Cleaning Up The Construction Sector Is Possible, Says UN

New report lays out an ambitious global plan to reduce embodied emissions

As of 2021, the buildings and construction sector was responsible for more than a third (37%) of global CO2 emissions, making it a significant contributor to climate change.

To date, large-scale efforts to decarbonize the sector have focused on reducing operational emissions – those that result from the function and maintenance of the building (e.g., heating, cooling and lighting). Currently representing just over two-thirds of the sector’s total footprint, operational emissions are expected to decrease considerably over the coming three decades, thanks to electricity grids increasingly making the shift to renewables.

But operations only represent part of a building’s carbon footprint. There are also embodied emissions, which are associated with the entire lifecycle of building materials. These include everything from the extraction of raw materials and product manufacturing (e.g., iron for steel-making), though the building’s construction, and to its eventual end-of-life (e.g., demolition). Embodied emissions aren’t evenly distributed. Most (65 – 85%) occur before a building begins construction, and global supply chains mean that they’re often produced far from the construction site. The scale and complexity involved in materials production makes reducing embodied emissions incredibly challenging. On top of that, demand for building materials is on the rise, powered by population growth and rapid urbanization (particularly in developing nations). According to the OECD, if ‘business as usual’ practices continue, the global consumption of raw materials will nearly double by 2060,“placing twice the pressure on the environment than we are seeing today.” Is it any wonder that embedded carbon, as it’s sometimes known, has been described as “the construction industry’s biggest obstacle to net-zero”?

A new report, published today by the UN Environment Programme and the Yale Center for Ecosystems + Architecture sets out to overcome that obstacle.

Called Building materials and the climate: Constructing a new future, it reads like an ambitious call-to-action for those working in buildings and construction. And while it’s not the first document to argue for urgent decarbonization of the sector, I suspect it’s the most comprehensive to date. The cohort of authors, researchers, and reviewers involved hail from six continents. It runs to 138 pages and includes ~350 references. Suffice to say, it covers far more ground that I can in this short article.*

The report is centered around three paths, dubbed Avoid-Shift-Improve. The authors say that if adopted to the fullest extent, this approach could help the sector reach net zero emissions by mid-century.

1. AVOID waste and new extraction of materials by moving to a data-driven circular economy that prioritizes reuse and recycling of materials.

Currently, material economies tend to be linear, and follow a ‘take, make, dispose’ approach. Linear economies involve constantly extracting raw – and often non-renewable – materials, processing them into products, and then disposing of those products when they reach end-of-life (or if we no longer want them). In circular economies, the goal is to close the cycles of raw materials; to use less initially (reduce), to maximize the utility of products (reuse), and to eliminate waste by recycling the materials again and again.

Moving to a circular economy requires rethinking how buildings are designed. From choosing renewable or recycled materials for construction, to designing for disassembly, the choices made early on have the greatest potential to reduce a building’s embodied carbon. For existing buildings, retrofitting and renovation should be prioritized as they generate considerably fewer (50-75% lower) emissions than new construction.

Efforts to use recycled materials in construction or renovation projects are often stymied by a growing gap between the supply and demand of these materials. The report authors argue that this gap could be filled by a new supply-and-demand model, “…with new enterprises that allow for the careful dismantling of buildings and for the storing, preparation and maintenance of second-cycle materials for resale.” An additional need, they say, is “the adoption of building codes that require designers to specify “circular” components made with re-usable, renewable materials.” All of this requires leadership from national and local government, as well as cooperation across sectors and borders.

2. SHIFT to using ethically managed earth- and bio-based building materials

Wood is a biomaterial that’s been used in construction for millennia, and even today, 38% of the world’s wood products are used in built environment. Recent years have seen a huge growth in the use of cross-laminated timber in mid-rise buildings, where it can replace or supplement steel or concrete, leading to lower embodied emissions. Engineered bamboo, too, has shown promise for use as a structural material, and waste biomass can be used to make reconstituted wood products. Overall consumption of processed wood products is predicted to grow 37% by mid-century.

