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Low-carbon buildings need low embodied energy

Low-carbon buildings will need to have low embodied energy. BSRIA's Peter Tse explains how the Inventory of Carbon and Energy will help designers choose the ideal materials.

If you want to consider embodied energy in your design, you need the Inventory of Carbon and Energy (ICE). Developed by Geoffrey Hammond and Craig Jones at the University of Bath, the ICE contains around 1,800 embodied energy and embodied carbon values for 35 classes of construction materials.

BSRIA has published the ICE to encourage designers to consider embodied energy and carbon (not just operational emissions) in their project designs. Arriving at a defensible figure for the carbon intensity of materials has long been a fraught process. The ICE now makes the calculations very much easier.

Embodied energy is the total primary energy consumed (carbon dioxide released) from direct and indirect processes associated with products or services. This includes material extraction, manufacture, transportation and any fabrication before the product is ready to leave the factory gate.

Current legislation in construction focuses solely on the operational aspects of carbon dioxide emissions. However, as legislation drives down operational carbon dioxide, embodied carbon will become more significant in overall emissions. In fact, it can be argued that the legislative drive to reduce operational carbon, with measures such as high thermal mass, increases the emissions associated with embodied energy, and could be ultimately counter-productive. One needs to know where the optimum balance lies.

To gain a more comprehensive picture we have to take a whole-life approach to carbon analysis, considering both the embodied and operational characteristics of materials, and to integrate the analysis with end-of-life issues, such as recyclability.

So how can designers apply embodied energy and carbon values? It's clear that the primary value of the ICE data is for comparative assessments of materials options. A typical use would be for a structural engineer who is weighing up the options for a concrete or steel-framed building. A simple calculation can begin with working out the weight of each material to achieve an equivalent structural system, and using the embodied factors to provide total embodied figures for comparison.

Additional factors can then be considered, for example material source and availability, transportation for each system, any energy associated with fabrication, and waste incurred during fabrication or construction.

It is vital to identify the project-specific contextual variables in order to arrive at accurate and relevant comparisons. Also, a material with a lower embodied energy (or carbon value per kilogram) doesn't mean it will be the best choice in terms of performance. Other issues need to be considered, such as longevity, maintenance, material density and durability.

The recyclability of materials is one of the more significant factors designers need to consider when conducting embodied energy, embodied carbon and life-cycle assessment studies, particularly when considering metals.

Metals are initially extracted from the ground in the form of metal ore, which has a low metallic concentration. The ore requires refining to provide a purer, usable form of the metal through an energy intensive process. An alternative is to use scrap metal, an act that eliminates ore processing, and usually results in a lower embodied energy and carbon than primary processed ore.

The use of recycable materials enables designers to potentially benefit twice. The first benefit is the use of recycled material. The second benefit comes at the end of the building's life, when the materials are recovered and recycled a second time.

However, in the study of a single building, both environmental benefits cannot be taken in full, or we would be double-counting the benefits from using recycled materials and creating recycled material.

The ICE may not enable a designer to grind fine on this level of detail, but it can provide answers to many questions that have long eluded construction professionals. The database makes it much easier to explore the relationship between operational emissions and embodied emissions.

Our outlook towards existing buildings and services may alter. Existing structures and components can be considered for their residual embodied carbon benefit, not just their functionality.

Informed decisions can be made about the virtue of demolishing an old building with high embodied carbon content and operating emissions, and replacing it with an ostensibly more efficient building. The ICE will also help designers assess the true benefits of proposed renewables, once embodied considerations are factored into the equation.

The ICE database has been applied widely in industry. Case studies have been provided in the ICE publication that shows how companies have been using the ICE database on real projects.
The ICE is also motivating the development of carbon assessment tools. These tools are aiming to analyse the embodied carbon data associated with building materials, so that key decision-makers will have access to a range of options regarding the potential embodied carbon of their designs.

For example, the Technology Strategy Board-funded Interoperable Carbon Information Modelling (iCIM) project, led by AEC3 (UK), has led to the creation of a collaborative industry project team, including BSRIA. This project is focusing on the feasibility and pre-design stages in order to help designers, cost consultants and their clients to make informed decisions based on life cycle carbon and economic costs.

Peter Tse MEng CEng MCIBSE is a senior design consultant with BSRIA.