Case Study: BIM Clash Detection on a Commercial Fitout Saved Two Weeks On-Site

Details have been generalised and client information withheld at their request.

The background

A commercial fitout project in a five-storey office building in Melbourne's western fringe involved a full strip-out and fitout of two floors — new mechanical, electrical and data services, new partitions and ceilings, and a substantial joinery package.

The project's documentation had been produced by separate consultants in separate packages — architectural in Revit, mechanical in AutoCAD, electrical in a PDF-only format. The head contractor's site supervisor had a strong track record on similar projects, but was concerned about coordination between the mechanical ductwork and the new partition and ceiling layouts.

One week before the contractor's planned mobilisation date, we were engaged to run a federated model and clash detection process on the available documentation.

The process

Step 1: Model consolidation. The architectural Revit model was the coordination base. The mechanical consultant's AutoCAD drawings were converted to 3D geometry and linked into the model. The electrical consultant's PDF drawings were insufficient for 3D coordination; the electrical consultant was asked to produce a simplified 3D layout of the main cable tray routes within 48 hours, which they did.

Step 2: Federated model review. With all three disciplines in a single federated model, a visual review identified the most obvious areas of concern before running automated clash detection — the main mechanical duct run on Level 3 was routed at a height that conflicted with the partition wall above the main boardroom entry.

Step 3: Automated clash detection. Running tolerance-based clash detection across the federated model returned 47 hard clashes and 31 soft clashes (clearance violations). Many were minor or located in service riser areas where coordination was straightforward. Fourteen required design resolution before construction.

Step 4: Clash resolution. Each of the fourteen significant clashes was logged with a description, a screenshot, and a recommended resolution. A coordination meeting was held with the mechanical and architectural consultants; eleven clashes were resolved by minor duct rerouting, two by adjusting partition heights, and one required a structural penetration that needed structural engineer approval.

The entire clash detection and resolution process took four working days.

What would have happened otherwise

The site supervisor's concern was well-founded. The main duct conflict on Level 3 — the one visible from the initial visual review — would have been discovered when the ductwork was being installed and the partition framing was already in place. The resolution would have required re-routing installed ductwork, coordinating a return visit from the mechanical contractor, and adjusting the ceiling grid layout.

Conservatively, that single clash would have cost two to three days of programme time and the associated labour and material costs. The fourteen clashes together, discovered progressively during construction, would likely have cost the project the better part of two weeks in cumulative delays.

The broader point

The value of BIM coordination isn't in the technology — it's in having all the disciplines visible in the same environment before the work starts. Problems that are expensive to fix on-site are cheap to fix at the documentation stage.

The four days spent on clash detection and resolution before mobilisation returned a multiple of that time in avoided on-site disruption.

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BIM coordination and clash detection is available as a standalone technical service. Contact us to discuss your project's documentation.