Tackling embodied carbon: how to specify the carbon cost of materials

Reducing embodied carbon is one of the biggest challenges facing the built environment sector. Specifying the carbon cost of materials right from the outset is one of the best ways to lower a project’s embodied carbon emissions. Simon Lerwill, AECOM’s Director of Specification Consulting, Joe Jack Williams, Associate at Feilden Clegg Bradley Studios, and Stuart Macalister, Technical Design Lead at Heatherwick Studio, recommend three key steps.

As buildings are currently responsible for 39 per cent of global carbon emissions, the built environment sector has a vital role to play in responding to the climate emergency.

Rahm Emanuel, the former chief of staff to President Barack Obama, is famous for saying: “You never let a serious crisis to go to waste. And what I mean by that is an opportunity to do things that you could not before.”  While Emanuel was talking about the 2008 financial collapse, we can apply the same sentiment to the climate emergency and how architects must now focus on reducing embodied carbon when designing new buildings or refurbishing and retrofitting existing ones.

Embodied carbon is defined by the charitable organisation UK Green Building Council (UKGBC) as ‘carbon emissions associated with materials and construction processes throughout the whole lifecycle of a building or infrastructure.’ With many projects now moving into digital common data environments we have access to more data on our buildings than ever before. As we understand more about our buildings, how they operate and the materials from which they are made, specifying the carbon cost of materials is one of the best ways we can lower embodied carbon emissions from the outset.

An increasing number of materials now have Environmental Product Declarations (EPDs) which allow us to review embodied carbon and other environmental impacts. Day-to-day however, we are still learning the best ways to specify carbon cost within the design process. In this article, we discuss the importance of obtaining buy-in from clients at the earliest possible stages, and three key steps for architects and designers to take in collaboration with sustainability and specification consultants.

Making the business case for lowering embodied carbon

Aside from the environmental benefits, lowering embodied carbon makes sound commercial sense. Increasingly, investors are scrutinising clients’ environmental credentials, and many clients have responded by making commitments to achieve net zero carbon emissions well in advance of the UK government’s 2050 target.

A UKGBC report points out investor rating and measurement indices are just starting to include assessments of embodied carbon, namely:

• The Dow Jones Sustainability Index (DJSI) now includes a section about the lifecycle assessment of building materials;
• The FTSE4Good Index asks questions on lifecycle studies and related carbon emissions reductions;
• Not-for-profit charity CDP includes voluntary reporting of Scope 3 emissions (defined as indirect emissions beyond building performance and materials);
• The Global Real Estate Sustainability Benchmark (GRESB) survey has a significant volume of questions on new construction and major renovations.

Three steps to effectively specify material and systems carbon costs

Reducing embodied carbon will accelerate us towards vital overall carbon reduction goals, so how can we do this most effectively? We look at three important steps:

1/Set embodied carbon KPIs

Benchmarking for embodied carbon is still relatively new.  The Royal Institute of British Architects (RIBA) set out ‘progressive but achievable targets in its 2030 Climate Challenge document that seek to reduce embodied carbon emissions from the current 2020 benchmark of 600 kg/CO₂e/m² to 450 kg/CO₂e/m² by 2025.

Clients and architects should work alongside their sustainability and specification consultants to set realistic operational and embodied carbon targets at RIBA Stage 1, which can be included in the Project Brief and Outline Specification documentation. Using industry benchmarks such as the one mentioned above is the best way to do this as initial concept designs or feasibility studies aren’t robust enough to model carbon emissions and are liable to change.

Currently one of the biggest challenges is to bring clients on this journey so that they understand and buy into this approach with a clear understanding of the benefits (lower carbon footprint) and implications (design or material changes). Once there is buy-in, then it is vital to ensure that consultant teams have the appropriate scope to undertake the requisite analysis.

 2/ Keep an eye on the carbon cost

Having set targets at RIBA Stage 1, it is important to keep an eye on carbon costs and potential material wastage while resolving geometric detailed design, alongside selecting materials in subsequent project stages.

Modelling various design scenarios to assess their carbon cost can be challenging, so involving sustainability consultants early and using carbon calculators is essential to provide feedback to the architects, design team and contractors throughout a project. Clear information, such as adding an adjacent carbon column to cost plans, makes decision making faster and more effective.

Looking to the future we could make the carbon cost even more evident; for example, what if there was a way to see the invisible carbon emissions when visualising projects in virtual reality (VR) environments? With increased adoption of digital tools these ideas may soon become reality.

3/Specify sustainability performance requirements

 The new RIBA Plan of Work 2020 Overview tells us “the value brought by the design team delivering Prescriptive Information will vary depending on the building type and the outcomes the client is seeking to achieve.” With this in mind, we advocate the following approach depending on whether items are specified prescriptively or descriptively:

• Prescriptive approach: Where systems and materials are prescribed, i.e. named in the specification, we strongly advise including specific carbon performance details. Making sure that carbon performance details are clearly visible helps ensure that carbon outcomes remain unaffected further down the line. In other words contractors would be able to reference prescribed carbon performance standards when proposing alternative solutions.
• Descriptive approach: Where systems and materials are described, i.e. by reference to performance requirements and design intent information, carbon performance details should be clearly defined. In this instance, the contractor is responsible for completing the detailed design in accordance with the defined performance requirements. Once the detailed design is accepted, the design team is then responsible for making sure the carbon performance requirements are achievable using available systems and materials.

Putting it into practice

Sustainability engineering workshops to action the above steps should be held at the very outset of a project. They are an invaluable part of the process when considering whole life carbon and are highly likely to influence early geometry and massing.

Ascertaining which materials and building methods produce the lowest embodied carbon takes research and investment, and this knowledge needs to be amassed and used from project to project. Feilden Clegg Bradley Studios has developed its own carbon calculation tool to advise their design teams and also has a full-time researcher to advise on the best materials to use to lower embodied carbon. Heatherwick Studio is working with AECOM’s Specification Consulting team to build a library of materials and their sustainability data to inform future designs and lower their embodied carbon.

In the near future, it is possible that British Standards will be created to set an important benchmark for our industry to measure embodied carbon in a unified way. Until then it is vital that designers, engineers and consultants work together to share data so we can specify a better built environment for generations to come.