Embodied Carbon in Buildings

Embodied carbon assessments of buildings are not methodologically very different from the more well-known life cycle assessments (LCAs). In particular, the two also share the frequent lack of uncertainty analysis in many assessments produced by academics as well as practitioners. An assessment that omits uncertainty analysis generally results in a single, very definite numerical output which however embeds no information on the likelihood of that value being true. Similarly, in comparative studies, the assessment produces two values, and the main outcome is merely reduced to a higher/lower comparison in order to choose the alternative allegedly less detrimental to the environment.

The chapter will provide the reader with a worked example through an overview of the whole process related to uncertainty analysis, from the rationale to the methodological challenges through to the increased usefulness of the results in comparison with single-value assessments. Addressing uncertainty and variability in LCA adds information about the significance and robustness of the results, as well as it benefits and facilitates environmentally conscious decisions by recognizing innovation opportunities that can be overlooked when not addressing uncertainty.

The measurement of embodied carbon in buildings or building components encounters many problems of uncertainty, which are increased for life cycle measurement. The level of uncertainty for a measurement varies on a spectrum from precise knowledge to total ignorance. The most rudimentary way of measuring an uncertain variable is to use a single-value ‘best guess’. Methods that acknowledge uncertainty and give a probabilistic measurement of the variable include: a range, a three-point estimate, an empirical distribution, or a mathematical distribution.

Life cycle measurement subject to uncertainty can be represented by a tree of possible future values, or by Monte Carlo simulation of sampled future values. When measurements are probabilistic, decision makers’ choices respond to their degree of risk aversion and time preference. In situations of uncertainty, flexible strategies that adapt to unfolding events can mitigate the risk of damaging outcomes.

A worked example compares deterministic and probabilistic measurement of the embodied carbon of a construction system with reusable steel modules. The system reduces embodied carbon if the modules are reused. For the probabilistic measurement, the length of the service life of the modules and the probability of reuse are uncertain variables. The steel module system is compared with conventional reinforced concrete construction. The probabilistic approach provides additional information and understanding for decision makers.

The embodied carbon of a material cannot be known deterministically. It is perhaps more accurate to speak of estimating, rather than calculating, embodied carbon. Uncertainty can be thought of as a consequence of this imperfect knowledge. The complexity and variability of supply chains and production processes, variations in the scope and boundaries applied, and the source, age and quality of data used all introduce uncertainty to an embodied carbon estimate. This applies both at the product and the building levels and makes it difficult to compare studies. At the design stage, uncertainty introduces the risk that a particular design choice, intended to reduce emissions, may not achieve the desired level of carbon abatement. To date, these uncertainties have either been dealt with only very superficially or, in many cases, simply ignored.

In this chapter we present a review of the uncertainties encountered in embodied carbon assessments and discuss which of these are relevant to comparative assessments of design alternatives. We apply a conceptual framework to identify and classify the types of uncertainty encountered in embodied carbon assessments and review common approaches to uncertainty assessment that have been applied in fields relevant to embodied carbon.

A case study of an embodied carbon assessment of two alternative designs for a supermarket structural frame is presented. In light of the types of uncertainty involved and the general lack of data to quantify uncertainty statistically, expert elicitation is used to assess both quantitative and qualitative aspects of uncertainty, combining this with quantitative scenario assessment to give an estimate of overall uncertainty and to evaluate the effects of this on the comparison of the two frame designs.

Quantifying the total life cycle embodied carbon of wood and reinforced concrete structures necessitates calculation of use-phase impacts, including expected in-service damage and replacement due to chronic and acute environmental hazards. Such prediction is difficult and often omitted in whole-building life cycle assessment (WBLCA).

To address this challenge, this chapter provides readers an overview of simple service-life prediction models that can be implemented to estimate expected in-service lifetime of wood and reinforced concrete materials and components exposed to chronic hazards (e.g., chloride, carbon dioxide).

In addition, it provides a review of models and methodologies for estimating contributions to WBLCA from damage to structural and nonstructural components caused by acute hazard events (e.g., earthquakes, floods). Using case studies, this chapter discusses how results from these analyses can be incorporated into a holistic LCA methodology for estimating total embodied carbon of wood and reinforced concrete structures that are prone to chronic and acute hazard events.

