BIM Interoperability

Plan and troubleshoot the movement of BIM data between tools: Revit, ArchiCAD, Tekla, Navisworks, and the IFC exchange format in the middle. Covers exchange setup, IFC export/import, federation, clash detection, and the classic failure modes.

When to use

• Setting up an exchange: "how do we get the Revit model to Tekla and back?"
• Fixing a broken IFC export/import (missing geometry, wrong units, shifted coordinates)
• Federating discipline models for coordination in Navisworks
• Running and interpreting clash detection
• Choosing IFC view definitions / model-checking settings

Workflow

1. Establish the exchange chain — who produces, what format, what view, what units, what coordinate origin. Write it down before exporting anything; most interop failures are setup failures.
2. IFC export basics (per authoring tool):
   • Use the current IFC version both tools understand (IFC4 is the safe common denominator; IFC2x3 for legacy tools)
   • Pick the right view: Coordination View for geometry/location, Design Transfer View for detailed elements, Reference View for lightweight reviews
   • Export with explicit units (mm/m/feet — mismatch is the #1 source of scale bugs)
   • Flatten/simplify if geometry breaks: export "coordination" model, not the full parametric one
3. Coordinate alignment — check origin + project base point before federating; translate all models to a shared origin. Common failure: models sharing the same "0,0,0" with different project offsets → everything lands in the wrong place.
4. Federation (Navisworks typical): combine NWD/NWC per discipline; set units; then run clash detective:
   • Hard clashes (geometry overlap)
   • Clearance clashes (with margins)
   • Duplicate items (same element in two models)
5. Clash review — see output format below. Triage by severity and ownership; don't send 3,000 clashes to the GC — group and deduplicate.
6. Round-trip check: after re-import, verify elements counts, geometry scale, and material/type data survived; report what was lost (e.g. parametric relationships rarely survive IFC).

Output format

Clash Report — federated model, Architecture + MEP + Structure
Total: 214 (hard 178, clearance 36) → grouped 41 by grid region
Top groups by severity:
G-12  High  Grid C/4, L2 corridor: duct vs beam (12 instances)
G-34  Med   Grid A/1, L1 mech: panel vs AHU piping (8)
G-41  Low   Grid F/6, L3: lighting vs cable tray (6)
Disposition: 33 resolved/assigned, 8 to review, 0 open-blocking
Exchange health: units OK, origin OK, element count drift +2.1% (expected)

Edge cases & cautions

• Never assume unit parity — always confirm mm vs m vs ft; a single wrong model corrupts the federation.
• IFC loses parametric behavior — doors/windows become static geometry; don't promise "live" round-tripping.
• Phantom clashes — duplicated elements (one model exports twice) and un-joined walls produce noise; clean the model before running clash detection.
• Large models — federate per-discipline NWC, use saved viewpoints, and run clash detection in batches; full-model federation on huge projects will time out.
• IFC export with wrong schema breaks importers — if a tool rejects the file, try re-exporting with a different schema (IFC2x3 → IFC4).
• Don't rely on default export settings — every tool has sub-optimal defaults for interop (e.g. Revit's "shared coordinates" export behavior).

Files

• references/ifc-exchange-guide.md — export/import settings per tool, view definitions, and the round-trip failure catalog.
• references/clash-workflow.md — federating and running clash detection step-by-step.