MEP Clash Detection with Revit and Navisworks: A Step-by-Step Workflow That Actually Reduces RFIs

Running clash detection sounds simple: load models into Navisworks, press a button, get a report. In practice, the difference between useful clash detection and a 5,000-item report that nobody reads comes down to how you set up your search sets, define your rules, and manage the results.

This guide covers the actual workflow for running MEP clash detection with Revit and Navisworks - from model preparation to a clash report that people will act on.

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Before Navisworks: Preparing Your Revit Models

Clash detection quality depends entirely on model quality. Garbage in, garbage out. Before exporting to Navisworks, check these:

Model Hygiene Checklist

Check	Why It Matters
Elements on correct worksets	Ensures search sets in Navisworks can filter by discipline
Correct levels assigned	Prevents false clashes from elements placed at wrong elevations
No duplicated elements	Copied-in-place elements create phantom clashes
MEP systems properly connected	Disconnected duct/pipe segments can overlap without flagging as clashes
Linked models correctly positioned	Misaligned coordinate origins create thousands of false clashes
Insulation modelled or accounted for	Bare duct clash clearance is different from insulated duct clearance

Shared Coordinates

This is the most common source of false clashes. All Revit models in a project must share a common coordinate system. If the architectural model origin is at a different position than the MEP model origin, every element will appear clashed when federated.

Check in Revit: Open each model, go to Manage > Coordinates > Specify Coordinates at Point. All models should report the same survey point and project base point coordinates relative to the shared origin.

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Exporting from Revit to Navisworks

You have two options:

Option 1: NWC Export (Recommended)

Use the Navisworks NWC exporter plugin (installed with Navisworks or available from Autodesk):

1. In Revit, go to Add-Ins > External Tools > Navisworks (or File > Export > NWC)
2. Set export settings:
   • Convert element parameters: ON (preserves Revit parameter data for filtering)
   • Convert element IDs: ON (enables linking clashes back to Revit elements)
   • Coordinates: Shared
   • Export scope: Entire model (not just current view)

Option 2: Direct Revit Append

Navisworks can open .rvt files directly via Append. This is simpler but slower for large models and gives you less control over what’s exported.

Recommendation: Use NWC for production workflows. Direct append for quick checks.

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Setting Up Navisworks: Search Sets and Selection Sets

This is the step most people skip - and it’s the difference between useful and useless clash detection.

What Are Search Sets?

Search sets are saved queries that filter the federated model by criteria (category, property, workset, etc.). You use them to define what clashes against what.

Essential Search Sets for MEP Coordination

Create these search sets in Navisworks:

Search Set Name	Filter Criteria	Purpose
HVAC Ductwork	Category = Ducts, Duct Fittings, Duct Accessories	All air distribution elements
HVAC Equipment	Category = Mechanical Equipment	AHUs, FCUs, VAVs, fans
Piping - Hydronic	Category = Pipes, Pipe Fittings; System Type = Hydronic	Heating/cooling pipework
Piping - Domestic	Category = Pipes, Pipe Fittings; System Type = Domestic	Hot/cold water, waste
Piping - Fire Protection	Category = Pipes; System Type = Fire Protection	Sprinklers
Electrical - Cable Trays	Category = Cable Trays, Cable Tray Fittings	Power and data routing
Electrical - Conduit	Category = Conduits, Conduit Fittings	Individual cable runs
Electrical - Equipment	Category = Electrical Equipment	Switchboards, panels, transformers
Structure - Beams	Category = Structural Framing	Steel/concrete beams
Structure - Columns	Category = Structural Columns	Columns
Structure - Floors/Slabs	Category = Floors	Floor slabs
Architecture - Walls	Category = Walls	All wall elements

How to create: In Navisworks, go to Home > Find Items. Build your query using the conditions above, then click Save Search to store it.

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Configuring Clash Detective

Open Clash Detective from the Home ribbon. Here’s the systematic approach:

Step 1: Define Clash Tests

Create separate tests for each meaningful combination:

Clash Test Name	Selection A	Selection B	Tolerance
HVAC vs Structure	HVAC Ductwork	Structure - Beams	25mm (soft clash for insulation)
HVAC vs HVAC Equipment	HVAC Ductwork	HVAC Equipment	0mm (hard clash)
Piping vs Structure	All Piping sets	Structure - Beams	25mm
Piping vs Ductwork	Piping sets	HVAC Ductwork	50mm (maintenance access)
Cable Trays vs Ductwork	Electrical - Cable Trays	HVAC Ductwork	25mm
Cable Trays vs Piping	Electrical - Cable Trays	All Piping sets	25mm
MEP vs Walls	All MEP sets	Architecture - Walls	0mm
Fire Protection vs All	Piping - Fire Protection	All MEP + Structure	0mm

Don’t create one giant “everything vs everything” test. This produces thousands of results and makes it impossible to assign responsibility. Separate tests let you assign each test to the responsible discipline.