Albedo is an optical property of surfaces. The higher is the surface albedo, the higher is the amount of solar radiation that a surface scatters back to space.

During the last centuries, urbanization, deforestation, afforestation, and all the modifications of extended areas on Earth have produced a variation in local albedo giving rise to an alteration of the Earth’s energy balance. In the urban environment, the use of low-albedo building materials in the building envelope can exert an effect at different scales. Specifically, it can contribute to a higher request of energy for cooling the indoor building spaces in summer, since low-albedo surfaces absorb a higher amount of solar energy compared to high-albedo ones and it can also contribute to the urban heat island effect (i.e., an increase in urban temperature compared to the surrounding rural areas). In turn, the urban heat island might affect the building energy use for summer cooling and contribute to an energy imbalance that has an impact on climate change. While, in the last years, a growing number of studies have explored the effect of the employment of low-albedo materials in building envelopes on the cooling energy budget and on the urban heat island, the evaluation of the effect of urban surface albedo on climate change belongs to a recent and a still exiguous strand of research. Climate science teaches us that surface albedo can exert an effect on climate change; such effect can be translated in terms of carbon dioxide equivalents and included in the accounting of the embodied carbon of the use phase of a building. However, traditionally, the contribution of albedo of materials or components for the building envelope is often disregarded in life-cycle assessment (LCA).

In this chapter, published literature concerning the inclusion of the effect of the variation in surface albedo in LCA has been investigated. First, the state of the art about the evaluation of the variation of surface albedo on climate has been showcased. Then, an overview of the published studies about the evaluation of the variation of surface albedo in the built environment and, in particular, of building components has followed. Notwithstanding the findings are not comparable due to the heterogeneity of the studies, the case studies examined show the importance of including the evaluation of the variation in surface albedo in LCA studies. In particular, the inclusion of the effect of surface albedo in LCA studies related to building materials and components can provide an important source of information for decision makers in the field of urban sustainability.

The significance of environmental impact quantification for various structural materials is increasingly important for structural engineers to both understand and communicate to others. Building owners and architects are beginning to request this data in the form of a life cycle analysis (LCA), so that the environmental impacts of structural materials from harvesting to processing and beyond can be reported as accurately as possible to an audience interested in more environmentally responsible buildings. Recently, there has also been added motivation in the United States to follow a trend in Canada and Europe to construct more structures out of mass timber products, such as cross-laminated timber (CLT) or nail-laminated timber (NLT). Companies market these mass timber products as viable, sustainable options to compete with conventional steel and concrete construction. Mass timber buildings are commonly perceived as more environmentally responsible than buildings with concrete and steel framing, but very few have attempted to accurately quantify the environmental impacts of this claim or to prove if the hype is indeed correct.

This paper reports the findings of a case study investigation on the above, a seven-story, 85-foot tall new construction office building. The case study focuses on comparing the “reported industry average” structural embodied carbon impacts between four different framing system combinations that include mass timber, steel, and concrete, using the GaBi database within the LCA software “Tally.” The limitations of this study are discussed including differences between the LCA data sets used for each material. The goal of this paper is to develop a comparison utilizing current LCA tools readily available, to highlight the variabilities within that comparison, to assess if an accurate comparison can indeed be made, and to make observations on what are the most critical variables in structural embodied carbon impacts for this building. The ultimate objective is to help advance the reliability of future LCA studies.

Environmental evaluation of the built environment has rapidly improved in our decade. As the architecture-engineering-construction (AEC) industry is proved to have a high share in resource demand, the environmental impact of construction activities draws attention of many parties. Starting from high-performance buildings to green rated examples, optimizing both the performance and profitability of AEC products has been the main goal of researchers and practitioners. Life cycle assessment (LCA) is considered a comprehensive method developed for this purpose.

Higher rates of waste and emissions put forward the fact that analysing and controlling the environmental impacts in construction sector is important. Carbon footprint assessment of buildings is one of the main methods utilized for this purpose. In order to provide this kind of evaluation, environmental data on materials and processes regarding the construction industry are needed. However, available data on construction materials are fragmented, hard-to-reach and even harder to confirm. In the absence of national databases, the quality of data in LCA studies must clearly be displayed, and a certain level of validation is required for reliable results.

