Embodied carbon can be calculated for anything that is manufactured, but the term is particularly prevalent within construction. The demand for raw materials to construct new buildings, combined with the built environment’s contribution to overall carbon emissions, means there is increasing focus on the complete life cycle of construction products.
Life cycle assessment (LCA) is the method used to capture and account for the carbon emissions associated with construction products. It examines the production and transport of building materials, how products are installed and used during the building’s operation, and how components are reused, recycled, or demolished at the end of a building’s life.
What are the different modules of life cycle assessment?
Following a standardised procedure set out in BS EN 15804:2012 + A2:2019 Sustainability of construction works. Environmental product declarations. Core rules for the product category of construction products, it is possible to establish the embodied carbon of individual construction products.
Construction product manufacturers can then issue environmental product declarations (EPDs) for the products they produce. EPDs feature declarations across some or all of the four different stages of construction that the standard identifies. Each stage has several modules.
Product stage:
- A1 - Raw material extraction and supply
- A2 - Transport to manufacturing plant
- A3 - Manufacturing and fabrication
Construction process stage:
- A4 - Transport to project site
- A5 - Construction and installation process
Together, these first two stages cover everything up to the practical completion of the building.
Use stage:
- B1 - Use
- B2 - Maintenance
- B3 - Repair
- B4 - Replacement
- B5 - Refurbishment
- B6 - Operational energy use
- B7 - Operational water use
End of life stage:
- C1 - Destruction and demolition
- C2 - Transport to disposal facility
- C3 - Waste processing for reuse, recovery, or recycling
- C4 - Disposal
How does embodied carbon change our thinking?
The scope of the modules across these four stages demonstrates the importance of taking a holistic view of construction materials. It also demonstrates the importance of thinking about more than just how a material helps a building to perform.
One type of insulation, for example, might help a building use slightly less energy over its lifetime than another insulation material. But if the embodied carbon of the first material is significantly higher than that of the second, any saving in the building’s operational carbon is inconsequential.
The first step to reducing embodied carbon is to ask questions. Is a building needed? If so, does it need to be constructed from raw materials? Can the need be met by adapting an ‘asset’ that already exists (and for which the carbon cost has therefore already been counted)?
Once answers to these questions have been established, it is possible to move on and look at reducing the embodied carbon of the materials that are specified.
How can the embodied carbon of buildings be reduced?
LCA includes a final module D, called ‘benefits and loads beyond the system boundary’. It deals with the potential for reuse, recovery, or recycling. Where a product can be reused, recovered, or recycled, it reduces the total amount of carbon calculated for the product in the rest of its life cycle.
When calculating the embodied carbon of a building, it is important to establish the scope of the assessment from the outset. This is where terms like ‘cradle to gate’ and ‘cradle to grave’ appear.
Not all products have the same LCA carried out for them. So, when embodied carbon is being considered it is important that products offer the relevant information through their EPDs to allow a proper assessment of the impact of their use.
‘Cradle to gate’ covers only modules A1 to A3 (the ‘product stage’). ‘Cradle to grave’, meanwhile, spans all four stages, from module A1 right through to module C4.
When reducing the environmental impact of products to grow the circular economy, it is increasingly common to hear the phrase ‘cradle to cradle’. If a product can be taken from a building that is no longer needed and reused, there are no carbon emissions to be accounted for across modules A1 to A3, which is a significant saving.
To date, ‘cradle to cradle’, incorporating module D, remains comparatively rare. There is a need to challenge the supply chain to provide a more thorough life cycle analysis for construction products and materials.
If manufacturers and distributors have no choice but to engage with the issue then it will become easier to make ‘better’ specification choices that target meaningful reductions in embodied carbon, alongside net zero operational carbon.
About the author
Darren Evans - Business leader connecting with people to treat people and planet as the precious resources they are so that we can build a better future together https://darren-evans.co.uk/