The construction industry has finally started to realise that embodied carbon is really important for sustainable buildings. In fact, it’s probably more important than carbon emissions related to energy use. But what exactly is embodied carbon?

Embodied carbon is all the carbon emissions related to the “making” process – the mining of raw ingredients, manufacture of building materials, transportation of these materials between factories and delivery to the building site, any waste materials that can’t be recycled, and all the energy used on the building site by plant and equipment. Embodied carbon emissions will come from many different sources, quite probably scattered all around the world, but they have all been released into the atmosphere by the time the building is completed. So when you get handed the keys to your new house it has already clocked up these carbon emissions, no matter how energy efficient it may be to live in.

Calling these carbon emissions “embodied” can be misleading because it suggests they are somehow different to carbon emissions from energy use, but they are not. As far as the science is concerned carbon is carbon. Some different terms are coming into use to make this clearer, such as “production carbon”. Another term is “capital carbon” to make the link to the capital expenditure (capex) phase of a project as opposed to operational expenditure (opex), with the implication that we need to consider the balance between them.

Research suggests that embodied carbon is more than 50% of the carbon emissions from a typical new-build home i.e. more carbon will be released in the building process than than from energy use for the whole life of the building. As the grid decarbonises the proportion of carbon related to energy use will reduce, to the point where embodied carbon is 100%.

That’s why embodied carbon is so important to an ecohouse. The general consensus is that we need to drastically reduce carbon emissions between now and 2030, and that means we have to be very mindful of the carbom emissions related to the construction materials we use.

By far the biggest proprotion of embodied carbon comes from concrete and steel. Plastic is the next biggest problem for embodied carbon, and the conundrum there is that most of the modern insulation materials we are using to make buildings more energy efficient are “plastics” of some form and are petro-chemical derivatives. Fired-clay products are next, things like bricks, roof tiles, and decorative interior tiles.

It is relatively simple to calculate the embodied carbon of a design – you just calculate the total quantity of each different material used and multiply it by the industry agreed rate for embodied carbon, and this is starting to become common place for building designers as part of the design process.

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