Clash Detection in Revit: Avoiding Ducting Conflicts with Structure and Other MEP Installations

On commercial and industrial building projects, HVAC ducting is not the only system competing for space above the ceiling. Structural beams, sprinkler pipes, plumbing runs, electrical cable trays, and sometimes ducting from other disciplines all cross through the same area. If clashes between these systems are only discovered once installation is underway, the fix is almost always rework. Clash detection in Revit makes it possible to find and resolve these conflicts long before a single meter of ducting is installed on site.

What Is Clash Detection

Clash detection is the systematic process of checking whether two 3D model elements occupy the same space, or sit too close together to be installed as planned. In an HVAC context, this means checking whether ducting routes, refrigerant piping, or indoor/outdoor units intersect with structural elements, other MEP installations, or architectural elements. This check runs on a federated model — a combination of models from every discipline in one coordination file — rather than on separate 2D drawings per discipline.

The Most Common Types of HVAC Clashes

Ducting vs. Beams and Structure

Main ducting routes are often planned along the shortest path without accounting for beam, column, or shear wall positions. Once the structural model is linked in, ducting that looked straight on a 2D drawing may turn out to pass through a beam, or need to step up and down repeatedly to clear beams along a corridor.

Ducting vs. Sprinklers, Plumbing, and Cable Trays

The space above the ceiling is usually the most congested part of a building. Large ducting can intersect with sprinkler pipe runs, clean or waste water piping, and electrical or data cable trays. Because each discipline is usually drawn by a different team, this type of clash is the one most likely to slip through 2D drawings and only become visible once several runs are already installed.

Insufficient Ceiling Height

Ducting, piping, cable trays, and ceiling framing all need vertical space. In buildings with low ceilings or frequent dropped beams, the total space required by every system combined is often greater than what is actually available. Without a 3D model, this is usually only noticed once ducting is partly installed and there is no room left for piping or light fixtures at the same point.

Blocked Maintenance Access

Clash detection does not only check for solid objects colliding — it also checks the working clearance needed for maintenance, such as the space in front of a filter panel, damper, or service valve. Ducting or other piping installed too close to an access panel makes a unit hard to maintain even if nothing is physically overlapping.

How Clash Detection Is Done in Revit

This process runs on top of an HVAC model already built to the planned capacity and layout. The typical stages are:

1. Linked models. The HVAC, structural, plumbing, and electrical models are each kept as separate files, then brought together as linked models in one coordination file. Each discipline can keep updating its own model without disrupting other disciplines' files.
2. Interference Check. Revit's Interference Check feature compares elements across categories — for example ducting against structure, or ducting against piping — and produces a list of clash points complete with location and the elements involved.
3. Reviewing and flagging results. Every detected clash point is checked individually to confirm it is a real conflict, not just elements that touch but can still be installed as-is on site.
4. Cross-discipline coordination. Valid clashes are discussed with the relevant discipline teams to decide who yields — rerouting the ducting, adjusting pipe elevation, or revising the cable tray position.
5. Model revision and re-checking. After revisions, Interference Check is run again to confirm the clashes are gone and that the changes have not introduced new ones.

This cycle typically repeats several times until every system route in an area is fully coordinated. For projects with a very large number of disciplines or models built in different software, some teams choose to run additional coordination in Navisworks as a supplement, although Revit's Interference Check is sufficient for most HVAC projects.

Benefits of Clash Detection for Project Cost and Schedule

Finding a clash at the design stage is far cheaper and faster to fix than finding it once installation is underway. A change in the model only requires adjusting drawings, while a change on site requires tearing out already-installed material, recutting ducting, and waiting for replacement material. Clash detection also reduces disputes between contractors on site, since every discipline works from a shop drawing already proven to fit with the others, rather than from a drawing that could still conflict.

Clash Detection Coordination Checklist

A few things to confirm before HVAC shop drawings are issued for installation:

• The HVAC model has been linked with the latest structural, plumbing, and electrical models.
• Interference Check has been run for every relevant combination of disciplines, not just ducting against structure.
• Every clash point has been reviewed and given a clear status: resolved, pending a decision, or accepted as a safe tolerance.
• Maintenance access clearance in front of dampers, valves, and filter panels has been checked, not just the physical distance between elements.
• Ceiling height at the most congested points has been verified as sufficient for every planned system.
• Interference Check is rerun after every major revision before final shop drawings are issued.

When to Contact an HVAC Consultant

Contact an HVAC consultant or contractor experienced in model coordination if your project involves multiple MEP disciplines sharing ceiling space, if existing 2D drawings have never been cross-checked against structural or other MEP models, or if a previous phase of installation already ran into clashes on site and you want to avoid repeating that on the next phase. Coordinating the model earlier, as described in our article on HVAC design with a 3D Revit model, leaves enough room to resolve clashes before material is ordered and installed.

Solusi Karya Nusantara helps MEP consultants, main contractors, and project owners in Medan and the surrounding area run clash detection coordination for HVAC systems from the design stage onward, through 3D Revit design and HVAC shop drawing services, through to installation by Daikin-certified technicians for commercial and industrial buildings.