2D vs 3D Clash Detection
When to use 2D PDF analysis vs full BIM coordination, and how they complement each other.
The Core Difference
2D Clash Detection
Analyzes PDF construction drawings to identify coordination issues, code violations, and missing information. Works with what contractors actually receive: 2D drawing sets.
- Works with PDFs (no model required)
- Catches specification mismatches
- Identifies code compliance issues
- Fast setup and results
- Lower cost per project
3D Clash Detection
Uses BIM models to find geometric conflicts where objects occupy the same space. Requires full 3D models from all trades coordinated in software like Navisworks.
- Precise geometric conflicts
- Clearance and tolerance checking
- 4D scheduling integration
- Requires complete BIM models
- Higher setup cost and time
What Each Approach Catches
| Issue Type | 2D Analysis | 3D BIM |
|---|---|---|
| Duct through beam (geometric) | Partial | Excellent |
| Pipe elevation conflicts | Good | Excellent |
| Door schedule vs floor plan mismatch | Excellent | Poor |
| Spec vs drawing material conflicts | Excellent | None |
| Code compliance (ADA, fire, egress) | Excellent | Limited |
| Missing dimensions/notes | Excellent | None |
| 4D sequencing conflicts | None | Excellent |
| Maintenance clearance violations | Partial | Excellent |
| Cross-discipline coordination | Good | Excellent |
The Reality of Most Projects
Here is what nobody tells you about BIM clash detection: it only works when everyone models everything, and the models match reality.
On most projects, you get a mix: some trades have BIM models, others submit 2D shop drawings. The architect's Revit model is version 47 but the structural engineer is on version 43. The MEP subcontractor's model is gorgeous but does not match what they are actually installing.
Meanwhile, the construction documents are what you build from. The 2D PDFs are the legal contract documents. If they have conflicts, those conflicts show up in the field, regardless of what the BIM model says.
Smart teams use both approaches: BIM coordination during design to optimize layouts, and 2D analysis on the final documents to catch what slipped through.
When to Use Each
Use 2D Analysis When:
- You do not have complete BIM models
- Reviewing bid documents before pricing
- Checking shop drawings from subs
- Verifying code compliance
- Budget or timeline precludes full BIM
- Final CD review before construction
Use 3D BIM When:
- All trades have quality BIM models
- Contract requires model-based coordination
- Complex MEP routing optimization
- 4D scheduling is critical
- Prefabrication depends on coordination
- Owner requires as-built BIM deliverable
The Combined Approach
The best results come from layering both methods:
- 1Run BIM coordination during design development to optimize MEP routing
- 2Use 2D analysis on each CD milestone (50%, 90%, IFC) to catch spec conflicts and code issues
- 3Review shop drawings with 2D AI analysis before approving
- 4Final 2D check on issued-for-construction documents
Related Comparisons
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