Whole-life carbon and buildings

To acquire an overall understanding of a built project’s total carbon impact, it is necessary to assess both the anticipated operational and embodied emissions over the life of the asset. Considering the combined operational and embodied carbon emissions over a project’s expected life cycle constitutes a whole-life approach. Its use can help identify the best combined opportunities for reducing lifetime emissions. It can also bring longer-term benefits to the forefront of the design process, ensuring a development is evaluated in the round. This is particularly relevant to concrete buildings, which provide performance attributes that extend to the complete building life cycle.

Concrete buildings also offer a level of flexibility not found in many other structural options, frequently enabling them to be repurposed to meet changing needs, greatly extending their useful lifespan. These qualities align well with the principles of a circular economy which are succinctly defined by the Ellen MacArthur Foundation:

“A circular economy is one that is restorative and regenerative by design, and which aims to keep products, components and materials at their highest utility and value at all times, distinguishing between technical and biological cycles”.

Whole-life carbon assessment has attracted broad support from construction sector organisations including the UKGBC with its Net Zero Whole Life Carbon Roadmap, and the RIBA with its Climate Challenge programme. Whole-life carbon assessment has also become a planning requirement for large-scale construction in Greater London and is now a government requirement for all new public works projects. Producing a practical whole-life carbon assessment will typically involve the use of a Life Cycle Assessment (LCA) tool that follows the LCA methodology set out by the RICS and/or BS EN 15978.

An example of a whole-life carbon assessment can be found in The Concrete Centre publication ‘Life cycle carbon analysis of a six-storey residential building’. This provides details of a whole-life carbon assessment of an apartment building in London, carried out using life cycle analysis (LCA) in accordance with the RICS whole-life carbon assessment methodology and BS EN 15978:2011. The guide is authored by The Concrete Centre and draws on technical analysis completed by Max Fordham, on behalf of The Concrete Centre. The initial designs that formed the basis of the analysis were developed by Adam Khan Architects, Price and Myers (structural engineer) and Max Fordham (environmental and services engineer). The apartment block was modeled firstly with a concrete frame and then with an equivalent CLT structure, allowing some comparisons to be made.

Some of the key findings of this research include:

• The whole-life carbon performance of the concrete and CLT apartment blocks were broadly similar, with the concrete building having around 6% more (A1-C4, excluding B7 water) over a 60-year lifespan.
• Both buildings meet the 2025 and 2030 RIBA Climate Challenge CO₂ targets.
• The passive performance of the concrete building was found to be significantly better, with a lower occurrence of overheating.
• The operational energy for both building were found to be very similar.
• The peak space heating load for the concrete building was 25% on average, which is beneficial from a plant sizing and embodied carbon point of view. More valuable, however, was the resulting difference in peak electrical demand: Limiting peak electrical demand, particularly in winter, is a vital part of a net zero carbon future as it helps facilitate decarbonisation of the national grid.

General guidance on this topic can be found in the RICS publication ‘Whole-Life Carbon Assessment for the Built Environment’ and within Circular Economy guidance such as the UKGBC’s ‘Circular economy guidance for construction clients’.

The Concrete Centre has also published a guide entitled ‘Whole-Life Carbon and Buildings’, which draws upon information from a range of sources to provide a largely qualitative overview of the potential whole-life CO₂ savings that are possible. It sets out the specific qualities of concrete construction that can be used to help minimise carbon impacts, both directly and through broader indirect design opportunities that the use of concrete often affords.

These include:

• Lean building design - Using concrete for multiple roles, enabling other materials to be designed out.
• Operational energy - Using the thermal mass provided by concrete to lower operational emissions.
• Designing for long life - The longevity of concrete allows a building’s useful life to be extended; a key tenet of whole-life thinking and a circular economy.
• Reuse and adaptability - Reducing whole-life CO₂ through the ability to reuse concrete structures.
• End-of-life - The absorption of CO₂ into concrete through the natural process of carbonation.