A Clash-Free Model Can Still Fail in the Field. Here Is Where BIM Coordination Actually Breaks
A clash-free model is not automatically a coordinated model.
A default hard-clash test answers a narrow question: do two modeled objects occupy the same physical space? It does not always tell us whether a routing decision is code-compliant, buildable, accessible or acceptable to another trade.
That is why our general rule at DDG is simple. If one trade makes a significant move, that trade should communicate the change to the other affected trades. Everyone then has an opportunity to review the area from the perspective of their own scope.
Coordination is multidisciplinary. A plumbing contractor may understand the plumbing system very well, but cannot be expected to recognize every electrical, mechanical, structural or architectural consequence without involving those teams.
A small plumbing move created a large field problem
On one project, the plumbing contractor shifted a pipe after the area had already been coordinated. The move appeared relatively simple. The revised route did not create a hard clash with another modeled object.
The problem was not visible as a physical collision.
The pipe passed above an electrical panel recessed in the wall. The project team determined that this routing did not comply with the dedicated electrical equipment space required by the applicable adopted code and project requirements. The electrical contractor had already installed slab sleeves serving that panel, so the late plumbing adjustment could not be treated as an isolated routing decision.
Plumbing had to find another route and complete additional field adjustments. What looked like a small, clash-free move in one trade's model created rework because the wider installation had not been reviewed.
The lesson is not that trades should stop adjusting their models. Models must change as designs, submittals and field conditions develop. The lesson is that the party making the change must also make the change visible.
Clash detection does not understand design intent
Recent practitioner discussion has focused on when a coordination item should become a formal request for information. A useful threshold is whether the proposed solution goes beyond the design intent of the contract documents or affects cost, schedule or another documented requirement.
That distinction matters because coordination teams should not quietly redesign another discipline's work to close an issue.
A model change may require broader review when it affects:
equipment working or dedicated space;
access and maintenance clearances;
fire-rated assemblies;
structural openings or sleeves;
ceiling height or headroom;
slope and drainage requirements;
installation sequence;
quantities, cost or schedule; or
information that should appear in the contract documents.
If the team cannot confirm that the change remains within the coordinated design intent, the issue should be documented and routed to the responsible party.
The trade making the move should own the notification
Change communication becomes unreliable when everyone assumes someone else will notice.
At DDG, we prefer a direct ownership rule: the trade making a significant adjustment is responsible for notifying the coordination team. The coordinator can then reopen the affected area, assign reviews and record the decision.
The notification should include enough information for another trade to evaluate the impact:
what changed;
why it changed;
where the change occurred;
which systems or areas may be affected;
whether the change alters previously approved openings, sleeves or supports; and
whether a design response or RFI is required.
This does not need to become an administrative burden for every minor model cleanup. The focus should be on changes that affect routing, elevation, clearance, access, installation sequence or previously coordinated work.
Closed areas need controlled reopening
An area sign-off should not mean that the model can never change. It should mean that later changes are controlled.
When a trade revises a signed-off area, the affected coordination items should be reopened or a new issue should be created. The team should review the complete run, not only the location where the original clash disappeared.
That final point is important. A local move may solve one collision and transfer the problem ten feet downstream. It may also cross a clearance zone without touching the equipment itself.
The plumbing reroute in this example was geometrically clean. It still failed the multidisciplinary review that should follow a significant change. BIM coordination works when trades communicate their moves and allow the people responsible for the surrounding systems to evaluate the consequences.
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