Detailed guide to BIM modelling for LCA automation

Detailed guide to BIM modelling for LCA automation

The main goal is to ensure that your BIM model contains sufficient information for LCA purposes. BIM models always contain a large amount of information about your building, however, for your LCA calculation you only need some of this information. Below provided is a detailed checklist to follow to design and check a BIM model for you LCA automation

Material labeling - Apply clear and consistent material labeling

When modelling

Apply clear and consistent material labeling. Verify if the materials are labeled correctly and understandably (using specific technical references is fine). You can use e.g. Ready-mix concrete or Cast-in-place C30/37 or Steel stairs, but avoid [NO MATERIAL], Airspace, Foreground, White, etc. You can use your own language.
Use specific material labels when possible (e.g. Metal – Steel S355, Concrete – Insitu Nwt – C20/25), and do avoid contradictory definitions, e.g. define object material as 'Concrete' and object name as 'Brick'. Verify if the materials are labeled correctly and understandably (using specific technical references is also fine). So you can use e.g. Ready-mix concrete or C30/37, but avoid [NO MATERIAL], Airspace, Foreground, Background

When checking

Does your material list contain individual materials such as “Concrete”, “Cast-in-place-concrete”, “steel”, “gypsum board” etc (in your own language) or is it something else?
If some of the labels are named as something else than individual materials or as technical references to e.g. steel or concrete strength classes, for instance, “Default wall” or “White”, then the name actually does not tell what material is in question and it cannot be used to identify the environmental impacts associated with the material automatically.

To solve this, open the detailed view of the label and check if some other material information category (such as type or name contains information on what the material is. If all the materials selected are the same fix the name in your BIM tool, or export the data to Excel from One Click LCA and continue to correct the labels there.
  1. If you cannot figure out what the material is, check design documents or check up the model with your modeler. You can edit the information in your modeling software.
  2. If some of the labels contain several different materials and the element is modeled as a single unit, you need to be able to split the materials in the import process or in the excel. If you use an excel spreadsheet, you can just split the material into as many separate rows as you need. Optionally, you can map the data to some of the ready constructions in the import process. You’ll be able to modify the individual layers in the building material input form if needed.
  3. If you choose to split the element to different materials in the import, you need to map the data to “decide later” mode and split it to several rows in One Click LCA building materials query page after the import has been completed.
Element definitions in Autodesk Revit – One Click LCA allows adjusting the exported names directly

Element layering - Prefer layered elements for multi-material objects

When modelling

When you add a multi-layer object, for example, an external wall, apply objects that contain the appropriate materials with relevant thicknesses, including eventual air spaces. If your objects are defined as solid objects and represent for example internal walls, apply labels such as 'Internal wall, gypsum + steel studs' to indicate it’s a build-up of several layers.

When checking

Check if layered structures have been detailed. This will tell you if you should map the materials to solid materials or to constructions or impact profiles containing the whole structure.
Here are some examples:
  1. External walls: the wall may be simplified and presented as a solid material, even if it consists of at least four discrete layers of materials, possibly more. Map it to suitable construction.
  2. Gypsum board walls / dry walls: Gypsum board should not be more than 24 mm thick. If it is thicker (for instance 100 mm), it probably contains the full structure including studs. Depending on your studs, map it to suitable construction.
  3. Metal roof: Check how thick it is, the metal roof layer is only a few millimeters thick. More thick structure means that the roof that actually contains other material such as trusses or insulation has been modeled as a solid block.
  4. Windows: Check if the window parts are modeled separately or simplified as a solid block. For instance, 2-layer window glazing might be presented as a 5 cm thick block even though it consists of air and glass. Also, check if window or external glass wall frame is modeled separately or if the whole window is one block. Most of the time you’ll want to map windows to a relevant window object.
All materials which are modeled as solid elements but should be containing several components can be addressed in three ways:
  1. You can map it to suitable construction or material for the whole structure (such as window or drywall) instead of a material and when necessary edit the material quantities in the building materials input form,
  2. Split the data in excel, or
  3. Mark such elements as 'decide later' and add split them in building materials question form manually or use the “Split” feature that can be found in the menu at the end of the row".

Hollow objects

When modelling

When objects are meant to be hollow, model them as hollows or otherwise indicate that in labeling. If hollow objects are represented as solids, call your slabs hollow core slabs.

