In our last blog, we reflected on where our sustainability path had taken us and shared that adopting carbon accounting tools within our workflows was central to that journey.
The accounting provides us with a tangible carbon metric to steer design decisions and promote meaningful sustainability discussions.
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The notion of counting carbon may seem quite daunting or incomprehensible at first, but it isn’t.
Once you get into it, it's relatively straightforward and makes sense. There are well-documented processes to follow, and they are designed to be clear and accessible to all.
So, we thought we would share our learning of the process to encourage all to use these tools to meaningfully address the desperately needed reduction in our carbon footprint.
Before embarking on any journey, one must research the best guidebook for the task.
Several excellent publications are available, but our suggestion would be to follow the internationally recognized ‘How to calculate embodied carbon’ guide by the Institution of Structural Engineers in the UK. The guide is available for free from their website: https://www.istructe.org/resources/guidance/how-to-calculate-embodied-carbon/.
The broad process is one of accounting, using a carbon factor to multiply the quantity of each material for each of the life cycle stages.
The process can be done by manual calculations or spreadsheets or within many commercially available software packages. For simplicity and clarity, we would suggest using the ‘Structural Carbon Tool’ spreadsheet developed in conjunction with the IStructE guide and again available for free from the same website https://www.istructe.org/resources/guidance/the-structural-carbon-tool/
There are four life cycle stages:
1. Product Stage (also known as ‘cradle to gate’).
Modules A1-A3. kgC0₂e equivalent carbon) is released during extraction, processing, manufacture (including prefabrication of components), and transportation of materials between these processes until the product leaves the factory gate to be taken to the site.
The recycled content of a product affects the kgC0₂e in these modules.
2. Construction Process Stage
Modules A4 and A5. kgC0₂ereleased during transport of materials/products to the site, energy usage due to activities on site (site huts, machinery use, etc.), and the kgC0₂eassociated with the production, transportation, and end-of-life processing of materials wasted on site.
3. Use Stage
Modules B1-B7. kgC0₂eare released due to use, maintenance, repair, replacement, refurbishment, operational energy, and water while the building is in use. Module B4 (replacement) is often the focus of the use stage when embodied carbon is being considered.
4. End of Life Stage
Modules C1-C4. kgC0₂e released during stripping out, demolition, deconstruction, transportation of materials away from the site, and disposal of materials.
There is one additional module beyond the life cycle of the asset that provides a broader view of its environmental impacts:
· Module D.. benefits beyond the system boundary associated with:
- Recycling of materials
- Energy recovered from materials, eg, incinerating timber products
- Full reuse of materials/products.
As a minimum scope, your calculation should include Modules A1-A5 for primary building and superstructure elements.
The reasons for this are that these elements are perhaps the most readily understood and quantified and that emissions within these modules typically make up to 50% of the total lifecycle value, so they should be the focus of our carbon reduction efforts.
The IStructE guide and spreadsheet steer the accounting for these Stages. It is quite a simple process of taking volumes of materials extracted from BIM models (e.g., Revit files) or could be hand estimates and multiplying by the published emission data for that material.. an example, say for blockwork or brick may be the default values here:
Tables are given for all common building materials.
Standard materials such as timber, steel, aluminum, glass, etc., have readily available published emission data, but how do you calculate the emission of, say, an air handling unit or, for ourselves, a specific tensile fabric?
For that, we need to obtain EPDs (environmental product declarations) from manufacturers and suppliers.
Suppliers who are serious about their environmental responsibilities will undertake their own assessments to recognize standards and will readily supply such environmental data.
There are also numerous websites that collate and publish EPD data, too—so say the emissions through the life cycle of a typical kitchen sink can be quantified.
The process of engaging with the supply chain to quantify such EPDs is a positive sustainability consideration in itself – it heightens awareness of sustainability responsibilities throughout and encourages openness and innovation discussions within that process.
Ultimately, it will be those suppliers that engage and respond positively to sustainability market pressures that thrive.
Quite a fun part of the accounting process is looking at the global sourcing of components and assigning a carbon cost to transportation both at the manufacture (A1) and installation stages (A5).
Here, Google Earth is our friend, and we can map the freight distances by air, sea, road, etc. The spreadsheet has an easy section for calculating total emissions for shipping, say, 1 ton of the aluminum profile from Mumbai to Cape Town.
So – you have a workflow in place now that allows us to calculate the tons of carbon emitted by your building or scheme during the various stages of its life, but what does that number mean? - what do you do with it?
The key here is not to focus on the number itself but on the magnitude of difference between numbers for one scheme and another - use it to highlight which material in your construction contributes most to the total count and concentrate efforts to reduce through seeking alternative materials, higher recycled contents, more efficient designs or improved supply chains.
At THS, for example, we have used it to compare life cycle emissions for alternative decking solutions, which also considers timber sequestration (carbon storage)—we’ll cover sequestration in another blog as this is a fascinating subject in itself.
It is also important to track your reductions in carbon emissions over time,
The IStructE and RIBA have set targets for reducing building embodied carbon using their ‘SCORS’ rating (structural carbon rating scheme)—it’s like an efficiency ‘sticker’ used to communicate the implications of design decisions to those we work with.
The rating considers equivalent carbon emissions during the cradle-to-construction stages A1 to A5 and only
A study of all building types was conducted through 276 consultancy practices in the UK. In 2020, the average rating of these was assessed at ‘E’.
From this, the RIBA and others have set yearly design targets for improvement, heading towards achieving carbon neutrality by 2050.
By plotting your building rating over time, you can see where it sits in relation to that neutrality path and make systematic improvements over time to maintain that trajectory.
The main takeaway is to embrace the process and not be put off by finite accuracy. The process itself provides learning and discovery and will benefit everyone.
Article Credit: Gavin Sayers. General Manager, Design at Tenthouse® Structures