Clash matrix: a tool for BIM coordination

How many times during the execution phase have you had to solve an unexpected problem that has suspended the construction site and caused delays? Surely at that moment you would have wished that problem had been identified and solved earlier, perhaps in the design phase.

With the BIM clash detection matrix this is now possible! Let’s find out what it is, how this matrix is made and how it can help you coordinate your project with a BIM coordination software.

BIM Coordination

What is a clash matrix?

The clash matrix is a tool that establishes coordination priorities deriving from a hierarchy of systems that follow each other chronologically throughout a building’s construction phases. This hierarchy is nothing more than a way to divide the various construction systems in order:

• architectural and structural elements
• mechanical systems (HVAC)
• plumbing systems
• electrical and fire-fighting systems

Once the systems hierarchy is defined, you can build the so-called Clash Matrix. It is usually presented in the form of a hierarchical table showing which disciplines have priority based on their distance from those listed in the upper-left part of the matrix table.

The matrix is a powerful tool which allows the project team and the BIM coordinator, to make quick decisions in case of conflicts and therefor introduce the necessary changes.

In its most simple representation, a clash detection matrix is structured as follows:

Example of clash detection matrix

Let’s see an example.

We’ll start of by specifying an alphabetical order but using numbers works too when indicating coordination priorities. The red letters identify interferences and/or responsibilities within the same discipline (architectural, structural, HVAC, etc.) and for each letter there’ll be a coordinator assigned as well.

The alphabetical sequence specifies the order in which the interference detection takes place, so first the architectural and structural model will be checked than the others, and so on. The process starts from the control of these model types because any geometrical changes may affect other models causing critical errors across to all other models involved in the BIM design workflow.

Should an interference occur between the architectural and structural model, this is therefore recognized as a priority and must be resolved before any other interference and as soon as possible. The electrical system, in fact, compared to the structural model, consists of objects that can be easily moved and adapted to a new configuration in consequence of a clash between the architectural and structural models.

Furthermore, if we modify the electrical system before even addressing a clash detection between the architectural and structural models, we could end up needing to modify the electrical system twice:

• to resolve a possible conflict with other disciplines;
• to adapt everything to changes introduced in the architectural model following a clash with the structural model.

Following this process, the interference that occurs in the area of the matrix specified in yellow (see figure below) have a greater priority compared to those detected in the red area.

priority in the clash matrix

How does the clash matrix help us?

Creating and knowing how to read a clash matrix correctly has more than one advantage:

1. you can find out which problems have major priority for resolution and on which model you’ll need to work on first;
2. you don’t need to “guess” which disclipline is responsible for a given collision. For example, the HVAC designers are responsible for resolving interferences with the architectural and structural models;
3. you know what checking rules are necessary to prepare during the coordination plans.

What is a detailed clash matrix?

The detailed clash matrix is another table that specifies coordination priorities. This time, instead of analyzing the model as a whole, it can be broken down into multiple parts.

Let’s see an example.

Consider the letter H of our clash matrix. This specifies a check between the structural model and the water distribution system. As you can see, so far we have considered the model as a whole. But now we’ll break down the structural model into its elementary members: floors, walls, columns, beams.

Example of a detailed clash matrix

A clash matrix, when based on this decomposition method, can be useful for large or complex projects with a large number of elements and for which a very precise level of control is required.

In conclusion, I really recommend trying the BIM clash detection software for free and see by yourself how easy it is to handle design interference issues when using the right tools.