Clash Detection Report

Modern buildings have complex MEP systems — HVAC ducts, plumbing pipes, fire-sprinkler lines, electrical conduits, structural beams, lighting, BMS cabling — all sharing the same overhead space. Without 3D coordination, these systems clash at construction: a duct hits a beam, a pipe runs through a structural column, a sprinkler line interferes with a return-air grille.

In 2D design, ~5-15% of MEP runs have unidentified clashes. Resolving them on site costs 5-20× more than resolving in design — site rework, demolition, re-routing, lost productivity, schedule slip. The Clash Detection Report is the formal output of BIM-based coordination (typically using Autodesk Navisworks or BIM360 / equivalent) that finds + classifies these clashes BEFORE construction.

For high-rise / commercial / institutional projects, clash detection has become standard practice. ISO 19650 (the international BIM standard, adopted as IS standard for India) explicitly requires clash coordination during the design phase.

Workflow: 1. Federated BIM model assembled from architectural + structural + MEP + plumbing + fire-safety disciplines 2. Clash detection run using Navisworks (or equivalent) — software identifies geometric collisions 3. Initial output typically has 500-5000 clashes (depending on project size + design maturity) 4. Triage: classify as Critical (must resolve), Major (resolve), Minor (cosmetic / acceptable), False (modelling artefact) 5. Resolution meetings: relevant designers + PMC + contractor work through Critical + Major clashes 6. Updated models + re-run cycle until Critical + Major count is < threshold (typically 0-5) 7. Sign-off: PMC + design team approve the federated model for construction 8. Pre-construction review: contractor's site team reviews resolved model before any installation

Report structure captures: - Clash ID + location (level + grid + element refs) - Clash type (e.g., HVAC duct vs structural beam) - Severity classification - Suggested resolution - Assigned designer - Status (open / in-progress / closed) - Final resolution + date

Tools commonly used: Autodesk Navisworks Manage, BIM 360 Coordinate, Solibri Model Checker, Trimble Connect.

1. Clash detection done too late — running it 80% through detailed design means significant rework. Best practice: clash detection cycles starting in concept design (initial coordination), repeating at preliminary + detailed milestones.

2. Disconnected models — designers working on different versions of the federated model. Use a Common Data Environment (CDE) per ISO 19650; single source of truth.

3. Designer non-attendance at resolution meetings — leads to one-sided 'resolutions' that come back to bite during construction. PMC must enforce attendance.

4. False clashes ignored without justification — minor modelling artefacts (e.g., a sprinkler head touching a ceiling tile in geometry) are dismissed without documentation. Future questions can't be answered.

5. No tolerance settings — running clash detection with zero tolerance gives thousands of trivial clashes. Set tolerance ~25-50 mm for general MEP; tighter (10 mm) for critical clearances.

6. Resolutions not propagated to construction drawings — model updated but 2D issue drawings not regenerated. Contractor builds to outdated 2D drawings.

7. No contract clause for clash detection — without contractual obligation, designers can argue 'not in scope'. PMC contract + design-team agreement must include BIM + clash detection.

Companion PMC formats: - Design Review Register (PMC-DES-REG-001) — broader design review including clash review meetings - BIM Coordination Log (PMC-DES-LOG-001) — running log of BIM-related coordination decisions - Drawing Transmittal (PMC-DES-FRM-001) — formal release of updated documents - RFI Review (PMC-MTG-MOM-012) — clarifications during construction (often arise from missed clashes)

Standards / methods: - ISO 19650 Parts 1-5 — BIM information management standard (adopted as IS standards) - IS 16711 Part 1:2017 — Building Information Modelling (BIM) — Information Management Standard - PAS 1192-2:2013 — Specification for information management during the capital / delivery phase (older British standard, referenced widely) - IS 17827 — BIM-related upcoming standard (under BIS CED 30 development)

For project specification: include 'BIM-based clash detection coordination' explicitly in the design consultant scope; specify deliverable (federated model, clash report, resolution log).