Life cycle assessment and embodied carbon

As the operational energy efficiency of new buildings has been improved over recent years, the relative importance of the embodied carbon impacts of buildings has increased. As a consequence, greater attention is being placed on how the embodied carbon (or carbon footprint) of buildings can be measured and reduced.

Embodied carbon assessment is a subset of a broader discipline called Life Cycle Assessment (LCA) which covers a range of different environmental impacts. As such, many of the principles are equally applicable to both assessment methods.

This article:

• Introduces LCA, embodied carbon and whole-life carbon assessment.
• Describes some key aspects that designers should be aware of
• Gives sources of construction LCA data
• Provides information on whole life embodied carbon data for steel and other common framing materials.
• Presents the results of some comparative embodied carbon studies.

Current end-of-life scenarios for three common construction materials

What is Life Cycle Assessment?

First developed in the 1960s, Life Cycle Assessment (LCA) is the most widely used and highly regarded tool for quantifying the environmental impacts of products and services. Despite being conceptually quite straightforward, LCA can be very complex with many important, often material-specific, assumptions than can significantly influence the outcome. LCA is the methodology that is used to develop Environmental Product Declarations (EPD) which are a standardised set of environmental information based on a common set of rules called Product Category Rules (PCRs). EPD are increasingly being used by construction product manufacturers in the UK and the EU to provide robust, quantified environmental data for their products. There are now over 6,000 verified EPD to EN 15804 for construction products registered globally.

LCA involves the collection and evaluation of quantitative data on the inputs and outputs of material, energy and waste flows associated with a product over its entire life cycle so that its whole-life environmental impacts can be determined.

An LCA essentially comprises three steps:

1. Compiling an inventory of relevant energy and material inputs and environmental releases (outputs) associated with a defined system. Releases can be solid wastes or emissions to air or water
2. Evaluating the potential impacts associated with these inputs and releases, e.g. the global warming impact from CO₂ and other greenhouse gas emissions
3. Interpreting the results to help make informed decisions.

If the LCA study is to make comparative results public then a critical review of the study to ISO 14044 must be provided.

An important first step in any LCA is to clearly define the goal and scope of the study. The goal and scope of the study should define key details of the study including:

• The functional unit of the product or system to be assessed, e.g. a tonne of structural steel, 1m² of external wall or a whole building, etc. over a defined timescale, typically 60 years in the case of building assessments
• The system boundaries, i.e. what is included/excluded from the scope of the assessment
• Any specific assumptions and limitations of the study
• The allocation methods used to partition the environmental load of a process when several products or functions share the same process, e.g. blast furnace slag is a valuable by-product of steelmaking from iron ore and therefore should carry a proportion of the environmental impact from steelmaking to the product in which it is used. Allocation is used to ‘allocate’ or share a proportion of the environmental impact from steelmaking to the blast furnace slag
• The environmental impact categories chosen, e.g. if only the climate change impact is included within the scope of the LCA, then the assessment is in fact an embodied carbon assessment.

LCA methodology is very flexible in terms of the goal and hence scope of assessment, however a robust LCA of a construction product (or a building) should include the impacts of:

• Extraction of the relevant raw materials, e.g. quarrying, mining
• Refinement and conversion to process materials, e.g. steelmaking or cement production
• Manufacturing and packaging processes, e.g. steelwork fabrication or making precast concrete products
• Transportation and distribution between each stage
• Waste at each stage
• On-site construction impacts, e.g. water and energy use, temporary works, shuttering, worker commuting, etc
• Operation during the lifetime of the building including maintenance, refurbishment, replacement, etc.
• At the end of its useful life, demolition, final transportation, waste treatment and disposal.

Any recycling or recovery operations built into the life cycle should lead to a proportionate reduction in the adverse environmental impact and should be accounted for.

LCA impact categories

The impact of the inventory of flows or outputs from a system is assessed and interpreted by linking them to environmental impact categories through a process known as characterisation. The environmental impact categories generally considered in a construction or building LCA study are shown; the most common categories assessed are shown in bold.

