Carbon Metrics: Assessing & Controlling GHG Emissions Across Scales

Carbon Metrics: Assessing & Controlling GHG Emissions Across Scales

What constitutes appropriate and scalable carbon metrics in the built environment? How can a basket of different metrics inform policy and practice?

Guest editor: Thomas Lützkendorf

This special issue examines the scientific approaches to create appropriate carbon metrics for the built environment and what format(s) those could take for embodied and operational emissions. These can be used effectively to identify and assess GHG emissions at different scales of the built environment. They can promote clarity, common understanding and a shared goal amongst diverse stakeholders. Carbon metrics have practical application in supporting decisions in design and product development as well as evaluating progress in reaching targets for net-zero.


This special issue provides a basis for creating a coherent set of targets and indicators based on the safe planetary boundary for GHG emissions. The intention is for these indicators to inform decisions and actions for the wide array of built-environment actors. Reasons for counting GHG emissions and developing carbon metrics include:

  • to assist with the development of national and city public policies, regulations, targets and other measures, along with their monitoring
  • to improve the decision-making processes for the delivery and operation of the built environment at different scales: city, neighbourhood and building levels
  • to identify individual places, buildings or neighbourhood areas that need additional support or specific positive interventions
  • to provide clarity to a wide range of stakeholders by providing clear data, targets and systems of measurement that are exchangeable between different actors
  • to create transparency for different circumstances and contexts
  • to ensure consistency in both data and units of measurement.

Several urgent questions for climate protection (e.g. staying within a 1.5–2 °C range of global warming) are addressed:

  • How can the overarching goal of large GHG reductions be allocated for particular places, functions and circumstances?
  • Can the overall goal be translated into a quantifiable system of measurement (carbon metrics) that is a transparent, consistent, measurable and scalable system (global, national, city, neighbourhood, site, etc.)?
  • How would a carbon metrics system operate? Who would use it and benefit from it?
  • What assessment criteria and indicators are needed by built environment decision-makers?
  • How can specific whole-life targets to be used to ensure actual performance and outcomes?
  • Given that many existing and new buildings will exist beyond 2050, what emission targets need to be implemented now?
  • Is differentiation needed for different building types, functions, construction types and location? How this can be done fairly and consistently whilst still meeting the overall target for climate protection?
  • Can such an approach be used to define a coherent set of responsibilities and actions for each of the different groups of involved actors?

The original Call for Papers (https://tinyurl.com/y6b9ftoa) provides a useful context for readers to refer to, as well as some recommended literature.  This special issue now contributes to that literature and advances our understanding of how carbon metrics can be developed and applied.


Table of Contents

The role of carbon metrics in supporting built environment professionals [editorial]
T. Lützkendorf

Carbon budgets for buildings: harmonising temporal, spatial and sectoral dimensions
G. Habert, M. Röck, K. Steininger, A. Lupísek, H. Birgisdottir, H. Desing, C. Chandrakumar, F. Pittau, A. Passer, R. Rovers, K. Slavkovic, A. Hollberg, E. Hoxha, T. Jusselme, E. Nault, K. Allacker & T. Lützkendorf

Sectoral carbon budgets as an evaluation framework for the built environment
K.W. Steininger, L. Meyer, S. Nabernegg & G. Kirchengast

Carbon footprints and reduction requirements: the Swiss real estate sector
R. Frischknecht, M. Alig, C. Nathani, P. Hellmüller & P. Stolz

Reduced carbon footprints of buildings: new Finnish standards and assessments
M. Kuittinen & T. Häkkinen

Metrics for energy performance in operation: the fallacy of single indicators
B. Bordass

(Net-) zero emission buildings: a typology of terms and definitions
T. Lützkendorf & R. Frischknecht

Carbon metrics for cities: production and consumption implications for policies
M. Balouktsi

Residential retrofit in the climate emergency: the role of metrics
T. Fawcett & M. Topouzi

Net-zero buildings: when carbon and energy metrics diverge
A. Parkin, M. Herrera and D.A. Coley

Biogenic carbon in buildings: a critical overview of LCA methods
E. Hoxha, A. Passer, M. R.M. Saade, D. Trigaux, A. Shuttleworth, F. Pittau, K. Allacker & G. Habert

