MEP Clash Detection Checklist Before Issuing Shop Drawings

Clash detection is often treated as a button in the software: run the test, get a list of clashes, and you are done. A list of thousands of clashes with no rules behind it stalls coordination, because 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 end in decisions the site team can act on. 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 checks the combined model of all disciplines for elements that collide or break a clearance rule, 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: the elements do not touch, but required space is missing, such as service space around a unit, 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. If they do not, the test results mean nothing.
2. Enough detail. MEP elements are modelled at real size, including insulation, main hangers and fittings. A single line 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 create false clashes.

Stage 2: Test rules

5. Agreed clash matrix. Define which pairs are tested, for example ducts against structure, pipes against ducts, and cable trays against sprinklers. Not every pair needs testing at every stage.
6. Defined tolerances. Set the hard-clash tolerance and clearance distance for each element type, so the report is not filled with small clashes that do not matter.
7. Test by zone. Run tests per floor or area. A report for one zone is easier to send to the right team.

Stage 3: Priority and resolution

8. Group clashes. One duct hitting ten beams is a single issue. Grouping makes the report much shorter.
9. Set a give-way hierarchy. A common rule is that gravity lines (drainage) and large elements (main ducts) keep their route, and small pipes and cable trays, which are easier to reroute, move around them.
10. Give every issue an owner and a deadline. Record who fixes it, in which model, and by when. Otherwise the same issue comes back in the next test.

Stage 4: Close-out

11. Retest after revisions. Run the same test to confirm the issues are closed and no new clashes have appeared.
12. Lock areas before shop drawings. Issue shop drawings only for areas marked clash-free, and record which 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 nobody can act on the report.
• Ignoring soft clashes. An installation can pass the test and still be impossible to maintain because there is no service space.
• Leaving the site team out. Installation sequence and method decide which solutions are realistic.

Conclusion

Clash detection only works as a routine: prepare the models, agree the rules, and close each issue. Done that way, most of the rework that would have happened on site is solved in the model instead.

The SOKANTARA MEP BIM team runs this process for consultants, main contractors and building owners across Indonesia. Because we also install MEP systems, we check each coordination solution against how it will be built on site. Send us your model or drawings for review.