CPD 13 2020: Steel and assessing embodied carbon

This Steel for Life sponsored CPD explains the assessment methods and standards for the embodied carbon impact of buildings and how they apply to steel


Within 30 years the global construction industry is being exhorted to have reduced carbon in all buildings, new and existing, to net zero. To achieve this not-inconsiderable goal the construction industry will need to tackle many issues, not least embodied carbon. This will require assessments of materials with a view to quantifying the embodied impacts of buildings. These can be more complex than for operational carbon impacts, and a number of standards cover how to go about conducting such assessments.

All of the substructure for 100 Liverpool Street was retained as well as approximately 50% of the original steel frames, which extend up to eight storeys high

This CPD will examine what will be required in the new era in terms of assessing materials, together with how the industry can address the impacts of the products it uses.

The construction industry has set itself ambitious targets for reducing its carbon footprint as part of the response to climate change and the accepted need to do more to protect the environment.

In its 2019 report “Bringing Embodied Carbon Upfront: Coordinated Action for the Building and Construction Sector to Tackle Embodied Carbon”, the World Green Building Council targeted at least a 40% reduction in embodied carbon from new buildings, infrastructure and renovations by 2030, and net zero by 2050.

Also by 2050, all buildings, including existing buildings, must be net zero operational carbon.

As the title of the World Green Building Council’s report acknowledges, a key milestone on the route to a zero-carbon future will be ensuring that the embodied carbon content of buildings and other structures is minimised.

To tackle the carbon issue will demand taking account of whole-life carbon, rather than more simplistic, “cradle-to-gate” calculations.

What is embodied carbon?

The term “embodied carbon” refers to the greenhouse gas emissions (expressed as carbon dioxide equivalent – CO2e) that occur during the manufacture and transport of construction materials and components, as well as the construction process itself and end-of-life aspects of the building.

In recent years, the term “embodied carbon” in reference to construction materials and products has become synonymous with “carbon footprint”. An embodied carbon or carbon footprint assessment is a subset of most lifecycle assessment (LCA) studies, for example only considering the global warming potential environmental impact category.

The embodied carbon and the in-use carbon emissions from the operation of a building (known as operational carbon) together make up the complete lifecycle carbon footprint of the building.

The scale of the potential threat of global climate change has focused attention on carbon emissions, and so most construction-related environmental impact studies focus on this impact category. While carbon emissions are clearly an important priority, more thorough environmental assessments should consider a wider range of impact categories, as is routinely done in LCA studies.

Recent initiatives to reduce operational carbon have increased the relative importance of embodied carbon as part of a whole-life building assessment, but the operational carbon of new buildings still makes up around two-thirds of the whole-life carbon emissions over 60 years.

Embodied carbon assessment

Quantification of the embodied impacts of buildings can be more complex than for operational carbon impacts. This is mainly due to the different scoping and methodology assumptions concerning the lifecycle stages to be included within the scope of the assessment.

Conceptually, embodied carbon assessments are quite straightforward. They involve the multiplication of quantities of construction products and materials (generally on a weight basis) with embodied carbon coefficients or carbon emission factors. Quantities are generally derived from a take-off from construction drawings or directly from bills of quantities. Increasingly, design software is being developed to automate the assessment process.

However, obtaining a comprehensive and compatible set of embodied carbon coefficients can be difficult. Carbon coefficients are dependent on a number of factors and assumptions that can significantly influence the final results.

There are several standards that set out how to undertake embodied carbon assessments. These include the ISO 14040 series, standards developed under CEN TC 350, specifically BS EN 15804, BS EN 15978, and others.

Steel and embodied carbon

The steel sector has always advocated the more meaningful LCA approach of considering a “cradle‑to-cradle” – or whole-life carbon – approach, which takes account of how, or if, a material can serve a meaningful purpose beyond simply being reduced to hardcore, for example, after its original use has ended.

Steel has exceptional circular economy credentials as it is typically either reused or recycled. Steel almost never adds to the construction and demolition waste sent to landfill.

LCAs show that steel’s long-proven sustainability advantages are strong when account is taken of what happens to the material when a building or other structure reaches the end of its useful life. Steel is not difficult or expensive to dispose of as it has a continuing value to society – it can be recycled or reused endlessly without detriment to its properties.

The recovery infrastructure for steel recycling is highly developed and highly efficient. It has been in place for decades. Current recovery rates from demolition sites in the UK are 99% for structural steelwork and, on average, 96% for all steel construction products.

Steel is manufactured by two production routes – basic oxygen steelmaking and electric arc furnace – which together comprise a single global system of supply to meet growing world demand. Both production routes include a significant recycled content, the average of which is 60% for structural steel used in the UK, according to WRAP, the circular economy consultant. British Steel advises a similar figure, and in the European steel industry as a whole, recycled scrap steel accounts for 56% of total steelmaking, being made up of 32% pre‑consumer and 24% post-consumer scrap.

For purchases of European steel, it is recommended to use a recycled content figure of 56%, which reflects the total industry position.