Comparison of GHG emissions from circular and conventional building components
C. E. Anderson, K. Kanafani, R. K. Zimmerman, F. N. Rasmussen & H. Birgisdóttir

Embodied carbon in construction products: a framework for quantifying data quality in EPDs
B. Waldman, M. Huang & K. Simonen

Integrating life-cycle GHG emissions into a building’s economic evaluation
M. Schmidt, R.H. Crawford & G. Warren-Myers


Feedback on the special issue

Carbon metrics can help the real estate sector
S. Bienert


Abstracts

The role of carbon metrics in supporting built environment professionals [editorial]
T. Lützkendorf
https://doi.org/10.5334/bc.73

Protecting the climate is an indispensable contribution to the conservation of the ecosystem. One approach is to reduce greenhouse gas (GHG) emissions to be within planetary boundaries. The quantification, allocation, assessment and control of GHG emissions affect a variety of actors, for example, manufacturers, planners, designers, clients, investors, contractors, facility managers, policy-makers, regulators, environmental economists, etc. To be effective, these actors need indicators to measure and influence GHG emissions associated with the creation and operation of the built environment. This editorial introduces the special issue and considers the creation and use of a coherent set of carbon metrics across different scales: construction products, buildings, neighbourhoods, cities as well as building stocks. Of particular importance is the agreement of clear terms, definitions, system boundaries and calculation procedures. Questions about scalability and aggregation are addressed as well as methodological issues associated with the use of biomass, a fair approach to budget-sharing and the design of emission balances including compensation options (e.g. offsetting and sequestration). Complementing the carbon metric approach is the development of a scalable carbon budget to determine the allocation of GHGs to a specific context: building, neighbourhood, building stock or city.

Carbon budgets for buildings: harmonising temporal, spatial and sectoral dimensions
G. Habert, M. Röck, K. Steininger, A. Lupísek, H. Birgisdottir, H. Desing, C. Chandrakumar, F. Pittau, A. Passer, R. Rovers, K. Slavkovic, A. Hollberg, E. Hoxha, T. Jusselme, E. Nault, K. Allacker & T. Lützkendorf
https://doi.org/10.5334/bc.47

Target values for creating carbon budgets for buildings are important for developing climate-neutral building stocks. A lack of clarity currently exists for defining carbon budgets for buildings and what constitutes a unit of assessment—particularly the distinction between production- and consumption-based accounting. These different perspectives on the system and the function that is assessed hinder a clear and commonly agreed definition of ‘carbon budgets’ for building construction and operation. This paper explores the processes for establishing a carbon budget for residential and non-residential buildings. A detailed review of current approaches to budget allocation is presented. The temporal and spatial scales of evaluation are considered as well as the distribution rules for sharing the budget between parties or activities. This analysis highlights the crucial need to define the temporal scale, the roles of buildings as physical artefacts and their economic activities. A framework is proposed to accommodate these different perspectives and spatio-temporal scales towards harmonised and comparable cross-sectoral budget definitions.

Policy relevance: The potential to develop, implement and monitor greenhouse gas-related policies and strategies for buildings will depend on the provision of clear targets. Based on global limits, a carbon budget can establish system boundaries and scalable targets. An operational framework is presented that clarifies greenhouse gas targets for buildings in the different parts of the world that is adaptable to the context and circumstances of a particular place. A carbon budget can enable national regulators to set feasible and legally binding requirements. This will assist the many different stakeholders responsible for decisions on buildings to coordinate and incorporate their specific responsibility at one specific level or scale of activity to ensure overall compliance. Therefore, determining a task specific carbon budget requires an appropriate management of the global carbon budget to ensure that specific budgets overlap, but that the sum of them is equal to the available global budget without double-counting.

Sectoral carbon budgets as an evaluation framework for the built environment
K.W. Steininger, L. Meyer, S. Nabernegg & G. Kirchengast
https://doi.org/10.5334/bc.32

The objective of the United Nations Paris Agreement to limit global warming to well below 2°C, with efforts to reach 1.5°C, requires a strict limitation of future global greenhouse gas (GHG) emissions based on a global carbon budget. Applying equity considerations allows for the derivation of national carbon budgets. A key question then arises: How can these national budgets be allocated at the sectoral level? A new method is proposed to allocate carbon budgets at the sectoral level. First, a cost-based approach is used to indicate a necessary carbon budget for each sector. However, the aggregation of these initial sectoral carbon budgets usually exceeds the available national carbon budget. This indicates the relevance of working with sectoral carbon budgets and the required reductions to remain within the overall national carbon budget. This conceptual approach aims at, first, a cost-effective sectoral effort-sharing; second, the design of corresponding strict carbon emission reduction pathways (at both the sector and aggregate levels); and, third, the redesign of investment policies for capital stock improvements to remain within the aggregate carbon budget (involving trade-offs in investment induced emissions for operational emission reduction).

