rethink sustainability
Decarbonisation in an urban world: the low-carbon materials that could slash construction emissions
Around the world, a new urban area the size of Paris is built every week1. Driven by a combination of population growth and migration from country to city, the global urban population has risen 450% since 1960, growing six times faster than the rural population2.
Much of this urbanisation is taking place in emerging market nations, where populations are growing fastest and the shift from a rural to an urban economy is still gathering pace. According to the United Nations Environment Programme, at least 200 new cities are expected to be built in Asia alone between 2020 and 20503.
As we face climate change, this poses a challenge – already the world’s buildings emit around 18 billion tonnes of CO2e each year, one third of all man-made greenhouse gas emissions (GHGs)4. 20% of these emissions come from construction, with materials such as concrete and steel responsible for huge quantities of “embodied carbon”. As the global population grows, and cities expand, it is essential that we find low-carbon materials to build tomorrow’s urban world.
Watch our video in partnership with the FT and discover the low-carbon materials that could slash construction emissions:
Turning cities into carbon stores
In 2025, ground will be broken on the construction of ‘Wood City’ in Stockholm.5 Dubbed “the world’s largest wooden city”, its 250,000 square metres of homes, offices and retail outlets will use more laminated timber (LT) than any previous construction project.
LT, made from layers of wood bonded together with moisture-resistant glue, is light, strong, and has good resistance to fire, and with a high strength-to-weight ratio it is ideal for constructing low- to mid-rise buildings, which are key to urban growth in emerging market nations.
Crucially, LT can be produced from renewable sources and can even be carbon negative. According to Building Materials and the Climate: Constructing a New Future, a report by the UN Environment Programme (UNEP), LT can store up to twice as much carbon as is emitted during the production process, locking it away for many decades. However, the report warns, as much as 30% of the global timber trade comes from illegal logging and poorly-managed forests. LT’s carbon-negative potential can only be realised where new trees are grown in place of felled trees, in forests managed in harmony with the local ecology.
The report also highlights the potential for buildings to be constructed from bamboo, which has “a tensile strength close to steel and a compressive strength twice that of concrete.” Bamboo is fast-growing – felled bamboo can grow back to maturity in just five years – and can store at least 50% more carbon per hectare than forests. However, the report notes, while bamboo ‘wood’, like LT, will act as a long-term carbon store, the chemical process currently employed to make bamboo construction materials viable is itself high in GHG emissions.
Building for reuse
Every year, construction, renovation and demolition produce at least 13 billion tonnes of waste8. 35% of this – the equivalent of more than 12,000 Empire State Buildings9 – ends in landfill10.
‘Selective deconstruction’ – where buildings are dismantled rather than demolished – could prevent much of this waste by enabling greater materials reuse. According to the UNEP report, studies in Peru and Canada found lifecycle GHG emissions for residential buildings were reduced by between 63% and 70% when buildings were selectively deconstructed and the materials reused, a greater reduction than was achieved by recycling. The report argues that as the world’s cities grow, designing modular buildings that can be disassembled easily could be an important part of cutting emissions.
Where materials cannot be re-used, there is fast-growing interest in finding new ways to recycle. For instance, researchers from the University of Cambridge have, for the first time, demonstrated that end of life cement can be recycled in electric arc furnaces as a by-product of the steel recycling process11. If done using renewably-generated electricity this could produce economically-competitive, zero-carbon cement at scale.
Calling for reuse first and recycling only as a last resort, the UNEP report urges governments and industry to view aging buildings not as obstacles to be cleared but as the primary source for materials, concluding, “In a circular economy, buildings will become material banks for future construction.”
Decarbonising concrete and steel
Despite these innovations, the pace of urbanisation means we will continue to need virgin materials for many years to come. With the industry under pressure to cut its emissions footprint, researchers and entrepreneurs are eyeing up an opportunity to decarbonise concrete, the world’s second most consumed material after water.
In 2022, British start-up Seratech won the prestigious Obel Award architecture prize, for their work producing cement – a key component of concrete – using waste CO2 emissions.12 By capturing this CO2 from a plant’s own emissions, Seratech promises “net zero concrete at scale” that can be produced without any modifications to the manufacturing process. Meanwhile researchers at the Massachusetts Institute of Technology have discovered that simply adding baking soda at an early stage of cement production can lead to concrete with 15% lower carbon emissions.13
Similar efforts are being made with steel, which, like concrete, is responsible for as much as 8% of all man-made CO2 emissions14. Steel production requires temperatures of up to 1,700 degrees Celsius, which can be near impossible to achieve without burning fossil fuels. Now, though, zero-emissions green hydrogen – hydrogen produced using renewably-generated electricity – is beginning to replace fossil fuels, bringing emissions-free steel within reach.
