Embodied Carbon and A Circularity Metric

Visualising Embodied Carbon in Past, Present and Future Projects

Recently on a project, I have been trying to illustrate how embodied carbon can ‘flow’ through generations of development projects. I hope this brief explanation and diagram bring this to life, plus I highlight some of the challenges we face.

I worked with McGee and Twin + Earth on this.

Embodied Only

So firstly, this is about EMBODIED carbon. This is all about the physical stuff we use to build, from the supply chain to manufacture it, to the energy to construct it, to the maintenance of it while in use, to the effort to deconstruct and dispose of it at end of life, to the possibility of reusing it. It is everything within the bold black rectangle on the modular information diagram for building assessment¹ below. It does not include Operational carbon (the orange bit) which is all about how efficient a building is to operate - think energy use which is driven by good insulation, heat recovery etc.

So why try and visualise this? A key point is that that module D (Reuse) is the final chapter of a development, not the first of the next one.

For example, materials salvaged during deconstruction on a development project today are actually savings from the previous development cycle - and unless those materials are reused within the same development, then there is no carbon saving on the new development’s embodied carbon metrics.

Similarly, if you design for deconstruction in a development today, all that effort (and possibly expense) only locks in the potential for carbon savings. The saving is only realised at the point years in the future when the development is being deconstructed.

Three Development Cycles

The diagram below illustrates this. The bars are coloured as per the module diagram above showing embodied carbon A1-A5, B1-B5, C1-C4 and D. The middle graph (2) is present day, but for the full picture you need to look one development cycle back (1), and one forward (3).

Why Deconstruct?

Using the diagram above as a guide, imagine you are on graph 2 and running a development project where deconstruction (hopefully not demolition) is necessary to prepare the site. There is no doubt that for the time being, deconstruction takes longer that ‘traditional demolition’ and possibly costs more too. So you need to see some upside from the salvaged material if you are to break away from traditional demolition.

But unless you use that salvaged material on the same site, there is no carbon benefit to your development project’s embodied carbon metrics (which are usually reported as A1-A5). This might not be possible, and having to reuse salvaged material on the same site is not what I envisage to be Circular Economy utopia.

So putting aside any carbon metric improvements or exemplar industry stories as incentives to salvage material, some simple criteria needs fulfilling:

effort/cost to salvage < value of material on reuse market

Right now, the market for second-hand materials is in its infancy and costs for these things are not well defined. Remember, the buyer will realise carbon savings in their reported A1-A5 metrics for their current development.

I think we need to see the value of salvaged material better understood - to the buyer it represents a good story, improved carbon metrics and avoids using virgin material… so should it attract a premium price? If it did, that would surely help fulfil the criteria above which would make the business case for more deconstruction.

There are also challenges with the way we approach development projects. All too quickly we develop programmes based on past experience and industry durations, and these do not allow for deconstruction. The same applies for cost plans. Once these are set and baked into business plans and appraisals, it is very hard to argue that a project cost should be increased or programme elongated to salvage some material which might not (in the infant reused materials market) pay back.

Why design for Disassembly and Deconstruction?

It is a similar story for when you design for disassembly. The careful work put into the design and construction of a development now, to enable it for future disassembly only see anecdotal benefit today. The actual carbon savings are only realised in the next development cycle when the disassembly happens.

So why bother designing for disassembly? This is the challenge. Another factor working against this is that buildings are often bought and sold, so where is the incentive to do something now to receive the benefit in the future, when the asset may no longer be yours?

A Circularity Metric

I think the emergence of a measure of how circular a development is the answer. Aside from the embodied carbon metrics, this could capture if an existing building was deconstructed/salvaged, if the design allows disassembly, and no doubt countless other factors that play a part in circularity such as not using prohibited materials (E.g. certain glues or fixing methods that cannot be ‘un-done’).

A strong circularity score for a development would shout about the credentials right now, could be used in marketing to command improved value today, and ultimately assist the business case underpinning why it is worth putting in that extra effort..

I know my peers in UKGBC Working Groups are looking at this and I look forward to seeing how the work progresses. Having written this article, I believe more strongly than ever that we need such a metric, and it needs to be more than just a ‘Circularity Statement’².

1. System Boundary EN 15978:2011

2. https://www.london.gov.uk/publications/circular-economy-statement-guidance