6 June, 2019

You may have heard the term ‘embodied energy’ (or ‘embedded energy’) used in relation to sustainable buildings and energy efficiency. The simplest explanation of embodied energy is the total energy required for the extraction, processing, manufacturing, and delivery of buildings[i]. In the construction industry, some definitions of ‘embodied energy’ do not include transportation from factory to site, while others include all energy expended from factory to site to end of construction. For this article, we’ll stick with the first definition: cradle-to-site.

By calculating the approximate embodied energy, it’s possible to estimate some of the environmental impact of a construction project in advance. This allows the surveyors, architects and/or designers to make choices based on the energy consumption and efficiency of specific types of materials. Buildings can then be designed using materials selected to balance embodied energy with factors such as climate, availability of materials and recycled content/recycling potential. Along the track, the embodied energy can be used to estimate the whole-life environmental load of a building.

Embodied Carbon, Carbon Footprint and Zero Carbon

The term ‘embodied carbon’ is sometimes used interchangeably with embodied energy, as is ‘carbon footprint’. ‘Embodied carbon’ in the construction industry measures the carbon dioxide emissions (CO₂/kg) produced from cradle-to-site. CO₂e may also be measured – carbon dioxide equivalent – which includes other greenhouse gases such as methane in the assessment. The gases are compared using a measurement called GWP – global warming potential. So if a building material is manufactured using methane sources such as coal, natural gas or oil, the GWP rockets from 1 GWP for CO₂ production to 25 GWP for methane production.

Just to confuse the issue, the term ‘zero carbon building’ means a building that produces as much energy onsite as it consumes. This relates to operating energy, not cradle-to-site embodied energy.

How is Embodied Energy measured?

Estimating embodied energy is not a straightforward task. The most commonly used method is to calculate the quantity of non-renewable energy per unit of building material in megajoules (MJ) or gigajoules (GJ) per kg.

Since the concept of calculating embodied energy came about, organisations worldwide have created lists of materials and their cost per kg, such as the table below published by the Royal Australian Institute of Architects.

Table showing the estimated embodied energy of common materials used in Australian construction [ii].

In general, the more processing involved in manufacturing a material, the higher the embodied energy. However, other factors may offset the high energy consumption involved in production. Although aluminium has a very high embodied energy cost compared to steel (due to the energy required to split the aluminium/oxygen chemical bonds vs iron/oxygen) it is easier to shape and three times lighter to transport. On the other hand, steel is stronger and more durable. Then there’s the potential for including recycled aluminium or steel content. You can see how the calculations become complex.

Reducing Energy Costs

Until recently, energy reduction efforts focused on reducing the operating energy of a building. Experts assumed that operating energy would far exceed embodied energy.

While reducing operating energy is a positive step, Australia’s CSIRO found that ‘the average house contains about 1,000GJ of energy embodied in the materials used in its construction, which equates to around 15 years of normal operational energy use’[iii].

When an architect or designer chooses building materials, the embodied energy of the materials should be considered with respect to:

• Durability
• Heating/cooling requirements (including insulation)
• How easily materials can be separated
• Local sourcing
• Recycled content
• Recycling potential
• Using standard manufacturing sizes rather than custom-specified
• Avoiding waste
• Selecting materials that are manufactured using renewable energy sources.

The responsibility for reducing energy consumption doesn’t just fall on the architect, though. Manufacturers can use smart meters to monitor their energy usage during production of materials. Factories can be fitted with energy-efficient lighting, sensor-controlled HVAC and monitor their processes through data upload and analysis.

Our belief is that reducing the embodied energy of an end product lies with people at all steps of the process, even if it makes quantifying that embodied energy far harder.

The need for standardisation

Using embodied energy calculations as a guide, building professionals can contribute to reducing the carbon footprint of new structures. Ideally the approach to quantifying and assessing embodied energy would be standardised across Australia and/or globally. Given all the different factors involved and the variations based on climate and location, it’s difficult to imagine a global standard in the near future.

[i] https://ec.europa.eu/energy/en/eu-buildings-factsheets-topics-tree/embodied-energy Accessed 5 June 2019.

[ii] Lawson, B. 1996. Building materials, energy and the environment: towards ecologically sustainable development. Royal Australian Institute of Architects, Red Hill, ACT.

[iii] Embodied energy and operating energy for buildings: cumulative energy over time. Design for sustainability. Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA. www.flickr.com