Policy relevance: Limiting global warming according to the United Nations Paris Agreement requires a strict limitation of future global GHG emissions. A new method is presented to allocate national carbon budgets to the national sectoral level. The carbon budget concept has the potential to provide a transparent and informative tool for the analysis, policy design and monitoring of GHG emission pathways, particularly for the long time horizons involved. The area of activity involving the construction and use of buildings, termed embodied and operational GHGs, requires a particularly large fraction of the national carbon budget. Compared with other sectors, these activities have the highest potential for keeping countries within their national carbon budgets as far as enabling capital stock improvements are concerned that over-proportionally reduce use emissions. The approach can link carbon budgets at the municipal, city and regional levels. It could lend itself to an initially voluntary initiative, later compulsory policy framework for substantial and cost-effective emission reductions.

Carbon footprints and reduction requirements: the Swiss real estate sector
R. Frischknecht, M. Alig, C. Nathani, P. Hellmüller & P. Stolz
https://doi.org/10.5334/bc.38

The real estate sector and its supply chains, i.e. up- and downstream processes, are responsible for a significant share of the greenhouse gas (GHG) emissions in most countries. The GHG emissions from the Swiss building stock are quantified and the hotspots identified along its supply chain using the multiregional, environmentally extended input–output tables Exiobase v3. Biodiversity impacts caused by land use, water stress due to water consumption, air pollution and eutrophication impacts are also quantified. The environmental impact-reduction requirements were estimated based on global planetary boundaries assuming that each economic sector will reduce its impacts according to the required global reduction. The Swiss real estate sector causes more than 24 Mt CO2e/year, which is 480 ppm of global emissions, while its gross value-added share is 200 ppm. Hence, the GHG emissions per US dollar gross value added of the Swiss real estate sector are above average. Two-thirds of the emissions are caused during the use stage of buildings, whereas 30% are caused by the supply chains. A reduction to net zero is needed within the next two to three decades to comply with the 1.5°C limit. The real estate sector must address its supply chains, but also must its tenants and users.

Policy relevance: The Swiss real estate sector building-related GHG emissions are analysed, taking into account the full building life cycle. The requirements for environmental impact reduction are estimated based on global planetary boundaries, assuming that each economic sector reduces its impacts with the same global percentage. The Swiss real estate sector is found to be environmentally inefficient: it causes more GHG emissions compared with its gross value-added share. Two-thirds of the emissions are caused during the use phase of buildings, with the remainder caused by the supply chain. A reduction to net zero is needed at the latest by 2050 in order to comply with the 1.5°C limit. The real estate sector should thus further increase the energy efficiency of buildings, phase out the use of fossil fuels and address its supply chains (particularly the construction materials and products) to develop zero emission products.

Reduced carbon footprints of buildings: new Finnish standards and assessments
M. Kuittinen & T. Häkkinen
https://doi.org/10.5334/bc.30

The Nordic countries are working towards regional carbon neutrality ahead of the European Union’s goals. Finland is aiming at carbon neutrality by 2035, and developing a set of policies, including legislation for low-carbon construction. The new approach includes normative carbon limits for different building types before 2025. Finland’s Ministry of the Environment has developed an assessment method and will develop a generic emission database. The database will cover all main types of products and materials, sources of energy, modes of transportation as well as other main processes such as site operations and waste management. Furthermore, the criteria for green public procurement have been developed from the viewpoint of reducing the climate impacts of buildings: incorporating global warming potential and climate benefits. However, there are several open questions regarding both the assessment method and the database. These questions are outlined and discussed. The consideration of the foreseen decarbonisation of energy, the relation of the generic data to specific data and the requirements for generating valid generic data are key issues of discussion. The Finnish assessment method is also compared with the methodological development in other Nordic countries and to the proposed Level(s) framework of the European Commission.