LCA environmental impact categories

Global warming potential	Ecotoxicity to land
Water extraction	Waste disposal
Mineral resource extraction	Fossil fuel depletion
Stratospheric ozone depletion	Eutrophocation
Human toxicity	Photochemical ozone creation
Ecotoxicity to freshwater	Acidification
Nuclear waste (high level)

Environmental impacts in one category can be caused by many different emissions and therefore characterisation factors are used to combine the impact of different substances. A good example of this, which is also relevant to embodied carbon assessments, is the impact category of global warming potential (GWP).

Global warming is caused by a number of different greenhouse gases each which have a greater or lesser impact on the climate over time. In LCA therefore (and in robust embodied carbon studies) climate change characterisation factors (or global warming potentials (GWP) - see table below) are used to combine the global warming potential of different greenhouse gases to derive a single metric, in this case CO₂e or carbon dioxide equivalents. Similar characterisation processes are undertaken for other LCA impact categories.

Characterisation (or GWP) factors for common greenhouse gases

Greenhouse gas	GWP – 100 year timeframe (kgCO2e)
Carbon dioxide (CO2)	1
Methane (CH4)	25
Nitrous oxide (N2O)	298
Sulphur hexafluoride (SF6)	22800
Perfluorobutane (C4F10)	8860
HFC 134a (tetrafluoroethane)	1430

The GWP of greenhouse gases (GHG) is also a function of time, i.e. some greenhouse gases are more persistent in the atmosphere than others. For most GWP assessments the 100-year timeframe is used.

Having established quantitative measures for each of the impact categories within the scope of the LCA, a further step undertaken in some LCA methodologies is to weight the different impact categories to produce a single value of environmental impact. Although this approach is not endorsed in LCA standards, it can be used to produce a single metric scoring system that is easy to understand for users.

An example of an LCA methodology which uses this approach is BRE’s Environmental Profiles, (for which a methodology guide is available). To produce a single value of environmental impact, two steps are employed:

1. Normalisation – the 13 environmental impact category scores assessed by BRE are normalised to the annual impact of an average European citizen
2. Weighting – the normalised category scores are then combined using weightings of environmental importance, derived from a panel of European experts.

The resulting single value of environmental impact has the units of Ecopoints where 100 Ecopoints is equivalent to the annual impact of an average European citizen. This methodology is intended to simplify the assessment and comparison of different environmental impacts however the approach is also criticised by some because the weightings applied are subjective and will vary over time.

LCA codes and standards

The principle standards governing the use of LCA are the ISO 14040 series of standards. These provide guidance on:

• LCA principles and framework ISO 14040
• LCA requirements and guidelines ISO 14044.

Previously, three additional ISO LCA standards existed:

• Goal and scope definition ISO 14041
• Life cycle impact assessment ISO 14042
• Life cycle interpretation ISO 14043

These have been withdrawn and are now covered by revised versions of ISO 14040 and 14044.

These are generic standards applicable to all types of LCA study, i.e. not just construction or building related studies.

In the context of building and construction LCA, the standards developed by CEN TC 350 are important in defining how the environmental impacts of construction products and buildings are assessed and will ensuring that such assessments are undertaken on a robust and consistent basis throughout the EU.

These standards were developed in response to the plethora of different sustainability schemes being developed in Europe, which prompted the European Commission to issue a mandate to CEN to develop horizontal standardised methods for the assessment of the integrated environmental performance of buildings. Subsequently the remit was broadened to include social and economic dimensions and to widen the scope to include civil engineering works.

European Standards Technical Committee CEN/TC350 and its various working groups, began work in 2005 and a suite of standards have been developed. These include:

• BS EN 15643-1
• BS EN 15643-2
• BS EN 15643-3
• BS EN 15643-4
• BS EN 15804
• BS EN 15978
• BS EN 16309.
• BS EN 16627.

The importance of European Standards is that EU Member States, must use European Standards where they exist when regulating and, if they exist, National Standards must be withdrawn if they are in conflict with European Standards. So, for example, if the UK decided to regulate on measuring the sustainability of buildings and construction products then the UK will have to use the CEN/TC350 standards.

European Standards remain voluntary but their transposition into national standards and the withdrawal of diverging national standards is mandatory according to the internal rules of the European Standards Organisations.

The Construction Products Regulation (CPR)

The Construction Products Directive (1989) was one of the first Directives from the EU Commission to create a common framework for the regulation of buildings and construction products. It was replaced by the Construction Products Regulation (CPR) in 2011, which is legally binding throughout the EU. The CPR includes requirements for:

• Sustainable use of natural resources – under Basic Construction Works requirement 7
• Reduced environmental impact from toxic gases, VOCs, greenhouse gases or dangerous particles, etc. over the life cycle – under Basic Construction Works requirement 3.

