In order to reduce the carbon footprint of infrastructure it is important that we account for the energy that is embodied in the materials that we use. This briefing sheet explores the current ways of measuring embodied energy and carbon, and makes recommendations on how to reduce these on construction projects.
The dictionary of energy defines ‘embodied energy’ as “the sum of the energy requirements associated, directly or indirectly, with the delivery of a good or service” (Cleveland & Morris, 2009). In practice however there are different ways of defining embodied energy depending on the chosen boundaries of the study. The three most common options are: cradle-to-gate, cradle-to-site, and cradle-to-grave (Densley Tingley & Davinson, 2011). The following definitions illustrate this more clearly:
1) A cradle-to-site study favours defining the embodied energy of individual building components. This includes the energy required to extract the raw materials, process them, assemble them into usable products and transport them to site. This definition is useful when looking at the comparative scale of building components and relates more to the ‘good’ in Cleveland & Morris’s definition as it neglects any maintenance or end of life costs. A cradle-to-gate model simply describes the energy required to produce the finished product without any further considerations.
2) A cradle-to-grave approach defines embodied energy as that ‘consumed’ by a building throughout its life. This definition is a far more useful one when looking at a building or project holistically, though admittedly much more complex to estimate. The energy consumption can be broken down further (Yohanis & Norton, 2002) into:
- Initial embodied energy: the energy required to initially produce the building. It includes the energy used for the abstraction, the processing and the manufacture of the materials of the building as well as their transportation and assembly on site
- Recurring embodied energy: the energy needed to refurbish and maintain the building over its lifetime
- Demolition energy: the energy necessary to demolish and dispose of the building at the end of its life
Note that the cradle-to-grave embodied energy, i.e. its life-cycle embodied energy, does not include the operational energy required to utilise the final product. In other terms it does not account for the heating, cooling, lighting and power of any appliances that allow the building to serve its intended function.
The above definitions are given for energy but are equally valid when considering embodied carbon (dioxide) emissions. Subtleties in correctly measuring embodied carbon include the sequestration of carbon within building materials such as timber, and the emission (or sequestration) of carbon dioxide through chemical reactions during the production of materials such as cement and the lifetime use of materials such as in the carbonation of concrete.
Importance of embodied energy
For the United Kingdom to reach its legal obligations of greenhouse gas emission reduction, a low carbon transition plan has been put into place. The plan covers the next 40 years and “the transition to low carbon can almost be read as a business plan for construction, bringing opportunities for growth” (IGT 2010.1, p.4). Still, the focus of the UK Building Regulations has been on operational energy use to date with embodied energy absent from legislative attention (Densley Tingley & Davinson, 2011).
The continued tightening of the Building Regulations’ requirements for operational efficiency (BRE 2006, p.4) may have the unintended consequence of increasing the embodied energy of the buildings they serve. This in turn offsets the carbon savings of the whole-life cost. It is therefore very important to standardise the industry’s reporting of embodied energy to prevent merely shifting the time at which energy is ‘spent’ and actually reducing the net carbon cost of any project.
The numbers resulting from studies analysing the proportion of embodied carbon against other energy costs continue to be widespread given the breadth of building usages. It is also worth noting that the proportion of initial embodied energy for residential and commercial buildings, which make an intensive use of operating energy, is very different to other forms of construction such as bridges or even stadia where the relative importance of embodied energy is likely to be even greater.
A study of the energy use of Swedish low-energy buildings found that the initial energy embodied in a one family home accounted for more than 40% of the whole-life energy requirements over a 50 years life span (Thormark 2002). Rawlinson and Weight (2007) suggest that in the UK the embodied energy in complex commercial buildings may be equivalent to 30 times annual operational energy use. At the same time Sturgis and Roberts (2010) suggest that this accounts for 45% of the whole life-cycle carbon of its structure.
It is important to recognise that there is no hard and fast rule in buildings. In some buildings effective control of ventilation requirements through the use of massive building materials can outweigh the initial additional embodied energy in the building. This demonstrates the importance of a full cradle to grave analysis in such cases.
Applications to civil engineering
Today the UK construction industry is the largest consumer of natural resources in the country with over 400 million tonnes of material consumed each year (Davis Langdon LLP, 2009). This accounts for approximately 10% of total UK carbon emissions (ENVEST, 2010). Civil engineers specify a large proportion of all the materials used in construction (Symons, 2009) and thus have a great potential impact in this field. Note below the estimated proportion that the construction industry has the ability to influence (IGT, 2010.2). This is This is calculated by piecing together existing evidence on CO2 emitted across the broad areas of a building’s life cycle. Demanding better specifications from the supply chain can therefore have a major impact on the sector as it accounts for the largest amount of emissions within the process of construction.
Recommended steps towards reducing the embodied energy of buildings include (IStructE, 1999):
- Better specification of current mainstream materials as steel and concrete are the main construction materials used in the UK today. Their energy and carbon content can be reduced by specifying them properly and sourcing them responsibly.
- Specification of alternative materials: timber, rammed earth, hempcrete etc.
- There are many alternative materials appropriate for some design and construction situations in which full advantage can be taken of their low embodied energy content
- Design leaner structures and material optimisation - by minimising the quantity of materials we reduce the energy used to make the building in the first place.
- Design for deconstruction, reuse and recovery - buildings often have a service life that is far less than that of the materials they are made of. Building with deconstruction in mind will enhance the reuse of construction materials. This will effectively increase their life-span and the energy efficiency of the buildings in which they are used.
- Design for future use, adaptability and flexibility - designing to make buildings suited to different uses will increase their life-span and reduce the need to use new construction materials.
