Embodied carbon is a very important source of carbon emissions, especially in the construction industry. But in practise most people aren’t really aware of it and it is rarely measured in construction or renovation projects. This article explores three reasons we should all care about embodied carbon. First though, what is it? Let's take an example:
I would like to replace my draughty single glazed wooden windows with some new, double glazed, plastic ones. The company selling the new windows has told me I could save energy and carbon because once I have the new windows I won’t have to use so much energy to heat my house. If I invest in buying their windows I’ll be saving money and saving the planet in one go, win-win, right?Unfortunately though it isn’t quite that simple. There are several stages to consider, explained in this short animation.
All of these processes take energy and this energy will have associated carbon emissions which together equals the embodied carbon. A home needs energy and carbon to heat, light and live in it, this is known as the operational carbon. The hope is that the new windows will reduce the amount of operational carbon needed to run the building. But from the amount saved, we need to deduct the ‘cost’, the embodied carbon, to see how much we actually save:
operational carbon saving − embodied carbon cost = lifecycle carbon of the new windows
This of course applies to everything, (not just windows!) and yet in construction, and especially in renovation projects, it is often only the operational carbon saving that is counted. This is partly because it’s quite complicated to calculate, although there are international standards. Here are three reasons we should consider embodied carbon, despite the calculation challenges.
Reason 1: To destroy or not to destroy, that is the question
Currently, there is a lot of discussion about how we can bring older, less energy efficient buildings up to scratch (in case you’re wondering, that’s the majority of UK buildings). Some of the more radical suggestions include knocking them all down and starting again. The main argument is that it would be a struggle to get them up to standard, so it might be better to replace them wholesale with super energy efficient buildings.
If you only think about operational carbon this doesn’t seem like an entirely foolish idea. Add embodied carbon to the mix however and the picture changes dramatically. Studies have shown that energy efficiency improvements to existing buildings are at least 4% and in some cases nearly 60% better in lifecycle terms than demolish and replace. Looks like we should keep those old buildings after all!
Reason 2: It’s all a matter of timing
Another reason to consider embodied carbon is the temporal aspect, or timing, of emissions. Take a look at Box 1 for an illustrative example!
Box 1: Carbon emissions of replacement windows, the timing aspect
Lifecycle emissions tend to be calculated over the predicted lifetime of the object.
Going back to our windows. Let’s say that:
- they save us 250kg of operational carbon per year through reduced heating requirements
- they last 20 years
- they cost 3000kg of embodied carbon to start with.
On this basis it will take 12 of the 20 years for the increased performance to pay back the embodied cost. Over the whole lifespan of our windows we’d save 2000kg of carbon. Which sounds like a good deal!
Unfortunately however it’s not quite that simple. Let’s think about money. Money now is considered more valuable than money in the future, (which is why banks can charge interest on loans!). It’s the same with carbon, we need to save carbon now, not in 12 years, in fact you may have seen on the news that scientists think that in 12 years it’ll be too to save the planet…
There’s another complication. Because of the increase in renewables, energy mixes in the future are expected to contain less and less carbon as we reduce fossil fuel use.
Going back to our example we might reasonably assume that because of this, each operational year we’ll save 5kg less carbon. So 250kg this year but only 245kg next year and only 195kg in year 12. If we redo the figures on this basis we won’t cover our initial carbon costs until year 14 and our total savings will be 1005kg instead of 2000kg.
What this means is that when we’re comparing different options we need to be aware, not just of their total lifecycle savings, but also how this is divided between costs now and savings later. Solutions with lower overall lifetime savings but much lower embodied carbon costs now, are likely to be better for saving the planet, than solutions that depend on savings in 10-20 years. So, for example, new windows with wooden frames might not save quite as much operational carbon but cost a lot less embodied carbon to make in the first place.
Major changes are needed, there is just little room to manoeuvre and we need to be discerning about the changes we make.
Reason 3: A curtain! A curtain! My kingdom for a curtain!
The final reason and perhaps the most important is that without considering the embodied carbon, not just the operational, we can’t know whether a solution is actually making lifecycle savings or not.
Some studies have identified that supposed carbon reduction changes to buildings can actually increase carbon emissions. This is because their embodied costs are higher than their operational savings. One study, for example, identified that a window replacement option increased the lifecycle carbon by 2%! While in contrast, installing thermally lined curtains reduced it by 3%, not to mention costing less in financial terms!
This figure is a bar graph showing example operational, embodied, and lifecycle carbon for two window improvements. Images of these are shown under each half of the chart and they are, new windows and new curtains.
For the new windows: the operational savings are -8 but the embodied costs are +10. This means that the lifecycle column is +2 indicating that these window would increase rather than reduce embodied carbon. There is a large red X on this side of the chart.
For the new curtains: The operational savings are -7 and the embodied costs are +4. Meaning the lifecycle column is -3 and showing that these curtains would save carbon. There is a large green tick on this side of the chart.
So, do we tell the window company 'no thank you' and open up the curtain catalogues, safe in the knowledge that it is saving the planet?! It isn’t quite that simple either, as it depends on the individual circumstances.
But if we don’t even calculate the embodied carbon, we won’t have the opportunity to find out what the best solution is and all our well intentioned actions could be making the situation worse. This is why you should care about embodied carbon and start asking searching questions the next time you’re thinking about how you could reduce your carbon emissions. As a society, and as consumers, we need to show that this is something we care about, and that it will affect our decisions, before sectors will start making the extra effort to find and publish the figures.
In the meantime it is advisable to be cautious when working out the carbon saving potential of anything (not just new windows)!
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Disclaimer: no windows or window salesman were harmed in the making of this article.