an ambitious goal given the world’s building stock is expected to double in size by about mid-century when the global population will near 11 billion. Much of the new building will be in the developing world, where, in the short-term, the priority will be to accommodate a fast-growing and less affluent population with basic homes, offices and schools rather than focus on emissions. Nonetheless, the latest UNEP Emissions Gap Report from November 2019 highlights construction materials as its next area of focus and the UN International Resource Panel in a December 2019 report says materials efficiency in housing in G7 countries could reduce greenhouse gas emissions in the sector by 2050 by 50-80%.

PROGRESS HAS STARTED

Stephen Richardson, head of Europe projects at the WorldGBC and co-author of the Bringing Carbon Upfront report, believes change is happening with Europe, North America and Australia recognising the importance of embodied carbon for climate action. He singles out Finland, the Netherlands and France, which are planning to adopt legislation on Lifecycle Assessment (LCA) for the construction industry. LCA examines a building’s entire life, including embodied and operational carbon. Meanwhile, the European Commission, the EU administration, EU member states, WorldGBC and others are developing Level(s), a tool that creates a common language to help evaluate the sustainability of buildings. Level(s) will be published in summer 2020.

California is trailblazing the way in the US with a 2017 law that will require state agencies from mid-2021 to account for full lifecycle embodied carbon when they evaluate infrastructure projects. The bill was prompted by controversy over a rebuilt portion of the Bay Bridge near San Francisco, when the state chose steel from a carbon-intensive Chinese mill rather than from cleaner competitors in California or Oregon.

The law’s impact will be dramatic because California, as the largest US state, has so many public buildings and infrastructure, says Ben Stapleton, executive director of the US Green Building Council – Los Angeles. Also, California tends to lead in the US on environmental issues and the law is expected to be copied elsewhere. Washington state is already considering a similar regulation. But while the law covers steel, glass and insulation, it excludes concrete, of which cement is a major component. Cement’s manufacture creates up to 8% of global man-made CO2 emissions.

BUILD LESS, BUILD CLEVER, BUILD EFFICIENTLY

In addition to using less carbon intensive materials, maximising a building’s existing use or recycling materials or even recycling an entire building makes sense. Next to Google’s main corporate campus in Silicon Valley, California, is what was once the 1994 corporate home of the technology firm Silicon Graphics. After being refashioned, it is now Googleplex 1.0 with a lower embodied carbon factor than that of the original building, torn down and rebuilt.

A building should have a carbon budget that contains embodied carbon just as it has a financial budget, says Lars Ostenfeld Riemann, executive director of Ramboll Buildings, a division of a global engineering company with headquarters in Denmark. Optimising the design of almost any building can slash embodied carbon by some 20-30% and the same amount can be saved by using low-carbon materials, he adds. Buildings often use more materials than are needed structurally. Less mass typically means less embodied carbon, says Anna Åkesson, senior environmental manager with construction company Skanska, headquartered in Sweden. Kate Simonen, an architect and structural engineer who founded the Carbon Leadership Forum at the University of Washington, US, estimates a reduction in embodied carbon of around 30% is feasible with products on the market today.

The costs of cutting embodied carbon may not be significant. A case study by Anglian Water in the UK shows that from 2011-2015, the utility cut the “capital carbon” or embodied carbon of new infrastructure by more than 50% while saving 20% in its investment. Most of the savings were achieved by using fewer materials, namely concrete and steel.

But materials, such as lower carbon concrete, cost more because of limited demand and the need for manufacturers to invest in new infrastructure. Cédric de Meeûs, head of group public affairs in Brussels for LafargeHolcim, says some low carbon concrete solutions can cost as little as 10-15% more than conventional counterparts. Given the massive costs of major construction projects, this relatively small price increase “usually does not have any significant impact on the overall project cost,” says de Meeûs. His company sells concrete and cement products offering up to 70% carbon savings. But for construction companies operating on low margins, even 5% pricier concrete can be too much. LafargeHolcim already offers carbon-neutral concrete in countries such as Belgium, Germany and Switzerland. These countries are all considered mature markets, but even with the carbon-neutral alternative costing only slightly more than conventional concrete, the response has been tepid. The developing world could be even harder to crack. People there “want a roof over their heads and today often have little or no concern about the carbon footprint of buildings,” says de Meeûs.

High-density, medium-rise buildings made from wood are considered better by many for a sustainable, liveable city. Wood embodies significantly lower carbon than steel or concrete. And the potential height of mostly wooden buildings is constantly advancing. “With timber, we keep being surprised by new taller and taller buildings,” says Richardson. Eighteen-storey wood hybrid skyscrapers have recently been completed in Vancouver, Canada and Oslo, Norway and far taller buildings are planned elsewhere. The tallest under discussion is the 80-storey W350 Project in Tokyo, Japan, which would be 90% timber and 10% steel if built by 2041 to celebrate the 350th anniversary of timber construction company Sumitomo Forestry.

