Integrating life cycle assessment into the building design process—a review

The environmental effects associated with buildings are significant and include considerable contributions towards global greenhouse gas emissions, energy use, and waste generation. Until recently, mitigation efforts have concentrated on improving the operational energy efficiency of buildings, largely ignoring embodied environmental effects. However, focusing solely on increasing energy efficiency can inadvertently cause an rise in embodied effects. It is therefore critical that embodied effects are considered alongside operational effects and are actively integrated into design decisions throughout the building design process. Life cycle assessment (LCA) can be used to achieve this, however, it is often perceived as difficult to incorporate into design workflows, or requiring specialist knowledge. Additionally, it is not always clear how well aligned LCA approaches are with the building design process. To address this gap, this study aims to provide a detailed analysis of LCA approaches, to assess how well they align with building design stages, and to identify key characteristics, including LCA tools and environmental data used to conduct assessments. A review of academic and grey literature is conducted. Three primary approaches are identified for integrating LCA into the building design process: simplified, detailed and incremental LCA. Simplified LCA uses streamlined data inputs and typically targets a specific design stage. Detailed LCA follows a traditional approach with comprehensive user inputs and results. Incremental LCA progressively evolves the assessment based on design requirements and available building data at each design stage. An analysis of each approach is performed, and key user requirements are mapped against the early design, and detailed design stages. Results reveal that no single approach fully satisfies all design requirements. Findings also highlight a lack of incremental LCA approaches and challenges operationalising these techniques. These approaches often rely on complicated methods or tools not suitable for common design workflows, or they are in early development and require additional verification before implementation.


Introduction
Buildings are responsible for a significant proportion of global environmental issues.They are major contributors to global energy use and greenhouse gas (GHG) emissions (IPCC 2022), and are a leading cause of resource depletion (Hansen et al 2013).An estimated 100 billion tonnes of waste is generated annually from construction, renovation, and demolition (Chen et al 2022).This large environmental footprint offers significant global mitigation potential, which could be realised through rapid and fundamental transformations to the building sector.At the policy level, interventions have been introduced to mitigate the environmental effects of buildings, mostly targeting operational energy performance (Pomponi and Table 1.Actors involved in the building design process.

Project team
Allied professionals, designers (architects, draftspeople, interior, landscape, urban), construction experts (builders, trades, construction companies, advisors, specialists and managers), contract administrators, engineers, programmers, risk managers, specialist consultants, and other built environment professionals Decision makers Building and landowners, community groups, developers, end users, interest groups, and traditional owners Stakeholders Academics, industry and standards bodies, investors, policy makers, property managers, and shareholders Suppliers and service providers Insurance and warranty providers, manufacturers, product developers, and utility companies Authorities Building authorities, environmental agencies, heritage and cultural bodies, and planning departments conclusions.Academic literature discussing the key limitations and challenges of LCA are reviewed by Haapio and Viitaniemi (2008), Nwodo and Anumba (2019), and Roberts et al (2020) among others.
In LCA, the entire product system (in this instance the building system) is assessed including all associated processes and services.Environmental effects are quantified across each life cycle stage of a building.Various standards have been developed to support the application of LCA.These include the international standard ISO 14040 (2006a) and ISO 14044 (2006b), which include guidelines, requirements, and a standard methodological framework.The European standard EN 15978:2011(CEN 2011) applies this international framework to buildings.There are four iterative stages defined in the LCA framework (shown in figure 1).
The first stage of LCA involves setting the goal of the assessment (including motivations for conducting the assessment and target audience) and scope definition (including system boundaries, assessment methods and functional unit).There are two primary modelling approaches used to conduct LCA.Attributional LCA (ALCA), which quantifies the total environmental flows for each process associated with a product across its life cycle, and consequential LCA (CLCA), which evaluates the impact of future market shifts and changes, including how this will influence environmental flows and predicted changes in demand for a product or process.ALCA is the most commonly known and applied assessment approach for buildings (Bamber et al 2020).Buyle et al (2014) argue that while ALCA can provide an extremely precise representation of the current circumstances, CLCA supports a more realistic estimation of environmental flows over time by taking into account market predictions.
The second stage of LCA involves conducting life cycle inventory (LCI) analysis.This includes collecting the relevant data for the assessment.There are three common methods used to compile LCI data: process analysis, environmentally extended input-output (EEIO) analysis, and hybrid analysis.Process analysis calculates environmental flows across the supply chain, primarily based on manufacturing data.It is considered one of the most reliable techniques, and is able to achieve a high level of detail (Crawford et al 2022).EEIO uses macroeconomic and environmental data to estimate environmental flows between economic sectors and can capture 'hidden' impacts which are otherwise difficult to track (Kitzes 2013).Hybrid methods combine process analysis with EEIO, leveraging the comprehensive coverage of EEIO data and prioritising detailed process data where it is available.A variety of methods are used to compile a hybrid LCI (Crawford et al 2018).
The third stage of LCA is life cycle impact assessment (LCIA), which involves converting LCI data into measurable environmental impacts.This is achieved through characterisation factors which quantify estimated environmental effects per unit of measurement (e.g. per kgCO 2 e or kg of GHG emissions).The last stage of LCA involves the interpretation of assessment results.Similar to other environmental assessment methodologies, LCA does not quantify actual environmental burdens, but instead provides insight into potential environmental effects based on the goal and scope of the assessment and the best available data and methods.Variations to data, methods, system boundaries, and assumptions may cause significant discrepancies in results (Dixit et al 2010) which must be taken into account when interpreting and comparing outputs.