It is likely that the use of Environmental Product Declarations (EPD) will be the principal means of assessing and reporting the environmental impacts of construction products under the CPR.

If an EU Member State wishes to regulate in these areas of sustainability it must use European standards where they exist when regulating and must withdraw national standards. This means that in the case of the CPR, a Member State must use the CEN/TC 350 suite of standards.

Environmental product declarations

Environmental Product Declarations (EPD), are used to provide environmental information from LCA studies in a common format, based on common rules, known as Product Category Rules (PCR). The construction industry has widely adopted EPD as the means of reporting and communicating environmental information. (Note: the plural of EPD is EPD).

BS EN ISO 14025 sets out standards for developing EPD. This standard also draws on the key LCA standards ISO 14040 and ISO 14044.

For construction in Europe, BS EN 15804 is the key standard which provides the core product category rules for producing EPD of construction products.

To be comparable, EPD must have been developed using the same PCR, to ensure scope, methodology, data quality and indicators are the same. EPD can only be compared when the same PCR have been used and all the relevant life cycle stages have been included. This is a frequent limitation or failing of many comparative LCA studies.

Within Europe, PCR for construction products have been developed in the UK, France, the Netherlands, Scandinavia and Germany and EPD are published by Scheme Operators.

Launched in 2013, the ECO platform is an international association established by European EPD programme operators, to develop verified environmental information on construction products, in particular, EPD. ECO platform’s mission is to produce consistent, high quality environmental information on construction products, and its members include many of the leading European organisations delivering construction EPD including BRE in the UK and IBU (Institut Bauen und Umwelt e.V.) in Germany.

What is embodied carbon?

The term ‘embodied carbon’ refers to the lifecycle greenhouse gas emissions (expressed as carbon dioxide equivalents – 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’ of construction materials and products has become synonymous with the term ‘carbon footprint’. An embodied carbon or carbon footprint assessment is a subset of most LCA studies, i.e. only considering the GHG environmental impact category.

The embodied carbon and the in-use carbon emissions from the operation of the building (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 therefore 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.

An embodied carbon footprint tool for buildings is available.

Current breakdown of whole life carbon for a typical office, residential and school development over 60 years
(LETI Climate emergency design guide)

While recent initiatives to reduce operational carbon have increased the relative importance of embodied carbon, as part of a whole life building assessment. As the figure (right) taken from the LETI Climate emergency design guide shows, operational carbon of new buildings still makes up most (around 2/3) of the whole life carbon emissions over 60 years and therefore remains the priority for further reductions.

Embodied carbon codes and standards

As a subset of LCA, embodied carbon assessments (or carbon footprinting) is subject to many of the same standards.

However, methodologies and protocols have begun to emerge on how to measure a carbon footprint in a standardised way; some of which relate to a company or organisational footprint, others to installations and others to a product. These include:

• The Greenhouse Gas Protocol - provides standards and guidance for companies and other organizations preparing a GHG emissions inventory
• PAS 2050 – specifies requirements for the assessment of the life cycle GHG emissions of goods and services based on key life cycle assessment techniques and principles
• ISO 14064-1 which specifies principles and requirements at the organization level for quantification and reporting of greenhouse gas (GHG) emissions and removals
• ISO 14064-2 which specifies principles and requirements and provides guidance at the project level for quantification, monitoring and reporting of activities intended to cause greenhouse gas (GHG) emission reductions or removal enhancements
• ISO 14064-3 which specifies principles and requirements and provides guidance for those conducting or managing the validation and/or verification of greenhouse gas (GHG) assertions.

There are also many publications giving guidance on how to assess the embodied carbon of buildings and construction products with some also suggesting benchmarks and targets. These include:

• LETI Climate emergency design guide
• WGBC Bringing embodied carbon upfront
• UKGBC: Net zero carbon buildings: A framework definition
• RIBA 2030 Climate challenge
• Whole Life-Cycle Carbon Assessments guidance published by the Major of London
• IStructE How to calculate embodied carbon
• RICS Whole life carbon assessment for the built environment

LCA scope and system boundaries

System boundaries determine which processes are included (or excluded) in an LCA or embodied carbon study or an EPD. Different scopes and systems boundaries that can be considered, and which should be clearly defined in LCA and embodied carbon studies, include:

• Geographical area, e.g. UK, EU, World, etc
• Time horizon, i.e. when the data were 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, i.e. which life cycle stages are included within the system boundary. Common examples include ‘cradle-to-gate’ and ‘cradle-to-cradle’ system boundaries.

