An acquaintance of mine who is in the business of Building Information Management phoned me recently and asked me if could help with a Navisworks clash. They were not overly familiar with Navisworks and were struggling to understand why, since the elements that were clashing were not strictly speaking interfering with each other, they were being identified as clashes.  

In this video, we consider a very simple clash of two models in an idealised scenario. We do not use a clash detection matrix as we would normally on a real project for the sake of simplicity.

Here is the glossary for Navisworks, taken from the online Autodesk Help for Navisworks 2027.

It turns out Navisworks has clash type options. It is good to understand them and how they can be applied.

Underlying the discussions is the understanding that:

• Navisworks geometry is composed of triangles.
• You should generally add a clearance allowance or “tolerance” to prevent false positives.

Hard Clashes find clashes where the element’s geometry is within another element’s geometry by more than your set tolerance. A more detailed explanation is that: “Hard clashes test to check for intersections between any of the triangles defining the two items being tested.” It is possible that the triangular approximation of pure geometry can cause a hard clash to miss a clash. It ignores co-incident lines and faces.

Hard Conservative Clashes does what a hard Clashes do, but they also consider coincident lines and faces. In other words, if elements are touching each other and you can’t to pick this up as a clash, then use this method.

Clearance Clashes find elements that are within a certain proximity of each other, and this would include touching faces and lines.

Duplicate Clashes find duplicate elements of the same geometry and that occupy the same space. If you are a Revit user, you can eliminate these clashes by running an interference clash test of your model against itself before submitting the model for Navisworks clash detection.

The option to Link to a Timeliner is also not considered in this video. The reason it exists is so that clashes can be time based. For instance, at what stage of the project does the building interfere with the building crane such that the building crane must be deconstructed and moved to another location?

Composite object clashing allows elements such as windows to be clashed as one object even though they are composed of frames and panes. A composite element is considered a sincle element within the selection tree.

There is a lot more that goes into clash detection. One of the more recent additions to Navisworks allows you to classify the severity of the clashes, although this is a manual process.

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