Policy relevance: The carbon limits for buildings will introduce the construction sector to life-cycle approach and assessment. The scope of optimisation will widen from operational emissions to buildings’ full life-cycle. This brings changes to building design, as the carbon footprint limit becomes an additional performance requirement for a building permission. For product manufacturers, this may lead to increased market demand of environmental product declarations and their availability in digital format. From the client side, the introduction of limits opens a possibility for setting quantitative targets that go beyond the legal minimum. Furthermore, the proposed concept of carbon handprint (for positive carbon impacts) may become an award criterion in public procurement. The ongoing normative development in the Nordic countries has timely relevance for the development of the Level(s) framework, a common assessment scheme for the European Union. Fora for discussion and co-development are therefore also required at the European level.

Metrics for energy performance in operation: the fallacy of single indicators
B. Bordass
https://doi.org/10.5334/bc.35

Many countries and organisations have now endorsed the climate emergency. New and existing buildings must play a big part in tackling this, though past history has been disappointing, e.g. with major gaps between predicted and actual energy performance. What metrics should be used to understand a building’s energy and carbon performance in operation? Here there is uncertainty. For example, the United States is introducing carbon metrics, the UK has used them for many years, while the European Union recently made primary energy the common standard. Even though the reduction of greenhouse gas emissions may be the prime objective, UK experience suggests that undue concentration on any single headline metric can lead to severe unintended outcomes. The paper outlines the history and some results of various energy and carbon metrics used in UK policies and publications for non-domestic buildings since the 1973 oil crisis, with a few examples from other countries. It suggests how multiple indicators may help resolve future problems, what metrics might be used and how to make the underlying detail more accessible, e.g. with component and system benchmarks.

Policy relevance: Recent UK policy on the climate impact of buildings has been largely framed in terms of CO2. This seemingly sensible paradigm has had unintended consequences. (1) Contributions from low-energy ‘passive’ design; efficient equipment; good construction, commissioning and handover; effective energy management; and renewable and low-carbon energy supplies are conflated. There is no target for energy consumption itself. (2) This has divorced building professionals from the realities of in-use performance and deprived many of the necessary agency to improve it. (3) The limited amount of feedback means that policies can favour measures that look good in theory, but which do not work well in practice. This can make buildings too complicated, with high operational and management costs. To stimulate sustainable investment in truly low-carbon buildings, a suite of metrics and benchmarks needs to focus on performance in practice and motivate all the players involved. Elements of a viable approach are presented. Once in-use energy performance becomes reliably visible, action can become more effective.

(Net-) zero emission buildings: a typology of terms and definitions
T. Lützkendorf & R. Frischknecht
https://doi.org/10.5334/bc.66

Several different definitions of ‘net-zero’ or ‘climate-neutral’ buildings have arisen and are causing confusion. Different approaches quantify the greenhouse gas (GHG) emissions of buildings over their life-cycle. A typology is proposed based on distinctions between absolute and net-zero-emission buildings in relation to operational and full life-cycle approaches. Besides the absolute zero-emission approach, three different net-zero-emission approaches are: (1) a net-balance approach, which includes credits caused by potentially avoided emissions beyond the system boundary provided by exported energy; (2) an offsetting approach, based on the purchase of CO2 certificates; and (3) a technical approach, based on negative-emission technologies. The declaration of the approach chosen will provide clarity when discussing (net/absolute)-zero emission or climate-neutral buildings.

Policy relevance: The use of suitable terms, definitions, system boundaries as well as calculation and assessment rules is a prerequisite for credibility and transparency. Legal requirements for limiting GHG emissions from buildings and their fulfilment should therefore be formulated in a way that is understandable by both industry professionals and stakeholders with clear rules for documentation and the provision of evidence. This is particularly important for the proof of the political goal to create a climate-neutral building stock. A typology of (net-) zero building approaches is presented that explains their level of ambition, fosters transparency, and reduces misperceptions and misunderstandings.

