Photo by Rhys Moult on Unsplash

Your questions answered about embodied carbon and scope three emissions.

Alex Herridge is something of an expert on embodied carbon. He works for one of the water utilities in the UK – Welsh Water. Herridge’s job is to reduce the company’s carbon footprint. He’s employed by The Capital Delivery Alliance, a group of six companies (Welsh Water, Skanska, Arcadis, Arup, Morgan Sindall and Mott Macdonald Bentley) that deliver Welsh Water’s £200m per annum capital program. This includes everything from pipelines, treatment works, dams and reservoirs, new builds and refurbishment to demolition.

Alex Herridge

Prior to this job he was part of the energy team where he was responsible for operational carbon accounting, energy analysis and delivering solar PV projects.

(Aside: uniquely, Welsh Water is the only UK utility owned by its customers. Thames Water, the country’s biggest water supplier, used to be part owned by Macquarie, the Australian infrastructure bank, until they sold their share to the Canadian pension fund Omers and the Kuwait Investment Authority Thames Water for an estimated £1.35bn. These utilities are great for investors, not necessarily providing such a good service to customers, but Welsh Water is an exception, being constituted as a mutual.)

The concept of embodied carbon

So what is embodied carbon? Herridge explains: “The concept of embodied carbon can be applied to any product, be it a water treatment works or a pencil. It is a greenhouse gas emissions arising from the manufacturer and distribution of the product up until the point it is handed over to the end use or customer.”

Most of these are invisible emissions – in the indirect supply chain.

He gives some examples, comparing Tesco’s Not From Concentrate orange juice (higher footprint from shipping the water content around the world) and Concentrated orange juice (lower footprint from less transport) and milk (high footprint from the inherent inefficiencies in using animal products and especially from cows as they naturally emit large quantities of methane – a greenhouse gas 28 times more powerful than CO2).

There used to be a product label for carbon footprinting but it was not widely taken up. Swedish oat milk brand Oatly has recently started publishing footprint values on the side of their cartons in order to promote the idea and challenge the rest of the food and drink industry to follow suit.

Types of whole life emissions

But somebody’s embodied and scope three emissions will be somebody else’s scope one emissions, says Herridge.

What does he mean? According to the rules laid down by the Independent Panel on Climate Change, greenhouse gas emissions are classified as either:

Scope 1 – all “direct” emissions from the activities of an organisation, or under their control, such as fuel use on site, gas boilers, fleet vehicles and air-conditioning leaks.

Scope 2 – “indirect” emissions from electricity purchased and used by the organisation caused when the electricity is produced.

Scope 3 – all other “indirect” emissions from the organisation’s activities from sources they don’t own or control. This is usually the largest share of the carbon footprint, and associated with business travel, procurement, waste and water.

Welsh Water has an aim to reduce its carbon emissions to net zero by 2050 and by at least 50 per cent by 2035. Different organisations have set themselves different targets.

For example, clothing supplier Zalando has committed to reduce its scope 1 and 2 emissions 80 per cent, increase its annual sourcing of renewable electricity to 100 per cent, reduce scope 3 emissions from its supplying private label products by 40 per cent, and that 90 per cent of its supply chain should have science-based targets for reduction, all by 2025.

While Welsh Water can reduce its operational emissions by doing things like using residual heat from its effluent treatment to produce energy to heat offices, Herridge is particularly focused on the embodied energy of construction.

The embodied energy of construction

“Before your asset is used, or the building occupied, it has already caused the emission of greenhouse gasses (GHGs),” he says.

“We use the ‘Cradle to Built Asset’ approach to footprinting,” he says, “without losing site of end of life impacts). This is because we have direct influence (but not always control) over all elements of the process (design, material choice, construction processes on site).

“If undertaking an assessment for an Environmental Product Declaration then there are internationally agreed ‘modules’ that define the scope of the analysis. The choice is up to the supplier. For example, a material supplier may choose to use a ‘Cradle to Gate’ approach, because after the product leaves the factory the supplier has little/no control over how the product is used.

“The supplier’s Scope 1 emissions would stop when it leaves the factory. Downstream emissions can be difficult to control. For example, 80 per cent of the energy use in the water cycle is the domestic and industrial heating of water that is not in Welsh Water’s control.”

