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The long road to zero – embodied carbon in the built environment

The focus of emissions in buildings is shifting from the operational phase to building materials. UK data shows cement and steel alone contribute more than 40 per cent of all industrial carbon emissions.

Leading industry organisations AECOM, Aurecon, BlueScope Steel and Sydney Water, in conjunction with research institutions UNSW Australia, the University of Melbourne and the University of South Australia, are collaborating to comprehensively quantify greenhouse gas emissions related to the built environment in Australia. The aim of the project is to identify the main factors responsible for carbon emissions in the design, construction and operation of the built environment. Armed with this information, designers, construction companies and legislators will be able to make evidence-based design decisions on the most effective way to reduce carbon emissions.

Zero-carbon living is the ultimate aim of a sustainable future that tackles the challenge of climate change. Materials, buildings and whole cities that do not add further greenhouse gas emissions to the atmosphere are at the heart of an environmentally sustainable built environment. In Australia, 20 per cent of all greenhouse gas emissions come from the operation of commercial and residential buildings alone. In addition to this, the buildings and construction sector is also responsible for indirect emissions from materials manufacturing, transport, maintenance and disposal. These “life-cycle” or “embodied” emissions are estimated to make up another 62 megatonnes or 11 per cent of national emissions.

A new project under the Cooperative Research Centre for Low Carbon Living sets out to analyse the carbon fabric of Australia’s built environment processes, quantify and track embodied emissions, evaluate low-carbon scenarios and define zero-carbon developments.

Current projections show that the worldwide carbon emissions are still increasing every year. The urgently required turnaround towards lower carbon emissions has not been achieved yet, even less so the long-term goal of reducing the CO2 concentration in the atmosphere. This alarming trend leads far above the generally accepted limit of a 2°C temperature rise, if not reversed within the very near future. The built environment – at all levels from materials to whole cities – is a key target sector for effective emission reductions. In recent years, “zero carbon” building and city models have become increasingly popular, providing options for a future with a drastically reduced carbon demand.

Most carbon reduction strategies focus on the operational energy needed for living in a building or city. But with increased energy efficiency during the use phase, carbon emissions from the production of the building materials play a larger role. These embodied emissions are released during raw material extraction, transport, material manufacture, construction and dismantling.

But embodied emissions are notoriously difficult to quantify. Supply chains are complex and many different processes and entities contribute to the total carbon load.

Building materials

Mainly steel and cement, as well as aluminium are responsible for the highest carbon emissions during building material production. Using UK data as an example, cement and steel alone contribute more than 40 per cent of all industrial carbon emissions.

In the cement production, the major contributor to carbon emissions is the clinker burning process. The main carbon reduction options are to optimise the process itself, to replace some or all of the clinker with less carbon intensive substances like fly ash or blast furnace slag, or to use geopolymer cement where no clinker burning is needed. Similar to cement, steel production is also highly dependent on fossil fuels. To lower its carbon intensity, fossil fuel replacement technologies need to be implemented. With steel being a very reusable material, recycling rates are already high and contribute to reduced embodied carbon emissions.

Planners and architects can find carbon efficient building materials through databases and tools for lifecycle assessment. But there is still a lack of sufficient data for building materials produced in Australia as the major databases are geared towards Europe or the USA.

Buildings

From the perspective of a whole building life cycle, the contribution of materials to the overall carbon emissions is no longer the only source. The operational phase of traditional buildings, including heating, cooling and technical appliances, can cover at least 80 per cent of overall carbon emissions. But this ratio decreases to around 50 per cent for current energy efficient buildings or even lower for passive buildings; then the building materials are the major source of carbon emissions. The main goal should be to find an optimal balance between reduced operational and moderate embodied carbon emissions.

As shown before, this can be influenced by the choice of materials. But comparisons between concrete and timber buildings are not always conclusive. This is partly due to the fact that even timber buildings require solid foundations and that concrete constructions need less replacement and maintenance over the whole lifecycle. As these studies usually compare standard building types, optimised architectural designs for timber constructions might lead to different conclusions.

Material recycling and component reuse during the construction stage contribute to minimised use of new materials and thus decreased embodied carbon emissions. This can also be achieved through the design of efficient floor plans with reduced ceiling spans and less floor area per person.

