Building materials producers are racing to justify the energy efficiency of their products in recognition that embodied energy assessments will come on stream in the next few years. Yet there are no clear guidelines to evaluate the embodied energy and associated carbon impact of various building materials.

Conceptually there are three issues that need to be tackled, that make the assessment of embodied energy difficult.

Issue 1: Energy emissions are a location and time dependent variable – The energy required to produce materials depends on the emissions from power stations in the region, at the time. This is defined through the emission of CO2/kW. The time dependency of energy is difficult to quantify as it is a function of future power supply technologies (carbon capture, renewable energy etc…) which will lower the CO2/kW emissions. This time effect reduces the future CO2 saving from recycling. Recycling is still essential but we shouldn’t use skewed data when assessing material options today.

Issue 2: Global recycle content is far less than total production content – Some manufacturers are trying to argue that the embodied energy equals the production energy per tonne less the recycle benefit of that material for future production. This seems a logical argument, but is it? Consider global aluminium production, the production volume is far higher than the recycling volume, and there is a global build up of aluminium so for every tonne of production only about 20% utilizes recycled aluminum. We could use this net global figure to represent production energy, but assigning a 100% recycle content to individual products is misleading.

Issue 3: The bathtub effect of CO2 accumulation in the atmosphere – Scientists refer to the bathtub effect of CO2 coming into the atmosphere at a faster rate than the rate of removal, and hence the atmosphere is like a bathtub that is filling up to a point of overflowing or irreversible climate change. 2050 has been identified as the key date at which we will hit peak population and after this both population and CO2 emissions will fall away. Effectively building materials with a life of more than 40 years are not going to contribute to emissions reduction until it is too late.

These three issues have a huge impact on our assessment of embodied energy. Rather than assuming a 100% recycled content of today’s materials we don’t know if and when they will be recycled. Instead we should consider the proportion of recycled material used in new building materials now to determine total embodied energy of building products.

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