It is important when undertaking LCA or embodied carbon assessments that the systems boundaries are clearly defined and, when comparative assessments are undertaken, that the data used are consistent in terms of the scope and boundaries defined above. This is a common failing of many comparative LCA studies.

Cradle-to-gate vs cradle-to-cradle

An important scoping decision in LCA and embodied carbon studies is which parts of the product life cycle are included.

Studies in which the impacts are assessed only to the point where the product leaves the factory gate are called ‘cradle-to-gate’ studies. Those which include all life cycle phases up to the point where the building is demolished and materials disposed of as waste or recovered and recycled, are called ‘cradle-to-cradle’ studies.

It is generally recognised that robust studies should include cradle-to-cradle impacts and there is a growing appreciation of the need to consider the whole life cycle. This is possible using both BS EN 15804 and ISO 14044

BS EN 15804 Life cycle stages

BS EN 15804 provides a core set of Product Category Rules (PCRs) for the Europe-wide generation of EPD for construction products. PCRs define the methods for the collection of data, the calculation of environmental impact and how the information should be presented.

BS EN 15804 defines the various building life cycle stages that can be included within LCAs and EPD and these are shown. Different life cycle stages are either mandatory or optional for different scope of EPD.

In the latest version of EN 15804, published in 2019, in recognition of the importance of the circular economy and the need to recycle and reuse construction materials more and better, reporting of Module C and D impacts in EPD is now mandatory. Cl 5.2 states that ‘All construction products and materials shall declare modules A1-A3, modules C1-C4 and module D’.

Definition of life cycle stages (from BS EN 15804)
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Module D allows supplementary information beyond the building life cycle to be considered. For construction products, this means the benefits and burdens of disposal after demolition are taken into account. The use of Module D is consistent with a cradle-to-cradle approach.

For the metals industries, Module D provides the opportunity to take into account the fact that metals are not limited to one life cycle, and can be recycled almost indefinitely without loss of properties, and also that this has the positive effect of displacing production from primary materials.

The net benefit of this indefinite recycling, taking care not to include the impacts of recycled material already used in production, can then be credited against the impacts of the original production from the primary materials.

In summary, the presence of Module D in BS EN 15804 allows credits to be taken now for the eventual reuse or recycling of material in the future as long as the reuse and recycling scenario is based on current practices (and supported by robust data).

Module D can be used in many scenarios. It is not required only in order to quantify material recovery benefits. It can also, for example, be used to quantify the benefits of surplus energy that might be generated by a building. For example, a building that generates renewable PV electricity and exports surplus energy to the grid, can report the carbon emission reduction benefits of generating that additional energy in Module D, since the building also has to report the embodied carbon of the PV installation in Module A. The use of Module D may be the only way to report these benefits and this gives validity to its use.

It is noted that BS EN 15978:2011, which has been produced by CEN TC 350 with the objective of aggregating the impacts from the EPD developed using EN 15804, to the whole building level, states that If relevant information is provided at the product level on Module D, this information should be reported. In other words, if the information required to use Module D is available (in the case of construction materials this is the recycling/reuse/landfill etc rates at end of life) it should be used.

BS EN 15978:2011 is currently being revised by CEN TC350 and it is expected that it will be aligned with BS EN 15804:2019 in mandating the inclusion of Modules C and D in whole building assessments.

Whole-life carbon

There is a growing appreciation of the need to consider the whole life cycle in the assessment of the carbon emissions associated with the design, construction, operation and ultimate disposal of buildings and civil engineering structures. Support for whole life carbon assessment comes from a number of recently published embodied carbon guides including:

The IStructE guide on How to calculate embodied carbon states:

‘best practice is to consider whole life embodied carbon (Stages A-C plus D), so that we not only minimise embodied carbon emissions today but also consider the future emissions impacts of using the asset, durability, longevity, end of life scenarios, reusability and recyclability. This will ensure that future emissions and resource consumption are also kept to a minimum.’

