Imagine: a project with 12,000 elements, and you run clash detection. Navisworks thinks for 40 minutes, then outputs 8,000 intersections — 7,500 of which are false, because IFC from Revit and ArchiCAD describe the wall-slab junction differently. Sound familiar? If so, this article is for you. We'll break down how BIM coordination actually works, why clash detection becomes a headache, and when Revit's built-in tools are enough.
Why BIM coordination is not just "pressing a button"
A BIM model is not just a 3D picture but a database with geometry and attributes. Coordination is the process of finding and resolving discrepancies between disciplines: architecture, structure, HVAC, electrical, plumbing. Ideally, everything is automated, but in practice 70% of the time goes into filtering out noise.
The key problem is different formats. Revit, ArchiCAD, Tekla, Civil 3D export data to IFC, but each does it its own way. For example, a wall in Revit may have a face that becomes a separate object in IFC, while in ArchiCAD it becomes part of another element. As a result, Navisworks sees an intersection where there is none. These are false clashes.
The second difficulty is scale. A residential complex model with 500,000 elements takes minutes to open in Navisworks, and clash detection can take hours. If you have 8 GB of RAM, the program will simply crash. Experienced coordinators know: before checking, you need to split the model into zones and use NWF (reference files) rather than loading everything at once.
Clash detection in practice: a step-by-step breakdown with numbers
Let's take a typical case: a 10-story residential building, architectural and structural disciplines, total area 15,000 m². The model has about 300,000 elements. The task is to find intersections of MEP systems with load-bearing structures.
Step 1. Model preparation. Export IFC from Revit. Important: before exporting, you need to set up Property Sets and disable unnecessary categories. If you don't, the file will grow 2–3 times, and there will be more clashes. In our example, after optimization the IFC weighs 120 MB instead of 350 MB.
Step 2. Loading into Navisworks. Create an NWF file, link the IFC. Tip: use "Append" for each discipline separately, not everything at once — it's easier to manage visibility.
Step 3. Setting up the search rule. Navisworks has "Clash Detective." Set the Tolerance — the distance within which an intersection is considered a clash. For MEP systems, it's usually 10–20 mm. If you set it to 0, you'll get thousands of false positives due to geometry inaccuracies.
Step 4. Running and filtering. In our example, the first run produced 5,400 clashes. After grouping by element and removing duplicates, 320 real ones remained. Next is manual review of each intersection: you need to understand whether it's truly an error or an acceptable solution (e.g., a pipe passing through a hole in a beam).
What goes wrong: if you don't set an exclusion rule for identical elements (wall-wall), you'll get thousands of false ones. If you don't limit the search area (e.g., only the basement), the check will take 3 times longer. And most importantly — don't forget about BCF exchange: Navisworks can export comments to BCF, which opens in Revit or ArchiCAD. This speeds up fixes.
Where the tool breaks: three causes of false positives
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Different geometry in IFC. As mentioned, Revit and ArchiCAD describe junctions differently. Solution: before exporting, unify IFC settings (e.g., use IFC 4 instead of IFC 2x3).
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Missing attributes. If the model lacks a "Zone" or "System" property, filtering clashes is difficult. Way out: add parameters in Revit before export.
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Complex shapes. Curved walls and slabs often produce false intersections due to approximation. Increasing tolerance or manual checking helps here.
How much Navisworks costs and who needs it
A subscription to Navisworks Manage (full version with Clash Detective) costs about $2,500 per year per workstation. There is a cheaper Navisworks Simulate (without clash detection) — about $1,250, but it's not suitable for coordination.
Alternatives:
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Revit built-in tools. Revit has "Interference Check." It works slower and is less flexible, but for small projects (up to 100,000 elements) it's quite sufficient. Savings — $2,500 per year.
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Free BCF exchange. If you only need to pass comments, you can use BCF plugins (e.g., BCFier for Revit) and a free viewer. This is suitable for coordination between two or three participants.
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Cloud services. Autodesk BIM 360 / ACC also have clash tools, but require a cloud subscription (from $400 per month per project).
Who needs Navisworks: large projects (5+ participants, complex MEP systems) where the volume of clashes is high and automation is needed. Who can get by with Revit: small studios where coordination is done manually and projects are typical.
Learning paths: self-study, courses, or practice
You can learn Navisworks on your own using Autodesk's official documentation and YouTube videos. But there are pitfalls: no feedback, it's hard to understand how to filter clashes in real projects, and it's easy to miss important settings. Time to learn — 2–3 months with daily practice.
Courses provide structure and case studies. For example, the course Architecture and BIM Technologies has a module on Navisworks that shows how to set up search rules and deal with false clashes. But a course is not the only path. If you already work in a studio, ask a mentor to show you a real project — that's the fastest way.
Trade-off: self-study is cheaper but takes longer and involves mistakes; a course is more expensive but provides a system and feedback. Practice on a real project is the best option, but requires access to a project and a mentor.
Who this suits and who it doesn't
BIM coordination is needed by those working on large projects with many disciplines and participants. If you design private houses or small facilities, Revit's built-in tools and BCF exchange will most likely be enough. Don't spend money on Navisworks until you face a real scale problem.
If you want to become a BIM coordinator, deep knowledge of Navisworks is essential — it's the industry standard. But remember: the tool doesn't solve all problems; you also need a modeling culture and discipline among participants.
The course Architecture and BIM Technologies covers these scenarios with examples and provides feedback on your decisions — details and enrollment on the course page.