Integration of LCA in the building design process
While LCA is a highly regarded approach, it is rarely used by building designers, and when it is, it is mostly used as a post-design evaluation assessment tool after the majority of design decisions have been finalised (Hollberg andRuth 2016, Meex et al 2018).It is rarely used to inform design decisions (Hollberg et al 2021), except in countries where mandatory requirements have already been introduced.Detailed LCA requires extensive building data inputs, LCA expertise, and is therefore mostly conducted by LCA experts.As a result, LCA is often perceived as a complex, time-consuming, and costly technique that is not suitable for early design which is characterised by fast, iterative decision making (Schlanbusch et al 2016, Meex et al 2018).
In current architectural practice, building designers still predominately rely on rules of thumb, experience, knowledge, and intuition to guide these early design decisions (Weytjens and Verbeeck 2010, Meex et al 2018, Sartori et al 2022a).There is often a lack of adequate training and education for building designers regarding quantitative assessment methods required for LCA (Sartori et al 2022b).Nonetheless, many countries are now introducing LCA into national building legislation (Hollberg et al 2022) and several European countries have developed policies, regulations and guidelines regarding embodied emissions.This includes the introduction of compulsory LCA-based impact assessment in countries such as the Netherlands and France (Attia et al 2021).
It is argued by Meex et al (2018) that the implementation of policies and building regulations will eventually lead to LCA becoming a mandatory step in the building design process.Indeed, this is already occurring in many countries, and there are a range of new initiatives that support upcoming (and recently introduced) EU legislation mandating the use of LCA for buildings.De Wolf et al (2023) discuss this topic in further detail, exploring the growing range of bespoke LCA calculation tools, guidance documents, and datasets that are designed specifically to support the introduction of LCA for buildings in different national contexts.These include tools such as TOTEM (Belgium), ELODIE/INIES (France), Nationale Milieudatabase (Netherlands) and LCAByg (Denmark).

The need to align LCA approaches with building design workflows
To integrate LCA into design workflows, LCA approaches must be better aligned with the requirements of building designers (Sartori et al 2022b).In this study, 'design requirements' are defined as the characteristics of LCA approaches that facilitate improved integration of LCA in the building design process, such as real-time feedback for designers.Extensive research has been conducted into the design requirements of early design, however only a limited number of studies have investigated how LCA can be applied across the entire building design process.This study aims to provide a detailed analysis of existing LCA approaches, to assess how well they align with building design stages and requirements, and to identify key characteristics of these approaches, including the LCA tools and environmental data currently used to conduct assessments.

Method
This review consists of two separate stages.Firstly, a systematic review of literature to determine the main characteristics of LCA approaches used during the design process, and secondly, an analysis of LCA case studies to assess how well LCA approaches align with design requirements for each building design stage.The data collection method for these two stages is summarised in figure 2.
Data collection was conducted using Scopus and Google Scholar, with the search terms 'LCA' or 'life cycle assessment' , and 'building design process' , and 'embodied impacts' or 'embodied effects' .The initial search was conducted in October 2022 and returned 156 results, which included academic journal articles and peer reviewed conference papers.Titles, abstracts, and keywords were screened for relevance and duplicate articles removed.Literature exclusively centred on a single material or building element was excluded.Articles were included if they focused on LCA and embodied effects, while also including reference to the building design process.A total of 42 LCA case studies and frameworks were selected for detailed analysis.A further 35 articles (including review articles, surveys, and commentaries) were selected for the literature review, and 72 articles were chosen based on a backward and forward snowball approach (including academic journal articles, reports, and book sections).The snowball approach included an additional search conducted using  Scopus in November 2023 to extend the scope of the literature review to include carbon footprint.A total of 149 documents were reviewed, including 42 selected for case study analysis.
Data analysis was conducted in two stages, shown in figure 3. Firstly, a literature review was conducted.General attributes of LCA approaches were identified, such as the types of LCA tools used, LCA methods, LCI data, and impact categories.A list of 'design requirements' was then compiled (see section 3.3), mapped against the early design and detailed design stages.This included manual analysis of the literature, and analysis using NVIVO data exploration tools, such as auto-coding of themes and identification of common keywords and references.Secondly, the selected case studies were analysed using search terms-including stemmed words and synonyms in NVIVO-to identify key attributes such as 'parametric' , 'generative' , or 'computational' .Each search instance was manually verified, and additional analysis was conducted to identify key features not detectable using search terms (such as the type of LCI data used).Analysis relied on the literature providing sufficient level of detail and transparency regarding LCA methods.

Review of LCA in the building design process
This review primarily focuses on building designers as an agent for change, as they are capable of having a significant influence on the environmental performance of buildings (Dubois et al 2016).Building designers are defined as 'individuals, or groups of individuals responsible for the architectural and technical design of a building.This definition is not exclusive to licensed architects and includes other actors commonly responsible for building design, including designers, contractors, engineers, builders and building owners' .(Prideaux et al 2023).

