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Operational carbon Vs Embodied carbon

Aeroplane flying through sky and one being constructed

As we creep ever closer to the 2050 net-zero deadline, reducing CO2 throughout the design, construction and operation phases of our new buildings and infrastructure is key. With engineers and construction professionals still adjusting to this sustainable movement, there can be the potential for confusion with many new phrases and terms flying around.

Embodied carbon and operational carbon, ECFs and EPDs are just a few examples. Here, we seek to take away some of the mystery.


Operational vs Embodied carbon

A crucial aspect of planning and designing using green alternatives is understanding operational versus embodied carbon. While both contribute to overall whole-life carbon emissions, embodied carbon can be defined as the carbon output produced during the construction of a building. It is the result of specific processes and design decisions, rather than an ongoing emittance of CO2. This includes the manufacture and extraction of materials used for the building’s construction and transporting those materials to the site.

Contrastingly, operational carbon is the CO2 emitted during the ongoing operation of the building, which of course, can fluctuate depending on the technology and level of usage over time. MEP services, appliances and other infrastructure like automatic doors all contribute to operational carbon.

To put this in real-life terms, a plane flying from the UK to Germany would be classed as operational carbon, whereas the CO2 generated from the plane’s original construction would be embodied carbon.

In recent years, significant steps have been taken to reduce operational carbon, with substantial improvements in technology and energy-efficient appliances. Inventions like LED lighting, smart heating and innovative home technologies are just some examples of the progress made to reduce operational carbon. These products should be standard across newly constructed buildings, and they will be vital in the effort for net-zero.

In comparison, we are still using carbon-intensive methods of making our building materials and constructing our buildings. As such, it’s crucial that we address embodied carbon levels and work to reduce this within the built environment.

One way to do this is to calculate embodied carbon throughout the initial design and engineering stages and monitor it throughout. By calculating the embodied carbon in these early design stages, engineers can make better and more informed design decisions, with more time to make changes based on the embodied carbon output.

Estimating the embodied carbon of each structural component, such as a steel beam or concrete slab, is typically calculated by multiplying the quantity of the material by a carbon factor, usually measured in kgCO2e per kg of material for each part of the lifecycle, which looks like this: Quantity of Material x Carbon Factor = Embodied Carbon


Construction Lifecycle 

The construction lifecycle includes suggested Embodied Carbon Factors (ECFs) at each section, making calculating and monitoring the embodied carbon much more manageable at each stage. As you can see from the graphic below, the lifecycle is split up into four stages and multiple modules for more accurate calculations.

The construction lifecycle for embodied carbon
Figure 1.1 – Taken from IStructE

Stages A1 to A5 relate to the product and construction phase and, in turn, embodied carbon generation. While the modules within the B stages relate to the building or structure’s lifetime use, classified under operational carbon. Beyond the four life cycle stages, a separate section covers some miscellaneous carbon outputs that should be considered. These are known as 'Beyond the Life' and cover the carbon benefit or load for recycling materials, energy recovered from materials, and the reuse of materials. Of course, the recycling or reuse of products at the end of their life contributes toward a circular economy that will go a long way in the UK's journey to net-zero.


ECFs vs EPDs

Environmental Product Declarations (EPDs), often confused for ECFs, are product-specific reports that document the environmental impact and performance of a building product or material. Essentially, an EPD is a tool that helps fabricators and specifiers opt for more environmentally conscious materials for production, thus lowering the overall carbon impact. 

While an EPD is specific to a particular product, ECFs take this insight further, considering the other life-cycle stages - including transportation to site and on-site assembly - to provide a more rounded view on its overall carbon value. The engineering industry will use ECFs when modelling the building or structure and providing a report on its embodied carbon emissions.

A vital issue with embodied carbon monitoring and calculating is the current lack of a strict code around it. While EPDs are standardised and regulated, ECFs are not – a clear sign of how new the industry is to the issue of embodied carbon calculations. As such, embodied carbon results can vary quite greatly between engineers, despite using the same materials in the same way. Of course, embodied carbon is an emerging topic in construction, and in due time, standards will most likely be set for everyone to work from.

Found within Trimble's Tekla Structural Designer, the Embodied Carbon Calculator works collaboratively with the 3D modelling and engineering design and analysis software. Purpose-designed for those early planning stages at the A1-A3 level, the tool enables an automatic view and understanding of the carbon impact on materials and plans, allowing engineers to make more informed choices in the early design stages of construction and understand each structure's embodied carbon output.

For more information and guidance on embodied carbon and calculating it, visit The Institution of Structural Engineers website, and view their guide on calculating carbon.