Hard clash & soft clash

Not every clash is the same kind of problem. A hard clash is a physical collision: two elements occupy the same space, a zero-tolerance intersection. A soft clash (or clearance clash) is a tolerance violation: one element encroaches into the clearance zone another needs. A third kind, the workflow or 4D clash, is a scheduling conflict — two activities needing the same space at the same time.

The examples are concrete. A hard clash is a structural beam driven through an HVAC duct, or a pipe intersecting a beam. A soft clash is a duct run too close to a light fixture, or equipment placed inside the access zone someone needs to maintain it. A 4D clash is a ceiling scheduled before the services above it are installed.

They are detected and prioritised differently. A hard clash has zero tolerance and is treated as critical; a soft clash is judged against a clearance of tens to hundreds of millimetres, depending on the element and the code, and ranks medium-to-high. Both are found on the federated model by defining clash rules, filtering out false positives, then classifying and assigning what remains before the coordination meeting — a discipline especially heavy in MEP coordination. ISO 19650-2 frames clash detection within delivery-phase coordination. In Italian a hard clash is an interferenza geometrica and a soft clash an interferenza di tolleranza.