This study aims to develop a validation system to ensure the quality of data in carbon-related LCA studies. The framework introduces a hybrid life cycle methodology which is based on data quality. Different environmental impact assessment methods are utilized depending on the quality score that is determined by pedigree matrix. The pedigree matrix is improved with a weighting factor which enables flexibility and higher precision while evaluating available data.

The use of the developed system has been demonstrated in an LCA analysis of an office building. The carbon footprint of the building components is calculated with an LCA software. As a final step, the results are compared with the impacts of a number of office buildings in the literature for validation purposes. The proposed framework suggests that data quality must explicitly be displayed and can also be used as a guidance for impact assessment.

Alterations of a building design are easier facilitated in the early stages of a building design where less strategic parameters are fixed. Tools for environmental assessments are aimed for decision support but are often used late in the building design process because the calculations rely on detailed volumes of material uses. This paradox can be addressed by using carbon profiles of a large set of prespecified, precalculated building elements together with limited, geometric input data of the early building design. The simplified approach allows for embodied carbon modelling within minutes and at a 5–10% margin of error compared to more detailed tools.

Since differences between academia and industry are well-documented, different types of embodied carbon and life cycle assessment may be necessary to meet the different needs of researchers and practitioners. Without a better grasp of the different types, however, assessment results or conclusions may be misunderstood or misused, and researcher-practitioner collaborations may prove challenging. The concept of a ‘taxonomy of assessments’ promises to help assessors manage the production of different types of assessment to meet the different needs of researchers and practitioners but also to prompt consideration of a potential middle ground or Third Way. This chapter introduces a proposed taxonomy which seeks to capture the production of an assessment as a set of questions each with alternative answers. The questions and alternative answers it captures relate to both assessment ends (purpose) and means (process) to reflect and recognise the range of different assessments being produced by researchers and practitioners. Using the proposed taxonomy to establish and compare ranges for cases of assessment produced by researchers and the author as practitioner, it is possible to outline a precise agenda for future assessments and supporting studies. A particular focus is the potential of the middle ground or Third Way.

Due to the rapid growth of the construction industry during the last decades, building-related waste has become a major source of concern from governments both nationally and internationally. Construction, maintenance and demolition waste is often neglected as it is perceived as less important than waste generated from operating activities. However, research studies reveal that waste is generated at all different stages of the building’s lifecycle and this has a profound impact not only in terms of increasing project cost but also adding to environmental pollution as the common type of treatments for wastes is landfilling and/or incineration. Reducing waste will reduce energy use, minimise degradation of the environment and reduce embodied carbon emissions. This chapter reviews the nature, characteristic and magnitude of construction, maintenance and demolition waste of buildings and their associated embodied carbon emissions. It also examines policies, initiatives and international regulations in dealing with the problem of waste and the calculation methods for the assessment of embodied carbon of waste in the various stages of a building’s life; it ends with a discussion on strategies of reducing waste and a case study.

The need for embodied carbon management is well recognised, and possible mitigation approaches are highly sought due to the increasing need arising of carbon reduction targets. This requires the unregulated embodied carbon to be tackled instantly. This chapter presents an approach to manage embodied carbon through the identification of carbon and cost hotspots. Carbon hotspots are the elements of buildings that encompass high levels of carbon (embodied carbon). Evidence from the literature suggest that careful design of such hotspot elements will result in the highest potential carbon savings. However, the state of knowledge regarding carbon hotspots has not been extended beyond a few case studies. Hence, this chapter explored the concept of hotspots by collecting data from a sample of 41 office buildings in the UK. The carbon and cost hotspots were identified based on 80:20 Pareto rule which suggest 80% of emissions are resulting from 20% of building elements. However, findings did not fully comply with Pareto’s 80:20 ratio, instead proposed a new ratio of 80:43 for embodied carbon. Substructure, frame, external walls and services were identified as both carbon and cost hotspots of the sample office buildings. In addition, elements were categorised into three types based on the probability of an element being identified as a carbon hotspot in the building. It was interesting to note that the identified carbon hotspots were also found to be contributing up to 72% of the capital cost and the identified cost hotspots contribute up to 81% of embodied carbon. This implies that there is a possibility of reducing both embodied carbon and capital cost, which are considered as the dual currencies of construction projects, by focusing on the design of the hotspots identified.

