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Summary and recommendations

Introduction

Building information modelling (BIM) can help low-carbon building design by supporting the comparison of alternative design choices in the initial phases of design by different design disciplines and thus finding optimal solutions. Also, the growing regulation of various Nordic countries regarding the low-carbon nature of construction projects sets requirements for evaluating the carbon footprint. Denmark, Finland, Norway and Sweden require it during the as-built phase. Estonia is planning to require it during the building permit phase, and Iceland plans to require it twice during the building project.
BIM has become more or less mainstream in professional building projects. Life cycle analysis of buildings is largely conducted based on the used building materials and their quantities. This BIM-related information is, in some ways, already described in the models. However, the models are currently not utilised in building life cycle analysis (LCA) to the extent they might be. The data required by the LCA analyst might be missing from the model or recorded in non-standard ways; properties may be absent, and some features may be modelled multiple times. This increases time and effort, as practitioners may need to input data manually or make assumptions. Unfortunately, the discussion between BIM modellers and LCA analysts is often lacking. BIM-related information is generally not usable for carbon footprint assessment without common standard practices and requirements for information to be included in BIM models, such as naming, presented parameters, and building parts to which components are related.
This BIM4LCA project, as part of the Nordic Sustainable Construction programme, tackled these challenges. The BIM4LCA work started in May 2023 by analysing the current enablers and hindrances for BIM-based building LCA in the Nordic countries and Estonia. The results were communicated in a report explaining the building LCA and BIM practices and the constraints and enablers for harmonising building LCA in the Nordics.
Report: The Operating Environment of Building LCA and BIM in the Nordics and Estonia, published 18.12.2023, available from https://nordicsustainableconstruction.com/Media/638379082362009468/The%20Operating%20Environment%20of%20Building%20LCA%20and%20BIM%20in%20the%20Nordics%20and%20Estonia.pdf.
 The report supported the creation of a common understanding for all the Nordic stakeholders and further work on the project.
The following work focused on developing a BIM-based building carbon footprint calculation process where BIM provides adequate information on quantities for a list of materials/­products, which is then linked with emission data. The BIM4LCA project aimed to reveal the information needs and minimum requirements for architectural, structural, electrical, and HVAC models and their IFCs to ensure the information can be used in the normative (required by legislation) carbon footprint assessment. Many countries have BIM guidelines and requirements to support modelling in general. Still, they are rarely nationally mandatory or support BIM modelling specifically for building carbon footprint calculation.
This current report mainly focuses on the normative building LCA required by the Nordic countries' legislation, but it needs to be noted that building LCA is a broader concept than normative LCA. At their best, building projects perform BIM-based building LCA in several project phases – conceptual design, detailed design, construction, and as-built – to ensure reaching sustainability goals. Currently, it is often the job of an LCA expert to do the work manually, perhaps taking some quantities from the BIM. The LCA is mainly done once or twice, and it may not have that big an impact on reducing emissions. In the future, there will be tools that will allow more automatic building LCA and suggest changes in the project to reduce emissions.

