Steps to Net Zero: Step 5 - Limit upfront embodied carbon

The World Green Building Council (WGBC) reports that buildings are responsible for 39% of global energy related carbon emissions of which 11% are from the upfront use of materials and construction. This upfront embodied carbon is defined as carbon footprint of construction materials from its extraction, through manufacture, to installation, and the emissions associated with the construction works.

The construction industry is therefore a major contributor globally in terms of the carbon footprint it creates. It is estimated globally 230 billion square meters of new construction and major renovations will be carried out by 2060; the equivalent of a brand-new New York City being built every month for the next 40 years. It is vital that we start to address this often-overlooked impact, especially given that carbon emissions from operational energy use will make up a declining proportion of a development’s whole life carbon emissions in future.

As operational carbon targets become more stringent, coupled with reduction in dependence on fossil fuels, decarbonisation of the grid and use of renewable energy, as discussed in the previous blogs, increases the impact and contribution of embodied carbon as the diagram below demonstrates (from Bionova Ltd, 2018).

Put simply, the whole industry has a responsibility to understand where it stands, and how it can reduce its carbon footprint through the whole life cycle - now is the time for embodied carbon to have the limelight.

Limiting embodied carbon cannot be an afterthought, it needs to be integrated early into the design attracting the same focus as other design considerations. There are many approaches to reduce the embodied carbon in a development and these include:

• Reuse the existing building structure, this can lead to creativity by the design team to yield substantial savings in terms of embodied carbon. The reuse of foundations can be another way to achieve a notable savings.
• Specifying lower carbon materials, for example; concrete mixes using cement replacement (Ground granulated blast-furnace slag (GGBS) and Pulverised Fuel Ash (PFA), materials with a higher recycled content (e.g. steel and rebar) or limiting carbon-intensive materials (e.g. aluminium cladding).
• Choosing lower carbon alternatives or sequestering materials such a timber instead of concrete and steel.
• Reusing materials from other projects rather than virgin materials, as carbon used to manufacture these have been captured elsewhere.
• Designing to enable Modular Integrated Construction and for deconstruction using the principles of circular economy.

To incorporate most of these opportunities’ consideration needs to be given upfront and requires the design team to take a creative approach to deliver solutions. The opportunity to capture these savings diminishes as the project develops so early integration is imperative (as shown in the United Kingdom Green Building Council (UKGBC) graphic below).

Early stage calculations using benchmarks can create baselines for considering design options and generating substantial savings. As the design evolves BIM can be used to stream line the process and improve the accuracy of the data. Savings should be tracked and improved upon during all design and construction stages with the final actual measured upfront embodied carbon report on completion for all projects using Environmental Product Declaration (EPD) for all products.

Saving can also be generated through the construction process and these include:

• Use of modular construction, precast and offsite prefabrication to increase resource efficiency, reduce material wastage and onsite construction impacts.
• Early connection to grid energy for cleaner energy use and where that is not possible using biofuel for plant and equipment.
• Limiting generation of waste on site and looking to reuse materials for temporary works where practical.

To deliver these ambitious savings in design and construction requires a change in our approach. Creative and critical thinking to ensure an optimised design and construction process can deliver a lower embodied carbon building. Taking the first step is often the hardest but, the results it yields drive change if we rise to the challenge.

Case Study - Carbon Assessment Tool

The development of the Carbon Assessment Tool for the Hong Kong Construction Industry Council will assist the industry to understand and reduce the upfront embodied carbon on building and infrastructure projects. The Tool considers the embodied carbon impact of the materials in the core and shell of a project from extraction through to installation including all construction site emissions.

The Tool has two interfaces: for design, and construction. The design interface enables options to be compared and demonstrates savings generated. A demo case output from the design calculator within the Tool is shown below:

The design base case forms the project target. The construction interface records the actual materials qualities used to understand the total embodied carbon impact of the project. Along with the data from the site operations including energy use, waste generated, and materials used in temporary works on the site. Reporting the total impact of the project.

Understanding the total impact and reviewing it against design estimations ensures the Tool can be used to set targets and develop an understanding of the embodied carbon impacts of projects in Hong Kong.

The tool is currently being trailed in Hong Kong and we are hoping to expand to mainland China and other countries. In Cundall Europe we are using similar tools to aid our design decisions.

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