When checking

Check if hollow objects are modeled as solids. This will tell you if you should map the materials to solid materials or if you need to reduce the amount of material or map them to hollow objects.
Here are some examples:
  1. Steel columns and beams: Zoom in to see if the structure is actually modeled as a structure or as a solid block (such as a solid column or solid wall for instance). If they are modeled as a solid block, then you need to find out, how much of the solid element actually the materials make.
  2. Hollow core concrete slabs: in structural models, these are often modeled so that the holes are included. In such cases, these need to be mapped to pure concrete and reinforcement. Please note that most hollow core concrete slabs are defined so that the volume contains the holes. Hollow core slabs should be mapped directly to hollow core slab objects if airspaces are not defined.

Reinforcement - Included/excluded reinforcement steel

When modelling

Export the model with reinforcement steel included. Structural models can be saved with reinforcements or omitting them for simplicity. If you have a model without reinforcement steel included in concretes, you will need to add back the right ratio of reinforcement by hand when using the model for LCA.

When checking

Check if reinforcement has been modeled and included in your BIM model. Look for steel objects and see if they are isolated columns, or if you can also find smaller objects embedded in concrete.
  1. If your model was created for structural purposes, it has very likely contained reinforcements. They might not have been exported when the model was created. This can be addressed by exporting the model again with setting defining as reinforcements to be included separately.
In One Click LCA if you have reinforcement included, match concrete to ready-mix concrete and reinforcement to reinforcement. If not match concretes to concrete elements including reinforcement or similar constructions, or add the missing reinforcement steel manually later.

If you need to add reinforcement only for one or a few rows, you can also use the Split feature (available on a row of the concrete product under More Actions). The split feature will have to be applied on a row by row basis. If you need to process a large number of rows you can add up the quantities and add a single lumped row for reinforcement steel into your bill of materials.


Concrete stairs – accurately modeled and best mapped to concrete stairs directly to avoid needing to add reinforcement

Classifications - Checklist for material classification

When modelling

Check that those elements are properly classified in terms of IFC Class. This will avoid ambiguities and errors in the use and analysis of the model. The classification is likely also going to be used for filtering, so your scope might be off unless the classification is correct.

When checking

To understand how the data will be grouped and allocated to different questions in One Click LCA building materials input form, check the classification of your materials. This uses the native classification of the software you use, e.g. Revit, or in case of IFC models, IFC Class. Open the material classes and check which classes the model contains.

You should also check the content of each IFC class:
  1. BEAMS: Some slab elements such as Hollow core concrete slabs are often modeled as beams.
  2. COLUMNS: Check if your columns just contain columns or if they contain other elements. If so, make sure to change their class in the mapping page or do it in excel.
  3. FOOTINGS or FOUNDATIONS: Does your model contain footings or foundations? And if it does are the marked to a separate class or are they modeled as part of columns /slabs or similar? If they are part of other classes check if there is a parameter that enables separating them.
  4. SLAB: this normally covers slabs for floors, roofs, and balconies. Thus, in One Click LCA this information will be automatically added to Horizontal structures question. Make sure if all the slabs modeled as slabs, if they are not, check in which category the remaining slabs are located.
  5. WALLS: Do you have external and internal walls separately or are all of your walls just modeled as WALLS?  If they are modeled together, check if some other parameter such as TYPE contains more information that allows you to separate between different wall types and use it in combine settings so that you can separate them in mapping (or separate data in excel). If you are working with BREEAM certification, you might also need to separate between the walls above ground and below ground level. Check if you have some parameter to separate between these and use this information for combining your materials correctly. If there is no clear way to separate them, modify information in your model. In that way, you have enough information for your mapping process.

Scope - Model only the required scope

When modelling

Do not worry about issues in parts of the model not needed for LCA. For example, LEED v4 LCA requires only structure and enclosure to be included, and many building certification systems such as BREEAM consider building site and installations as optional elements in LCA (though they may be required by a particular project to achieve higher rating). Verify the required scope from your client and focus on that.

When checking

Check if your model has all the data you need for your desired outcome or if you need to add something later on.
Typical elements to check:
  • Finishing materials (never present in a structural model, likely present in the architectural model)
  • External walls (might not be present in a structural model)
  • External layer of walls and roof (often not separated in models)
  • Foundations (normally present in the structural model, might be missing from the architectural model)
  • Windows
  • Doors
  • Light internal walls
  • Building technology
If you have a detailed model it might be also valuable to check which of the CLASSES are not necessary for your calculation. One Click LCA filters CLASSES automatically based on the typically needed ones for certain certification scheme but sometimes the CLASSES are used in a different manner.
Examples of materials that are normally not needed in LCA: Flow fittings, Furniture.
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One Click LCA also allows adding any materials to the model separately of the model. You can add them easily as parts or numbers of units or use some simplified mechanisms as well.

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