Clash detection is a safety net, not a routing strategy. The MEP teams that produce genuinely low-clash models aren't running better clash software — they're following a small set of routing conventions consistently from the first layout pass, long before anyone opens Navisworks.
Rule 1: establish a routing hierarchy before laying anything out
Gravity-dependent systems (sanitary drainage, storm drainage) get priority over pressurized systems (supply ductwork, chilled water piping) because gravity systems have far less flexibility in slope and routing path. Establishing this hierarchy at the start of layout — and having every discipline agree to it — prevents the common scenario where ductwork gets routed first and a drainage line later discovers it has nowhere left to fall correctly.
Rule 2: reserve consistent vertical zones in ceiling voids
| Typical ceiling void allocation (top to bottom) | Reasoning |
|---|---|
| Structure | Fixed, non-negotiable |
| Largest ductwork (supply/return air) | Least flexible in routing path; needs the most continuous space |
| Cable trays / electrical | Moderate flexibility, benefits from a dedicated, undisturbed zone |
| Piping (chilled water, domestic water) | More flexible routing paths; can navigate around fixed elements more easily |
| Sprinkler/fire protection | Typically routed last, fitting around the established systems above |
Agreeing on this zoning convention across disciplines before detailed routing begins eliminates a large share of the "who gets this 200mm of ceiling void" disputes that otherwise surface as clashes weeks later.
Rule 3: maintain consistent clearance standards, not just zero-overlap geometry
A duct and a structural beam not touching isn't automatically "clash-free" if there's no room left for insulation, access for maintenance, or installation tolerance. Define and apply consistent clearance standards (commonly a minimum buffer around ducts for insulation thickness, and additional clearance for maintenance access on equipment) as a routing rule, not just a post-hoc clash detection tolerance setting.
Rule 4: route around fixed points first, flexible runs second
Equipment connection points, structural penetrations, and shaft locations are fixed; the pipe or duct run between them is flexible. Routing should always start from fixed points and work toward flexible runs, not the reverse — laying out a "convenient" straight run first and then discovering it doesn't actually reach a fixed connection point cleanly is a common source of late rework.
Rule 5: coordinate riser and shaft locations early, across all disciplines simultaneously
Vertical risers and shafts are where multiple disciplines' systems all compete for the same limited space, often the worst clash hotspot on any multi-story building. A joint riser/shaft coordination session — architecture, structure, and all MEP disciplines in the same room, looking at the same federated model — held early in design development prevents far more clashes than waiting for an automated clash report to surface the conflict.
Why prevention beats detection
None of this replaces clash detection (see our Clash Detective guide) — it reduces what clash detection needs to catch, which means the clash reports that do surface are higher-signal and easier for discipline leads to act on quickly, instead of being buried under preventable, routine conflicts.
MEP routing strategy and clash prevention discipline are covered in our Structure plan MEP track. Full curriculum on the Programs page.