One major stumbling block is the high and often volatile cost of green hydrogen. In Sweden, HYBRIT – a collaboration between a steel producer, a mining company and an energy provider – has launched one of the world’s first large-scale hydrogen storage facilities in an underground cavern.15 Research has shown that storage on this scale can reduce the variable cost of green hydrogen by as much as 40%, making fossil-free steel more cost-competitive.
Read also: Green hydrogen: the key to decarbonising heavy industry
Regulations create new investment opportunities
The push for construction decarbonisation is being created, in part, by new regulations. In late 2023, New York Governor Kathy Hochul announced new ‘Buy Clean Concrete’ rules, which set emissions limits on the concrete used in all New York state-funded construction projects16. A similar law has been passed in New Jersey.17 In the EU, a minimum of 70% of construction waste must be reused or recycled; while the recent update to the Construction Products Regulations obliges manufacturers to declare the sustainability-performance of their products, so that the environmental impact of construction projects can be calculated18.
The regulatory direction of travel is clear. Increasingly, bio-based, renewable and other low-carbon materials will be preferred, while materials with a large emissions footprint will fall from favour. For investors this represents both a risk and an opportunity in a vast industry worth almost USD 10 trillion each year21. This opportunity will arise not only in the materials themselves, but also in digital solutions like Digital Product Passports, which help developers keep track of the environmental impact of their projects.
The UN’s Food and Agriculture Organisation estimates that almost 70% of the global population will live in cities by 205022, up from 56% today23. As the urban jungle grows, it’s vital that we build with materials fit for a sustainable, low-carbon future.
1 Building Paris every week: Urgent need to cut emissions in construction sector | UN News
2 Urbanization - Our World in Data
3 Cities of the future: the ultimate design challenge (unep.org)
4 Buildings are the foundation of our energy-efficient future | World Economic Forum (weforum.org); Global GHG emissions 1970-2022 | Statista
5 Stockholm Wood City to be the largest wooden city in the world | World Economic Forum (weforum.org)
6 Evaluation of mechanical properties and carbonation of mortars produced with construction and demolition waste - ScienceDirect
7 Microsoft Word - ESB Fact Sheet 4 9 14 (esbnyc.com)
8 Evaluation of mechanical properties and carbonation of mortars produced with construction and demolition waste - ScienceDirect
9 Microsoft Word - ESB Fact Sheet 4 9 14 (esbnyc.com)
10 Circular Economy of Construction and Demolition Waste: A Literature Review on Lessons, Challenges, and Benefits - PMC (nih.gov)
11 Electric recycling of Portland cement at scale | Nature; Cement recycling method could help solve one of the world’s biggest climate challenges (cam.ac.uk)
12 Seratech carbon-neutral concrete wins Obel Award 2022 (dezeen.com)
13 New additives could turn concrete into an effective carbon sink | MIT News | Massachusetts Institute of Technology
14 What is green steel and how can it help us reach net zero? | World Economic Forum (weforum.org)
15 4 breakthrough actions to decarbonize steelmaking | World Economic Forum (weforum.org); Hybrit (hybritdevelopment.se); World’s first storage facility for fossil-free hydrogen gas up and running - IO (innovationorigins.com)
16 Governor Hochul Announces Adoption of First-in-the-nation ‘buy Clean Concrete’ Mandate for State Agencies | Governor Kathy Hochul (ny.gov)
17 New Jersey Adopts First-of-a-Kind Low Carbon Concrete Law (nrdc.org)
18 The Commission welcomes provisional agreement on the revised Construction Products Regulation, which strengthens the Single Market and supports the green transition - European Commission (europa.eu); Press Release – New Regulation on Construction Products adopted: first EU-level rules for green public procurement of building materials - Bellona.org
19 Microsoft Word - Synthesis_Report.doc (fao.org)
20 Urban Development Overview (worldbank.org)
21 https://www.oxfordeconomics.com/wp-content/uploads/2023/10/Global-Construction-Chartbook-Q3-2023.pdf
22 Microsoft Word - Synthesis_Report.doc (fao.org)
23 Urban Development Overview (worldbank.org)
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