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The transition to zero carbon housing is relatively new and, as with all emerging technologies, it spawns a lexicon terminology some of which is difficult to understand. One such term being widely used is “embodied energy.”

Carbon -v- energy

Higher energy use almost always translates to higher carbon emissions. But you can’t generalise about the energy and carbon relationship, because different fuels emit different amounts of carbon. Hydro electric energy is very carbon efficient; burning natural gas is not. When engineers calculate the carbon emissions in houses, they always consider the “energy mix,” or how energy is generated in the geographic area where the house is located. Energy is generated in a variety of ways almost everywhere, and it is common in the UK to have a mix of nuclear (low carbon), natural gas (high carbon) and an increasing amount of renewable (low carbon).

Embodied energy

In the timber frame industry we talk about “embodied carbon”. which converts the embodied energy into carbon by determining the energy mix at every step of the process. Timber does extremely well in embodied carbon calculations because it is an organic material. It holds, or sequesters carbon. As long as the carbon is in the wood that is inside your walls, it is not in the atmosphere. Since wood used in the UK comes from sustainable forests, there is another tree growing where the one used to make the wall was cut down, so the wood in your wall is keeping carbon out of the atmosphere, and the new one growing in its place is taking up even more carbon. It really is that simple!

Life-cycle assessment

Steel panel manufacturers like to talk about “life cycle assessment”. This is either embodied energy or embodied carbon plus the amount of energy required to dispose of the construction material after the building has lived its useful life. Steel panels score very well here, because 90 percent of steel panels are recycled and a further 9 percent are re-used.

So, which is best?

Because of the complexity of the calculations, and trying to take everything into account, most low-carbon programmes are currently considering only embodied energy. However, even these programmes realise embodied energy is not the whole story. Eventually, as numbers for embodied energy and embodied carbon become widely accepted, there will be an attempt to do more life cycle assessments.

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