The redevelopment of the former Royal Mail sorting office made use of significant elements of its existing frame

Comprehensive lifecycle assessment data

Assessment of embodied carbon of materials should be based on robust data derived using an LCA as set out in BS EN 15804. This standard gives guidance around core product category rules relating to environmental product declarations (EPDs) for construction products and services. A key distinction has to be drawn between assessments based on all of the lifecycle stages identified in this standard – which is steel industry practice – and materials that only include some of these lifecycle stages.

These partial and incomplete analyses use data that can be called “cradle-to-gate”, as they only consider the impacts from extraction and manufacturing processes – modules A1-A3 – ignoring whole-life data. 

The steel sector is among those that present data for their products that consider all of BS EN 15804’s lifecycle stages, sometimes called “cradle-to-cradle” to reflect the inclusion of reuse and recycling data, and increasingly referred to as whole-life carbon assessments.

An LCA study comprises three steps:

  • Compiling an inventory of relevant energy and material inputs and environmental releases, or outputs, associated with a defined system. Releases can be solid wastes or emissions to air or water.
  • Evaluating the potential impacts associated with these inputs and releases, for example the global warming impact from greenhouse gas emissions.
  • Interpreting the results to help make informed decisions.

A common failing of some studies that try to compare one construction material with another, either at structural frame or whole building level, is an inadequate appreciation of the importance of system boundaries in the analysis.

System boundaries determine which processes are included or excluded in an LCA or other embodied carbon study. EPDs, which are derived using an LCA, are increasingly used by construction product manufacturers to provide environmental data on their products. Such analyses must be clearly defined and consistent with the system boundaries.

Different scopes and systems boundaries that can be considered, and must be clearly defined, include:

  • Geographical area
  • Time horizon, for example when the data was collected
  • Boundaries between the specific system studied and related technical systems, for example, the production of capital goods used to manufacture a product
  • Boundaries between the technological system and nature, such as which lifecycle stages are included within the system boundary, perhaps cradle-to-gate and whole-life carbon system boundaries.

Adopting a cradle-to-gate rather than a more comprehensive whole-life carbon approach in LCA and carbon-footprinting studies has, in the past, been blamed on a lack of sufficiently robust data concerning what happens to materials during and after demolition, and the fact that such information is an estimate based on current practice – which may of course change in the future. This is the module C and D information as defined in BS EN 15804. Reporting of module C and D values is now mandatory in EPDs produced to EN 15804.

The lack of sufficiently robust “end-of-life” data was addressed in relation to steel by PE International, now called Sphera, several years ago. The firm examined these factors for a range of materials commonly used in building framing systems and derived module C and D data for steel, concrete and brick/block products.

At the level of individual products, it is mandatory in BS EN 15804 to report module D information, and for very good reasons. At the level of an entire building, module D reporting is not yet mandatory in EN 15978, but this is currently under review and the two standards are likely to be aligned.

There is a growing appreciation of the need to include building end-of-life impacts (module C) and module D benefits from reuse and recycling as part of a robust, whole-life carbon assessment. Limiting the scope to just module A equates a 100% recyclable building to one that is 100% landfilled when it is demolished.

Landfill avoidance through downcycling construction materials is unsustainable to deliver a truly circular, zero carbon built environment. As a sector the construction industry has to move up the waste management hierarchy and reuse buildings and their constituent parts.

Cellular beams are used to accommodate building services within their depth and provide the flexibility to accept any future requirements

Environmental product declarations

Designers and specifiers looking for evidence that they are making low-carbon selections of products can use the appropriate steel manufacturer’s EPD, assuming they know where their steel product will be sourced from.

If the source of steel product is unknown – which is generally the case at the design stage – then it is recommended that an average embodied carbon value, reflecting a UK average consumption mix, is used. This is because steel is a globally traded commodity and therefore taking, for example, a UK average production value is not representative of UK consumption.

The most appropriate average value for steel on the European market is published by bauforumstahl, an independent steel promotional organisation in Germany. This is based on data collected from the largest hot-rolled steel sections and plates manufacturers in Europe and includes the most up-to-date embodied carbon data currently available (see table 2).

The module D figure in the bauforumstahl EPD represents current practice in Europe, that on average 11% of steel is reused at end of life, 88% is recycled and 1% goes to landfill.

EN 15804 states that the figures for the various modules should generally be reported separately, but offers no guidance on how to use the data to make decisions on a project. If decisions are made on a short-term cradle-to-gate or “product stage” basis, then the figure of 1.13 would be used. However, if a more comprehensive long-term whole-life carbon basis is adopted, then the figure of 0.72 could be used, which is an aggregate of the three reported modules A, C and D.

Circular economy action plan

The EU has adopted a Circular Economy Action Plan, one of the main strands of the European Green Deal, the EU’s new agenda for sustainable growth.

It refers to the Levels study which recommends the whole-life carbon approach, for example including modules C and D.

The action plan incorporates initiatives throughout the lifecycle of products, targeting their design, promoting circular economy processes and promoting sustainable consumption. This is with the aim of ensuring that the resources used are kept with in the EU economy for as long as possible.

The plan introduces legislative and non‑legislative measures targeting areas where action at the EU level brings real added value.

Among other things, the measures aim to make sustainable products the norm in the EU, focusing on the sectors that use most resources and where the potential for circularity is high, which includes construction and buildings.

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