The RICS Whole life carbon assessment for the built environment states:

‘A complete whole life carbon assessment should account for all emissions arising over the entire life of a built asset. It should also account for any future reusability and/or recyclability of its different constituent elements - modules (A) to (D): cradle to grave including impacts beyond the system boundary - as applicable to each project.’

EN 15804:2019 mandates the reporting of Modules C and D stating in Cl 5.2 that all construction products and materials shall declare modules A1-A3, modules C1-C4 and module D.

WGBC in their document Bringing embodied carbon upfront state:

‘Consideration of module D is key for maximising resource efficient uses of materials at the end of life. Under forthcoming updates to European standards, it will be mandatory for product EPDs to report module D alongside other lifecycle stages in most cases and will also be required for building assessments.

Metals like steel are recycled, often without any loss in physical qualities. Recycling and re-use contribute to the reduction of embodied carbon. These benefits can be credited upfront as recycled content or at the end of life in terms of future recyclability. Alternatively, in a full lifecycle approach, the net balance of recycled content and end of life credits can be calculated (thus avoiding double counting). These effects are captured in module D, which will be mandatory to declare under forthcoming updates to EN 15978 and EN 15804.’

The latest version of the ICE database (v3.0) states:

‘The modular approach of the EU wide standards EN 15978 and EN 15804 is particularly encouraged, due to the transparency it brings to method for recycling. These standards require that the lifecycle results are broken down by lifecycle stage. Module A being cradle to gate. Module B is in-use. Module C is end of life. Module D is benefits and burdens beyond the lifecycle.

Module D is particularly relevant for steel and users are encouraged to estimate module D benefits in addition to the Module A-C results - but to always report them transparently, e.g. results broken down by the EN 15978 modules. This gives users all the information they require to judge the benefits of both recycled content and end of life recyclability.

It is recommended to read the recycling methodology guide from ICE V2.0 (Annex A on recycling methods) before using this data, which also contains guidance on end of life issues for steel.’

The Whole Life-Cycle Carbon Assessments draft guidance published by the Major of London states:

‘In developing a WLC assessment for compliance with Policy SI 2, applicants should follow BS EN 15978 using the RICS PS as the methodology for assessment.

A WLC assessment should cover the entirety of modules A, B, C and D to comply with Policy SI 2. Applicants should note that they will be expected to report against all of these life-cycle modules in their WLC assessment, not just the minimum requirements identified in the RICS PS.

In order to transform London to a resource-efficient, zero-carbon economy, it is essential that these issues are given careful consideration at the design stage. The Circular Economy Statement for the development will set out the carbon reduction activities undertaken for Module D. The potential carbon costs or benefits associated with these activities should be calculated and included in the appropriate section of the WLC assessment.

The objective is to facilitate future reuse, recovery and recycling at the highest possible level. The applicant is required to develop realistic and feasible scenarios, supported by evidence, to support any carbon benefits included in the reporting of Module D. Due to the speculative nature of these scenarios this module is reported separately. Module D is essentially (in combination with module C3) the ‘circular economy’ module. Its importance is that it provides a carbon emissions quantification of the potential circular benefits of a scheme.’

Embodied carbon targets

Embodied carbon targets for domestic and non-domestic buildings (Modules A1-A5)
(LETI Climate emergency design guide)

In the absence of UK regulation of embodied carbon and definitive targets or benchmarks, several recent industry guides have proposed embodied carbon targets that would go a long way to achieving the 2050 UK Climate Change Act targets. These include:

The LETI Climate emergency design guide which proposes the following baseline and 2020 and 2030 best practice targets for embodied carbon (Modules A1-A5). Note that although LETI does not include Modules C and D within the scope of these targets, they do propose targets both for incorporating reclaimed construction products in new buildings and designing new buildings for deconstruction and reuse.

The RIBA 2030 Climate Challenge includes the following embodied carbon targets for non-domestic buildings.

RIBA 2030 Climate Challenge targets

Whole Life-Cycle Carbon Assessments guidance published by the Mayor of London proposes the following whole life carbon benchmarks and aspirational targets. The life cycle benchmarks cover Modules A1-A5, B and C but exclude Modules B6, B7 and D.