The typical method used for building carbon balances from construction until disassembly is lifecycle assessment. Some voluntary green building systems include LCA and embodied carbon emissions in their evaluation, most recently the Australian Green Star. This is an encouraging development towards a more holistic carbon emissions perspective. On the other hand, embodied emissions are still not integrated in any legal regulations; this should be the next step to a comprehensive energy efficiency strategy.

Figure 1: Energy requirements (and associated carbon emissions) of buildings by life cycle stage. Source: BZE

 

City level

The city level is currently much promoted in terms of “carbon neutral”, “zero carbon” and similar labels. Projects like Masdar City received much publicity as pioneer carbon neutral city developments. Up to now, there are no clear-cut definitions for these terms. In most cases, embodied carbon emissions are not yet explicitly included. There are examples of precinct or city developments, however, that set separate targets for reduced embodied carbon emissions for the built environment. Masdar itself does so by aiming to reduce the embodied carbon in materials by 30 per cent. Sydney’s flagship development Barangaroo South has similar goals in reducing the embodied carbon by 20 per cent compared with standard construction practices.

Two major strategies for embodied carbon reduction exist. Besides improving building envelopes, one consideration is that densely built cities are more resource and material efficient than wide-spread cities. In particular, the former require less transport and supply infrastructure. Newton et al., in Australia’s Unintended Cities: The Impact of Housing on Urban Development, mention this briefly while arguing for denser city structures. The second strategy is to consider the existing building and infrastructure stock as a material resource. This way, recycling and reuse can be optimised on the city scale. The concept of urban mining can for instance be realised by recycling local demolition material and complete building components in new construction projects or by reusing the whole supporting structure of old buildings for refurbishments.

Sector level

Despite recently repealing the national carbon tax, Australia still adheres to the ambitious goal of cutting its overall carbon emissions by 80 per cent by 2050 compared to 2000. This overarching reduction target should be tied into the carbon reduction measures on the different levels as discussed above, which would add authority to them as a realistic means to achieve the proposed outcome.

Giesekam et al. have applied this approach to the construction sector. It was pointed out that, assuming an 80 per cent reduction target is to be achieved within the construction sector, this goal would be rather difficult to accomplish by reducing operational carbon emissions alone. Rather, a sensible approach would include to also address the embodied emissions in building materials.

Linking a reduction of embodied emissions to the national reduction targets may support the prospects of success by introducing an added degree of precision, while in turn prioritising the role of material efficiency as an important means to achieve these targets.

Other countries like Germany with similar goals (80 per cent reduction until 2050 compared to 1990 levels) have specifically applied their reduction target to their building sector. Nonetheless, this did not include parameters with respect to embodied emissions. It will remain to be seen whether such an approach will lead to an appropriate reduction of embodied energy.

Integrated Carbon Metrics – The ICM Project

Embodied emissions play a significant role in the built environment. This may not always be evident when considering any one of the above mentioned levels in itself. However, when taking into account all four levels (building materials, buildings, city and sector level) in one consistent framework, sensible and integrated solutions can be derived.

A current project of the Cooperative Research Centre for Low Carbon Living, the Integrated Carbon Metrics project aims at comprehensively quantifying greenhouse gas emissions related to the built environment in Australia. The project develops metrics and decision support tools for building designers, manufacturers, planners and developers and identifies cost-effective emission reduction opportunities.

The ICM project will contribute on all four levels to new solutions: with an Australia specific embodied carbon database, with a carbon visualisation integrated in a 3D precinct development tool and with an additional tool that maps embodied carbon emissions throughout Australian industry sectors. The project is a collaboration of industry partners and research, including AECOM, Aurecon, BlueScope Steel, Sydney Water, UNSW Australia (project lead), the University of Melbourne and the University of South Australia.

Implementation of integrated concepts will require identifying the different stakeholders best suited to drive the efficient carbon reductions at their respective level: producers of building materials such as cement and steel companies can reduce the carbon emissions of their production processes.

Architects and planners are responsible, together with building owners, for the design of sustainable and carbon efficient buildings. On a city level, local and regional governments and planning authorities come into play by designing denser city structures and adapting their regulatory frameworks accordingly. Construction companies can help adhering to these goals on all levels by providing know-how and upgrading industry standards as required. On the national level, parliaments and executive decision-makers are responsible for setting the overarching goals.

If all stakeholders agree that reducing carbon emissions also means reducing embodied carbon emissions, effective change can be achieved.

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