MEP Clash Detection Checklist Before Issuing Shop Drawings

Clash detection is often treated as a button in the software: run the test, get a clash list, done. In reality, a list of thousands of clashes without rules paralyses coordination. Nobody knows which clashes matter or who should fix them.

This checklist is for MEP engineers, BIM coordinators and contractors who want clash detection to produce decisions, not just reports. The principle is simple: prepare the model properly, test with clear rules, and close every issue with an owner and a deadline.

What is MEP clash detection?

Clash detection is checking the federated model of all disciplines for elements that collide or violate clearance, before anything is installed on site.

There are two main types:

• Hard clash: two elements intersect, such as a duct passing through a beam.
• Soft (clearance) clash: no collision, but required space is violated — unit service space, insulation thickness, or maintenance access.

Stage 1 — Model preparation

1. Same coordinates and levels. All models (architectural, structural, MEP) use shared coordinates and identical levels. Without this, test results are meaningless.
2. Sufficient detail. MEP elements are modelled at real size, including insulation, main hangers and fittings. Single lines cannot be clash-tested.
3. Clear naming and systems. Every element has the correct system type and workset, so clashes can be filtered by discipline.
4. Temporary elements removed. Delete reference elements, sketches and duplicate objects that would generate false clashes.

Stage 2 — Test rules

5. Agreed clash matrix. Define which pairs are tested, e.g. ducts vs structure, pipes vs ducts, cable trays vs sprinklers. Not every pair needs testing at every stage.
6. Defined tolerances. Set hard-clash tolerance and clearance distances per element type, so small irrelevant clashes do not flood the report.
7. Test by zone. Run tests per floor or area. Zone reports are easier to route to the right team.

Stage 3 — Priority and resolution

8. Group clashes. One duct hitting ten beams is one issue, not ten. Grouping shrinks the report dramatically.
9. Set a give-way hierarchy. A common rule: gravity elements (drainage) and large elements (main ducts) take priority; small pipes and cable trays that are easier to reroute adapt.
10. Every issue has an owner and deadline. Record who fixes it, in which model, and by when. Without this, the same issue returns in the next test.

Stage 4 — Close-out

11. Retest after revisions. Run the same test to confirm issues are truly closed and no new clashes appeared.
12. Lock areas before shop drawings. Issue shop drawings only for areas marked clash-free, and record the model version they are based on.

Checklist summary

| # | Point | Stage | |---|---|---| | 1–4 | Coordinates, detail, naming, clean-up | Model preparation | | 5–7 | Matrix, tolerances, by zone | Test rules | | 8–10 | Grouping, hierarchy, owner & deadline | Priority | | 11–12 | Retest, lock area | Close-out |

The most common mistakes

• Testing too early, while the model is still conceptual, so the report cannot be acted on.
• Ignoring soft clashes. An installation can pass the test yet be impossible to maintain because there is no service space.
• Leaving the site team out. Installation sequence and method determine which solutions are realistic.

Conclusion

Good clash detection is a process, not a feature. With properly prepared models, agreed rules and disciplined issue close-out, rework on site can be cut before it starts — on screen.

The SOKANTARA MEP BIM team runs this process for consultants, main contractors and building owners across Indonesia — and because we also install MEP systems, every coordination solution is tested against site reality. Send us your model or drawings for review.