How to calculate embodied carbon for the 2030 Climate Challenge

Launched in 2019, the RIBA 2030 Climate Challenge is the Institute’s response to the climate emergency. The challenge sets out ambitious targets for operational energy, embodied carbon and potable water to be achieved in buildings in use. Signatories undertake to attempt the targets and to submit project performance data to the RIBA via the Data Submission Form, and some analysis is required to submit completed projects.

But how do you analyse your buildings’ embodied carbon and check their alignment against the challenge targets? This outline of the basics is followed by a case study that provides an example for how projects may be self-assessed, and how lessons learnt can feed into future design work.

Objectives

The objective of the RIBA challenge targets is to reduce the climate change impact of the constructed building itself – its materials, products and the maintenance of these over its lifetime.

To do this, architects need to make informed choices based on knowledge of the relative carbon impacts between different building systems and materials. Lean building design is the precursor to material choice. Materials must therefore be chosen judiciously, fulfilling performance specification requirements at the lowest carbon ‘cost’.

Collaboration with the design team

By focussing on a measured target for embodied carbon in completed building projects, the challenge urges the architectural community to get to grips with data analysis, even though this is a task that some may feel less comfortable undertaking.

The institute highlights architects’ professional role in steering a collaborative design process. By advocating for embodied carbon targets and a whole life carbon approach on all projects, architects can lead the team to synthesise the design decisions and pay-offs between structural systems, material choice and replacement vs operational longevity and use early in the design process to optimise low carbon design.

What you need to check project performance against the RIBA targets:

1. Material quantities: For finished projects the bill of quantities, cost plan or equivalent is the best source of data. During design development approximate measurements might be made manually from plans/sections or by software. Materials information should amount to 95% of the cost of project materials within each of the following categories:  substructure, superstructure including building envelope, finishes, fixed FF&E, building services and associated refrigerant leakage. (Please refer to RICS Guidance Whole life Carbon Assessment For The Built Environment (Nov 2017))
2. Carbon factors: Industry standard carbon factors per material type can be found in The Inventory of Carbon and Energy (also known as the ICE database) which is freely available, or from Environmental Product Declarations (EPDs) from manufacturers.
3. Maintenance and end-of-live carbon assumptions.

How to do the calculations

Embodied carbon in building is commonly measured in kgCO₂e/m² (kilograms of carbon dioxide equivalent per square meter of building. This measure allows for the global-warming potential of various greenhouse gasses to be expressed in a single unit, presenting the inherent impact of the total building by floor area provided.)

In its most basic form, the calculation is:

Quantity of material or thing     x     Carbon factor of material or thing     =     Product stage upfront carbon

To undertake the calculation, you need to check that the functional or declared units between the material quantities and carbon factors are aligned (for example, if you have a volume (m³) of concrete, you need to multiply it by its density to get the weight (kg)). 

The ‘product stage’ that covers emissions relating to the raw material extraction, shipping to factory and manufacturing is what is most commonly available in embodied carbon databases.  So the calculation above, using figures from the carbon database, gives you the carbon emissions of materials only up to the factory gate (this has been shown to be approximately 65% of the building materials’ total embodied carbon for schools – see Figure 1 below). Emissions for transport to site and the construction process need to be added to fully evaluate a project’s upfront carbon. The easiest way to do this is to use some industry accepted proxies, such as those in LETI’s Climate Emergency Design Guide.

From upfront to embodied carbon

At early design stages, a simple upfront carbon assessment of projects is fine. However, if you want to check performance and alignment against the RIBA targets then other lifecycle stages need to be considered.  

Embodied carbon is defined as the greenhouse gas emissions relating to four lifecycle stages of a building: product, construction, in-use and end of life (as defined by BS EN 15978:2011).

It is therefore essential to state which carbon figure you are using and to be clear of the lifecycle stages being considered in any analysis. The lifecycle stages are sub-divided into modules, as shown in Figure 2. The structure allows for transparent and comparable reporting of project carbon impacts.

Proxies may be used to extrapolate the impacts of later lifecycle stages (Modules B and C) or to estimate transport impacts. For example, RICS guidance gives transport scenarios and wastage rates per £100,000 material cost for different materials. Some freely available embodied carbon calculators, such as the FCBS Carbon tool, automatically use percentage uplift factors (based on the LETI Climate Emergency Design Guide) for the different lifecycle stages beyond the product stage (Modules A1-A3) upfront carbon.

A worked example of embodied carbon can be found here 

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Jess Hrivnak is sustainable development adviser and freelance sustainability consultant at the RIBA

 

Case study: Thomas Gainsborough Secondary School, Sudbury, Suffolk by Feilden Clegg Bradley Studios

Completed in 2017, the four-storey brick building is arranged around three atria; allowing natural ventilation and light to enter the circulation spaces. With concrete foundations, precast concrete slabs and aluminium windows, this secondary school has a traditional palette of building materials.

To fulfil its ambitions for low carbon architecture and reduce embodied carbon in its projects, FCBS developed an in-house carbon calculator to help estimate whole life carbon of a building to inform design decisions before detailed design.

In 2020 the practice decided to make this tool, FCBS CARBON, freely accessible to all. It also embarked on an in-house benchmarking programme, measuring the embodied carbon performance of some of its completed projects. With the help of paid interns, who were given access to materials quantities and plans of the completed projects, as well as training with the excel based tool, several completed schools’ projects were efficiently and effectively analysed. 

The analysis shows the embodied carbon footprint of The Thomas Gainsborough School is 1067kgCO₂e/m²

The updated (V2) edition of the 2030 Climate Challenge provides a baseline of 1000kgCO₂e/m² for current business as is usual in newbuild schools. While Thomas Gainsborough is innovative in its approaches to space, light and passive ventilation, the project is typical in embodied carbon emissions for the period of construction. FCBS has adopted these learnings and its subsequent school designs show increasing embodied carbon savings achieved through structural efficiencies and material selection.