ISO 19650-2:2018 · ISO 19650-2 — Delivery Phase of Assets; Clash Detection as part of Model Coordination
Comprehensive guide to BIM clash detection covering hard clashes, soft/clearance clashes, and workflow clashes. Includes the discipline coordination matrix, priority classification, resolution workflow, and common clash rules used in Indian construction projects.
Three fundamental types of clashes detected in federated BIM models
Clash Type
Disciplines
Tolerance
Priority
Hard Clash
Any two physical elements occupying the same space
0 mm (physical intersection)
Critical
Soft Clash (Clearance Clash)
Element violating required clearance or maintenance access zone around another element
25–300 mm depending on element type and code requirements
High to Medium
Workflow Clash (4D/Time Clash)
Scheduling conflict — two trades or activities requiring the same space at the same time
N/A (time-based)
Medium
Duplicate Element Clash
Same element modeled twice — from linked models or copy errors
0 mm (exact or near-exact overlap)
Low
Design Intent Clash
Element violates design standards or code requirements (not physical intersection)
Varies by code requirement
High
Priority Classification
Classify each clash by severity to prioritise resolution — typical project classification
Clash Type
Disciplines
Tolerance
Priority
Priority 1 — Critical
Structural vs MEP (major services)
0 mm
Critical — resolve within 48 hours
Priority 2 — Major
Architecture vs Structure, MEP vs MEP (different services)
0–50 mm
High — resolve within 1 week
Priority 3 — Moderate
Clearance violations, maintenance access issues
25–150 mm
Medium — resolve before construction of that zone
Priority 4 — Minor
Cosmetic or non-structural items
50–300 mm
Low — resolve before finishing works
Priority 5 — Acceptable / Approved
Known conditions accepted by design team
N/A
None — approved exception
Clash Resolution Workflow
Step-by-step process from detection to sign-off
Clash Type
Disciplines
Tolerance
Priority
Step 1 — Federated Model Setup
All disciplines
N/A
N/A
Step 2 — Define Clash Rules
BIM Coordinator
Set per rule
N/A
Step 3 — Run Clash Detection
BIM Coordinator
Per rule
N/A
Step 4 — Filter False Positives
BIM Coordinator
N/A
N/A
Step 5 — Classify and Assign
BIM Coordinator + Discipline Leads
N/A
Assign P1–P5
Step 6 — Coordination Meeting
All discipline leads
N/A
Focus on P1 and P2
Step 7 — Model Update and Re-check
Assigned discipline
N/A
N/A
Step 8 — Sign-off and Close
BIM Coordinator + Project Manager
N/A
N/A
Common Clash Rules
Standard discipline-vs-discipline clash tests used in building projects
Clash Type
Disciplines
Tolerance
Priority
Hard Clash
Structural vs HVAC Ducts
0 mm
Critical
Hard Clash
Structural vs Plumbing Pipes
0 mm
Critical
Hard Clash
Structural vs Electrical Conduits/Trays
0 mm
High
Hard Clash
HVAC Ducts vs Plumbing Pipes
0 mm
High
Hard Clash
HVAC Ducts vs Electrical Cable Trays
0 mm
High
Soft Clash
HVAC Equipment vs Maintenance Access
600–900 mm clearance
Medium
Soft Clash
Architecture (False Ceiling) vs MEP Services
50–100 mm below lowest service
Medium
Hard Clash
Architecture (Walls/Doors) vs Structure (Columns/Beams)
0 mm
High
Soft Clash
Fire Protection (Sprinkler) vs All Services
Varies — sprinkler deflector clearance per NBC
High
Notes
• False positive management is critical — poorly configured clash rules generate thousands of irrelevant results. Invest time in refining selection sets and exclusion rules before the first coordination meeting.
• Clash batching: group related clashes by zone/floor/system rather than reviewing individually. A single routing change may resolve 20+ related clashes at once.
• Sign-off process: every resolved clash must be verified in the updated federated model and signed off by the responsible discipline lead. Verbal agreements are not sufficient under ISO 19650.
• Establish a service zone hierarchy at project kickoff: typical order from ceiling down is (1) HVAC ducts, (2) cable trays, (3) plumbing pipes, (4) sprinkler pipes, (5) electrical conduits.
• Run clash detection at minimum fortnightly intervals during design development; weekly during construction documentation phase.
• For Indian projects, clash detection reports should be part of the BIM Execution Plan (BEP) deliverables per IS 19650 adoption guidelines.