Practical BIM Clash Detection for Constructible Coordination

On a simple build – say, a two-storey house – coordinating what needs to be built where and when is fairly straightforward. However, as a project grows in scale, so does the number of systems and components it requires. This complexity makes positioning all those pieces increasingly difficult.

To ensure building systems won't conflict, construction project teams coordinate the project by integrating designs and drawings from different stakeholders. They aim to create a unified plan that contains no clashes and remains constructible. In practical terms, they make sure the spatial layout of everything makes sense – that no ductwork runs where steel beams sit, no wiring cuts through plumbing, and no systems sit too close to walls to allow maintenance access.

Teams call this spatial coordination effort clash detection. As Building Information Modelling (BIM) becomes more widespread, it's transforming how this key planning piece happens. Now, teams can use the model to analyse the project and look for clashes and constructability in a virtual environment.

This guide helps UK contractors, BIM managers and design consultants satisfy the Building Safety Act 2022, Part L energy mandates and ISO 19650 information-management requirements while keeping programmes on track.

What is Clash Detection in BIM?

When coordinating multiple trades, clash detection enables teams to spot problems long before they hit site. In the UK construction sector, effective BIM coordination ensures design packages meet the duties the Building Safety Act and ISO 19650-2 set out. Most teams begin digital clash reviews at RIBA Stage 3 (Spatial Coordination) and close actions by Stage 4 (Technical Design).

Understanding Clash Types

By one definition, a clash seems fairly simple: it occurs when project drawings call for two objects to intersect one another. Yet because different types of clashes exist, the concept grows more complex.

Hard Clashes

When drawings or models show two solids occupying the same place, this constitutes a hard clash.

Soft Clashes

Two tangible objects don't necessarily need to intersect to create a clash. Instead, a soft clash occurs when objects graze one another or sit too close to function properly. If a system requiring maintenance sits too near another object and personnel consequently cannot service it, this creates a soft clash. Some platforms let BIM managers build required tolerances into the model to enable soft clash detection.

Sequencing Clashes

These clashes develop not because objects overlap, but because programmes do. If the project deploys 4D BIM, teams might detect a clash when programmes don't align. For example, if the 4D BIM model schedules drywall installation before the ductwork behind it, this constitutes a sequencing clash.

How Clash Detection Has Evolved

While BIM clash detection makes spotting clashes easier by modelling them in a virtual environment, clash detection existed long before BIM. Because teams can't physically install two things in the same place, construction projects have always required spatial coordination.

Traditional 2D Methods

Decades ago, project managers laid paper drawings over a light box to look for overlapping systems and components. As software advanced, teams could perform clash detection digitally by overlaying drawings from different disciplines and looking for congestion areas. Some software solutions even enable colour-coding to make clashes more visible and easier to detect.

Today, UK surveyors increasingly deploy drones and LiDAR scans to capture existing conditions and enrich federated models before conducting 2D or 3D clash testing. Despite these advances, however, traditional coordination efforts remained confined to the 2D realm.

Moving to 3D Detection

2D clash detection can work effectively, but taking spatial coordination into three dimensions makes it more robust. This shift represents a fundamental change in how teams approach coordination.

The BIM clash detection process typically doesn't begin during design development. Rather, it starts once trade partners have sufficiently populated the model. In other words, teams need to add the systems and components from trade partners' drawings to the model before clash detection becomes effective. (If trade partners lack their own team to handle what the BIM model requires, third-party companies can help.)

As a clash-avoidance measure, project managers typically organise which items teams add to the BIM model and when they add them. The BIM Execution Plan (BEP) – issued in response to the Exchange Information Requirements (EIR) – and the company's established system hierarchy help here.

Many main contractors prioritise populating the building's structural components and hard-to-move aspects, like sloped piping, first. This approach enables teams to populate more flexible systems and components later around those elements, ideally minimising clashes. Teams share the plan for populating the BIM model in a sequenced, clash-avoiding way with stakeholders at the kick-off meeting.

Once the model has been sufficiently populated, the work of BIM clash detection begins. Many companies have a template of predefined sets of clashes they can use to run clash analysis on the model. That said, each project usually has its own set of rules that get applied during clash detection. Some projects might require a more granular level of detail than others, for example. 

Prevention Beats Detection

Detecting clashes provides value, but avoiding them altogether saves even more time and money. Consequently, UK contractors increasingly:

• Aggregate models in a Common Data Environment (CDE) early
• Run rules that auto-route services around the primary structure
• Assign issues to design leads for prompt action
• Verify resolutions before procurement

Applying Focused Detection Strategies

Even with BIM clash detection, project managers shouldn't rely wholly on the model. Effective coordination processes might require 2D coordination alongside 3D coordination efforts, because teams don't model everything – and not every model achieves 100% accuracy.

For example, coordinating items in a ceiling may need 2D work because objects sit above and below the ceiling, and 3D clash detection may not effectively identify conflicts when working from 2D plans that show all ceiling objects on a single plane.

The Targeted Approach

Many people think BIM clash detection requires an all-or-nothing approach. Either coordination and clash detection happens in 2D, or teams model the entire project in 3D and perform clash detection there. In reality, however, stakeholders can apply BIM clash detection judiciously. Rather than modelling everything, they might model specific areas of concern. 2D coordination can help them pinpoint potential congestion areas that they then model in 3D while leaving straightforward areas unmodelled.