Mayor of London’s Whole Life-Cycle Carbon Assessments benchmarks (Modules A1 to A5)

Accounting for end-of-life impacts

Assumptions made about the treatment and disposal of materials from buildings after they are demolished can have a significant effect on their whole lifecycle environmental impacts. For example, an LCA of bio-based products which includes that fact that some of these end up in landfill where they decompose and emit methane can have a significant adverse impact on the result. By contrast, an LCA of steel construction products which takes into account that fact that 96% are reused or recycled can have a very positive impact.

Studies that exclude end-of-life impacts, such as cradle-to-gate studies, make no differentiation between these two very different scenarios.

Recycling material at end of life obviously provides a benefit, as does using recycled material in the first place. Different approaches for accounting for this benefit are used in LCA and embodied carbon studies.

It is generally recognised that a robust and thorough LCA study should include end-of-life impacts and therefore cradle-to-cradle studies are preferred over cradle-to-gate studies. There are several different methods for accounting for recycling within cradle-to-cradle studies. Three of the most common methods are:

• Recycled content approach in which the full benefits of material recycling are allocated to the input side of a product system. This leaves no benefit for end of life recyclability.
• Closed loop recycling, in which the creation of recyclable material is allocated the full benefit of recycling at end of life (called recyclability). This leaves no benefit for incoming recycled materials, which are effectively neglected.
• Methods in which the impacts and benefits of recycling are shared (or allocated), by some means, between the input and output sides of the product system.

In LCA studies, the type of recycling is significant and can be described as either open or closed loop which reflects the changes in inherent properties of the materials that are recycled.

• Open loop recycling involves the conversion of material from one product life cycle into another product life cycle. This usually involves a change in the inherent properties of the material itself (often a degradation in quality). For example, recycling plastic bottles into plastic drainage pipes. Often this is called downcycling or reprocessing.
• Closed loop recycling describes the recycling of a product into an identical product, for example recycling a steel beam into another steel beam.

Closed-loop recycling poses relatively small methodological problems in LCA, whereas open-loop recycling can incur major allocation problems. Basically, open-loop recycling creates a new, larger system which should be treated as one system. Since this is often not possible, or very difficult and complex, allocation rules have to be applied in order to treat one of the subsystems separately.

In LCA terms, steel products are described as flowing in ‘open loop’ recycling systems, e.g. a steel beam can be recycled into another steel beam but is just as likely to be recycled into a car or a tin can, etc. However, since there is no change in the inherent material properties, recycling steel can be considered as ‘closed loop’ and allocation avoided by expanding the system to include both primary and secondary production. This ‘closed-loop’ approach forms the basis of the recycling methodology adopted by the metals industries generally, including the World Steel Association.

A common example of open loop recycling or downcycling in construction is the crushing of concrete and masonry to produce general fill which is often used on-site, for example as a piling mat. Although this avoids landfill, it only substitutes aggregate production not the production of new concrete or masonry. Consequently, the environmental benefit, as reported in Module D, reflects this lower quality of recycling.

Annex D in BS EN 15804 provides end-of-life formulae for calculating Module D which includes a quality ratio between the recovered material and the substituted material

Accounting for the recycling of steel

Accounting for the benefits of recycling in LCA and embodied carbon studies is important for highly recycled materials like steel. The impact of using the Module D approach in BS EN 15804 and the closed loop recycling approach of ISO 14044 to calculating the benefits and burdens of disposal after demolition are very similar. Illustrations of closed loop recycling calculations for steel slab production are available.

Construction LCA and embodied carbon data sources

There are a number of sources of LCA and embodied carbon data for construction products. These include:

The Building Research Establishment (BRE)

The BRE provides several types of LCA data and tools including:

• EPD (called BRE Environmental Profiles) of construction products and materials. Both generic and proprietary EPD have been produced but only a few are currently publicly available. The EPD data generated by BRE have been used in other BRE resources and tools including the Green Guide to Specification, Envest2 and IMPACT.
• Green Guide to Specification provides environmental ratings (summary and individual category rating) and embodied carbon data for over 1,200 common construction specifications used in various building types. Although the Green Guide has largely been superseded by newer data sources, the Green Guide ratings are still available online however they have not been updated since 2008.
• IMPACT is designed to allow simple integration into 3D CAD/BIM (Building Information Management) software tools or bespoke LCA applications. The results generated by IMPACT can be used to award credits within whole building assessment schemes like BREEAM. IMPACT is a specification and database for software developers to incorporate into their tools to enable consistent LCA and Life Cycle Costing (LCC). IMPACT compliant tools work by allowing the user to attribute environmental and cost information to drawn or scheduled items in the BIM. The IMPACT Database (version 5) contains approximately 350 datasets that are compliant with BS EN 15804 and have been modelled in SimaPro, using BRE Global EN 15804 PCR, ecoinvent v3.2 and various Trade Association/representative manufacturers’ primary data where applicable.