Results of the BIM4LCA project

This BIM4LCA report provides a generic description of the BIM to LCA process, which can support calculating and reporting normative LCA in building construction projects. The project developed generic guidelines for reliable BIM-based material inventory (bill of materials), specifications for information needed for modelled building components, data transfer from BIM tools to LCA tools, and iterative design and analysis workflow between BIM and LCA tools. The guidelines target the architects, structural engineers, heating, ventilation, and air conditioning (HVAC) and electrical designers who create the BIM models and the LCA analysts who extract information from the models. The starting point for the guidelines has been that they require as small changes as possible to the current BIM modellers’ workflow. Locations for data in the models are recommended so the LCA analyst will receive material quantity information from the model, as designed by the architects and other designers, with reliable outcomes. Also, the level of detail in different stages of construction projects is recognised, and best practices for amending that information are recommended.
The BIM4LCA project produced two examples of buildings and their BIM models, which can be used by practitioners – architects, structural engineers, HVAC and electrical designers and LCA analysts – to learn how to do the modelling to support BIM-based building LCA in practice. The buildings are designed according to the Finnish Construction Act and building codes. The design principles have emphasised the life-cycle properties of buildings, e.g. in terms of multi-purpose usability, adaptability and access to natural light. The report provides links to the native architectural, structural, HVAC and electrical BIM models and their Industry Foundation Classes (IFCs) files, including their BIM specification documents and related material and product information. These files
https://www.nordicsustainableconstruction.com/knowledge/2024/august/bim4lca-files
 are provided for free with a Creative Commons license.
The project also created seven educational videos that support practitioners in learning BIM-based building LCA. The videos explain how BIM model authors should do the modelling to support the LCA specialists in BIM-based quantity take-off and mapping of the result to the LCA calculation software (see more specifically Appendix F: Educational videos on BIM-based building LCA). The videos are on the YouTube channel of the Nordic Sustainable Construction programme.
The BIM4LCA project suggests BIM data requirements and best practices for modelling and data processing that can enhance the usability and accuracy of BIM data for LCA purposes. The project also recommends that Nordic authorities set BIM requirements for BIM modellers if a climate declaration is required and support information harmonisation in the construction sector. The project proposes a future vision of automated BIM-based LCA that can provide instant feedback and optimal solutions for low-carbon building design.
The results have been co-created by a consortium of VTT Technical Research Centre of Finland, Granlund, Gravicon and Insinööritoimisto Kallinen, and the Nordic partners: Sberesearch, Rangi Maja OÜ, Bengt Dahlgren Stockholm AB, Gravicon DK and Asplan Viak AS. The draft results have been communicated to the advisory board of the Nordic Sustainable Construction programme, and their comments and requests for changes have been considered. The draft BIM-based building LCA process was communicated to a broader public audience in a “BIM-Based Building LCA” webinar
Recording and Presentation from Webinar “BIM-Based Building LCA”, published 14.12.2023, available from https://nordicsustainableconstruction.com/knowledge/2023/december/webinar-on-bim-based-lca.
 organised on the 12th of December 2023, and the oral and written comments from the audience have been considered when finalising this report. The BIM4LCA working group has also participated and presented results in internal meetings with the sister tasks of the Nordic Sustainable Construction programme.

Set BIM requirements

The BIM4LCA project raises action recommendations to support country-specific BIM-based building LCA processes. It is advisable to set BIM requirements for the BIM model authors if a climate declaration is required during the building permit or as-built phases. This project suggests BIM data requirements (See section Instructions for BIM-based material inventory), which can be used as guidelines. These requirements are part of the increased information harmonisation that has taken place in the real estate and construction sector since early 2000. Information harmonisation can significantly impact the sector’s productivity and support creating a more sustainable built environment. However, information harmonisation comes with certain burdens: the designers need to learn to model in a more detailed and structured way. This entails a learning curve, which will at first take resources. However, stakeholders agree that information standardisation is the right path.
Currently, the level of detail in BIM models in the Nordics is governed by national regulations and established modelling practices, such as​ required components in the models​, classification of components​ and requirements for model data​. The Nordic countries use different classification systems​, and the countries’ normative building LCA regulations use local classifications for definitions and reporting requirements​. From the LCA perspective, the classification should help recognise model content for the LCA reporting: the ability to separate all elements that must be reported separately​.

Integrate classification systems for effective BIM and LCA alignment

The basic feature of classification systems is to group information from a particular perspective or for a specific purpose. Thus, an activity is always built into them, such as purchasing, installation, or maintenance. The prEN 15978 standard provides a table showing the grouping of building elements according to the needs of the LCA calculation. It can be considered as a classification system for BIM models used in LCA. Although the classification of building elements presented in prEN 15978 has some minor shortcomings, it proved to be very useful in the BIM4LCA project. It has the advantage of being quite coarse but, at the same time, sufficiently accurate; the coarseness allows the different national classification systems to be mapped to prEN 15978 (see Appendix B), and the accuracy enables the elements in the IFC models to be identified accordingly (see Appendix A). One of the key recommendations of this project is that the classification of building elements in prEN 15978 should be considered as a starting point for developing LCA reporting requirements.
BIM represents design results (currently also in the as-built phase, which should represent the as-built data), a source for several information needs in the building construction, use, and maintenance phases. BIM should include data required to produce needed information in these downstream operations. The designers are not capable of producing all the needed information. Still, the role of the designers is to produce the core data for further processing by other value-chain stakeholders.
This BIM4LCA report suggests that BIM should contain identifiers for element types in all design models. However, it does not suggest a harmonised way of naming/identifying the different materials/sub-elements included in the element types. The report proposes that the elements’ details be attached to the LCA calculation phase to ensure correct emission data will be used.

