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3. Instructions for BIM-based material inventory

This description focuses mainly on assessing carbon hand and footprint during the life cycle of a new construction project, not projects focused on renovating the existing building stock, as only one Nordic country, Norway, includes major renovations in its LCA-related legislation for the time being. It is important to note that due to the nature of LCA calculations of renovation projects, the requirements for BIM differ slightly in these types of projects. The following instructions have been translated into Nordic languages and Estonian (Appendix E: Instructions for BIM-based material inventory in native Nordic languages).
BIM modelling should follow the EN ISO 19650 standard series principles for building information modelling. Countries may have more specific national standards or guidelines based on this standard (e.g., “RAVA3Pro” in Finland, “Tillämpningsanvisningar BIM” being developed in Sweden, “SIMBA” for public buildings in Norway and DS/EN ISO 19650 and Molio’s guidelines in Denmark). A European standard, CEN/TC 442, is also being developed. The EN ISO 19650 standard series includes conventions such as project information requirements and managing and storing model data.

3.1 General requirements for BIM

The information required for LCA is like the information needed for cost calculations. Building elements must be modelled so that the quantities are generated correctly in the design model and consequently exported correctly into the IFC model. For BIM to be most useful in LCA calculation, the general requirements for BIM modelling are:
  • High-quality modelling - According to national best practices
  • Precise - The model's contents are accurate, and the elements are modelled to be exported correctly into the IFC model.
  • Descriptive and informative – The model's contents consider the needs of the end-users of the BIM.
    • A description file is provided along with the BIM model specifying which information fields contain relevant data and for what purposes the model is intended. Software may generate unintended information, which may not be accurate, and thus, it is relevant to specify which fields are intended to be used.
  • Correct naming and categorising - According to national standards or best practices (or project-specific naming, in which case the naming conventions must remain the same throughout the entire project)
    • All building elements are given descriptive type names, also used in other documents. For example, all wall elements with the same structure have the same wall type identifier defined in the BIM, which is also found in the structural plans. This enables the retrieval of information from sources outside of the BIM models.
    • When the manufacturer and product names of installed products are known (mostly in the case of as-built models), these are disclosed in the BIM to support the mapping of product-specific environmental product declarations (EPD). Alternatively, a mapping of product type names in the model to the installed products is provided externally.
    • If installed products are not specified, materials are named in a harmonised way throughout the models, utilising established classifications where possible. The materials are either recorded in the model or referenced externally with the type name in the BIM model.

3.2. BIM specification documents

The contents and modelling principles of the BIMs are documented and described in  according to national best practices. The BIM specification format employed is based on a Finnish BIM specification convention.
The specification documents should disclose, for example, which information fields are generated in the information model. This is important, as software may generate information (additional fields automatically) that may not be accurate.
The specification document is also used as a tool for communicating information about the completeness of the model by indicating, for example, any assumptions made by the designer or any yet unmodelled elements. This is relevant, particularly for modelling done in the earlier stages of the design process. Information added as a draft (structure type, material, etc.) and subject to change should also be clearly indicated in the BIM specification document.

3.3. Required data in the BIM model for information take-off

Quantities and properties within BIM models are extracted through information take-off features in BIM or IFC software. Below are listed data that are required, at minimum, to perform LCA. The quantity take-off units are further discussed later in the section “Managing the overlap between BIM models”.
LCA software may currently support direct IFC input, and these features may be employed in such cases. It is, however, worth noting that the programs’ handling of preferred units may differ from the ones presented in this document. Here, we present how to extract information from the models and then import them into the LCA software. This way, if manual verification or conversion of quantities is required, they can be performed before importing the quantities to the LCA program. Manual selection of the structures may also be necessary if the building classification required by the normative LCA is not readily available in the BIM model or the modelled content differs from the LCA system boundary.
High-quality, precise, descriptive, and informative data in the information take-off increases the efficiency and accuracy of the process both during the export from IFC software and the import of information to LCA software. The most important requirements are listed in the following:

Building element

Building element classification is done according to the national best practices. The building element type is used to categorise emissions according to the building element. Categorisation according to the building element is crucial for the LCA assessment, as it enables component-level assessment.