- Minimise waste - the construction industry is responsible for some 120 million tonnes of construction, demolition and excavation waste every year – around a third of all waste arising in the UK (Davis Langdon LLP 2009) – what accounts for 22% of all construction embodied energy and 19% of embodied carbon (Jones & Hammond 2008). The potential impact on energy efficiency is hence significant.
All these proposed solutions will be most effective when used in an integrated approach to design, construction, operation and maintenance as part of a global energy efficiency strategy.
Numerous private companies, both in the engineering and other built environment sectors, have developed in-house tools to measure the carbon and energy associated with a project. The Environment Agency (EA) and the Building Research Establishment (BRE) have produced carbon calculators which primarily reference figures from the Bath University Inventory of Carbon and Energy. This latter comparative list contains average absolute values for the embodied carbon associated with common construction materials in the UK, and explains the factors which have been taken into account when compiling the lists (Hammond & Jones, 2008). The database continues to be open and is updated regularly based on data extracted from peer-reviewed literature.
The CESMM4 Carbon & Price Book 2013 (Andrews, June 2013) includes the embodied carbon of every material, enabling users to calculate not just the economic impact of material specification but also the carbon cost.
Embodied energy plays an important role in the modelling of life-cycle assessments (LCA) of structures. European standards have been developed to specify the boundaries of these models, which should increase the reliability of analysis and allow for useful comparisons to be drawn across materials with respect to functionality.
Many companies are now producing Environmental Product Declarations (EPD) for their materials. Within the civil engineering domain, manufacturers of steel re-bar, glulam, and precast concrete for example produce certified documents which detail the environmental impact of their products (and this includes carbon impact).
While not everyone is producing EPDs, the number is growing every year. The increase in projects taking part in envisronmental programs like LEED (Leadership in Energy & Environmental Design) in the US and BREEAM (Building Research Establishment Environmental Assessment Methodology) "rewards" the usage or products with supporting EPDs.
In May 2016 the UK Green Construction Board launched a new specification to encourage a consistent industry approach to reducing carbon in infrastructure – a world first. PAS 2080:2016 Carbon management in infrastructure and its associated guidance document aim to bring a joined up approach to the way industry evaluates and manages whole life carbon emissions to deliver reduced carbon, reduced cost solutions.
Embodied carbon in particular will gain in relative importance more rapidly with the decoupling of energy generation and carbon emissions. In the UK, Zero Carbon buildings are to become a reality in 2016 for residential and 2019 for other buildings. Embodied carbon will then represent the majority of a project’s whole-life carbon emissions.
Measuring and reporting embodied carbon would put the savings made in operational carbon back in context. Some of those savings might be made through the use of high embodied energy components, negating the benefit. Also as improvements in operational energy have been achieved, further improvements become harder and more costly, reducing the embodied carbon content of the building might be significantly more cost effective.
It is important that designers and regulators begin to take embodied energy and carbon into account. Move from a vision where zero-operational emissions is the ultimate aspiration to one where minimising whole-life carbon emissions is the norm. It also important to begin to appreciate the implications of embodied carbon beyond national boundaries. To truly mitigate any environmental impact, understanding the embodied (embedded) carbon relationship between imports and exports associated with UK trade flows is vital and needs continued development (DEFRA, 2008). Research on this is ongoing at the University of Leeds (DEFRA, 2012).
References and further reading
- BRE. (2006). Part L explained - The BRE Guide, Watford: BRE
- Cleveland, C.J. & Morris, C.G. (2009). Dictionary of Energy: Expanded Edition Expanded. Elsevier Science
- Davis Langdon LLP (2009). Designing out waste: a design team guide for buildings. Oxon: WRAP
- Densley Tingley, D. & Davison, B. (2011). Design for deconstruction and material reuse. Proceedings of the ICE - Energy, 164, 195-204
- DEFRA (2008). Development of and embedded carbon emissions indicator. Department for Environment, Food and Rural Affairs. [accessed 29/09/2012]
- DEFRA (2012).Embedded Carbon Emissions Indicator Department for Environment, Food and Rural Affairs.
- ENVEST (2010) Environmental impact and Whole Life Costs analysis for buildings. [accessed 08/03/2010]
- IGT (Innovation and Growth Team). (2010.1) Low carbon construction innovation & growth team: final report. Executive summary. (PDF) Department for Business Innovation and skills.
- IGT (Innovation and Growth Team). (2010.2). Estimating the amount of CO2 emissions that the construction industry can influence: supporting material for the low carbon construction IGT report. Department for Business Innovation and skills.
- IStructE (Institution of Structural Engineers).(1999). Building for a sustainable future: Construction without depletion, London: Institution of Structural Engineers
- Jones, C.I. & Hammond, G.P. (2008). Embodied energy and carbon in construction materials. Proceedings of the ICE - Energy, 161(2), 87-98
- Rawlinson, S., Weight, D. (2007). ‘Sustainability: Embodied carbon’, Building,12 October 2007, p 88-91
- Smith, P. (2005). Architecture in a climate of change: a guide to sustainable design, Oxford: Elsevier/Architectural Press
- Sturgis,S. & Roberts, G. (2010). Redefining zero: carbon profiling as a solution to whole life carbon emission measurement in buildings. RICS Research Report. (accessed 16/08/2010)
- Thormark, C. (2002). A low energy building in a life cycle—its embodied energy, energy need for operation and recycling potential. Building and environment, 37(4), 429–435
- Yohanis, Y.G. & Norton, B. (2002). Life-cycle operational and embodied energy for a generic single-storey office building in the UK. Energy, 27(1), 77–92.
Embodied Energy and Carbon
Content type: Briefing sheet
Last updated: 27/04/2022