Carbon metrics for cities: production and consumption implications for policies
M. Balouktsi
https://doi.org/10.5334/bc.33

The estimated cities’ contribution to climate change varies depending on the methods chosen by a given city for compiling its greenhouse gas (GHG) emission inventory. This study provides an interpretative synthesis of existing research to explore the differences of three emerging approaches to city-level GHG emissions accounting, based on methodological dimensions: boundary-setting, the categorisation of emissions and the type of emissions. The policy relevance and implications of selecting different system boundaries are explored: each approach can reveal important information which the others fail to identify. This suggests the value of using different and complementary approaches to address as many policy questions and relevant actors possible in climate action planning. Next, key methodological considerations that arise in target-setting approaches involving bringing the emissions balance to zero are presented. An analysis of actual ‘net-zero emission’ concepts used by eight cities reveals that their precise meaning and applicability remain ambiguous. Finally, to improve both the transparency about such metrics and their usability for policy and decision-making, this paper synthesises all key considerations occurring from the analysis of inventorying approaches and net-zero targets into a reporting and communication framework.

Policy relevance: Many cities are assuming responsibility for measures to mitigate climate change, but they need greater clarity on ‘climate neutral’ or ‘net-zero’ approaches. Each city’s intended purpose needs careful alignment with a choice of methods. The diverse accounting and target-setting landscape and the associated policy implications are elucidated. This can empower more cities to select appropriate methods and set ambitious targets. Calculation of a GHG emission balance is a means to an end and not the end itself. Its purpose is to show the options for action and measure success. Non-transparent methods involve reputational and ethical risks for city governments. A framework to improve transparency is presented. Dual-accounting approaches involving both production and consumption are now the new trend. Individual actors must be able to identify their influence and potential action scope for mitigating climate change. Agreement is needed on how to approach consumption-based accounting and create more city-specific data.

Residential retrofit in the climate emergency: the role of metrics
T. Fawcett & M. Topouzi
https://doi.org/10.5334/bc.37

This paper examines whether current residential retrofit metrics are fit for purpose and if they can help deliver swift and significant cuts in carbon emissions. Information is presented on metrics used for a variety of UK and European Union building and building retrofit standards and evaluation and assessment tools. An analytical approach is developed that offers a simplified set of four key aspects of metrics: scope, headline measurement, normalisation factor and timescale. This helps to unpack the complexity of metric design. However, choice of metrics is not simply a technocratic issue, because their design is not value free. Two examples where metrics form the basis for policy-making for retrofit and energy use in buildings are described: UK Energy Performance Certificates and the Energiesprong approach to deep retrofit. Use of multiple metrics improves their fitness for purpose and is already established practice in some standards and policy. Metrics in common use omit many aspects of energy use in buildings. New metrics are required that can take account of the whole life of a building, the time profile of retrofit, or the ability of the building to be flexible as to when energy is used.

Policy relevance

  • Existing and new metrics can contribute to the transformation of the building stock. They have real-world impacts on buildings, those retrofitting them and their occupants.
  • Retrofit metrics embody values and views about how retrofit should be undertaken.
  • Unpacking metric design and considering scope, headline measures, normalisation factors and timescale separately can help inform better policy decisions.
  • There is no one ideal metric for building retrofit—many policies and standards use multiple metrics.
  • A focus on carbon metrics only for retrofit can lead to missing opportunities for high-quality building fabric. Energy metrics remain important.

Net-zero buildings: when carbon and energy metrics diverge
A. Parkin, M. Herrera and D.A. Coley
https://doi.org/10.5334/bc.27

Many climate change-related building frameworks are designed to improve environmental performance by requiring reduced net energy demand, as it is widely assumed that energy demand (e.g. delivered/final, primary, primary non-renewable) is a good proxy for carbon emissions. However, energy grids are becoming less carbon intensive, meaning that the climate change mitigation value of renewably generated energy is not static, and is likely to decrease. In this research, a global integrated building carbon and energy model was created to explore how assessed building performance responded to stepwise variation in multiple building features. Operational and embodied metrics were measured concurrently on the basis of carbon emissions and delivered final energy demand, and included renewable energy generation (via roof-mounted photovoltaics), resulting in two 12.3 million-point data sets. Logistic regression was used to identify patterns in the data sets using binary building classifications (zero or non-zero energy or carbon). The results demonstrate that the profiles of the energy and carbon metric data sets do not mirror each other, indicating that a delivered energy demand assessment is not necessarily a good proxy for carbon emissions. The divergence of these metrics is likely to grow in future as energy grids are increasingly decarbonised.