This chapter explores the connections between the circular economy and the reduction of embodied carbon. Circular economic approaches focus on maintaining the value of materials for as long as possible. A circular economy seeks to keep materials in circulation, removing the concept of waste from the system and the need for material extraction from primary sources. In a completely circular economy, all ‘waste’ outputs would equal system inputs. If the built environment is thought about in this way, as a system, then the inputs are construction materials, and these materials accumulate in buildings, which can also be thought of as the stock. Demolition waste is the output flow of materials in this system. This concept can also be extended to embodied carbon. Construction materials are input flows of embodied carbon. These emissions are new to the system. The adoption of circular economic design approaches that facilitate longer building lifetimes, greater component and material reuse can reduce the input flow of embodied emissions and ensure already expended embodied carbon remains in stock. This chapter commences with a review of the key literature on the circular economy in construction in general terms and provides an overview of four related design strategies: building reuse, material reuse, design for deconstruction and design for adaptability. A series of ‘good practice’ case studies illustrate the respective strategies across a range of structural types. Each case study is used to provide practical insights on project processes, drivers, enabling conditions and the perceived benefits and challenges of adopting circular economic approaches. These insights are drawn from semi-structured interviews with members of each design team, supplemented by supporting literature. The chapter concludes by drawing out common lessons of how circular economic approaches can contribute to the delivery of a low carbon built environment.

There is global emphasis on the creation of zero energy and therefore zero carbon buildings. The vast majority of work is focused on reducing the so-called ‘operational’ energy in buildings, i.e. investigating methods to reduce energy consumption within the building and using more efficient equipment and source energy from zero carbon renewable energy sources. There is less work undertaken on measuring the ‘embodied’ energy of a building, i.e. the life cycle impact of materials and products. Moreover, there is even less research into the impact of new sustainable technologies that are used to replace existing systems. It is this latter point that is investigated in this chapter. The results show that the impact of new sustainable technologies is significantly less than conventional systems, when compared on a whole-life basis. However, each development and building is unique with a combination of technologies commonly used; therefore, generalisations should be avoided. It is recommended that it is mandatory for all sustainable technologies to have an Environmental Product Declaration (EPD) to enable the decision maker to make the best informed choice possible.

To mitigate the environmental impacts of construction-related activities, environmental factors should be incorporated within the planning procedure to inform the decision-making process at all levels. A large amount of embodied carbon of buildings is the result of material processing, transportation and construction. An opportunity therefore exists to alleviate the emissions of greenhouse gasses in the construction industry through optimising the associated construction operations while minimising carbon emissions. In this chapter, the focus is on the applications of smart planning approaches that incorporate the use of mathematical optimisation to manage and mitigate the embodied carbon of buildings, through proposing a relevant decision-making framework. Both on-site and off-site transportation in construction are considered since such operations contribute considerably to embodied carbon of buildings. The interrelation of several classes of well-known and relevant optimisation models is addressed, along with their applications in the planning stages of material transportation. A case study is presented to highlight the major benefits attainable through employing different classes of models within a scheme targeting the reduction of the carbon emissions in the transportation activities of a building’s life cycle.

The zero emission building (ZEB) research centre in Norway has a series of concept and pilot buildings that investigate design strategies for low embodied carbon in building materials in order to achieve a net ZEB balance; these include two conceptual studies or virtual building models (ZEB office building and ZEB single-family house) and six pilot buildings (Powerhouse Kjørbo, Campus Evenstad, Heimdal high school, Multikomfort house, Living Laboratory and Skarpnes). According to the centre’s definition, a net ZEB balance can be achieved by offsetting the life cycle greenhouse gas (GHG) emissions through the production and exportation of on-site renewable energy. This balance becomes ambitious if embodied carbon from building materials is also considered. Experiences collected from the ZEB pilots demonstrate that a combination of carbon reduction design strategies are necessary in order to achieve this net ZEB balance.

One low embodied carbon design strategy considers area and material quantity reduction. For example, compared to the raft foundation design in the single-family house concept study, the Living Laboratory uses three narrow strip foundations. This results in a 68% decrease in carbon emissions arising from reduced concrete use. These emissions can be further reduced if low-carbon concrete is implemented, as demonstrated in both Heimdal and Evenstad high schools. The next strategy considers reuse and recycling. In the Multikomfort house, bricks are reclaimed from a nearby derelict barn. This reuse strategy leads to a saving of more than 100 kgCO₂e/m² of wall, when compared to a conventional concrete wall. Similarly, the renovated Powerhouse Kjørbo offices reuse the external glass facade as internal glass partitions; this not only prolongs the service life of building materials but also avoids emissions associated with end-of-life treatment.