Step 2: Set Clash Rules

In the Rules tab of each test, configure:

• Same file: Ignore (prevents clashing elements within the same model)
• Same layer/workset: Optional - ignore if you want to skip intra-discipline clashes
• Composite overlap: Consider enabling for complex wall assemblies

Step 3: Set Tolerances

• Hard clash (0mm): Elements physically occupying the same space
• Soft clash (25-50mm): Elements within a clearance buffer - accounts for insulation, maintenance access, or construction tolerances
• Workflow clash (custom): Access clearances for valves, dampers, electrical panels (typically 600-900mm)

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Running Tests and Managing Results

The First Run Problem

Your first clash detection run will produce hundreds or thousands of results. This is normal. The goal of the first run is not to resolve everything - it’s to classify and reduce.

Clash Status Workflow

Navisworks provides status labels for each clash:

Status	Meaning	Action
New	Just detected, not yet reviewed	Needs triage
Active	Reviewed, confirmed as real issue	Assign to responsible party
Reviewed	Under investigation	Awaiting design decision
Approved	Accepted (intentional or tolerable)	No action needed
Resolved	Fixed in updated model	Will disappear on next run

Grouping Clashes

A single misrouted duct can generate 15+ individual clashes (one for each beam or pipe it intersects). Group related clashes to reduce the report from 500 items to 50 actual issues:

1. Sort clashes by grid location
2. Select related clashes (same duct run, same area)
3. Right-click > Group Clashes
4. Name the group descriptively: “Level 3 - Supply duct clashes with beams at gridline C3-C5”

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Reporting and Communication

BCF Export (Best Practice)

Export clash results as BCF (BIM Collaboration Format) files. BCF captures:

• The 3D viewpoint of each clash
• The elements involved
• Status and comments
• Assignment information

BCF files can be imported directly into Revit (via plugins like BIMcollab), Solibri, Tekla, and other BIM tools - so the responsible engineer sees the exact clash location in their own software.

HTML Reports (For Stakeholders)

For project managers or clients who don’t use BIM tools, export an HTML report from Clash Detective. This produces a browsable document with screenshots, clash descriptions, and status summaries.

Dashboard Metrics to Track

Metric	What It Tells You
Total clashes (new)	Model quality trend - should decrease over time
Active clashes by discipline	Who has the most work to do
Resolved rate	How quickly issues are being fixed
Clashes by area/level	Where the problem zones are
Repeat clashes	Issues that were resolved but reappeared (indicates model regression)

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Common Mistakes That Waste Everyone’s Time

1. Running clash detection too early If models are at LOD 200 (schematic routing), clash detection produces noise. Wait until LOD 300 (sized, routed systems) before running formal coordination.

2. Not filtering irrelevant clashes Pipes passing through sleeved penetrations aren’t clashes. Set up rules to ignore elements that are intentionally intersecting (e.g., pipes with sleeve families).

3. Treating the report as the deliverable A 200-page clash report that sits in a shared folder is worthless. The deliverable is resolved clashes - which means someone has to review, assign, track, and close each issue.

4. Running tests only at milestones Monthly clash detection is too infrequent. Weekly runs catch issues before they compound. Ideally, automate the process with batch utilities that run clash tests on updated models every time they’re published.

5. No ownership of the coordination process Clash detection without a BIM coordinator who owns the results, chases resolution, and tracks progress is a bureaucratic exercise. Assign one person as the coordination lead.

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Navisworks Alternatives Worth Knowing

Tool	Strengths	Best For
Navisworks Manage	Full clash detection, simulation, review	The industry standard for Revit-based projects
Solibri	Rule-based checking beyond geometry	IFC-based projects, code compliance
BIMcollab Zoom	Free viewer, BCF issue management	Teams using BCF workflow
Trimble Connect	Cloud-based coordination	Mixed-software teams
Autodesk Construction Cloud	Cloud coordination with Revit integration	Teams already on Autodesk platform

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Ready to build your coordination skills? The Archgyan Academy covers BIM coordination, Revit MEP, and clash detection through practical project workflows.