Alignment of LCA with the building design stages
The building design process is characterised by highly iterative design cycles, typically moving from abstract, to more refined and specific ideas, with additional detail added as the design progresses (Tabrizi and Brambilla 2019).Efforts have been made in previous literature to describe the various processes, stakeholders, and instruments in the built environment.However, as highlighted by Hürlimann et al (2022), these descriptions frequently oversimplify the complexity of processes and overlapping stages.They typically focus on a narrow range of built environment life stages and fail to explicitly articulate the role of environmental sectors, key actors, and the relationships and coordination of activities between stages.To delineate these complex interconnections in the design process, visual representations such as process maps can be employed.The most common building design process maps are produced by professional institutes and sector bodies.Examples include the Australian Institute of Architects client architectural agreement (AIA 2019), the American Institute of Architects best practice guide (AIA 2007), and RIBA Plan of Work 2020 (RIBA 2020).One limitation of these types of process maps is their linear representation of the design process.Linear representations with sequential stages often fail to fully capture the cyclical and iterative nature of design (Moosavi 2018).This research uses the RIBA Plan of Work to describe the design stages.In this framework, the design process is divided into eight different stages: 0. strategic definition, 1. preparation and briefing, 2. concept design, 3. spatial coordination, 4. technical design, 5. manufacturing and construction, 6. handover, and 7. use.Stages zero through to five are the focus of this research, as they are the main 'design' stages.Construction has been included in this definition, recognising that additional design decisions are made during this stage.A concordance table is provided by RIBA (2020) for translating the RIBA Plan of Work to different countries.
One aspect that is not readily available in the RIBA Plan of Work, is the level of building information available to the designer at each design stage.This is a critical consideration when conducting LCA and is articulated through the level of development (LOD), which was formalised by the American Institute of Architects (AIA) (Abualdenien and Borrmann 2022), and is commonly used for building information modelling (BIM).The LOD acts as an agreement between stakeholders, for the level of modelled and exchanged information, across a project's life cycle (Abualdenien and Borrmann 2022).While this topic is not explored in detail here, Abualdenien and Borrmann (2022) review 58 international LOD guidelines, providing a comprehensive overview of the topic.They present a concordance table of different LOD guidelines, including clarification of key terminology, which varies between countries (e.g.Level of Detail, LOD (USA), Level of definition (UK), information levels (Denmark)).For this research, the American Institute of Architects' definition of LODs is used which ranges from LOD 100-LOD 500.The levels correspond to the amount of data resolution and information available at different project stages.Table 2 demonstrates how the LOD aligns with the building design stages, as specified in the RIBA Plan of Work.These have been mapped to the broader terms 'early design' and 'detailed design' , which are commonly used in LCA literature.

LCA tools for building designers
Various environmental assessment tools can be used to quantify the embodied and life cycle environmental flows throughout the building design process.These can be broadly categorised into generic LCA tools (such as SimaPro and LCA for Experts/GaBi), and specific LCA tools for building and construction (such as Athena Impact Estimator and TOTEM).While generic LCA tools can be extremely versatile and provide detailed information, they are not typically designed to account for the complexity of the building life cycle and design stages.
Specific LCA tools for building and construction come in a variety of formats including spreadsheets, standalone software, web-based platforms, or integrated into design tools and CAD programs.These can be broadly separated into three categories.Firstly, basic tools that require minimal experience to conduct and often rely on 'rules of thumb' , or predefined life cycle inventory (LCI) coefficients to conduct.Secondly, standard design orientated tools that use a simplified LCA method to streamline calculations (see section 3.4.1)and require a basic level of experience and/or training to use.Lastly, advanced tools that allow for comprehensive assessments and detailed life cycle results, but typically require large quantities of building data and expert knowledge to use.Due to variability in features, attributes, stakeholders, and platforms it can be difficult to compare between products (Haapio and Viitaniemi 2008), and challenging for building practitioners to select appropriate LCA tools (De Wolf et al 2023).
Existing tools are often intended for use by LCA experts, and are not necessarily compatible for use by building designers to inform decisions during the design process (Prideaux et al 2022).Consequently they are frequently perceived as time-consuming, require specialist knowledge, or are not suited to rapid and iterative decision-making (Meex et al 2018).In addition to this, many LCA tools are not compatible with common CAD/3D software and are missing user-friendly features, making it difficult for building designers to incorporate these tools into existing workflows (Prideaux et al 2022).Considerable work still needs to be done to mainstream these tools in design practice.Despite these challenges, there is a growing range of LCA tools and calculators available for built environment practitioners, and work is being done to evaluate and improve the user-friendliness of environmental assessment tools.This is explored further in section 3.3.
The most prominent emerging themes found in the literature review regarding LCA tools were BIM-LCA (section 3.2.1)and parametric-LCA (section 3.2.2).Unlike conventional LCA tools, these techniques typically integrate with 3D/CAD software, and can facilitate real-time assessment based on embedded building information data, offering a potential integrated solution for LCA in the building design process.The increased level of building information embedded in these models can also be leveraged by machine learning techniques to enhance decision making capabilities (Venkatraj and Dixit 2021).Despite the potential of these tools, parametric-LCA and BIM-LCA are still in early development, and there are significant challenges incorporating them into design workflows (Hollberg et al 2020).
Scholars such as Santos et al (2020) argue that the architecture, engineering and construction (AEC) sector must embrace new digital design supportive technologies in order to improve the environmental performance of buildings.However, while these new fields offer a range of exciting opportunities for streamlining LCA in building design, it is unlikely that these solutions alone will be able to completely address all of the issues at hand.Rates and uptake for innovation are likely to vary, and not every solution will be appropriate for every designer (RIBA 2020).For example, many designers still prefer analogue tools (such as hand drawn sketches, physical models, material boards, design journals, hand drafting and other techniques), particularly for design ideation (Frich et al 2021), and completely digital workflows are unlikely to be compatible with existing workflows.Simplified tools could compliment analogue workflows and may be able to assist in bridging this gap.Additional technical expertise and knowledge of LCA will be required for building designers to be able to use and interpret results from these tools to inform design decisions.

