Buildings account for almost 40% of carbon emissions generated globally, making them one of the most significant contributors to our carbon footprint [1].

The CO2 emissions they produce are generated from a number of sources which are broadly categorized into operational emissions and embodied emissions. Operational emissions, which are the more widely recognized and understood of the two, link to the in-use performance of the building. Embodied emissions are made up of the carbon associated with the sourcing of the building materials, construction processes, ongoing refurbishment and maintenance, and end of life.

To date, much of the sector’s efforts have focused on reducing operational emissions. In part due to legislation, which has prioritized operational reductions, interventions such as LED lighting upgrades, improving building insulation and increasing uptake of on-site low carbon technologies have been widespread.

Increased awareness of the financial savings that can be made by enhancing a building’s operational efficiency has also contributed to the focus on tackling operational emissions. While over time tackling operational emissions has become even more compelling financially as a result of improving technology delivering further operational cost savings (e.g. through lower energy use). Additionally, the decreasing cost of low carbon technologies has made them more affordable to the mass market.

Across the sector, these changes have contributed to marked reductions in operational carbon emissions. This has been driven particularly by advances within the prime sector by high-status projects, such as recent Stirling Prize winner the Bloomberg Building which has been able to take advantage of the best technology and expertise on the market. Costing £1 billion to construct, the Bloomberg building achieved the highest BREEAM score ever of 98.5% for a major office project. At the other end of the spectrum though, in the secondary and tertiary sectors, progress has been slower as the focus has tended to be more on the quicker and inexpensive carbon savings.

Despite these variances, overall progress has been made. Twenty years ago, operational emissions accounted for as much as 94% of buildings whole lifetime emissions[2]. Since then, improvements to the operational efficiency of many buildings has seen these emissions decrease. However, as a consequence, many buildings have seen an increase in the embodied carbon share of whole lifetime emissions.

For example, in low-energy buildings, which may have implemented some of the measures listed above, the embodied carbon share could have increased to 26 – 57 %[3]. While further still, in operationally zero-carbon buildings the embodied carbon share could be up to 100 %. As such, as buildings have become more efficient, the relative contribution of embodied carbon over the building lifecycle has become more significant.

Operational vs Embodied Carbon over time

Acknowledging that the property industry is at different stages on its journey towards carbon neutrality, it is important that we do not lose focus on the challenge posed by operational carbon. Tackling operational carbon is the most cost-effective and easy way to make significant carbon savings.

Despite this, once these ‘quick wins’ are exhausted, continuation towards true zero-carbon will require us to consider more integrally the role of embodied carbon. While embodied carbon is inherently more difficult to influence as a result of most of it being locked within the building fabric, we must now turn our attention to it, to ensure the built environment’s progress in reducing its CO2 emissions is continued.

To support us in this journey, the cradle to grave approach provides us with a clear set of boundaries which delineates the different stages within the whole life of a building. This allows us to successfully apply life-cycle analysis to identify the CO2 associated with each step in the building lifecycle. Utilizing this more holistic approach, it is possible to establish a more complete picture of our buildings actual carbon footprint. Thereby allowing us to take more considered decisions such as whether to use pre-fabricated cross-laminated timber modular elements, which will have high processing related emissions, but low construction related emission, or to use a more traditional construction method. In many cases, such decisions will need to be taken on a site-specific basis.

Cradle to Cradle Approach

As well as being a way to avoid poor decision-making, the application of life-cycle analysis early in the development process also actively encourages forward thinking. It encourages conversation about how best to future-proof buildings against embodied carbon related to the ongoing maintenance and refurbishment, and end of life management. For example, to reduce the embodied carbon related to maintenance, buildings can be designed with less complex finishes and in a modular way. This can both reduce the need for refurbishment and allow for any necessary refurbishments to target the specific areas which require maintenance.

Taking this idea further still buildings can be designed with eventual deconstruction in mind. Although the sector has made great advancements in recycling construction waste which should be commended, this has largely been part of an attempt to see what we can get out of it at the end, rather than by design. Designing for deconstruction turns this idea on its head, allowing us to make plans for building disassembly from the outset. While in practice examples are limited, projects including Venlo City Hall and the Environment Building highlight the potential of this approach. Funded through the EU Horizon 2020 programme, BRE is also contributing to the Buildings as Material Banks (BAMB) project which aims to help the building industry make this shift towards a circular economy.

A potential reason embodied carbon isn’t currently considered as frequently as it should be is because of the difficulties in measuring it. Although the concept is becoming more widely understood, a study by Pomponi and Moncaster[6] found that the science behind embodied carbon assessments is yet to reach maturity and as such it is hard to verify, replicate and draw useful comparisons between them. Moreover, they suggest that similar to the performance gap in the operational phase of the building, inaccurate embodied carbon assessments run the risk of causing a second performance gap relating to the embodied impacts. The significant difference being that there is no way of putting right a performance gap for embodied carbon.

For this reason, it is essential that the sector comes together to develop a standardized approach to measuring embodied carbon. In time this could happen through the inclusion of embodied carbon calculations at the design stage in national building regulations. However, until then, voluntary certifications such as BREEAM have a key role to play. As well as increasing the comparability of assessments using programs such as IMPACT, BREEAM provides a framework for project teams to think holistically about their building’s requirements across the full life cycle. Instead of thinking solely in terms of operational emissions, this encourages project teams to consider the design through the lens of embodied emissions as well. Ultimately it is only through understanding and then optimizing these relationships that we can hope to achieve a genuinely zero-carbon built environment.

[1] https://www.worldgbc.org/sites/default/files/UNEP%20188_GABC_en%20(web).pdf

[2] https://buildingscience.com/documents/insights/bsi-012-why-energy-matters#Reppe

[3] Chastas, P., Theodosiou, T., Bikas, D. and Kontoleon, K., 2017. Embodied energy and nearly zero energy buildings: A review in residential buildings. Procedia environmental sciences, 38, pp.554-561.

[4] https://www.architectsjournal.co.uk/home/the-elephant-in-the-room-embodied-energy/8637400.article

[5] https://continuingeducation.bnpmedia.com/courses/tally/promoting-sustainable-design-through-life-cycle-assessment-applications/2/ 

[6] Pomponi, F. and Moncaster, A., 2017. Scrutinising embodied carbon in buildings: The next performance gap made manifest. Renewable and Sustainable Energy Reviews.