Component type (class)

Crucial for the import of data to LCA software. Component types are, e.g. slab, column or beam.
Displays by which tool in the modelling software the component has been generated and enables a level of quality assurance that information is correct in the model.

Type (Reference)

Built element type according to national best practice and depending on what has been agreed on in the project. The reference is descriptive information about the element, which corresponds with naming in other design documents. For example, the built element type of a ground floor slab.

Quantity information

  • Volume - Crucial for building elements for which the preferred unit is volume (m3)
  • Area - Crucial for building elements for which the preferred unit is area (m2).
  • Linear meter - Crucial for building elements for which the preferred unit is length (m).
  • Number of pieces - Crucial for building elements for which the preferred unit is the number of units (unit).

Material

Material information is used to describe the material used in the structure. Displays the material used in the component, e.g., wood, concrete, or steel. Additional information related to the material, such as the strength class of concrete, may be disclosed in sources for supplementary data. Displays the thickness of material layers in structure (when available).

Total thickness

The total thickness of a structure is crucial, especially for components of the structural frame.

3.4. Managing the overlap between BIM models

Architectural and structural BIM models are the main sources of information for life cycle assessments. Information on building parts not available in any BIM model (e.g., internal finishes and number of elevators) must be supplemented from other design documents. The availability of information depends on the stage of the modelling. LCAs often require estimating material and amounts in project phases where designs are not yet available or quantity take-off from the model cannot be performed. This is especially typical for early-phase assessments. Draft information may be added to the BIM to support the early phase LCA. However, such information should be clearly labelled as a draft to inform the LCA specialist that the information is subject to change. It is recommended that information on the maturity level is disclosed in the BIM description document or in a part of the model where it can be easily identified by the life cycle assessor.
Based on the EN 15978 standard, Table 2 describes the recommended BIM model to be used as a material and quantity information source in building permit and as-built phases. Furthermore, the table shows with which units of measurement the relevant building elements are catalogued for LCA calculation from the BIM models. The table also shows if the information is based on a generic design-based estimate. This is often necessary, especially at the building permit stage, because accurate information on the building element is not yet available. If the preferred unit for the structure is area, length, volume or other information other than the number of units, then these measures are supplemented with additional information about the building part, such as the materials in the structure. Table 2 also presents the building parts which typically require assumptions.
The range of building elements included in each national assessment method varies, and thus, not all categories presented are necessarily included in the national assessment method for all countries. The BIM model is recommended to include the building element classification according to the national best practices.
Table 2. The breakdown structure and phasing of the components in BIM models
Arch BIM = architectural BIM; Arch design = architectural design; no of units = number of units; QTO = quantity take-off; *Sustainability of construction works. Assessment of environmental performance of buildings. Calculation method.
prEN 15978*
QTO
Lifecycle stage
Building parts
Building elements and processes
QTO
Building permit
As-Built
Facilitating works
Temporary/Enabling works
 
 
 
Pre-construction works
Specialist groundworks
 
 
 
Work on the existing building
Demolition and alterations
 
 
 
