Embodied Carbon vs Operational Carbon
Embodied carbon vs Operational Carbon – By Holly Peirson Graduate Structural Engineer.
It has long been speculated that to limit our effect on climate change and thus, avoid reaching the ‘point of no return’ for protecting some regions and vulnerable ecosystems, we must collectively ensure that global warming does not exceed the pre-industrial average by 2 degrees for more than a decade. In an aim to address this issue, in 2015 nearly every country pledged to limit the Earth’s temperature increase to 1.5 degrees above pre-industrial levels.
With temperatures continuing to increase and record temperatures being readily broken, particularly within the last year, it comes as no surprise that 2023 was confirmed as the warmest year on record, with about a third of days over the global average temperature. There are varying instrumental factors which have caused this, one large contributor of this is the built environment which produces around 40% of the UKs carbon emissions. Subsequently, the construction sector is responsible for around 60% of UK total waste.
To tackle this issue, two types of carbon reductions in the built environment can be focused upon; embodied carbon and operational carbon.
What is embodied carbon?
Embodied carbon refers to the greenhouse gases emitted up to and during a building’s construction and lifespan, such as the manufacturing of materials, their transportation to site, plant and equipment used to install them, any maintenance required during the building’s lifespan and eventual disposal at the end of the building’s lifespan.
What is operational carbon?
Operational carbon represents the greenhouse gases emitted through the use of energy consumption during the building’s lifespan.
What is currently being actioned to help reduce the demand for fossil fuels?
With the continuous development of renewable energy sources, operational carbon will certainly reduce demand on the current fossil fuel energy production. This is already becoming apparent from statistical research carried out by the Department for Energy Security & Net Zero, with the total energy production for the third quarter of 2023 down by 8% on the same period to last year, as well as renewable electricity generation growth by 7%. As suggested from these figures, fossil fuel generated electricity decreased by 31% in the third quarter of 2023, with renewable generation increasing by 44.5%, outpacing fossil fuel’s share for the fourth consecutive quarter.
With continued operational carbon decarbonisation net gains in renewable energy, the trajectory of embodied carbon emissions indicates that they will form over half of the built environment emissions by 2035. We therefore believe the primary focus within the built environment and construction sector should be based upon employing techniques in reducing embodied carbon emissions, from inception of a structure or building, to its end of life. Currently there is no legislation, nor mitigation to enforce the reduction of embodied carbon emissions, and therefore the industry typically continues to be driven by one key influencer….COST.
Our Commitment. Your choice – what is our responsibility as Structural Engineers?
As Structural Engineer’s, we are not directly able to influence the amount of operational carbon emissions within a structure or building. Nevertheless, through collaboration and early involvement with architects and mechanical and electrical engineers, we are able to support their initiative in reducing operational carbon.
We also have a responsibility, as leading technical designers to collaboratively influence how the built environment is formed, to offer options and advise to our clients on how embodied carbon can be reduced.
There are various techniques that can be employed to reduce embodied carbon emissions. Broadly, these are; design optimisations through lean design techniques, material changes to more sustainable resources, and collaboration and raising awareness through influencing the brief of a project. Unlike operational carbon, as Structural Engineers, we are able to meticulously utilise these techniques to reduce the amount of embodied carbon apparent from structures and buildings, pre-use. As it currently stands, this value makes up approximately 55% of the whole lifecycle embodied carbon, thus small changes could have a big impact.
How Can We Optimise Design Through Lean Design?
By employing lean design, there are various ‘quick win’ tactics that can be exploited. The obvious being, ‘Don’t build’. This may seem counterintuitive, however if the clients brief works in a way in which an existing structure or building can be upgraded or repurposed to meet the brief, then not only will this incorporate circular economy principles for reducing embodied carbon, but will likely save money. For example, even if the superstructure (above ground elements) cannot be reused then can the substructure (below ground elements) be reused? Typically the substructure forms 20% of the total embodied carbon we as structural engineers have direct control over.
