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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Drafting / CAD / BIM › BIM Workflows for Manufacturing and Marine Drafting › Lesson 7
MFG-DRAF17-06 · Lesson 7 · 13 clock hours · lab

Clash Detection with Navisworks Manage

Objective. Students will export a Revit model to NWC format, combine architecture and MEP models in Navisworks Manage, run a Clash Detective test, and produce a written clash report with element IDs and recommended resolutions.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

What Is Clash Detection and Why Does It Matter?

In manufacturing and marine drafting, multiple building systems — structural steel, HVAC ductwork, piping, conduit, and architectural elements — must share the same three-dimensional space. When two or more components occupy the same location, or when clearance requirements are violated, the result is called a clash. Discovering clashes on paper or on screen before fabrication and installation saves significant rework costs and schedule delays. Autodesk Navisworks Manage is the industry-standard tool for aggregating models from multiple disciplines and running automated clash detection across them.

NWC Export from Revit

Navisworks cannot open native Revit (`.rvt`) files directly without conversion. The NWC exporter plugin for Revit writes a lightweight cache file (`.nwc`) that Navisworks reads quickly while preserving element geometry, properties, and element IDs. To export, open each Revit model — the architectural model and the MEP model separately — navigate to the Add-Ins tab, and use the Navisworks NWC export command. Confirm the correct coordinate settings so both files share the same project origin. Mismatched origins are the most common cause of models appearing offset from each other after appending.

Building the Combined Navisworks Session

Open Navisworks Manage and use Append (not Open) to bring in the first NWC file, then Append again to add the second. Using Append preserves each file as a separate item in the Selection Tree, which is essential for configuring clash tests between specific disciplines. After appending, verify alignment by activating both items in the Selection Tree and visually confirming that floors, grids, and column centerlines coincide. Save the combined session as an NWF file — this is a pointer file that references the NWC files rather than embedding them, keeping file size manageable.

Clash Detective Panel

Access Clash Detective from the Home tab or the Tools menu. A clash test requires you to define two selection sets — Set A and Set B — and specify the clash type:

For this lab, Set A should contain the HVAC ductwork and Set B should contain the structural framing. Select the relevant items from the Selection Tree or use saved Navisworks selection sets. Set the clash type to Hard, leave the tolerance at 0.000 m (or 0 in) to catch true intersections, and click Run Test.

Reviewing Clash Results

Navisworks lists every detected clash in a results grid. Each result shows a Clash Name (auto-numbered), the Status, the distance of penetration, and the Element IDs of both clashing components. Click any row to fly the camera to that clash location. Use the viewpoint to assess severity:

Assign a Status to each clash:

Avoid marking a clash Reviewed without a documented rationale; doing so defeats the audit trail purpose of the tool.

Exporting the Clash Report

With clashes reviewed and statused, click Report at the bottom of the Clash Detective panel. Choose HTML (Tabular) format. The report embeds viewpoint screenshots, element IDs, clash coordinates, status, and any comments entered during review. This report becomes the primary communication document sent to the structural engineer and mechanical contractor for resolution coordination.

Writing Resolution Recommendations

For each high-priority clash, your written recommendation must include:

1. Element IDs of both clashing components.

2. Location described by grid line intersection or deck/level.

3. Recommended action — for example, lower the duct run by a specified amount, offset the duct to pass below the beam, resize the duct, or coordinate with the structural engineer for a beam penetration sleeve.

Be specific and reference the element IDs so the receiving discipline can locate the exact component in their model.

Workstation Safety and File Hygiene

Navisworks sessions that reference large NWC files can consume substantial RAM. Close unnecessary applications before loading models. Save your NWF session frequently. Do not work from a USB drive — copy files to the local drive first to prevent data loss from disconnection. Handle shared workstation equipment with care: report any hardware issues to the instructor rather than attempting repairs. Follow the shop's posted lockout/tagout procedures if any plotters or large-format printers associated with the workstation require clearing a paper jam or mechanical servicing — de-energize before opening covers.

Key terms8

NWC fileA lightweight Navisworks cache file exported from Revit (or other authoring software) that stores geometry, object properties, and element IDs in a format Navisworks can read quickly.
NWF fileA Navisworks session file that stores pointers to appended NWC or NWD files along with clash tests, viewpoints, and comments, without embedding the full geometry.
Clash DetectiveThe Navisworks Manage tool that compares two sets of model geometry and reports all locations where they intersect or violate a defined clearance.
Hard clashA clash condition in which the geometry of two components physically overlaps or intersects in three-dimensional space.
Clearance clashA clash condition in which two components do not physically intersect but come closer than a specified minimum distance, violating maintenance or installation clearance requirements.
Element IDA unique integer assigned by Revit (and preserved in the NWC export) that identifies a specific model element, used to locate that element precisely in either Navisworks or Revit.
Selection setA saved group of model elements in Navisworks used to define the 'A' and 'B' sides of a clash test so that only the relevant disciplines are compared.
Clash statusA label (New, Active, Reviewed, or Approved) assigned to each clash result in Clash Detective to track review progress and resolution decisions.
In class: Students export the architectural and MEP Revit models to NWC files and append both into a single Navisworks Manage session, verifying alignment using the model tree. · Students configure and run a hard-clash test between the HVAC ductwork and structural framing, then review each clash result and assign status (New, Active, Reviewed) in the Clash Detective panel. · Students export the clash report to HTML, identify the three highest-priority clashes by location and element ID, and write a one-paragraph resolution recommendation for each.
Materials: Autodesk Navisworks Manage (current program version), student workstations, NWC exporter plugin for Revit, instructor-prepared combined model with known clashes, clash report template.
Check: Instructor compares the student clash report against a master answer key; report must correctly identify at least 80% of seeded clashes and include a resolution note for each identified clash.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

BIM coordination and model management
1. What is the primary reason both Revit models must share the same project origin before NWC export?
Clash detection and coordination
2. In Navisworks Clash Detective, which clash type detects geometry that physically intersects?
BIM coordination and model management
3. A student appends two NWC files into Navisworks and notices the HVAC model appears one story above the structural model. What is the most likely cause?
Navisworks file management
4. Which Navisworks file type stores clash test configurations and saved viewpoints without embedding full model geometry?
Clash detection and coordination
5. After running a hard-clash test, a student wants to indicate that a particular clash has been evaluated and requires rerouting but has not yet been resolved. Which status should be assigned?
BIM documentation and reporting
6. A clash report must include element IDs because they allow the receiving engineer or contractor to:
Clash detection and coordination
7. When configuring a clash test between HVAC ductwork and structural framing, which selection setup is correct?
BIM documentation and reporting
8. A student is writing a resolution recommendation for a clash where a supply air duct intersects a wide-flange beam. Which information is essential to include in the recommendation paragraph?
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