Substructure
Foundations
m3
Structural estimate
Structural BIM
Piles
m
Structural estimate
Structural BIM
Basement walls
m2
Arch BIM
Structural BIM
Retaining walls
m2
Arch BIM
Structural BIM
Waterproofing
m2
Arch BIM
Arch BIM
Ground floor construction
m2
Arch BIM
Arch BIM
Columns
kg (steel structure),
m3 (concrete, wood)
Arch BIM
Structural BIM
Frame
Beams
kg (steel structure),
m3 (concrete, wood)
Arch BIM
Structural BIM
Shear walls
kg (steel structure),
m3 (concrete, wood)
Arch BIM
Structural BIM
Superstructure
Upper floors
m2 (net area)
Arch BIM
Arch BIM
Balconies
square meters, meters
Arch BIM
Structural BIM
Roof
Roof structure
m2
Arch BIM
Arch BIM
Weatherproofing
m2
Arch BIM
Arch BIM
Stairs and ramps
m3
Arch BIM
Arch BIM
Fabric
External envelope
External walls
m2 (net area)
Arch BIM
Arch BIM
Windows
No. of units
Arch BIM
Arch BIM
External doors
No. of units
Arch BIM
Arch BIM
Shading devices
No. of units
Arch BIM
Arch BIM
Internal walls
Internal walls – load bearing
m2 (net area)
Arch BIM
Structural BIM
Internal walls – non-loadbearing
m2 (net area)
Arch BIM
Arch BIM
Internal doors
No. of units
Arch BIM
Arch BIM
Finishes
External finishes
Cladding
m2
Estimate, based on arch design
Arch BIM
Coatings
m2
Estimate, based on arch design
Arch BIM
Internal finishes
Wall finishes
m2
Estimate, based on arch design
Arch BIM, based on room geometry
Raised floors
m2
Estimate, based on arch design
Arch BIM, based on room geometry
Floor finishes
m2
Estimate, based on arch design
Arch BIM, based on room geometry
Ceiling finishes
m2
Estimate, based on arch design
Arch BIM, based on room geometry
Water systems
Hot water distribution
m (pipes, insulations),
No. of units
Estimate, based on arch design
MEP BIM
Cold water distribution
m (pipes, insulations),
No. of units
Estimate, based on arch design
MEP BIM
Water treatment systems
m (pipes, insulations),
No. of units
Estimate, based on arch design
MEP BIM
Rainwater systems
m (pipes, insulations),
No. of units
Estimate, based on arch design
MEP BIM
Sewage systems
m (pipes, insulations),
No. of units 
Estimate, based on arch design
MEP BIM
Lighting
Internal lighting
No. of units 
Estimate, based on arch design
MEP BIM
External lighting
No. of units 
Estimate, based on arch design
MEP BIM
Building services
Electricity generation and distribution
m (wires), No. of units
Estimate, based on arch design
MEP BIM
Renewable generation systems
No. of units 
Estimate, based on arch design
MEP BIM
Heating systems
No. of units 
Estimate, based on arch design
MEP BIM
Cooling systems
No. of units 
Estimate, based on arch design
MEP BIM
Ventilation systems
m (ducts, insulations)
No. of units
Estimate, based on arch design
MEP BIM
Conveying systems
No. of units 
Estimate, based on arch design
MEP BIM
Telecoms and data systems
No. of units 
Estimate, based on arch design
MEP BIM
Fire protection systems
m (pipes),
No. of units
Estimate, based on arch design
MEP BIM
Communication and security installations
m (wires),
No. of units
Estimate, based on arch design
MEP BIM
Additional categories not specified in prEN 15978
Accessories
Furniture systems
Built-in furniture
No. of units
Estimate, based on room types
Arch BIM
Movable furniture
No. of units
Estimate, based on room types
Estimate, based on room types
Appliances
No. of units
Arch BIM
Arch BIM
Sanitary fittings
No. of units
Arch BIM
MEP BIM
Transportation systems
Elevators
No. of units
Estimate, based on room types
Arch BIM
Escalators
No. of units
Estimate, based on room types
Arch BIM
Mowing walkways
No. of units
Estimate, based on room types
Arch BIM
Craneways, lifting gear and other transport elements
No. of units
Estimate, based on room types
Arch BIM
Safety systems
Railings
m
Arch BIM
Arch BIM
Handrails
m
Arch BIM
Arch BIM
Areas
Gross floor area
m2
Arch BIM
Arch BIM
Net room area
m2
Arch BIM
Arch BIM
Appendix A: prEN 15978 comparison to IFC 4.3 (ISO 16739-1:2024) shows how the EN 15978 building component categories are expressed according to EN ISO 16739-1, the IFC standard. IFC, Industry Foundation Classes, is not a classification system. In contrast, in a BIM model according to the IFC standard, the identification of building elements requires a class, a class subtype and often also property attributes. Under the IFC standard, these are called IFC entity class, PredifinedType and property (grouped into property sets). For example, to identify a building component group 'exterior walls' in the IFC model according to EN 15978, all components belonging to it must have the class IfcWall, the PredefinedType SOLIDWALL and the IsExternal property of the Pset_WallCommon group set to TRUE.
Building elements and components that may be included or excluded in the BIM (such as parking garages, often included in BIM but not necessarily included in LCA) are agreed upon separately in the project, and included or excluded elements are documented in the building information model description. The inclusion or exclusion of building elements may vary depending on the local best practice and building area specification used. The inclusion of building parts relevant to the defined assessment method is ensured through quality assurance of the calculation.
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