MEng Engineering Science student, University of Oxford
The building sector is responsible for around 40% of global energy use, which contributes over one third of global CO2 emissions. Heading towards climate goals in future years, considering embodied energy of buildings is increasingly important if we want to accurately assess environmental impact of buildings.
What is embodied energy?
A building’s life cycle energy is composed of its embodied energy and its operational energy. The operational energy of a building is the energy used daily, for things like cooling and heating. Embodied energy is the energy associated with a building’s life cycle, often including but not limited to production of building materials, and replacement of building parts. In recent years there has been lots of research into technologies which have led to reductions in operational energy use. There has not yet been much research into reducing embodied energy. As a result, embodied energy is becoming relatively more important to consider when designing a building.
As there is no consistent methodology for measuring the embodied energy of a building, findings are often hard to compare. Based on a recent study, 98% of embodied energy values considered a building’s production stage, with 71% also taking replacement of building parts into account. After this, boundaries differ significantly with some other methods accounting for construction energy and others accounting for demolition energy. Clearly a universal methodology, with defined system boundaries which clarify what is included in measurements, must be established so that embodied energy can be compared more easily and accurately.
A material’s embodied carbon depends on the energy mix of the nation where the raw materials are sourced, and where the desired material is produced. A material could have the same embodied energy across many countries, but if the processing takes place in a country with a higher proportion of green energy sources in its energy mix, the embodied carbon is likely to be less. Therefore, considering where a material comes from before buying it can minimise environmental impact.
Let’s also not forget the carbon footprint of transporting materials to the construction site.
How can we reduce embodied energy?
For conventional single-family homes embodied energy can contribute 50% of the life cycle energy use and for low energy/net zero homes this can be up to 100%. Reducing embodied energy within homes will have a significant impact on the life cycle energy used by a house. For instance, using timber instead of concrete or steel can reduce embodied energy and adjusting concrete composition by substituting clinker with mineral additions can reduce CO2 emissions.
Alternatively, a Passive House is a building standard which aims to minimise operational energy use. Although Passive Houses generally require more energy to build than conventional houses, the design can reduce life cycle energy by approximately 30%. Passive houses generally have thick insulation, external and internal, up to 40cm thick, made from materials with low embodied energy such as wood or mineral wool. This insulation also helps to protect the building from additional thermal stresses. Passive Houses can use high performance low emissivity windows to prevent thermal losses and reduce peak cooling and heating loads. Overall, Passive House design can reduce operational energy demand by up to 90% showing that a higher embodied energy of a building can lead to significant reductions elsewhere.
To conclude, embodied energy is something that still seems to be brushed to the side in research. Establishing a consistent, universal methodology and system boundaries for measuring it is likely to make comparison significantly easier; this is key for progress and research in the field of embodied energy. Furthermore, in order to head towards climate neutrality and as buildings become more efficient in the way they operate, embodied energy in homes is something that needs to be reduced as it still contributes greatly to life cycle energy use.