The UK government published its long-awaited heat and buildings strategy in October. What's missing is how it plans to tackle embodied carbon in the built environment, what the UK Green Building Council (UKGBC) has called a “non-negotiable” for net zero.
Here we explore what it is, why it's important and how you can reduce it.
To put it broadly, embodied carbon is the carbon emitted from producing materials. In the built environment, it's emitted from the energy used to extract and transport raw materials, and to put them together again as a building.
These emissions also come from the energy it takes to demolish a building at the end of its lifetime – and to throw away or re-use the materials. Operational carbon is the other side of the coin: the emissions that come from producing a building's heat and electricity.
Embodied carbon isn't to be confused with a carbon footprint. Embodied carbon simply refers to the emissions from producing materials or products. A carbon footprint encompasses the embodied emissions and operational emissions.
Embodied carbon contributes to about 6% of the UK’s annual emissions. Between 30-50% of a new building's emissions across its lifetime are emitted during its construction, with operational carbon taking care of the rest.
Experts say not taking steps to reduce embodied carbon will slow down the UK's journey to net zero by 2050. Both Lord Deben, Chair of the Climate Change Committee, and Julie Hirigoyen, CEO of the UK Green Building Council, have recently weighed in on the issue.
"We really must come to grips with the issue of embodied carbon in buildings – we’ll never hit our climate targets unless we do," said Julie Hirigoyen. While Lord Deben said "we are simply not going to win the battle against climate change unless we fight on every front."
Part of the problem is draughty buildings being knocked down and replaced by more energy efficient ones. On the face of it that might seem like a good idea. In reality, the energy-intensive demolition just creates more embodied carbon. Then you have to rebuild.
Architects’ Journal, backed by a group of architects, developers and politicians, is urging the government to put retrofit first – i.e. refurbishing buildings to be more energy efficient. It says demolition and rebuild should be reserved only for exceptional circumstances.
When a staggering two thirds of UK homes don't meet energy efficiency targets, this makes sense. Tearing down millions of old buildings in the UK and starting again is not only impractical – it would make the problem worse.
These often thrown around terms are used to describe where you decide to draw a line in the construction process. To start, the 'cradle' is basically the earth - we're extracting raw materials from the ground.
Cradle-to-gate encompasses taking raw materials from the earth, transporting them to the factory and getting them ready for construction. It's everything up to the point of leaving the factory gate. Cradle-to-site simply includes the next step: delivering them to the site.
Cradle-to-grave goes a step further. It adds operational emissions and those that come from end-of-life processes including demolition and disposal. Cradle-to-cradle avoids the grave altogether – materials are designed to be reused and never lay eyes on landfill.
Before jumping into a new development, ask if you can rather re-use or renovate an existing one. This can save between half and three quarters of embodied carbon compared to constructing a brand new building.
Concrete is a massive source of embodied carbon on most construction sites. Try to use lower carbon concrete mixes with fly ash, slag and calcined clays. It's also best to avoid using too many high carbon materials like aluminium.
UCL recommends finding raw materials with a long lifespan and using low emission processes to extract them. Extract them locally where possible, and use low emission trucks to transport them.
You can also find ways to minimise waste and reuse products. Much of the steel in the UK's first major zero-carbon community, BedZED, was once part of Brighton railway station. When the station was refurbished, the extracted steel was reused for the village.
You could also design the buildings in a way that makes it easy for its use to change overtime, reducing the need for refurbishment.
Knowing the embodied carbon of a potential construction project will help you compare which materials would be the least harmful on the planet and most in line with getting to net zero.
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