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Embodied carbon: the untold story
A largely overlooked problem, and one fraught with challenges, is the embodied carbon emissions associated with buildings. But what are they and what is hindering progress. Sustainability and ESG Consultant, Zhenghan Zhang explains.
Embodied carbon emissions are the greenhouse gas emissions associated with the entire life cycle of building materials, including manufacturing, transportation, construction, maintenance, and demolition. The holistic assessment of these emissions throughout a development's life stages is known as the Whole Life Carbon Assessment (WLCA). The diagram below, originally created by Green Building Council Australia, explains the whole life carbon stages as per EN 15978 in more detail.
Traditionally the focus of the construction industry has been on operational carbon emissions, primarily stemming from energy use, but achieving net-zero buildings requires a comparable emphasis on embodied carbon emissions. These emissions play a crucial role in a building's overall environmental impact.
In the UK, as operational efficiency improves and the electrical grid decarbonises, the relative impact of embodied carbon in buildings becomes more pronounced. Based on recent estimates1, these emissions are likely to form over half of built environment emissions by 2035.
This suggests that a Net Zero 2050 goal is meaningless without action on embodied carbon.
Reducing embodied carbon: challenges and progress
So with action needed, what are the barriers and where are we seeing progress being made.
The lack of Government policy mandating the assessment or control of embodied carbon in buildings hinders progress in emission reduction.
Some local authorities2 independently mandate WLCA. To address this gap at the national level, the proposed building regulations document Part Z3 aims to make WLCAs and reporting mandatory. This move is seen as a straightforward way for the Government to substantially reduce carbon emissions.
Quantifying embodied carbon through a comprehensive database4 is essential for accurate assessments. However, there is a scarcity of robust databases which has a knock-on impact on transparency, with many assumptions undisclosed, and concerns about the consistency in assumptions, measurements, and reporting.
To overcome these issues, the Royal Institute of Chartered Surveyors (RICS) released the WLCA Standard (2nd edition) methodology. This provides default figures, allowing deviations only when explicitly specified by users and requiring strong justification, thus enhancing transparency in the assessment process.
The challenges previously mentioned make it difficult to establish reliable benchmarks for embodied carbon, especially in the context of retrofit and refurbishment projects, which vary widely in each instance.
The organisation LETI5 has played a pioneering role in researching and providing insights into embodied carbon emissions in the real estate sector for several years. Their notable contributions include the Embodied Carbon Primer5 and embodied carbon targets. However, there remain limitations, for instance, there are no benchmarks for logistics buildings which have seen record breaking take-up in recent years6.
What is more sustainable – to retrofit or demolish?
This debate has gained a high profile in cases such as the Oxford Street M&S building. Financial viability often favours a demolish and rebuild solution but this is associated with a higher carbon cost.The Greater London Authority’s (GLA’s)7 committees are exploring how the carbon costs associated with retrofit versus rebuild are weighed up with other factors like structural and design issues, financial viability, and heritage.
There is a huge drive, driven by initiatives like the Carbon Risk Real Estate Monitor (CRREM) to retrofit buildings for energy efficiency and ultimately reduce operational carbon emissions. But at what point does the embodied carbon of retrofit exceed the operational carbon savings generated?
CRREM8 published a report providing practical tips on achieving a balance between reducing operational emissions and mitigating embodied emissions. Based on an analysis of 36 global energetic retrofit projects, they identified a carbon payback of up to eight years.
Timber, as a naturally sourced material, has long been acknowledged for its substantial potential in constructing more sustainable buildings, serving as an alternative to traditional materials like concrete and steel. Despite this recognition, challenges in risk management have impeded its widespread adoption.
Last year, Aviva9 highlighted its commitment to sustainability by expanding its underwriting scope to include engineered timber. This development is encouraging, marking the beginning of a journey towards integrating timber structures as already seen in Ireland and mainland Europe.
The pursuit of carbon reduction measures in design faces significant challenges within the supply chain, particularly when it comes to the limited accessibility and high costs of low-carbon materials.
One prominent example is steel, which contributes to about 8%10 of global carbon emissions and normally ranks among the top five materials with the highest embodied carbon impact in construction. Virgin steel produced in a basic oxygen furnace has a substantial embodied carbon of approximately 2,800 kgCO₂e/tonne. In contrast, steel made from 95% scrap in an electric arc furnace (EAF) results in significantly lower embodied emissions, at approximately 800 kgCO₂e/tonne.
Similar challenges are observed in the realm of concrete. Incorporating low-carbon cement replacements like ground granulated blast-furnace slag (GGBS) is a common approach. However, as industries associated with these substitutes, such as steel manufacturing and coal burning, are expected to decline in a low-carbon future, the availability of GGBS and fly ash may diminish and are being sourced from countries such as China to the detriment of transport emissions.
These challenges highlight the necessity for innovative solutions and a diversified approach to address issues in the supply chain and reduce embodied carbon in construction materials. The market must be able to adapt and move quickly to support the trialling of new materials.
Our Sustainability and ESG team create project specific solutions, driving innovation and integration of embodied carbon within exemplar schemes. To find out how we can support your project, or for a discussion on formulating low-carbon solutions, please get in touch with Zhenghan Zhang.
14 February 2024
[1] Reducing embodied carbon footprint: A key consideration to meet UK’s 2050 net-zero target
[2] Greater London, also emerging policies in Manchester and Edinburgh
[3] Part Z
[4] Database to include manufacturing emissions, transportation details, and maintenance scenarios
[5] Embodied Carbon Primer
[6] Logistics: Insight into the industry
[7] The carbon footprint of retrofit vs rebuild
[8] Embodied Carbon of Retrofits
[9] Aviva expands underwriting appetite to include engineered timber for commercial buildings
[10] World Steel Association, “Climate change and the production of iron and steel,” 2020