Inventory of Carbon and Energy (ICE)

Developed by the University of Bath in 2004, the ICE is a database of embodied carbon and energy values for common construction materials. As such it has been widely used in many assessment tools developed by others and in many construction embodied carbon studies. The most recent version of the ICE database is v3.0 released in 2019.

It is important to note that the ICE is not the product of a rigorous LCA study but rather a review of published information from other sources, in particular EN 15804-compliant EPD. As such, the values in the database are variable in terms of scope, age and quality and consequently data from the ICE should be used with care in comparative embodied carbon studies.

The ICE database scope is ‘cradle-to-gate’ (Modules A1-A3) only. However, for metals, the database includes compatible Module D data.

Specialist LCA software providers

There are a number of specialist providers of LCA services that develop and sell LCA construction datasets. These include:

• Ecoinvent
• GaBi
• OneClickLCA
• eTool

Manufacturers and trade associations

Many large manufacturers of construction products and trade associations have either commissioned or developed their own LCA and embodied carbon datasets or EPD. As at 2019, it is estimated that more than 6,000 EN 15804-compliant EPD of construction products have been published.

In the case of steel data, worldsteel is the source of comprehensive and up-to-date data. Many commercial LCA databases use the worldsteel steel data.

RICS Building Carbon Database

First developed by WRAP, RICS has taken over, enhanced and in May 2019, launched the whole life Building Carbon Database.

The aim of the database is to allow users to identify where associated carbon emission reductions can be made, during all stages of a building's life cycle. For organisations who submit their data, the database is free to use. To access the data, users are required to input construction project data into the database (both theoretical and completed projects), which in turn allows users to estimate/benchmark whole life carbon emissions.

Within the database, the most important tool is 'New Project', which allows users to enter their data into the databank. This can be accomplished via a downloadable excel spreadsheet where the user inputs all the data at once, then uploads the spreadsheet as a document. The other route is via the 'Wizard', which permits the user to enter the projects data on a step-by-step basis. Both methods allow the user to select whether the project is whole life (one value representing a combination of life cycle stages) or life cycle (results separated by life cycle stages).

Steel LCA and embodied carbon data

In 1996, worldsteel launched its innovative worldwide life cycle inventory (LCI) study for steel products. This was the first time that such an international study of a specific material had been carried out. The study is regularly repeated and updated and is in accordance with the BS EN ISO 14040 series of environmental standards. The closed-loop recycling method from BS EN ISO 14044 is used to account for the benefits of steel recycling.

The worldsteel LCA data have been used in many LCAs; around 200 requests for data are made each year. LCAs are used for benchmarking performance, improving products, addressing legislative requirements and assessing competition between materials. Requests for worldsteel LCA data can be made by filling in the online questionnaire to describe how the data are to be used. The request is then discussed with the worldsteel LCA Manager. The latest dataset was published by worldsteel in 2019.

Designers and specifiers can use the appropriate steel manufacturer’s Environmental Product Declaration (EPD), assuming that they know where their steel product will be sourced from.

However, if the source of steel product is unknown, which is generally the case at the design stage, then it is recommended that an average 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 BCSA recommends the following UK average emissions factors for embodied carbon assessments of structural steelwork:

Embodied carbon (CO_2e) impacts of common steel construction products / (tonnes per tonne)
(BCSA 2021)

Product	BS EN 15804 Modules		Whole Life Carbon
	Product stage	Recycling potential
	Modules A1 to A3	Module D
Structural steelwork	1.74	-0.93	0.81

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 1.74 would be used. However, if a more comprehensive long-term Whole Life Carbon basis is adopted, then the figure of 0.81 could be used, which is an aggregate of the tabulated modules A and D.