BIM-LCA
BIM is a digital representation of the physical attributes and functional characteristics of a construction project.BIM models facilitate the creation, management and exchange of detailed information throughout the life cycle of a project (Durão et al 2020).Information can include material specifications, performance attributes, spatial relationships, and/or other relevant information.This framework can streamline decision making, coordination, and communication between stakeholders and serves as a centralised repository of project information.BIM-LCA is an extension of the BIM framework that includes LCA considerations.It is a frequently discussed theme in LCA literature and was mentioned in a vast majority of the reviewed papers.Half of the reviewed case studies used BIM-LCA tools.In practice, adoption of BIM tools remains relatively limited (Hollberg and Ruth 2016), particularly in smaller firms where they are often perceived as being excessively time-consuming and therefore not feasible for use (Giordano et al 2021).This is partially due to the complexity of existing tools, and extensive information requirements.
The strength of BIM-LCA lies in its ability to leverage detailed material property information, quantities and cost estimations embedded within BIM models to directly conduct LCA (Cavalliere et al 2019).Because information is contained within a single model, it can (in theory) be automatically passed to LCA or environmental simulation software (Basbagill et al 2013).This reduces the need for designers to manually input building data and material quantities (Castro and Pasanen 2019), and can significantly streamline  2021) and Obrecht et al (2020) report that within academic studies, this exchange process is rarely streamlined and mostly relies on manual or semi-automated processes.Wastiels and Decuypere (2019) identify five workflows that integrate LCA with BIM (figure 4), each with varying degrees of automation.These include exporting a bill of quantities (BOQ), exporting with Industry Foundation Classes (IFC), utilising the BIM viewer, using LCA plug-ins, and enriching BIM objects with LCA information.
One consideration discussed by multiple authors, is the opportunity for aligning BIM-LCA with the LOD (Cavalliere et al 2019, Durão et al 2020, Naneva et al 2020, Safari and AzariJafari 2021).This approach would theoretically allow for incremental LCA assessment across the design stages.However, Cavalliere et al (2019) highlight that most historical studies have only used this technique for discrete stages of the design process.Despite the exciting potential of BIM-LCA tools, they often face similar challenges to traditional LCA (Roberts et al 2020), including variations in LCA goals and scope, lack of access to comprehensive and transparent environmental data, disparities between life cycle impact assessment methodologies, inconsistent treatment of uncertainty information, difficulties interpreting results by non-experts, and other considerations.2016) demonstrate how a parametric-LCA workflow can be used throughout the design process to enhance decision making regarding environmental performance.Säwén et al (2022) identify three primary workflows that can be used to incorporate LCA into parametric software (figure 5).These include exporting a BOQ, direct connections with LCA software, and using LCA plug-ins.Utilising plug-ins within the parametric environment allows for results to be visualised alongside, or overlayed onto, 3D geometry.This enables real-time feedback based on changes made to input parameters or geometry.
Popular parametric tools include Grasshopper and Revit, which feature a visual interface that can be used to update and modify parameters dynamically.A list of active tools is provided by Säwén et al (2022).Parametric-LCA typically utilises embedded building information and 3D geometry to quickly approximate material quantities required for LCA.Calculations are performed dynamically, with real-time updates based on user inputs or algorithms.Parametric approaches often require a completely different design approach compared to traditional design techniques, as geometry is determined by a set of interlinked parameters, defined by the designer, which can lead to exceedingly complex geometric outputs.Therefore, one major limitation of this approach is the significant adaptations required to integrate with existing design workflows, with interfaces and approaches often unfamiliar to designers, requiring additional technical knowledge, particularly when contrasted with analogue design iteration techniques.Parametric-LCA tools are still relatively uncommon and primarily target early design.

Design requirements: improving the integration of LCA in the building design process
Certain characteristics can make LCA tools and approaches more accessible and user-friendly for design professionals.These have been termed 'design requirements' .Examples include streamlined data inputs, enhanced result interpretation, improved usability within the design process, and adherence to best practices (such as transparent communication of the LCA methodology employed in a tool).Several studies have investigated design requirements for user-friendly environmental impact assessment and energy performance tools.Table 3 provides a summary of findings distilled from five studies.This includes research by Hollberg et al (2022), who propose a framework for user-centric LCA tool development, prioritising end users (in this instance building designers) in the tool development process to ensure that final products meet user requirements; a study by Meex et al (2017), who present a framework for the evaluation of the architect-friendliness of environmental assessment tools in early design (based on analysis of the Flemish architectural design practice); a review by Prideaux et al (2022) investigating tools used to assess embodied environmental effects throughout the design process; a survey of Flemish architects by Weytjens and Verbeeck (2010), looking at the user friendliness of energy evaluation tools; and survey findings from Sartori et al (2022b) from an international survey of building designers, listing guidelines for LCA tool developers to improve the compatibility of LCA tools for the building design process, mapped against the RIBA Plan of Work.
The following two sections provide a summary of design requirements relating to early and detailed design.Various requirements are also identified as being important across all design stages.These include basic graphical outputs (Meex et al 2018, Hollberg et al 2021), integration with other design objectives and assessment tools (Mateus andBragança 2011, Meex et al 2018), optimisation (Basbagill et al 2014), and sensitivity/hotspot analysis (Sartori et al 2022a).