Develop a machine-readable data structure to integrate BIM and LCA processes

The next development phase would be to define a machine-readable data structure to express the contents of component types (materials/layers) as they are currently presented in PDF documents. This data would be outside the BIM, and this suggestion should be tested to determine how it will support LCA calculation as needed. In the longer term, with further development and testing, detailed materials would be linked to BIM for more automated processing of BIM data, including LCA.
A big question about BIM-based design is often how much extra work it creates for designers. This project investigated the minimum level of BIM models required to achieve significant benefits supporting LCA calculations. The finding is that modelling does not increase the amount of information produced. In any case, designers must produce similar information for permitting, procurement, construction, and maintenance for every project. However, if the timing for producing the data needed for the LCA calculations is different from the timing of other processes or if the information content to be produced differs from the other information needs of the project, the additional work involved in producing the data will be significant.

Synchronise BIM and LCA information for improved accuracy and efficiency

The accuracy and timing of the information produced for the LCA calculation should be synchronised with other project information processes. The BIM4LCA project identified the content of the information required for procuring construction products and aligned the information to be produced from the BIM models for LCA. In this way, the same information serves two different processes, which increases the motivation to produce needed LCA and other information and, thus, the quality of the information.

Equip designers with BIM skills and harmonise information

Another question related to BIM-based design is what kind of new skills it requires and what capabilities the different parties involved need to adopt the required skills. There are certainly major national differences in this respect. The BIM4LCA project found that in Finland, designers have been using BIM-based design software for a long time and have a reasonable basic understanding of how to use it. Getting the geometry of the models right did not pose significant problems beyond the usual design issues. The challenge, however, was the consistent information on the elements in the models. Uniform information specifications have only been developed nationally in recent years, but designers do not yet have experience using them. There are also still gaps in the definitions. The information content in the models should be highly harmonised to enable automated and reliable data generation using BIM models. This requires both specification work and national efforts to implement the specifications. Again, motivation and information quality can be improved by drawing up specifications so that harmonised information content serves as many processes as possible, such as LCA calculation, permitting, procurement and construction.
We hope this report will pave the way towards more automatic BIM-based building LCA calculation and significantly better building data management in construction, leading to efficiency gains and better living environments. This report has pictured steps towards a future where BIM-based building LCA could take place automatically (see Figure 2). Since the quantity information required in LCA is identical to the quantity information in cost accounting, the principles described in this document also serve cost accounting and thus improve the quality of the information content of the BIM models more broadly.

The structure of the report

The structure of the rest of the report is as follows:
  • Section 1 introduces a process of using Building Information Modelling (BIM) for building Life Cycle Assessment (LCA). It discusses the challenges for employing BIM models in LCA calculations, emphasizing the need for accurate quantity take-off and data specification. It also outlines steps towards automating BIM-based LCA and the key principles for calculating embodied emissions using BIM. Additionally, it addresses the organization of data for quality assurance and the scope of Nordic climate declarations in the context of building LCA.
  • Section 2 presents the LCA requirements and data availability in different building project phases.
  • Section 3 provides instructions for BIM-based material inventory.
  • Section 4 discusses supplementing BIM data from external sources.
  • Section 5 guides the transferring of data from BIM tools to LCA tools
  • Section 6 guides the iterative design and analysis workflow between BIM and LCA tools.
  • Section 7 provides an example for information take-off for LCA calculations
  • Section 8 details the design principles of the example buildings, a residential and an office building, which were developed. The models of these buildings can be used to demonstrate how BIM models support BIM-based building Life Cycle Assessment (LCA). The section presents the multidisciplinary design team involved and explains the availability of BIM models under a Creative Commons license. The section also discusses the design process, the information content in models for different project phases, and the use of IFC for quantity data in LCA calculations.
The contents of the appendices are as follows:
  • Appendix A provides a comparison of an LCA standard (prEN 15978) to IFC 4.3.
  • Appendix B provides a comparison between several classification systems.
  • Appendix C lists the BIM models and their authors
  • Appendix D provides example BIM specification documents of the architectural, structural, HVAC, and electrical BIM models
  • Appendix E provides links to educational videos supporting practitioners in learning BIM-based building LCA
  • Appendix F provides instructions for BIM-based material inventory in native Nordic languages and in Estonian.
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