On some projects – for example, healthcare builds – corridors can become jam-packed. As a result, a BIM manager might model corridors specifically. This allows stakeholders not only to detect clashes but also to deploy clash-avoidance exercises. They might take slices of the modelled corridors and develop predefined areas and elevations where teams should place necessary components. Corridors narrower than 1.8 m often trigger early clash reviews.

Meeting UK Compliance Requirements

In the UK, clash detection underpins compliance and business outcomes:

• ISO 19650-2

  Robust information-management processes - including clash reviews, issue tracking and model federation - are required on many public frameworks. Exchange Information Requirements and the BIM Execution Plan define when and how clashes are tested, resolved and evidenced.

• Part L

  Coordinated services layouts help achieve airtightness, reduce thermal bridging and maintain insulation continuity. Clash‑free routes avoid ad‑hoc penetrations that can jeopardise compliance and performance.

• Building Safety Act 2022

  Clash detection supports the golden thread and Gateway reviews by proving that life-safety systems are coordinated. Fire compartments, penetrations, smoke control, evacuation routes and plant access must be demonstrably clash‑free and traceable from design through to handover.

Quantifying the Benefits

When teams catch problems in the virtual environment, they fix them faster, easier and at lower cost. For example, a single MEP clash discovered on site might cost upwards of £8,000 in rework; detecting 100 such issues virtually saves £800,000. Projects therefore see time and money savings (often tens of thousands of pounds) by deploying BIM clash detection.

This is particularly useful in modern construction, where programmes have become especially aggressive. In fact, when stakeholders argue they lack time to perform BIM modelling, that project might need it more. Projects with tight timelines leave little room for error correction. BIM clash detection can minimise the potentially extensive delays that arise when teams install something incorrectly, from the time people spend finding a solution to the time required to uninstall the problem and reinstall it correctly.

Enhancing Safety Outcomes

Beyond cost savings, robust clash detection promotes on site safety. Industry research indicates that rework accounts for around 5% of project value in UK construction and contributes to increased safety risks. Quality work therefore provides a safety buffer, and thorough analysis looking for potential problems helps reduce the rework needed. CDM 2015 specifically tasks designers with eliminating hazards at source; clash detection offers a practical compliance method.

Supporting Prefabrication

Coordination – including BIM clash detection – is particularly useful for prefabrication. Clash detection allows stakeholders to trust the model, which enables them to prefabricate systems and components in a safer, more quality-controlled environment than on site. Teams can then ship these elements to site and install them much more quickly than if they built them from scratch. Clash-free kits (components designed to fit together without conflict) also support the UK's MMC drive.

Overcoming Detection Challenges

While BIM clash detection yields serious benefits, it presents some drawbacks. Understanding these limitations helps teams use the tool more effectively.

The Constructible Model Goal

First and foremost, there's no such thing as a clash-free model. Pursuing one can waste time. Certain things in the model simply don't justify the effort required to clear clashes. If a clash involves flexible ducting, for example, asking the mechanical team to change the model wastes time and money. Instead, the BIM manager will generally approve the clash in the model.

Instances also exist where clearing a clash would interfere with operability. Adding several bends to a pipe might clear a clash, but too many bends could inhibit its performance.

Ultimately, we shouldn't focus on achieving a clash-free model. Rather, the emphasis should fall on creating a constructible model. Here, the knowledge and expertise of people with experience on similar projects is invaluable.

Addressing Scope Gaps

BIM teams at general contracting firms must also watch for potential scope gaps in the model. Soffit walls, access zones, equipment furnished by others, fireproofing and scope changes that teams may not include as part of the BIM coordination efforts typically need to be added to guarantee a robust coordination effort for the project.

Emerging Technology Advances

Today, BIM models enable the automation of much planning work required for construction projects (for example, 3D take-offs). This extends to coordination and clash detection as well.

As technology advances, BIM clash detection should grow faster, easier and more accurate. Stakeholders can develop rules, then use AI to automate clash detection based on those rules. Some software will even auto-route certain systems to avoid clashes. UK contractors are already piloting AI-driven auto-routing aligned to ISO 19650 rulesets. However, keeping a human in the loop remains important to ensure automatic changes don't interfere with constructibility or operability.

Streamlining Clash Management

Additionally, advancements make clash management easier to handle. Some current solutions can group similar clashes together. This way, the person tasked with resolving them only needs to review, say, a dozen categories rather than hundreds of individual clashes. When the clash-detection tool connects to the coordination tool, the team can manage and track clash resolution in an organised, streamlined manner.

The Strategic Perspective

While BIM clash detection will likely change in the coming years as technology advances, one thing won't: clash detection should form part of a broader coordination strategy, not stand alone as a solution. Teams need to emphasise developing a constructible model, not necessarily a clash-free one.

Quick Answers

Can Revit detect clashes? Yes. Use Revit's Interference Check before exporting for more granular rule sets.

What is a BIM Execution Plan? It's the agreed process map – mandated by ISO 19650 – that sets modelling standards, data drops and clash-review cycles.

Key Takeaways

• Eliminate rework costs by detecting clashes virtually
• Meet Building Safety Act duties and Part L energy targets
• Support MMC and prefabrication to speed delivery

Ready to streamline coordination? Speak to a product expert or explore more resources in Procore's UK Library.

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