Early design requirements
During the early building design stages, represented by stages zero to two, the opportunities to reduce the environmental effects of a building are very high (Kovacic and Zoller 2015).These stages are characterised by rapid and iterative design cycles with a low level of building information and hence high levels of uncertainty.The limited building information conflicts with the data-intensive method of LCA.As a result, LCA is often conducted as a reactive measure in the later stages of design, or after a project has been completed (Roberts et al 2020).
Simplifying or reducing the number of LCA inputs can help streamline assessments and reduce complexity without dramatically reducing the accuracy of results (Bonnet et al 2014).A non-exhaustive list of simplification strategies is provided in section 3.4.1.To meet the needs of building designers, early design LCA tools must be flexible and be able to provide rapid feedback to inform decision making.This includes providing designers with the means to compare design alternatives through techniques such as sensitivity analysis and hotspot analysis (Sartori et al 2022a).Ideally, tools should feature instant feedback via the 3D model with the ability to quickly generate design alternatives/suggestions.They should also include supplementary advice for the designer with graphical outputs to assist rapid decision making.Providing access to reliable data in a visual format that is accessible and easily interpretable is critical (Miyamoto et al 2022), and having at least a basic knowledge of LCA can greatly improve the designer's ability to conduct assessments and interpret/optimise results.
In early design, the exact material composition of a building/project is often unclear and likely to change.It can therefore be beneficial to use generic elements from databases to serve as a quick starting point for assessments, rather than specific products and environmental product declarations (EPDs) (Loli et al 2023).Libraries of predefined building data or elements can be utilised to address building information gaps, and the use of benchmarks and target values can assist designers to set performance targets and interpret LCA results (Hollberg et al 2019).In some cases, certification and/or compliance actions are required during these earlier stages, depending on the project and country (Sartori et al 2022a).If it is a renovation or reuse project, a more detailed assessment may be conducted of existing conditions, providing a benchmark for potential changes/additions.

Detailed design requirements
RIBA stages three to five include the design of building services and structural systems, generation of preliminary cost information, the refinement of materials and design elements, and coordination with various stakeholders and consultants.Many of the key design decisions, such as building orientation, size, shape and floor area have already been finalised, which reduces the opportunity to significantly influence the environmental performance of a building (Prideaux et al 2022).Inter-disciplinary connections are particularly important during these design stages (Sartori et al 2022a), as there are often multiple technical experts contributing towards design drawings.Certification for building compliance, LCA and GBRS assessments are commonly conducted during these stages, often by external specialists.While LCA is more common during detailed design, it is typically conducted by external consultants and is not necessarily treated as a decision tool for design.Due to the additional building information that is available during these later stages, a more reliable and complete estimation of environmental flows can be calculated.However, this additional information can also make assessments time-consuming.Through the use of BIM, detailed CAD models can be used to automatically feed into LCA software to reduce or eliminate the need for manual data entry of LCA inputs (Ansah et al 2021).This can facilitate streamlined LCA workflows for designers.Unfortunately these approaches are still somewhat uncommon and most still require manual, or semi-automated exchange (Safari and AzariJafari 2021).Generic LCI databases can be used for detailed design, however, specific data (generally sourced from EPDs) can also be introduced to increase the level of detail for the LCA.If multiple data sources are used, it is critical that they follow the same assumptions and LCA methods to ensure comparability and consistency.This is particularly important when including EPDs, which are often criticised for their lack of transparency, and inability to compare between products (Galindro et al 2020).

Approaches for integrating LCA in the design process
There are many techniques for incorporating LCA into the building design process, which vary depending on the scope and goal of the assessment, and the technical expertise of the user conducting the study.There remains a high degree of variability between approaches for national tools, guidelines, regulations, common practices, and certification schemes available in different countries.Documents such as the EeBGuide have been developed as guidelines intended to bridge research and practice (Lasvaux et al 2014) and are widely cited in academic literature (Bonnet et al 2014, Lasvaux et al 2014, Llatas et al 2020, Budig et al 2021, Safari and AzariJafari 2021).The EeBGuide defines three levels of LCA: screening, simplified and detailed LCA (referred to as complete LCA).Recommendations are provided regarding the scope of assessments, number of impact indicators, types of building elements, and the preferred type of LCI data for each level of LCA (Budig et al 2021).For this review, 'screening LCA' was excluded due to insufficient detail provided in the literature to clearly distinguish between 'screening' and 'simplified' approaches.All screening approaches have been classified as simplified LCA.
A selection of 42 LCA case studies and frameworks have been analysed and broadly categorised into three categories: simplified LCA, detailed LCA, and incremental LCA.Approaches were categorised as simplified if they included a simplification of data inputs and targeted a specific design stage, detailed if they adhered to a more conventional LCA approach with extensive user inputs, and incremental if the assessment evolved progressively, responding to available building data and designer requirements at each stage.Each of the three LCA approaches are described in further detail in the sections below, including a brief overview of the LCA approach, followed by key findings from the case study analysis.An overview of the case study analysis findings is provided in table 4. The most common general attributes of LCA approaches included the use of BIM-LCA tools (50%), process based LCI data (90%), an attributional modelling approach (98%), and GHG emissions/global warming potential (GWP) as the primary impact indicator (98%).
A one-way analysis of variance (ANOVA) was conducted to assess statistical differences between design requirements for the three LCA approaches.The results indicated notable variations in the early design category (p < 0.05), while the detailed design and 'all stages' categories exhibited no significant differences (p > 0.05).Post hoc tests for detailed LCA confirmed significant differences when compared with simplified LCA in early design (p < 0.05).It is necessary to approach these findings with caution due to the relatively low number of case studies analysed.The average number of design requirements included in each LCA case study is shown in table 5. On average, simplified LCA techniques included 6.7 (61%) of the 11 early design requirements, which was higher than incremental approaches (50%), and more than double the average for detailed LCA studies (27%).Simplified LCA also included a higher number of 'all stages' design requirements (55%), compared with other approaches (45%).Detailed and incremental LCA included a higher number of detailed design requirements on average than simplified approaches (38% compared with 23%).

