Forget the numbers, statistics, calculations and confusion; this is what designers of buildings should do.
Toby Maclean, posted 3rd February 2021
If there is one thing to remember from this post it is this:
Use timber in preference to other materials.
If you don’t fancy reading the next 800 words then you can stop now.
There has rightly been a lot of discussion recently about CO2 emissions from the built environment and increasingly about the embodied carbon in the built environment.
As a result, lots of engineers, architects, scientists, climate thinkers and other good people have spent a lot of time thinking about how to measure embodied carbon and how to relate different things so the embodied carbon can be scored. It is possible to quickly run into some difficulties. For example, how do you compare CO2 emissions now and CO2 emissions in 50 years in a simple way? What if the future emissions are only possible rather than definite? How can you predict how long your building will last, or what happens to the material in it at the end of its life (should it ever inadvisably be allowed to reach an end of life)? How should you score the carbon stored in biogenic materials like timber? Do you ignore it as CO2 emissions can be no more than the CO2 sequestered? Do you give it some benefit because the emissions are delayed by a period equal to the life of the timber product? Do you treat the sequestered CO2 as a negative emission for the life of the building (which, I may remind you should be forever)? Or do you ignore the carbon in the timber that you used to build your building and consider only the carbon that is slowly being sequestered by new trees that someone has planted to replace the trees used in your building?
Sometimes people, well intentioned or otherwise, muddy the waters even further. And before you know it, it is all just too confusing and no one knows what to do.
But it doesn’t need to be like that.
There are a few incontrovertible things that designers of buildings can do to make sure that they are responsible for lower embodied carbon emissions that need no understanding of life cycle analyses, radiative forcing, or the intentions of a person that planted a tree.
Never build anything
Just like flat screen TVs, mobile phones and black polo neck jumpers, we need to consume less and build fewer buildings.
If you really, really need to build something then read on.
Never demolish anything
The embodied carbon in existing buildings is free so retrofit existing buildings, do not demolish and rebuild. And if the existing building contains biogenic materials like timber then by prolonging the lifetime of those materials you increase the total carbon stored in timber products.
If you really, really need to build something new then read on.
Don’t build empty space, don’t build inflexible space, don’t build space that gets used very little.
Use building materials with inherently low embodied carbon
In terms of the structural frame of a building a timber (from sustainable forestry) building will almost always have lower embodied carbon than a concrete or steel framed building (without any benefit claimed for the carbon sequestered in the timber – that’s a bonus, whatever you think it means).
In short, if you have got to step 4) and you need to build something then use materials like timber in preference to other materials.
Structure should not be overdesigned. The number of buildings that have collapsed because an engineer used too low a live load assumption can be counted on the fingers of one fingerless hand. In the case of timber, while we want to put as much timber as possible into long term store, it is better to share the timber over more buildings so a greater amount of more carbon intensive materials can be displaced, or just so we can build more buildings.
Finishes should be chosen wisely, applied in moderation and only where necessary.
Insulation should be applied until the carbon benefit in operation does not justify the embodied carbon in the product.
That’s it but we just have time for one final question:
What if we run out of sustainable timber?
That would be good news, if we have used as much as possible of that timber in long-lasting things like buildings then it means we have built the largest carbon store in timber products that we are able to.
We’d love to hear thoughts on this, so please get in touch on social media, by email, or through the Contact page on this website.
1: But not universally, the UK government’s position on embodied carbon relates largely to operational carbon (page 109: The Government Response to the Committee on Climate Change’s 2020 Report to Parliament)
2: The answer to this by the way is that the built environment builds a carbon store in timber products that grows larger the longer the buildings last and the more timber is used and so sequestration is a significant tool at our disposal and shoud not be ignored. More information is here. )