What are IFC versions?

The IFC standard has been through several major versions. The three you'll encounter most often are:

• IFC2X3 is the most widely used version, supported by virtually all BIM software. Most existing models are IFC2X3.
• IFC4 is a newer version with more detailed property definitions and better support for building services. Adoption is growing but not yet universal.
• IFC4X3 is the latest version, extending IFC4 with support for infrastructure like roads, rail, and bridges. It is primarily used on infrastructure projects.

When your BIM software exports an IFC file, it writes the version into the file. Similarly, when someone creates an IDS checklist, they specify which IFC version the checklist is designed for.

Why does a version mismatch matter?

Each version of IFC defines a different set of entities, properties, and data types. A checklist written for IFC4 might reference properties or entities that don't exist in IFC2X3, or that have different names in IFC4X3. When the checker encounters these mismatches, it can't reliably determine whether your model passes or fails because the question it's being asked doesn't make sense for the model it's looking at.

Depending on the severity of the mismatch, you might see:

• Individual specifications skipped: These are shown with a yellow "Skipped" label and a message explaining that the specification was written for a different version. The checker could not run that particular check against your model.
• All specifications failed or skipped: If every check in the checklist targets a different version from your model, none of them can produce reliable results. You will see an error page explaining that the checklist needs updating.
• Results with a warning: In some cases the checker can still run a mismatched check by upgrading the schema internally, but the results may not be accurate. You will see a suggested improvement noting the mismatch.

How to check which versions you have

Your IFC model's version is usually shown in your BIM software's export settings. You can also open the .ifc file in a text editor. The version appears near the top in the FILE_SCHEMA line, for example FILE_SCHEMA(('IFC2X3')); or FILE_SCHEMA(('IFC4'));.

Your IDS checklist's version is set by whoever created the checklist. It is specified in the XML of the .ids file, but you should not need to check this yourself. Data Octopus tells you both versions in the suggested improvement message when there's a mismatch.

How to fix it

The fix depends on your situation:

• If you control the IDS checklist: Update the checklist to target your model's IFC version. If you're using an IDS authoring tool, look for the target version setting. If you're editing the XML directly, the ifcVersion attribute on each specification element controls which version that check targets.
• If you received the checklist from someone else: Ask them to provide a version that matches your model. Share the suggested improvement message from Data Octopus so they can see exactly which versions are involved.
• If you control the IFC export: You may be able to export your model in a different IFC version from your BIM software. Check your export settings. Be aware that converting between versions can sometimes lose data, so check with your project team before changing the export version.
• If neither file is under your control: This is common on projects where the model comes from one party and the checklist from another. Raise the mismatch with whoever is managing the information requirements. The suggested improvement message from Data Octopus gives you the specific details to share.

Which versions are compatible?

Data Octopus follows the buildingSMART IDS standard, which requires an exact match between the model schema and the checklist specification. The checker will only run a specification if it explicitly targets your model's version:

• A model exported as IFC2X3 requires a checklist targeting IFC2X3.
• A model exported as IFC4 requires a checklist targeting IFC4.
• A model exported as IFC4X3 requires a checklist targeting IFC4X3.

A single checklist specification can target multiple versions, for example, both IFC4 and IFC4X3. As long as one of the targeted versions matches your model, that specification will run. Specifications targeting versions that do not match your model will be skipped.

Related suggested improvement messages

You might have arrived at this page from one of these messages:

• "Specification '[name]' was written for an older/different version...": One specific check in your checklist targets a different version. The rest may still work fine.
• "Your checklist was written for a different version... None of the checks could be performed.": Every check in the checklist is incompatible with your model. The checklist needs updating before it can be used with this model.
• "Specification '[name]' could not be checked because it was written for [version]...": This check was skipped entirely because the version mismatch was too severe to produce any useful results.