Simplified LCA
Simplified LCA is a streamlined assessment method, designed to make LCA more accessible, practical and less data intensive.It can be used to integrate life cycle thinking in the design process, in lieu of conducting detailed LCA (Roberts et al 2020).It achieves this by aligning with assessment goals, available building data, user knowledge and requirements available at specific design stages.
Simplified LCA is particularly useful for the early design stages.Soust-Verdaguer et al (2016) argue that simplified approaches are essential for early design, where time is limited, data availability is often poor, and non-expert LCA users are required to make rapid comparisons of design options.It can enable designers to perform assessments that would normally be difficult or impractical to conduct (Giordano et al 2021).Each of the four steps prescribed by the ISO 14040 standard plays a significant role in the simplification of the LCA method (Tabrizi and Brambilla 2019), and a good understanding of the target audience, scope and goals of the assessment can guide the selection of the most appropriate simplification techniques.Functional units used for simplified LCA vary depending on the goals of the assessment, available data, simplification strategies used, and desired depth of analysis.They should ideally include information regarding the project being assessed, technical and functional requirements, pattern of use, and period of assessment (Nwodo and  The use of target values, benchmarks, and or reference values for rapid comparisons 2, 3, 4 1 Bonnet et al (2014). 2 Malmqvist et al (2011).
Anumba 2019).Employing multiple functional units can provide meaningful insights into the various trade-offs faced by building designers (Stephan and Crawford 2016).Bonnet et al (2014) propose that simplification strategies should actively involve the user in development to ensure a user-centric product, and prioritise a high level of accuracy with reduced modelling time and improved reproducibility of results.Several techniques can be used to 'simplify' the LCA method.A non-exhaustive list of simplification strategies has been formulated based on the literature review, divided into three categories shown in table 6.These strategies include data acquisition (typically a reduction in inputs or an optimisation of the data acquisition process), scope (a simplification of LCA stages, LCI methods, life cycle impact assessment categories, or scenarios), and results communication (simplification of assessment results, or generation of information to streamline the interpretation of results).
Simplified LCA does not automatically imply a 'worse' or 'less accurate' assessment.This is exemplified by a study conducted by Bonnet et al (2014), who demonstrate that in some instances simplified LCA can improve the reproducibility of results, speed up calculations, while retaining a high degree of accuracy.However, there is only limited research on the deviation of results between approaches (Meex et al 2018), and few studies have categorised characteristics of simplified LCA, and how they could be leveraged to streamline LCA in building design.
There was a relatively even spread of LCA tools employed for simplified LCA (shown in table 4), with BIM-LCA and Parametric-LCA being the most prominent (32% each).All studies used process based LCI data, except for three studies that failed to indicate the type of data used.GWP was the primary indicator, with some assessments also including energy, a single sustainability score (NG), and/or other impact categories (abiotic depletion potential of elements/fossil resources, acidification potential, eutrophication potential, ozone depletion potential, photochemical ozone creation potential, radioactive waste production, water consumption, and waste production).
In contrast to detailed LCA, there was a much higher inclusion of early design requirements in simplified LCA approaches (figure 6).All cases included a simplification of input parameters.Design requirements commonly integrated into simplified LCA included comparison with design alternatives or scenarios (89%), results that could be easily interpreted by non-LCA experts (84%), rapid assessment and results (79%), basic graphical outputs (79%), and sensitivity analysis/hotspot identification (79%).Despite the increased incorporation of early design requirements, less than a third of simplified approaches included comparison with benchmarks or target values (32%), libraries of predefined solutions (32%), or rules of thumb/advice (5%).Overall, simplified approaches were reasonably well aligned with 'early design' and 'all stages' design requirements, but less so with detailed design attributes.

Detailed LCA
Detailed LCA involves a comprehensive assessment of environmental effects, based on detailed building information.It is also referred to as 'complete' , 'conventional' , 'traditional' , 'baseline' , and 'comprehensive' LCA.Due to extensive input requirements, detailed LCA can be difficult to conduct during early design when building information is scarce (Roberts et al 2020), and assessments are often time-consuming, complex and require special expertise to undertake (Meex et al 2018).As a result, detailed LCA is predominately used late in the design process, after the majority of key design decisions have been finalised and there are only limited opportunities to make changes (Hollberg and Ruth 2016).Assessment results are often extensive and allow for thorough analysis of the environmental effects associated with each life cycle stage of a building.However, this can mean results are not always easy to interpret by non LCA experts (Cerdas et al 2017).A high level of detail is often required in order to meet regulatory or certification requirements (Lasvaux et al 2014), which may also necessitate the use of specific functional units for the assessment.
The majority of detailed LCA case studies in this review used BIM-LCA tools (59%), and none used parametric tools (table 4).Process based LCI data was used exclusively, with one study failing to declare the type of data used.All, except one study, focused on GWP as the primary impact indicator, with six including energy, and five including other indicators (abiotic depletion potential of elements/fossil resources, acidification potential, components for re-use, freshwater aquatic ecotoxicity/eutrophication, freshwater use, human toxicity, marine eutrophication, materials for recycling, non-hazardous waste, ozone depletion potential, photochemical ozone creation potential, and secondary material).In general, the results showed that detailed LCA approaches included a low number of early design requirements (figure 7).None of the examples included a connection to 3D models with instant feedback, rules of thumb and advice, or simplification of input parameters.Commonly integrated design requirements included comparison with design alternatives (82%), basic graphical outputs (76%), use of generic data (65%), and connection to a detailed 3D model (65%).