DEMOLISHING IS DIRTY

Reducing construction waste remains a sub-sector of cutting embodied carbon, but is gaining some attention. Whole components or smaller pieces of existing buildings can be reused. Existing buildings should be seen as material banks, says Skanska’s Åkesson. Ramboll’s Ostenfeld Riemann estimates as much as 50% of embodied carbon could be saved by reusing building waste.

The Netherlands is leading efforts to tackle embodied carbon in construction waste, says Richardson. It is developing a public database of materials in existing buildings and their potential for reuse (2.5 million square metres of them have already been added). Its founder, architect Thomas Rau, is working with Amsterdam to include all public buildings within the city’s boundaries.

To be re-used, materials must be separated out at the end of a building’s life. Often a complicated process, Rao’s firm designed the new headquarters of the ethical bank Triodos in the Netherlands so the materials could be reused with as little fuss as possible. Billed as the world’s first temporary material bank, the five-storey building, mostly made from wood, is held together with 165,312 screws, making it easy to disassemble.

Skanska is reusing enough concrete in the redevelopment of LaGuardia Airport, New York to save some 15,000 truckloads of waste — and a great deal of fuel given the lorries transporting the concrete would almost certainly not be electric.

Legal barriers to recycling remain, however. Materials classified as waste are generally subject to transportation or reuse restrictions. Building codes are written for virgin materials, says Åkesson. In a step forward, the UK Steel Construction Institute has produced a draft protocol for the re-use of steel.

Another challenge can be how to estimate embodied carbon. Typically, the estimated electricity, fuel or material is multiplied by an appropriate carbon factor, says Richardson. But it is more complex than estimating operational carbon, which probably only includes a couple of energy sources. For embodied carbon, it may require contending with hundreds of materials and products. “It is not mathematically more complex, but it is a lot more time-consuming,” he says.

Renovations can also be trickier to measure because a wide palette of relatively small amounts of materials is involved, making the data harder to track down. In contrast, a new project typically involves large quantities of the highest-carbon building materials, cement and steel.

THE ROAD AHEAD

The construction sector is conservative and for liability reasons likes to use materials it knows it can trust. WorldGBC believes a “radical collaboration” of investors, developers, designers, contractors and materials manufacturers, backed by policy and regulatory support and access to finance can move work forward on embodied emissions. An example of collaboration is the partnership of more than 30 companies and non-profits in an Embodied Carbon in Construction Calculator, dubbed the EC3 tool, which allows architects and engineers to identify North American products on the basis of their embodied carbon. Another example is a collaboration by Skanska and Volvo on devising electric vehicles suitable for construction sites. “Neither could have done it on their own,” says Richardson.

For some, the main lever is legislation. “We need to create demand — that is the key,” says De Meeûs. He cites France, where a new law will create a voluntary system to label building projects according to a lifecycle assessment of their environmental impacts, including embodied carbon. And existing laws need to change. “Today in most municipalities, it is illegal to build higher density, transit-oriented development out of low embodied energy materials like tall timber, which is a fight we should all take on together,” says Vishaan Chakrabarti, founder of the PAU Studio for architecture and urbanism in New York and professor at Columbia University.

More generally, incentives can be offered to the private sector, such as accelerating permitting for projects with lower embodied carbon or density bonuses, says the WorldGBC report. Cities must require LCAs of buildings and set targets and timelines for public procurement. National level policymaking, however, is most important for reducing embodied carbon, says Richardson. WorldGBC suggests steps to encourage heavy industry to decarbonize and for investment in research and development of new, low and zero carbon materials. Most cities and local authorities simply don’t have the scale or budget for such actions, he notes. 

The report says investors, developers and designers should plan to avoid embodied carbon from the outset by considering alternative strategies; reduce and optimise by evaluating each design choice in terms of upfront carbon reductions; take steps to avoid future embodied carbon during and at end of life; and, as a last resort, offset residual embodied carbon emissions through verified programmes. Communication and education, encouragement for innovation and accelerating and leveraging market demand, are also vital.

Focusing only on eliminating embodied energy cannot be the only consideration when meeting global needs for housing, schools and hospitals. Building nothing is not an option in the developing world. But in mature markets, building nothing or less that uses new materials, and building cleverly and efficiently should reduce embodied carbon.

TEXT Ros Davidson

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