The different extents of embodied carbon scopes.

“The relative impact of each section above will depend upon the material. Recycled material will often have a lower carbon footprint as less energy and transport may be required. Heavier products may have more impact in transport and more highly processed materials may have most emissions within the manufacturing process.”

Low carbon concrete

Naturally, new infrastructure usually involves pouring concrete. Alex Herridge has some tips that he uses for minimising the carbon footprint of this notoriously high carbon material.

“Processing concrete releases CO2 directly, unlike steel, where the emissions come from the energy used in making it,” he says. “Although in the future the cement industry is planning to capture and store or use that CO2, there are several opportunities to reduce the carbon impact of concrete.

“These include using recycled aggregate (reducing the requirement for quarrying of virgin material), sourcing locally, using less, not overspecifying, using the correct strength, or substituting Portland Cement with a lower carbon version such as Ground Granulated Blast Furnace Slag or Pulverised Fly Ash, both byproducts of other industries. South Wales does produce its own low carbon concrete replacement.”

The shrinking operational footprint

As the electrical grid decarbonises and buildings become better performing, and if you source renewable electricity, then the amount of carbon emissions embodied in the manufacturing process becomes a greater part of the whole life cycle emissions of a building or operation.

“In the built environment there may tradeoffs – for example enhanced insulation may require a greater embodied carbon, but result in lower whole life emissions,” says Herridge.

Comparing the whole life carbon of a current building with an ultra-low carbon one. As operational carbon falls, the relative importance of embodied carbon increases. Source: LETI embodied carbon primer.

Building maintenance becomes a higher proportion of operational carbon – so design for low maintenance requirements and flexibility of use.

Sources of data

Where does Herridge go for information about the embodied carbon of materials? He says he finds the revised ICE database [the Inventory of Carbon and Energy] invaluable (this is produced by of Bristol university, which was recalculated in 2019. Also EPDs (for products), BEIS emission factors (BEIS is a UK government department) and BIM models.

The time value of carbon

Herridge says “I am acutely aware that the climate crisis is now and we need emissions reductions now. The value of emissions saved down is therefore higher than emissions saved in the future. Also, delaying construction of a new building gives us more time for innovation and decarbonisation so that the building in the future will be more efficient than the one now.”

To guide him, he says he uses the build hierarchy pyramid:

“Firstly, challenge the root cause of the need. Undertake a detailed root cause analysis. Can the need be met another way, such as re-purposing another asset or building? Can you refurbish and optimise existing assets to optimise their use? Build clever means introducing low carbon materials and making the design lean. For example, avoiding compulsive over-specification, going for easy and efficient construction, such as using standard modules to reduce off cuts. Utilise offsite construction techniques.

“On site, use a low carbon site setup (electric and hybrid plant, solar powered welfare facilities with diesel as a backup only), reduce waste. and at the end of life, design for resource recovery and for flexibility to delay capital maintenance and refurbishment.

“The size of the pyramid is the size of the opportunity. When the design is complete and you are on site, your ability to influence the outcome has almost totally gone.”

This logic results in the carbon reduction curve, taken from the UK government’s Infrastructure Carbon Review:

And other carbon mitigation curves, plus this:

“Saving carbon also saves costs over the building’s life,” he says.

So after all his experience, what are his top tips? “Well, obviously you make it a contractual obligation in your supply chain, but you must also work collaboratively and be prepared to learn from others. Develop a robust baseline and the measurement and monitoring framework. Don’t get too hung up on accuracy instead use the principles and apply them with ’round numbers’,” he concludes.

The PAS 2080 standard contains the full protocol for reducing whole life carbon emissions.

David Thorpe is the author of Passive Solar Architecture Pocket Reference, Energy Management in Buildings and Sustainable Home Refurbishment. He is based in the UK.

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  1. David, the article includes this aside comment – “These utilities are great for investors, not necessarily providing such a good service to customers, but Welsh Water is an exception, being constituted as a mutual” – where is the evidence for that? Does being a mutual mean that the service provided is automatically better? There are plenty of companies across mutuals, government-owned, and corporates that provide good and bad service and everything in between. I’m interested in your justification for stating this correlation.