Repair walls with openings exported to ifc from ArchiCAD

Comments

• theoryshaw

  February 18 edited February 18

  I'm not an archicad user, but...

  
  

  here's a possible AI answer, for your architect collaborator to try

  Why the walls are Brep right now

  The Graphisoft documentation states this explicitly and unambiguously:

  "If the Export gross geometry option is unchecked, then elements cannot be created using extrusion. In this case, extruded elements with holes are exported as BREP."

  That one unchecked box is the root cause. When it's off, ArchiCAD computes the boolean result of wall minus all its openings and hands you the pre-cut mesh as a Brep. The IfcOpeningElement entities become decorative — they describe voids that are already baked into the geometry. When it's on, the wall is exported as its full uncut gross solid, and each door/window void is expressed as a proper IfcOpeningElement with IfcRelVoidsElement linking back to the wall. That's exactly the structure Revit's IFC importer knows how to consume as a system family with editable hosted openings.

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  The full translator recipe

  Tell the architect to open File → Interoperability → IFC → IFC Translators, duplicate their current translator to a new one (don't mangle the original), and set the following under Geometry Conversion:

  1. Export all model elements' geometry as: Parametric (Extruded/revolved) Or use Parametric with exceptions if they want junctions on plain walls to be correct:

  • Elements in Solid Element Operations: Extruded/revolved
  • Elements with junctions: Extruded/revolved without junctions (already their current setting — this is fine for Revit)

  2. ✅ Check "Export gross geometry of elements (Export holes separately)" This is the critical fix. It enables the wall to be a SweptSolid and moves the voids into the IfcOpeningElement hierarchy where they belong.

  3. Material preservation mode (IFC2x3 schema): Never explode elements Do NOT use "Explode all elements into parts" for the Revit workflow. That mode turns the IfcWall into a geometry-less container and puts each composite skin into its own IfcBuildingElementPart. Revit will not interpret that as a system family wall. You want a single IfcWall with the layer set attached to it.

  4. Partial Structure Display — this is a view/export option, not strictly translator-side, but critical: the file you received has the header flag Option [Partial Structure Display: Core of Load-Bearing Elements Only]. That's why your Brep walls are 200mm Y-extent while BaseQuantities.Width says 410mm — you're only getting the structural core. The architect should export with Entire Structure so the composite build-up is represented in the geometry, not just in the quantities.

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  For IfcMaterialLayerSet

  Switch these on under Data Conversion in the translator:

  • ✅ Building Material Properties — currently OFF in your file. This is what causes ArchiCAD to emit IfcMaterialLayerSet / IfcMaterialLayerSetUsage attached via IfcRelAssociatesMaterial to each wall. Without it, material data simply isn't written.
  • ✅ Element Properties — currently also OFF. Needed for Revit to pick up the property sets.
  • ✅ IFC Base Quantities — already ON in your file, keep it.

  With "Never explode" + Building Material Properties on + gross geometry checked, ArchiCAD will produce walls structured like this in the IFC:

  IfcWall
   ├─ Body / SweptSolid → IfcExtrudedAreaSolid (full uncut gross section)
   ├─ Axis / Curve2D → IfcPolyline
   ├─ IfcRelAssociatesMaterial → IfcMaterialLayerSetUsage → IfcMaterialLayerSet
   │   ├─ IfcMaterialLayer (plaster, 10mm)
   │   ├─ IfcMaterialLayer (concrete, 300mm)
   │   └─ IfcMaterialLayer (insulation, 100mm)
   └─ IfcRelVoidsElement → IfcOpeningElement (one per door/window)
        └─ Body / SweptSolid → IfcExtrudedAreaSolid (the void shape)
             └─ IfcRelFillsElement → IfcDoor / IfcWindow
  

  Revit's IFC importer maps IfcMaterialLayerSetUsage to a compound wall type, matches each layer's material name to Revit materials, and creates a proper hosted door or window family from the IfcDoor/IfcWindow in the filling element. That's the best achievable result from the ArchiCAD → IFC → Revit path.

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  What to realistically expect

  Even with perfect settings, two limitations remain:

  • Junction geometry with Extruded/revolved without junctions: walls will be simple rectangular extrusions that overlap at corners rather than being properly mitered. This is fine for Revit system families, which redo the junctions on import using its own wall cleanup rules. It actually works better for Revit this way.
  • Complex wall profiles: any wall that isn't a straight prismatic extrusion (tapered, polygonal footprint, curved) will still fall back to Brep regardless. The parametric option only covers vanilla straight walls. Those you'll still need to handle with the repair script.

  https://help.graphisoft.com/AC/25/INT/_AC25_Help/121_IFC/121_IFC-37.htm
• Vlad

  February 23

  "That one unchecked box is the root cause." is typical chatbotspeak. Just checking the box leads to a slightly different body representation (CSG), but still not what I need (SweptSolid). Thanks anyway, it did bring some useful stuff to my attention.

  It turns there's a lot of settings for ifc export from ArchiCAD and optimizing it via calls and emails with the architect was a little difficult. However, we did find a good solution for our particular case in the end. He used the default export settings from ArchiCAD version 25, which he transfered to his current version 28 (based on an older dataset we found that had the desired properties, so we tried to recreate the conditions). The resulting export had walls as SweptSolids and Revit reconstructed them nicely as system families and opening families. For some reason, ArchiCAD 28's default export settings lacked the correct classification rules and exported everything as BuildingElementProxy. I fail to see why Graphisoft would change this, so I think there may be something off about the architect's local installation. Can't say for sure, though, because I don't have the software and I don't want to pester the architect with further investigation after getting what I needed.

  Most importantly, I can confirm that it's possible to go from ArchiCAD to Revit via ifc and retain walls with openings as editable system families. And shoutout to Bonsai for being a tool that allowed me to understand exactly how the geometry needs to be defined.