Incremental LCA
Incremental LCA approaches are applied throughout the entire project life cycle of a building, as a continual, iterative assessment used to track environmental performance.Incremental approaches can be used to guide design decisions during the design process based on the best data available to the designer, making them particularly valuable as a decision making tool (Cavalliere et al 2019, Safari andAzariJafari 2021).However, they require an adaptable methodology that can respond to the shifting level of building data and changing designer requirements at each stage of the design process.With this objective in mind, incremental approaches typically vary the granularity of assessments according to the project stage.In the early design stages, rapid, coarse, and iterative assessments are used, transitioning to increasingly refined assessments as more building information becomes available, and the design progresses.This concept is adopted by Cavalliere et al (2019), who proposes an incremental BIM-LCA approach where different LCA databases and simplification techniques are used, based on the design stage/LOD.
Only six incremental LCA approaches appeared in the review, representing 14% of the reviewed case studies, consistent with the low number of examples discussed in the literature (refer to table 4).The majority utlilised BIM-LCA tools (83%), with the exception of one instance that used a standalone tool.All approaches included a simplification of input parameters to help streamline the assessment workflow, and generic, process based LCI data, with GWP as the primary impact indicator.Some case studies also included energy, a single score indicator (Umweltbelastungspunkte [UBP]), or other impact categories (abiotic depletion potential of elements/fossil resources, acidification potential, economic [euros], eutrophication potential, ozone depletion potential, photochemical ozone creation potential, and social [working hours]).
Design requirements most commonly integrated into incremental LCA approaches (figure 8) included libraries of predefined solutions or elements (83%), connection to a detailed 3D model (83%), basic graphical outputs (83%), and comparison with design alternatives/scenarios (67%).Less common requirements were graphical outputs to assist rapid decision making (17%), rules of thumb and advice (17%), promotion of interdisciplinary connections (17%), and the use of specific data/EPDs (17%).None of the examples included functionality to suggest or generate design alternatives.

Discussion
In this review, seven key areas have been identified for improving the integration of LCA in the building design process.

Continued development and improved alignment of LCA tools
While the user-friendliness of LCA tools has improved in recent years, substantial process still needs to be made.Critical design requirements such as libraries of predefined solutions, benchmarks and target values, and supplementary advice are often missing from current LCA approaches.LCA tools must continue to better align themselves with design workflows.This could be achieved through improved engagement and collaboration between building designers, building and construction professionals, and researchers/tool developers.Similar calls for action have been expressed by Sartori et al (2022b) and Dubois et al (2016).
The emergence of machine learning and artificial intelligence tools offers significant opportunities for managing large quantities of building information data, design optimisation, and streamlining design workflows, among other possibilities (Płoszaj-Mazurek et al 2020, Venkatraj et al 2023).However, these tools also risk further reducing the transparency of underlying assumptions, data and LCA methods used for calculations.Maintaining high levels of transparency while also leveraging new technologies is of utmost importance.This will enable practitioners to conduct assessments more efficiently, evaluate software choices, understand uncertainties, and effectively interpret/compare results.

Increased methodological transparency
In general, there was a lack of transparency across the reviewed case studies.Specifically, studies often neglected to clearly articulate LCA methods, data included, assumptions, and uncertainty.This issue has been highlighted in other studies by Bamber et al (2020) and Marsh et al (2023).Transparency is essential for informed decision making and can have a significant influence on decision making and assessment results (Cooper and Fava 2006).It is imperative that designers understand the uncertainties and limitations involved with different data selection choices.For example, the reviewed case studies heavily relied on the use of process data which is known to underestimate embodied environmental flows (Ward et al 2018), including EPDs which can be challenging to streamline into LCA workflows due to issues regarding transparency, comparability and harmonisation (Marsh et al 2023).These considerations are particularly pertinent in regions of the world where data are limited.In these instances, uncertainties can be significant, and it can be challenging to conduct accurate assessments.It is critical that academic studies are explicit and transparent regarding the LCA methods, assumptions made, data used, uncertainties, and limitations.

Further research into simplified LCA approaches
One of the major challenges for applying LCA during the design process is the low level of building information available in early design.Simplifying the LCA method is essential during these stages and can aid decision making without significantly compromising accuracy (Bonnet et al 2014, Oregi et al 2015).These techniques can also be used to improve incremental LCA approaches, which are still largely underdeveloped in the literature.More research is needed to identify the most appropriate types of simplification, the levels of accuracy for these methods, and the distinct stages of design they are best suited to.

Upskilling opportunities for existing practitioners and the inclusion of LCA in education pathways
Designers require a foundational level of knowledge and skills to be able to perform basic LCA tasks, such as selecting the most appropriate tools, defining the scope and goals for assessments, choosing the most appropriate data sources, and effectively interpreting LCA results to guide design decisions.This knowledge has not traditionally been included in architectural education and practice (Sartori et al 2022b).New approaches to architectural education are therefore required that incorporate these considerations into formal education curriculum, professional training, and other learning pathways.Thoughtful attention must be given to anticipating the skills and knowledge required by upcoming generations of built environment professionals.Upskilling opportunities for existing practitioners and other built environment actors will also need to be prioritised.Beyond formal education pathways, the exchange of knowledge among design practitioners is an important facet, as are continued efforts to raise awareness and knowledge among consumers, clients, homeowners, and the general public about the urgent need to reduce whole building environmental effects.

Improved building design workflow models
As LCA is gradually integrated into certification systems and building regulations, building design processes will need to adapt and evolve.Additional guidance is needed on how to operationalise LCA approaches and to adapt existing design workflows.To achieve this, detailed and nuanced models of existing building design workflows are required, including better descriptions of the actors, processes, and critical decisions taken during the design process.This should not only focus on the role of the architect, but also other stakeholders/multidisciplinary processes involved in the project life cycle.As presented in this review, various approaches in the academic literature describe how LCA could be included in the design process.However, these accounts often fail to provide sufficient detail explaining how building designers could fully operationalise these approaches.To improve the reproducibility and transparency of LCA approaches, additional detail should be provided by researchers, including comprehensive accounts of steps taken, assumptions made, and the tools and data used for assessments.4.6.The development of targets, benchmarks, and regulatory levers to encourage proactive integration of LCA New regulatory changes have introduced regulatory hurdles late in the design process.In addition to these changes, regulatory bodies should also be prioritising levers that encourage building designers to integrate embodied environmental considerations as a proactive, integral part of the design process.National design associations (such as RIBA and AIA) and industry bodies are well-positioned to assess, and provide guidance on, how changes could best be implemented to align with existing design processes.To support upcoming regulations, benchmarks and target values should be introduced.This will ensure regulations align more closely with overarching environmental goals, while aiding designers in comparing outcomes and facilitating informed decision-making.