End of life LCA and embodied carbon data for construction materials

One of the reasons commonly given for choosing a cradle-to-gate rather than a cradle-to-cradle scope in LCA and carbon footprinting studies in construction is the lack of robust data on what happens to materials during and after demolition. This is the Module C and D information as defined in BS EN 15804. PE International (now sphera) examined these impacts 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.

This data has been added to existing Module A1 to A3 data to derive a summary of whole life embodied CO_2e emissions data.

Excerpt from the summary of lifetime CO_2e emissions data for common framing materials

Embodied carbon comparisons

EPD provide environmental data at the component or material level but it is only when these data are aggregated at the building level that sensible comparisons can be made. The reasons for this are principally two-fold:

• EPD are generally produced on a per unit weight basis and therefore take no account of the efficiency of the material or product, for example the weight of structural steel required to support a building is substantially less than the weight of structural concrete required for the equivalent building
• Whole building assessments take account of consequential impacts, for example, if a lighter superstructure is used, then fewer foundations may be required for the building.

The graph shows the variation in embodied carbon in five different, recently constructed non-domestic buildings – see Target Zero. It shows the total embodied carbon in five buildings each of which has different structural forms. For each building, the base case building (i.e. the building as constructed) has a steel superstructure; the alternative structural options for each building type are defined here. Further details of the embodied carbon assessment methodology are provided here. It should be noted that the embodied carbon emission factors for the principal structural materials used in Target Zero are different to those to be found elsewhere on this site. That is because data changes over time as newer and better information becomes available.

Total embodied carbon emissions for each building and structural alternative

The graph below shows the same results but with the total embodied carbon emissions normalised to the gross internal floor area (GIFA) of each building. The normalised carbon emissions vary between 234 kgCO₂e/m² for the distribution warehouse (Base Case) up to 506 kgCO₂e/m² for the high-rise office building (Structural option 2). Note that the embodied carbon target in the LETI Climate emergency design guide for non-domestic buildings for 2020 is 600 kgCO₂e/m² GIFA (Modules A1-A5).

Total embodied carbon emissions normalised to floor area

The variation in the embodied carbon in the frame and upper floors for each building normalised to the gross internal floor area is also shown. The normalised carbon emissions vary between 32kgCO₂e/m² for the distribution warehouse (Base case building) up to 270kgCO₂e/m² for the mixed-use building (Base case).

Embodied carbon emissions in the frame and upper floors (normalised to floor area)

The low rise buildings (warehouse and supermarket) show similar results as do the high rise buildings assessed (office and mixed-use). The school building (three storeys) lies midway between the two datasets. The frame and upper floors in the low-rise buildings represent 14% to 22% of the total building embodied carbon. For the high-rise buildings, the frame and upper floors make up 48% to 66% of the total impact.

The breakdown of embodied carbon (by element) for a large distribution warehouse is shown here.

Breakdown of embodied carbon by element – distribution warehouse

As is the breakdown of embodied carbon (by element) for a large city centre office building.

Breakdown of embodied carbon by element – large city centre office building

Detailed breakdowns of the embodied carbon by building element for all five buildings, are presented in the Target Zero design guides.

Further reading

• A guide to understanding the embodied impacts of construction products. Construction Products Association
• A short guide to embodied carbon in building structures. The Institution of Structural Engineers
• Allwood, J. and Cullen, J. M.: Sustainable materials with both eyes open, UIT Cambridge Ltd, 2012
• A comparative embodied carbon assessment of commercial buildings, The Structural Engineer, October 2012

Resources

• The whole story – From cradle to grave
• Carbon footprint tool for buildings
• Steel construction – Carbon Credentials
• Target Zero – Cost effective routes to carbon reduction

Target Zero design guides:

• Guidance on the design and construction of sustainable, low carbon office buildings
• Guidance on the design and construction of sustainable, low carbon warehouse buildings
• Guidance on the design and construction of sustainable, low carbon supermarket buildings
• Guidance on the design and construction of sustainable, low carbon mixed-use buildings
• Guidance on the design and construction of sustainable, low carbon school buildings

See also

• Recycling and reuse
• Target Zero
• The recycling and reuse survey
• End of life LCA and embodied carbon data for common framing materials

CPD

• Sustainability and steel construction
• Sustainable steel buildings