Another important strategy involves selecting low-carbon building materials. The office concept study demonstrates that changing the original concrete and steel structure to a timber structure of similar technical performance leads to a 30% reduction in weight and 50% reduction in embodied carbon. Furthermore, a sensitivity analysis of different concrete hollow core slabs and cross-laminated timber floors in Heimdal high school shows a high level of variation in emissions between manufacturers and the importance of a holistic evaluation when selecting low-carbon building materials. Another design strategy involves sourcing local materials. In Evenstad high school, excavated material is sourced from a local quarry, steel connections are formed by a local workshop and other local manufacturers are selected to reduce transport emissions. Another effective measure is demonstrated by adopting materials with high durability and a long service life. Calculations from Heimdal compare timber window frames with and without a protective aluminium cladding. The aluminium cladding, despite its elevated embodied emissions, gives the frame a longer service life. This results in fewer replacements during the service life of the school. Over a 60-year calculation period, more than 20 kgCO₂e/window are saved when the aluminium cladding is implemented.

In conclusion, the most efficient low embodied carbon design strategies, identified through the pilot projects, are area and material reduction and application of reused and recycled materials, using materials with low embodied carbon, sourcing local materials and adopting materials with high durability and a long service life. Embodied carbon calculations from eight of the ZEB pilot buildings (including two concept studies) provide an insight into the measured effect of low embodied carbon design strategies.

Tall buildings are becoming the predominant building typology in cities and megacities worldwide, with only a few regional exceptions. These buildings have unique construction and fire and life safety characteristics, which increase their initial embodied carbon footprints over other building typologies for the same built areas. However, when considering the longevity that also often goes with the more robust construction of tall buildings, as well as the overall site density that they bring to an urban core, where residents can live close enough to walk to work and the population density allows for mass transit to be affordable and functional, the total carbon footprint of the population with time tells a different story.

This chapter explores these issues and helps identify the largest areas of embodied carbon that go into tall buildings. It also looks at opportunities for their optimization and some of the life cycle topics currently being debated within the tall building community. Much of the focus is on the “shell and core” of the tall building and those decisions the initial building design team will often face as they may look to optimize the embodied carbon footprint of the project.

Embodied carbon (EC) in buildings continues to attract attention and, as such, measurement and management of EC in buildings are also becoming prominent. However, much of the management of EC has hitherto focused on the developed world. In this chapter, we demonstrate the use of a disaggregated mathematical model to show how, in the context of Uganda, the acclaimed global carbon management scheme of Clean Development Mechanism (CDM) can be extended to buildings. We argue that a CDM initiative generated from this idea can lead to a project-level carbon trading scheme that can be used to manage EC, moreover, cost effectively. We demonstrate that 20ktCO2 could be avoided annually if the suggested CDM is implemented in the capital city of Uganda, Kampala. Using the example of Kampala, we show that carbon trading is a viable strategy of delivering sustainable low-EC buildings in Africa.

Australia is at the forefront of the development of embodied carbon quantification techniques. This chapter explores the current status of these developments within the global context of embodied carbon assessment. It covers the evolving techniques of multi-region input-output (MRIO) analysis and hybrid analysis, as well as Australian data sources for estimating the carbon embodied within buildings. Current regulations relating to embodied carbon in Australia are discussed, and several case studies provide examples of current approaches that are being used to optimise embodied carbon within Australia’s buildings. This chapter concludes by offering a pathway for advancing the current awareness and development of embodied carbon tools, data, and policy within Australia as we strive towards the ultimate goal of ‘net-positive life cycle carbon’ buildings.