Other things such as designing each individual item to its maximum utilisation to reduce waste and optimise the materials used. Not to mention, this helps to make the structure lighter and in turn reduce substructure size. Typically the average utilisation of steel buildings is below 50%, this is usually for buildability, connections and simplification purposes. For a competent contractor, with the right guidance and information from the structural engineer, this norm should be challenged in order to make notable embodied carbon savings.
What Material Changes Can We Make To Become more Sustainable?
It comes as no surprise that some building materials are more sustainable than others. Typically this is associated with natural materials with minimum manufacturing processes being low in embodied carbon, and manmade materials with lots of manufacturing processes being high in embodied carbon. Of course there is more to it than just that; like the distance in which the material travels, how readily available it is and has it been repurposed etc?
As Structural Engineers, there are four typical materials used to form a structure; these are masonry, reinforced concrete, steel and timber. Though the obvious choice for low embodied carbon is timber, we can’t build everything out of it. We must ensure that it is sourced sustainably, and whether it works for the type of building. We therefore must ask the following question:
Some key considerations for each materials may be:
Masonry:
Where long panels of masonry are present, requiring further reinforcement or steel wind posts, can piers be utilised to remove this requirement. Furthermore, as an addition to this, good detailing practices such as provision of optimum movement joint locations and correct masonry specification allows for extending the design life of masonry, thus directly reducing the embodied carbon of the material.
Reinforced concrete:
The key items in which kill concrete’s chance of being low in embodied carbon are; its cement content and quantity required. Thus, if these things can be focused upon, substantial savings can be made. For example, can concrete curing time be extended in order to reduce the cement content required. Or perhaps rather than a flat slab design, can a ribbed or waffled slab be used to reduced the mass of concrete within the structure.
Steel:
The most obvious saving in steel can be found from optimising each member size. Furthermore, it is becoming more readily available for steel to be reused and repurposed. Where possible this has a significant impact, as there is no embodied carbon within the manufacturing process as there isn’t one, and like masonry, if the lifespan of the steelwork can be extended this reduces embodied carbon.
Timber:
As timber is a biogenic material (absorbing carbon dioxide and releasing oxygen in its living state), it is already an excellent material for reducing embodied carbon, but ensuring it is detailed correctly in order to avoid contact with water and rot to ensure its longevity is paramount in maximising its carbon neutral qualities.
Lower carbon material alternatives such as cob, straw bales, rubble stone footings and bamboo may also be considered for clients with an appetite for lower embodied carbon materials.
Collaboration and Raising Awareness through Influencing the Brief
Ultimately, to make a true and impactful difference in reducing embodied carbon and its wider impact on decarbonising the built environment, is how technical designers and the clients can collaborate to influence the brief of a project. Simply, this can be done by optimising the design, selecting the right materials for the right situation and using them efficiently, as well as being smart with how the structure is put together. To do this, not only is collaboration important, but knowledge is king!
Having a basic understanding and awareness of the impact of different materials, ‘quick win’ savings and their application is important. But how they are put together is equally significant. For example, the modern sort-after open plan living isn’t always sustainable, with longer spans required, thus heavier and larger members (which are typically more expensive). We understand that this is typically a non-negotiable item within a client’s brief, but through collaboration and knowledge, can compromises be found? For example, can a column be added to reduce the span of a beam and therefore reduced its weight? Or can an alternative material such as glulam timber be used? What is the use above this open plan space being used as, and can its loading criteria be reduced? Simple acts can have a considerable impact in reducing embodied carbon and typically, a reduction in operational carbon. i.e. a smaller room is easier to heat.
All things considered, we must ensure that in making embodied carbon savings, we are not adversely affecting operational carbon savings. Therefore, a balance must be struck. We cannot, and must not ignore the importance of embodied carbon, and therefore, we at Superstructures use tools to provide this knowledge, experience and collaboration with our clients and technical associates. But it is the client’s choice whether they utilise these tools to adapt their brief and aid in decarbonising the built environment.
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