A broader focus beyond GHG emissions
The predominant environmental indicator used in case studies was GHG emissions.Care must be taken to avoid the shifting of burden onto other environmental, social, or economic impacts (Janjua et al 2019, Reisinger et al 2022).Understanding how embodied environmental considerations can be integrated with other sustainability indicators and design objectives is a complex issue and was addressed in less than 20% of the reviewed case studies.Utilising GBRS is one option, however the primary focus of these systems is on certifications and ratings, rather than progressively informing design decisions.There can also be significant differences between systems, with weighting choices significantly influencing results (Zimmermann et al 2019).

Limitations and future research
A major limitation of this study is that it relies on academic literature to extrapolate generalisations of design practice.Due to the complexity of both building design and LCA, themes are only explored at a broad level, and more detailed examination of individual workflows is required for in depth analysis of specific LCA approaches.In addition to this, literature included in this review only incorporates English-based literature and is therefore limited in its scope and reach.While this research predominantly focuses on academic discourse, the authors plan to conduct future studies that integrate building designer perspectives.Studies are required at the practitioner level to better understand how to effectively operationalise LCA to ensure that approaches align with the needs of building designers.Specifically, there is a lack of research targeting building professionals regarding how to mainstream whole LCAs (De Wolf et al 2023), and only limited studies that compare the deviation of LCA results between different approaches (Meex et al 2018).
While every effort was made to accurately code data collected from the case study review, data analysis required a high level of detail and transparency regarding the LCA method, which was not always provided.Many studies excluded details about simplifications made, LCI data used, data outputs, or how the LCA methodology could be operationalised by building designers.Due to the lack of specificity, it is expected that many of the detailed LCA studies contained in this review would not fit the true definition of 'detailed LCA' , however, they were categorised as such because these studies did not explicitly aim for a simplified approach, and the type of simplification strategies used were not always clear.Another data analysis limitation was that some case studies only provided minimal details regarding the selected design requirements.In these instances, design requirements were marked as 'absent' .

Conclusion
This study examined LCA approaches in academic literature, seeking to understand how well aligned they were with the building design process.A systematic review of literature was conducted to identify the main design requirements for LCA during the early design (RIBA stages 0-2) and detailed design (RIBA stages 3-5) stages.A selection of 42 LCA case studies was analysed and broadly divided into three categories: simplified LCA, detailed LCA, and incremental LCA.Results showed that half of the case studies used BIM-LCA tools, and the overwhelming majority were based on attributional LCA modelling, process-based LCI data, and GHG emissions/GWP as the primary impact indicator.The selected case studies often lacked supplementary advice to guide designers, features that promoted interdisciplinary connections, and integration with other design objectives or sustainability indicators.
Simplified LCA techniques offered a streamlined approach for incorporating LCA into the design process, primarily targeting the early design stages.These approaches typically included results that were easily interpretable by non-LCA experts, graphical outputs to support decision making, and a strong integration with 3D modelling software which included rapid feedback for the user.They were generally well aligned with early design requirements but frequently lacked key requirements such as libraries of predefined solutions to streamline assessments, integration with benchmarks/target values, and advice/rules of thumb to guide designers.Detailed LCA approaches included more extensive building information inputs, resulting in comprehensive and granular results, but also requiring a higher level of expertise to conduct and interpret assessments.They typically utilised BIM-LCA tools and had a strong connection to detailed 3D modelling software with basic graphical outputs, although were frequently missing early design requirements such as 3D models with instant feedback, simplified input parameters and generation of design alternatives.Incremental LCA approaches were designed to continuously assess environmental performance throughout the building design process by responding to the changing level of building data and designer requirements at each stage.These approaches commonly utilised BIM-LCA tools and libraries of predefined solutions or elements to simplify assessments.While incremental LCA shared many common attributes with simplified LCA, there were only a limited number of case studies identified, and many approaches were still in early development.
To achieve the greatest impact, LCA should be conducted as a proactive measure in the early stages of design, or preferably, incrementally throughout the design process.While there is a growing range of simplified LCA approaches for early design, integrating LCA throughout the entire design process is inherently complex and demands careful consideration of design workflows, stakeholders, and design instruments involved in building design.LCA approaches that embrace this paradigm are often underdeveloped, adopt overly complicated workflows, or are difficult to operationalise.Additional research is therefore necessary to map building designer requirements for common design workflows; to inform the development of new LCA approaches that better align with building designer needs.This will require increased dialogue, engagement and collaboration between researchers, practitioners, educators, and policy makers.

Figure 2 .
Figure 2. Overview of the data collection method for the literature review and case study analysis.

Figure 3 .
Figure 3. Steps for data collection and analysis.

Figure 6 .
Figure 6.Percentage of simplified LCA case studies that incorporate design requirements.

Figure 7 .
Figure 7. Percentage of detailed LCA case studies that incorporate design requirements.

Figure 8 .
Figure 8. Percentage of incremental LCA case studies that incorporate design requirements.

Table 3 .
Design requirements for user-friendly LCA tools.

Table 5 .
Summary of design requirements included in reviewed LCA case studies.

Table 6 .
A list of common LCA simplification strategies.