In China, the building sector, as a pillar industry of China’s modern economy, plays a vital role in generating carbon emissions, which is responsible for about 40% of the national total carbon emissions. To provide insights into the current carbon assessment practice of buildings in China, this chapter conducted an overview of current policies and industry initiatives promulgated for building carbon reduction and approaches currently being used to assess embodied carbon of buildings in China. To address the issues that are related to quantify embodied carbon of buildings under different scales, this chapter introduces assessment approaches and uncertainty analysis methods from both the macro and micro perspectives. The results show that the current focus of China is still on the buildings’ operational carbon reduction rather than the embodied phase. Such policy orientation does not match the increasing role of embodied carbon reduction in the creation of sustainability in the building sector. In China, the single-region input-output analysis (SRIO), multiregional input-output analysis (MRIO), and structural path analysis (SPA) are commonly used to assess embodied carbon at the macro level, while the process-based and hybrid LCA models are dominant in micro-level analysis. Although the process-based approach is most frequently used for embodied carbon assessment of buildings, a clear trend can be observed that the relevant studies gradually shift their focus from process-based individual cases to a more hybrid and macro sense in China.

This chapter provides a comprehensive overview of the state of the art on this subject within Europe. In order to do so, it draws on a cross-case analysis of over 60 European case studies, developed and analysed by the authors as part of the International Energy Agency Annex 57 project.

Embodied impacts have been considered for many years in this part of the world and have now reached a certain level of maturity; recently the publication of European standards EN 15978 and EN 15804 has helped to develop a more harmonised approach, while environmental certification schemes such as BREEAM from the UK and DGNB from Germany are increasingly encouraging European designers to use LCA to measure and reduce the whole-life carbon and energy of buildings. However, there are still a wide range of methodological approaches in use both in academic studies and in industry tools, hampering efforts to draw conclusive recommendations for low-carbon design strategies.

Two issues are of particular importance for the European context. First, as in other areas of the world, there is a focus on minimising the whole-life energy and carbon cost of new buildings. This paper uses the analysis of the Annex 57 case studies to provide a general quantification of embodied carbon and energy in European buildings for different life cycle stages and building components. It then identifies a number of approaches to reducing these impacts and, by comparing with a review of the international literature, discusses which of these identified mitigation strategies are particularly suitable in Europe.

The second issue recognises the unique aspects of this historically urbanised region of the world. Here the high proportion of old and very old buildings means that refurbishment and adaptation projects account for a significant proportion of construction sector impacts. Meanwhile, rising populations are leading to increased pressures for the densification of already-developed brownfield sites. While refurbishment, in preference to demolition and rebuild, has been identified in the academic literature as frequently a lower-carbon strategy, this is seldom an issue taken into account in industry practice. This chapter concludes that this area is one of particular importance on which industry and academia should work together across Europe.

This chapter reviews the efforts in North America on assessing and lowering the embodied carbon in buildings. The Intergovernmental Panel on Climate Change warns that the building sector needs to be zero carbon by 2050. While initiatives such as the American Institute of Architects 2030 Commitment have incentivized the reduction of operational impacts related to the use of buildings, new initiatives such as the Structural Engineers 2050 Commitment emphasize the reduction of embodied impacts related to material extraction, production, transportation to the site, construction, maintenance, and demolition. To assess and lower these impacts, three challenges arise in North America: the inconsistency in available databases and tools, the difficulty of including embodied carbon credits in rating schemes, and the scarcity of benchmarks. First, we review life cycle assessment databases and environmental product declarations available in North America. Then, we present the challenges of life cycle assessment in the Leadership in Energy and Environmental Design (LEED) rating scheme. Finally, the authors propose two benchmarking paradigms initiated in the USA to create a baseline for the embodied carbon of buildings, expressed in carbon dioxide-equivalent emissions normalized by floor area (kgCO₂e/m²).

This chapter provides a comprehensive overview of the state of the art on embodied carbon and life cycle assessment (LCA) of buildings in the context of Latin America. It reviews the current situation by assessing existing policies and initiatives aimed at, or related to, the themes of embodied carbon and life cycle environmental impacts caused by buildings. Additionally, it investigates the availability of geographically relevant data, which forms the basis of reliable and realistic assessments. An in-depth review of available sources reveals a severe scarcity of building-related data in Latin America. To this end, we suggest three methods to sensibly adapt available world data to Latin America as a temporary measure to utilise until more robust datasets are developed by governments and other stakeholders. Each of the methods relates to one of the three main approaches currently used in LCAs, namely, process-based, input-output and hybrid – thus allowing more accurate assessments across the whole spectrum of LCA methodologies. The chapter concludes with suggestions for future efforts and with a plea to all stakeholders to work together for a quicker transition to sustainable built environments in Latin America.