Policy relevance: The energy metric is often relied upon as an indicator of climate-related building performance. However, policy-makers and designers should instead focus their attention on a carbon metric in order to achieve the drastic reduction in carbon emissions needed for the 1.5°C limit on rising global temperatures. Grid generated energy (particularly electricity) tends to be viewed as universally carbon intensive, so offsetting even a small amount with renewable energy is seen as beneficial. This research demonstrates that design philosophies underpinning zero-energy building (ZEB) assessment outcomes are likely to be driven by environmental factors (i.e. overcoming temperature and insolation challenges). However, the zero-carbon equivalent is likely to be more closely associated with the characteristics of the electricity grid servicing the building. This study highlights the fact that, to accrue real benefits, long-term policy and design decisions need to factor in the changing nature of the carbon implications of energy demand and generation.

Biogenic carbon in buildings: a critical overview of LCA methods
E. Hoxha, A. Passer, M.R.M. Saade, D. Trigaux, A. Shuttleworth, F. Pittau, K. Allacker & G. Habert
https://doi.org/10.5334/bc.46

The increasing pressure to reduce greenhouse gas emissions from buildings has motivated specialists to develop low-carbon products incorporating bio-based materials. The impact of these materials is often evaluated through life-cycle assessment (LCA), but there is no clear consensus on how to model the biogenic carbon released or absorbed during their life-cycle. This study investigates and compares existing methods used for biogenic carbon assessment. The most common approaches were identified through an extensive literature review. The possible discrepancies between the results obtained when adopting different methods are made evident through an LCA study of a timber building. Results identified that land-use and land-use-change (LULUC) impacts and carbon-storage credits are not included in most existing methods. In addition, when limiting the system boundary to certain life-cycle stages, methods using the –1/+1 criterion can lead to net negative results for the global warming (GW) score, failing to provide accurate data to inform decision-making. Deviation between the results obtained from different methods was 16% at the building scale and between 35% and 200% at the component scale. Of all the methods studied, the dynamic approach of evaluating biogenic carbon uptake is the most robust and transparent.

Practice relevance: This critical review identified key methodological differences between the most commonly used methods and recommended standards for biogenic carbon accounting in buildings. This indicates a lack of consensus and guidance for conducting LCAs of bio-based construction products and buildings using bio-based materials. A case study applying four different LCA approaches on a timber building identified the inability to compare results and create proper benchmarks. Moreover, different methods lead designers to pursue different strategies to reduce a building’s carbon footprint. Regulators, the construction industry and the construction products industry are directly affected by this lack of comparability. This research highlights the flaws and benefits of commonly used methods. A clear and grounded recommendation is for practitioners to adopt dynamic biogenic carbon accounting for future assessments of bio-based materials and buildings.

Comparison of GHG emissions from circular and conventional building components
C.E. Anderson, K. Kanafani, R.K. Zimmerman, F. N. Rasmussen & H. Birgisdóttir
https://doi.org/10.5334/bc.55

The concept of circular economy has been introduced as a strategy to reduce the greenhouse gas (GHG) emissions from buildings and mitigate climate change. Although many innovative circular solutions exist, the business model is challenged by a lack of environmental data on the circular solutions, and thus the potential benefits are not verifiable. The study assesses the embodied GHG emissions of five circular building elements/components. Circular solutions are compared with conventional solutions to ascertain whether the business model has the potential to reduce GHG emissions. The GHG emissions are quantified using life-cycle assessment (LCA) for five circular-economy and three conventional building elements/components. The environmental data show that circular building components have the potential to reduce GHG emissions. However, there is a risk of increasing the GHG emissions when compared with conventional solutions, emphasising the need for standardised environmental data. Lastly, the study identifies logistic, economic, technological and regulatory barriers that prevent complete implementation of circular economy.

Practice relevance: Standardised environmental data on building elements/components are needed to support decision-making at local and national levels. Uncertainties about waste from manufacture and transport in the production stage can affect the environmental potential to such an extent that the benefits from introducing circular economy are lost. One central barrier is identified that prevents complete implementation of the circular economy in buildings; the industry is not geared to support a steady supply of some circular building elements/components. In general, it is clear that the implementation of circular economy requires the identification of environmental, logistical, economic, technological and regulatory concerns.