The authors write that the shift towards these materials “…could lead to compounded emission savings in the sector of up to 40 per cent by 2050 in many regions, even when compared to savings from low-carbon concrete and steel.” But, they caution, a perquisite to this is a transition away from “…the high carbon impacts of much “business-as-usual” forestry and agriculture.” If not managed correctly, a wholesale shift to biomaterials poses risks to natural ecosystems, as well as the potential “… perpetuation or exacerbation of unjust labour practices.”

As part of this, there’s a need to shift perceptions of different building materials. In many regions, concrete, steel and glass are associated with modernity and progress, despite the fact that these materials “only give the illusion of durability”, ending up in landfills after a limited period of time, and contributing to the growing climate crisis.

3. IMPROVE production methods for hard-to-replace materials

Cement, steel and aluminium are the three largest sources of embodied carbon in the buildings sector. Decarbonizing their production methods would be a major step toward the sector’s net-zero ambitions.

There are three steps involved in producing Portland cement, and the second of these steps – producing the clinker – offers the greatest potential for emissions savings. Clinker is a key ingredient of cement, and it’s produced by heating limestone and clay to such intense temperatures (up to 1500°C) that they melt. Replacing some of the clinker in cement with alternative materials, combined with using electric kilns powered by renewable energy in clinker’s production, can cause cement’s emissions footprint to shrink. In addition, the authors write that “As much as 25 per cent of emissions from cement and concrete can be readily saved by adapting building codes [to incentivize the use of lower-carbon forms] and by educating architects, engineers and builders to use the best available technologies.”

For steel, most of the benefits will come from avoiding raw material extraction, because “producing steel from scrap saves around 60-80 per cent energy.” They write that shifting to direct reduced iron technology – whereby oxygen is removed from iron ore without melting – “could reduce the CO2 emissions from primary steel production 61-97 per cent over the next 15-20 years.”

Similarly, for aluminum, there’s a huge benefit to producing from scrap, rather than mining from ore. As of 2019, only 34% of aluminum was made from scrap, but the authors say that “by 2060, aluminium production could be mostly based on scrap, and production could be electrified using renewable energy sources.”

Underpinning this three-pronged approach is the need for global and cross-sectoral cooperation. They write, “Rapid decarbonisation of building materials will not be possible without simultaneously supporting material producers and users such as manufacturers, architects, developers, communities and building occupants, to make the decision to decarbonise.” Access to reliable, transparent data will enable fair comparison between different building materials in terms of their embodied, operational and end-of-life emissions, and should also greatly reduce the risk of greenwashing.

The report lays out a series of policy recommendations and actions that will apply to differing degrees across regions and economies. These include mandating the use of living systems and biomass to protect urban climates, promoting clear and consistent standards for carbon labeling, closing the gender pay gap and improving working conditions, enforcing performance-based building codes that include a material’s environmental performance, and incentivizing circular economy approaches for re-use and recycling. In the final section of the report, the authors highlight seven ‘case study’ countries – Canada, Finland, Ghana, Guatemala, India, Peru and Senegal – each with its own materials challenges, and discuss how the Avoid-Shift-Improve strategy could apply.

As I see it, what this group is proposing is a wholesale reinvention and re-prioritization of the way we plan and build our towns and cities. It’s incredibly ambitious, and reflects the urgency and the scale of action needed in order to mitigate the impacts of climate change.

Anna Dyson, Founding Director of Yale CEA and lead author of the report, summarized it as such, “Since the built environment sector is so complex, with interdependencies across actors, all hands on deck are required to decarbonise, and we can’t leave anyone behind. Policies must support the development of new cooperative economic models across the building, forestry and agricultural industries, in order to galvanise a just transition towards circular, bio-based material economies that can also work synergistically with the conventional material sectors.”

* The report is free to access from If you’re interested in learning more, I encourage you read it for yourself.



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