Clash Detection

Finding where ducts, pipes, and structure collide on screen, before they collide on site.

Quick Answer

Clash detection is the process of checking combined design models or drawings to find places where building elements physically conflict or violate clearances, such as a duct passing through a beam. Teams run it during coordination so the conflicts are resolved in design and preconstruction, before they cause rework in the field.

The Full Picture

Every discipline designs its own systems, and the systems all have to share the same ceiling space, shafts, and walls. Structure, ductwork, piping, conduit, and fire protection can each look correct in isolation yet occupy the same place once combined. Clash detection is the check that surfaces those conflicts while fixing them still costs a model edit rather than a field change.

In a BIM workflow, discipline models are federated into one environment and a rule-based check compares elements. A hard clash is two elements occupying the same space. A soft clash, sometimes called a clearance clash, is an element that does not intersect another but violates required access or maintenance space. Teams also look at workflow or 4D clashes, where the construction sequence creates a conflict.

Software finds clashes quickly, but it does not decide what matters. A large model can return thousands of results, many of them trivial, duplicates, or caused by modeling convention rather than a real problem. The value comes from the coordination meeting, where trade representatives group the results, decide who moves, and track resolution to closure in a clash report.

Clash detection does not require 3D models. On projects without models, coordination issues are found by reviewing 2D drawings across disciplines, comparing plans, sections, and details to catch conflicts and missing information. In preconstruction, catching these issues before bid or during buyout reduces change orders and gives subcontractors a clearer scope to price.

Real Examples

→Hard clash: A 24-inch supply duct runs through a steel beam on the third floor. The coordination team lowers the duct and adds a transfer section before drawings are issued for construction.

→Clearance clash: A sprinkler main is modeled in the space a mechanical unit needs for filter access, so the pipe is rerouted.

→2D document coordination: On a project with PDF drawings only, an estimator notices that the structural plan shows a beam where the mechanical plan routes a main duct and raises it before bids are leveled.

Common Misconceptions

People assume: People assume clash detection software finds the real problems automatically.

Actually: it flags geometric overlaps, and people still have to filter noise, decide ownership, and confirm each resolution.

People assume: People assume a clean clash report means the design is coordinated.

Actually: it only means the modeled elements do not conflict; unmodeled items, clearances, and sequencing issues can still exist.

People assume: People assume clash detection is only possible with BIM.

Actually: teams also find coordination conflicts by comparing 2D drawings across disciplines, though it is slower and more manual.

Does MeltPlan Solve This?

Partially — adjacent

Partially — MeltPlan's Design Review reads 2D drawings and specifications and flags coordination issues between disciplines, such as structural and MEP conflicts and inconsistencies within a drawing set. It does not run 3D model clash detection; that stays in your BIM coordination tools.

Catch cross-discipline conflicts in your drawings →

Frequently Asked Questions

What is clash detection in construction?

Clash detection is the process of checking combined models or drawings to find conflicts between building elements, such as ducts through beams, so they can be resolved before construction.

What is the difference between a hard clash and a soft clash?

A hard clash is two elements physically occupying the same space. A soft clash is a clearance or access violation where elements do not touch but leave too little room.

Which software is used for clash detection?

Teams commonly use model coordination tools such as Autodesk Navisworks or Autodesk Construction Cloud's coordination tools, Solibri, and similar platforms that can combine models.

Who resolves the clashes?

Trade and design representatives resolve them together in coordination meetings. The affected discipline owners agree who changes and the team tracks each issue to closure.

Can clashes be found without a 3D model?

Yes. Teams can find conflicts by reviewing 2D drawings across disciplines, though this is more manual and relies on reviewer experience.