Embodied carbon in construction products: a framework for quantifying data quality in EPDs
B. Waldman, M. Huang & K. Simonen
https://doi.org/10.5334/bc.31

Embodied carbon constitutes a significant portion of a building’s greenhouse gas (GHG) emissions and is a key challenge for the construction and real estate sectors. Embodied carbon includes construction product manufacturing, building construction, material replacement and end of life. During the specification and procurement stage, designers and contractors have the opportunity to prioritize products with lower carbon footprints. Environmental product declarations (EPDs) are a growing source of environmental data in the construction products market, and are increasingly being used for (1) environmental performance assessment of buildings and (2) product comparison for procurement decisions during the later stages of building design. An obstacle to identifying and purchasing lower embodied carbon products is a lack of data quality and the transparency of EPDs. However, EPDs vary widely in their data quality and specificity, which can lead to inaccurate and misleading comparisons. A new method is presented to account quantitatively for estimates of variation in underlying data specificity in EPDs to enable fairer comparisons between EPDs and to motivate the reporting of actual variability and uncertainty in EPDs. The application of this approach can help purchasers to assess EPDs quantitatively.

Practice relevance: Life-cycle assessments (LCAs) and LCA data can be used within the construction sector to evaluate buildings and to assist in design, specification and procurement decision-making. A new method is presented to support the assessment of comparability of functionally equivalent materials and products during the specification and procurement stage. Given the known variation and lack of precision within EPDs, this method provides quantitative metrics that correlate to a qualitative interpretation of EPD precision. This method can be used by anyone who is using EPD data to make product comparisons at the specification and procurement stage:

  • It provides more confidence in choosing low-carbon material or product options when comparing between functionally equivalent options.
  • It can incentivize product manufacturers and LCA practitioners to improve data quality and transparently report known variation in their EPDs.
  • It may also motivate manufacturers to reduce GHGs from their products and processes.

Integrating life-cycle GHG emissions into a building’s economic evaluation
M. Schmidt, R.H. Crawford & G. Warren-Myers
https://doi.org/10.5334/bc.36

Buildings contribute to greenhouse gas (GHG) emissions throughout their life—from material extraction and production to building demolition and disposal. Current GHG emission reduction efforts largely focus on building operation, typically ignoring embodied emissions. One of the main barriers affecting the uptake of embodied GHG emissions considerations is the uncertainty related to the economic value of a building with reduced life-cycle GHG emissions. A conceptual approach is presented for integrating the life-cycle GHG emissions of a building into an economic evaluation. A case study detached residential dwelling located in Melbourne, Australia, is used to demonstrate the approach using a range of economic valuation approaches. One approach, using a carbon tax, shows that the effective cost for a single household would be over A$2000 for the first year, rising to almost A$5000 in 10 years. Across the range of evaluation approaches considered, the total cost to the householder is found to be between A$4600 and A$7860. With the embodied GHG emissions accounting for over 66% of the case study’s life-cycle GHG emissions, the majority of the economic liability for the householder relates to the initial construction and ongoing material replacement of the building.

Policy relevance: This research provides a comprehensive and integrated approach to GHG emissions and economic assessment of residential buildings. This could be used to drive better decisions in building construction and operation through policy improvement, generating greater understanding of the GHG emissions of buildings and the economic value of GHG emissions. By quantifying the total GHG emissions over a building’s life-cycle and examining ecological and financial implications, new data can provide the basis for policy measures that transform the value of GHG emissions in property. The total life-cycle approach to GHG emissions can be used by developers or builders, for example, to demonstrate the potential financial implications of their choices. However, given its current format, there is a need to improve policy measures such as improved carbon tax strategies and the generation of an annual tax for the economic value implications to be realised.

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Latest Commentaries

The Debate around Low-Carbon Heating Systems: Part 2

Engineer Chris Twinn (Twinn Sustainability Innovation and LETI member) argues that the urgency of decarbonisation means that UK (and other countries) must make clear decisions about a heating system strategy and its implementation. Prevaricating will make the transition slower and risk missing important climate commitments.

Social Value: An Architect’s Perspective

Edward Ng (Chinese University of Hong Kong) provides an architect’s perspective on the Buildings & Cities special issue ‘Social Value of the Built Environment’.

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