Clash detection inside Revit: how Collision Manager works without exports
Zakhar Vityk, CEO, Consedge Tech
Most clashes are found late because finding them is a separate job. Someone exports the models, opens a coordination tool, runs the tests, writes a report and sends it back to the people who work in Revit.
For formal coordination between trades, that process is right. For the daily question "did I just route this duct through a beam?" it is far too heavy. This article explains how clash detection in Revit itself works, what makes it usable, and where our own tool, Collision Manager, fits.
Three places to find clashes
| Revit Interference Check | A plugin inside Revit | Navisworks or cloud coordination | |
|---|---|---|---|
| Where it runs | Revit | Revit | A separate application |
| Rules | Category against category | Custom rule sets, filters, tolerances | Full rule sets and clearance tests |
| File formats | Revit models | Revit models and links | Many formats in one federated model |
| Tracking over time | A one-off report | Statuses that survive a re-check | Full issue history |
| Who uses it | Any modeller | Any modeller | A coordinator with training |
| Best for | A quick look | Daily self-checks by designers | Multi-trade coordination |
The middle column is the gap. Designers need more than the built-in check and less than a coordination suite.
How clash detection works inside Revit
- Define the two sets. For example structural framing against ducts and pipes, or a linked model against the host model.
- Pre-filter by bounding box. A cheap test removes the pairs that cannot touch. This step decides whether the check takes seconds or an hour.
- Test real geometry. For the remaining pairs, intersect the solids. Elements from links are moved into host coordinates first.
- Apply tolerance. Ignore overlaps below a set volume or depth, so a pipe that grazes insulation does not become an issue.
- Store the result. Each clash is a pair of element identities plus the rule that found it.
Storing the pair and its rule, not a row number, is what lets a status survive the next re-check.
Two engineering details matter. The check must show progress and be cancellable, because a large model can produce millions of candidate pairs. And geometry should be cached between runs, since most of the model has not changed since yesterday.
From raw clashes to issues
A raw clash list is useless at scale. One duct run crossing a row of beams is one design problem, and it appears as a dozen rows.
Grouping is what makes the list workable:
- by element: everything one duct run collides with,
- by location: level, grid zone or room,
- by system or discipline,
- by rule.
Ignore rules matter just as much. A pipe through a wall where a sleeve is modelled is not a clash. Each office has a handful of such cases, and a usable tool lets them be written down once.
Statuses that survive a re-check
The difference between a report and a workflow is memory. Because each clash is stored as a pair of stable element identities, the next run can tell which clashes are new, which are still there and which have gone.
That enables the loop designers need: find, assign, fix, re-check. A clash someone reviewed and accepted stays accepted. A fixed clash closes itself.
Seeing the clash
A row in a table does not tell a designer what to do. The tool should take them to the problem: a 3D view with a section box around the two elements, both highlighted, everything else faded. In our newer plugin design each row also gets a small 3D preview, as described in React and WebView2 inside a Revit plugin.
What Collision Manager does
Collision Manager is our own Revit plugin for this middle ground. The whole workflow runs inside Revit, with no export and no second application. It offers:
- custom clash rule sets, such as structure against MEP or linked models against the host,
- filtering and grouping of elements by category, type or instance,
- clash visualization in Revit views,
- grouping, prioritisation, assignment and re-checking of clashes,
- export of results to XML, Excel and PDF,
- an interface built for designers, not only for BIM managers.
When you still need Navisworks
An in-Revit tool does not replace coordination software. You still need it when:
- trades deliver in different formats and the models must be federated,
- a general contractor runs formal coordination meetings across many companies,
- clashes are checked against the construction sequence. We cover that in 4D BIM without manual linking.
The two levels work together. Designers who check their own work daily bring fewer clashes to the coordination meeting.
Collision Manager is listed on our products page. If your team needs clash rules of its own, or a check built into another tool, book a Feasibility Review. More on how we build: plugin development.
FAQ
Can Revit detect clashes with linked models?
Yes. The built-in Interference Check handles simple cases. A plugin can add rule sets, tolerances and tracking for links.
Do I need Navisworks for clash detection?
Not for daily checks inside one team's Revit models. For multi-format, multi-company coordination it remains the standard tool.
What is the difference between a hard clash and a clearance clash?
A hard clash is two elements occupying the same space. A clearance clash is two elements closer than a required distance, such as access space around equipment.
Can clash results be shared outside Revit?
Yes. Results can be exported as reports, for example to Excel or PDF, for people who do not open the model.
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