Remove Your Blinders

In March 2013 I wrote an AUGIWORLD article about easily managing thousands of clashes in Autodesk® Navisworks® without being overwhelmed; that article was only a part of my workflow. What I will cover in this article is actually more important than merely how you handle clashes. This article will show you how to utilize custom clash tests to gain a better understanding of coordination issues and cut meeting prep time in half.


Before we get into custom clash tests we need to talk about the current workflows that I have seen from many BIM managers when preparing for a coordination meeting.

How many times have you seen 25 or more clash tests in one file waiting to be scrubbed?

Figure 1: 25+ clash tests

Anyone who has had to comb through 25+ clash tests knows how long it can take.

And how many times have you been flying through the model in your “Fire vs. HVAC” test and you run into a situation like that shown in Figure 2?

Figure 2: Train wreck

Even though you have multiple hits with multiple trades, you don’t mark all of them because you’re in the wrong clash test and worried about creating duplicates when you get to your “Plumbing vs. HVAC” test. Even more important than duplicates, what happens if you create a view for the plumbing hit in one clash test and a separate view for the electrical hit in another? You might end up telling the electrician to raise over the duct only to find out later that the duct has to move up to miss the plumbing lines. Even more frustrating are the issues that involve complex solutions that take a lot of time just to plan, and then finding out it won’t work because another trade down the line wasn’t taken into consideration.

When you have 25+ clash tests, whether they be trade against trade or priority against priority it is still like clashing with blinders on. In order to efficiently solve constructability issues you have to be able to understand the whole issue, which is almost never limited to just two trades. I’ve heard it asked before: “Why would you clash everything against everything?” To that I respond, “Why wouldn’t you?”

There have been whispers of Navisworks one day being able to clash by area. Until that day comes, clashing multiple trades at the same time is essentially the same thing. Instead of marking clashes individually you can start marking areas of concern and working through areas instead of instances. Besides the huge time saver of scrubbing areas instead of instances, your comprehension of all trades involved and their limitations will be greater.

I don’t actually clash everything against everything. I have four custom clash tests.

One for All

What is a custom clash test? Some of you may have seen the custom clash tests folder buried in your Navisworks root directory and wondered why it was there. And some of you may already know what custom clashes are, but have never seen a practical use for them. Whatever your experience with custom clash tests may be, my goal is to help you see their value and create your own.

Custom clash tests are a powerful Navisworks tool that enables you to combine multiple tests and rules into one clash test. Here are my four tests and what they include.

Figure 3: 4 = 25?

I’m sure one of the first questions that comes to mind when seeing this many clash tests being reduced to four is, “How do you manage the amount of clashes that kind of a test will produce?” That will take too long to explain in this article, but my 2013 article, “Thousands of Clashes in a Thousand Seconds,” gives a good overview of how to manage that many clashes.

This article will show you how to create your own custom clash tests that can transfer to any job while keeping all your rules and search sets, as well as some of the sorting and filtering options you will have that normal clash tests don’t offer.

I broke my workflow into four custom tests that I felt were manageable, but broad enough to give me a clear understanding of problem areas:   

            Structural vs. All Trades

            Ceilings vs. All Trades

            Framing vs. All Trades

            All Trades vs. All Trades

You might decide you want to combine different tests. I would encourage you to evaluate your workflow and think about what tests you can combine. Even if you only combine half of your current tests it will still shorten your meeting prep time considerably and help you understand the issues more clearly.

Creating Custom Tests

Creating a custom clash test is actually very simple. To begin with, create all the tests you want to combine into one custom test. Check all the rules you want to apply to each test and make sure you use search sets for all your tests. If you do not use search sets for your tests, the custom tests won’t work on other projects. Creating unbreakable search sets is the first obstacle that people ask me about: “How do I create a search set that will work for every project?” Some turn to naming conventions in order to create search sets that transfer between all projects, but there are a number of issues that occur more often than not when trying to control the deliverables from some contractors. Why not use something that you always have control over, such as the folder structure you copy from project to project?

Figure 4: Search sets by folders

The file name in Navisworks shows the entire file path. Because you have a standard folder structure you can create search sets to select everything in the plumbing folder and everything in the fire folder, then use those for your plumbing vs. fire clash test. Search sets based on folders on your computer that should never change will never break.

Now that you have your clash tests made using unbreakable search sets it’s time to start the long process of creating your custom clash test. On the Output tab of the ribbon, click “Clash Tests” to export an XML of all your clash tests, then save that file to your custom clash tests folder here: C:\ProgramData\Autodesk Navisworks Manage 2016\custom_clash_tests. The “ProgramData” folder is a hidden folder so you need to make sure your computer folder settings allow you to see hidden folders.

Figure 5: Export an XML

That’s it. You’re done. Now after restarting Navisworks you will see a new test option under “Type.” As soon as you select that new type of test, you will see the selection A and B become greyed out. This is because your new custom clash test has all of the information it needs stored inside that XML you exported.

Figure 6: Your new custom clash test

Advanced Sorting and Filtering

Custom clash tests make sorting, filtering, and isolation much more powerful. One of the first things you will notice when reviewing a custom clash test is the description of your clashes no longer says “Hard,” but instead it is replaced with the names of the individual clash tests you used to create the custom clash test.

Figure 7: New description

With unique information in the description you can now sort and group by those original clash tests if you desire. But if I group all my clashes by their original tests, then what’s the point of a custom clash test? With the “Highlight all clashes” box checked, the “Dim Other” and “Hide Other” commands will now allow you to clearly see everything that’s hitting or just the trades that you want to see.

What if I want to clash very specific items inside my HVAC file? Easy. With the “Inclusive” filter, I can select those items through any means and then group the related clashes together. Then using “Hide Other” I can see where those specific clashes are, and “Dim Other” will let me see any surrounding issues that might affect me.

My common workflow is to group all of the clashes together and review by area. This allows me to quickly break a building out into trouble areas and understand all the issues in each area so it’s easier to determine a solution. Clashing by area also cuts scrubbing time in half. For example, instead of having six clash viewpoints each in different clash tests, I have one clash viewpoint.

I have been using custom clash tests for three years now and will never go back to the mind-numbing task of scrubbing 25+ clash tests while wearing blinders.

With a little sorting and filtering, custom clash tests will be a powerful tool for you—no matter how you manage clashes.

The Navis Ninja, aka Mark Hunter, is an innovative and talented Navisworks professional.  After being recruited by C.W. Driver as a BIM Manager, the Navis Ninja developed a new workflow for coordinating buildings that slashed the prep time in half.  Key to the Navis Ninja’s success was his ability to help his team members “take their blinders off” and shift the paradigm for coordination that made the process twice as efficient and twice as fun. Outside of coordinating some of the most complex and congested buildings for C.W. Driver, the Navis Ninja is known for vetting new technologies (i.e., integrating augmented reality through a high-end professional quadcopter) and constantly finds himself evading sleep while working on his next innovative project.  To follow and track some of the Navis Ninja’s latest developments, frequent Mark can also be reached at, or at 909.945.1919.

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