BIM Project Coordination - Initial Clash Detection

BIM Project Coordination, when reduced to its lowest terms, is simply building a project in virtual space first, in order to uncover and fix as many construction problems or conflicts as possible.  In a perfect world, it would find all of the problems and the actual construction would go smoothly, be completed on time and within budget.  Alas … this is not a perfect world.

With Autodesk® Navisworks, we have come a long way from the days when a group of high-priced journeymen from several trades stood around pointing fingers and saying things like: “Well that’s your problem? We were here first,” or “Mine is bigger than yours” (referring, of course, to ducts versus pipes), or the ever popular “It’s already installed!  You can submit a change order and we’ll be happy to move it for $,$$$.” The huge waste of time and money wasn’t limited to needless change orders and wasted material. The cost of those impromptu “Oops, it doesn’t fit” meetings was phenomenal.

When BIM project coordination is done right, everyone comes out ahead.  Owners get expected results, at or below budget, GC’s get to manage the project instead of dealing with crisis after crisis, sub-contractors have predictable material and labor costs and can pre-fabricate large sections in house, then ship them to the jobsite for installation.  This creates material and labor efficiencies, along with added profit.

Line ‘Em Up

For now let’s look at what to do when all of the models have been submitted to you for initial clash detection.  The number of models that will become part of your compiled work will vary from project to project, but typically will include at least: architectural, structural, mechanical (ducts and hydronics), electrical, plumbing, and fire prevention.  More often than not, your model will also include framing and/or drywall, acoustical ceilings, and any special building features such as sky lights or solar tubes.

Navisworks is very good at interpreting, combining, and displaying 3D files from many different software packages.  At last count, I think the number was over 40 file formats.  However, it takes a little planning and a great deal of reminding your group of contributing contractors what the project origin is and its proper orientation.  That seems simple, but don’t ever assume it is understood by everyone, even after it has been discussed. 

Different 3D design packages treat origin and orientation in vastly different ways.  So be very clear on these points at the kick- off meeting and all pre-coordination meetings.  If you think you’ve mentioned it too often, it's time to bring it up again.  Think of it the way we used to vote in Chicago, under the original Mayor Daley: do it early and often! 

In Figure 1 we see a project where these two “minor” details were apparently not very clear to all parties.  As you can see, clash detection can become downright impossible when individual models are not lined up properly in all three planes.  When you're coordinating multiple trades in tight spaces, even fractions of an inch matter.

Figure 1: Origin and orientation may not be understood by all.

Initial Clash Detection

Before you actually run your first clash detection, open the clash detective, go to the "Batch" tab and set up the items you want to compare in your Navisworks model.  These would be the same things you would be looking for on the job site, if there was no BIM coordination being used.  Typical examples are mechanical versus electric; fire versus plumbing; steel versus mechanical;  electric versus framing; and so on.  Be sure you include every combination of the trades you are coordinating.  There is nothing worse than getting to a point in your coordination effort where it looks like everyone is clash free and  then realizing you forgot to include “something versus something.”  It is truly a "Wanna Get Away" moment.  Not that I have ever experienced such a thing.  Uh ... moving right along.

The results Navisworks gives you the first time you do a clash detection on a newly compiled model might be a bit daunting.  You may get numbers in the hundreds, maybe even thousands, depending on the size and scope of the models you have brought together.  Don’t let the numbers scare you.  This is why you get the big bucks, but more importantly, this is your opportunity to differentiate yourself from others who claim to be BIM project coordinators.  Now is the time to work your magic.  It is up to you to take the seemingly endless sea of clashes laid out before you and make it understandable.  Not just understandable to you, but to everyone in your coordination meetings and everyone who will ever view the file. 

There are several tools at your disposal to help make this happen. The first one you should employ is the Rules tab in the clash detective.  This is especially helpful when managing clashes involving drywall, floors, footings, architecture, and others. We all know that pipes and ducts have to go through walls.  Navisworks, being ever vigilant, generates a clash each time something goes into and out of a wall.  By defining some Rules, Navisworks will look the other way, when you tell it to, and you can eliminate a multitude of clashes that would just end up being approved anyway.  Figure 2 shows some common rules that might be helpful.  Use rules to your advantage, but be careful not to rule out too many conditions.  A pipe that is supposed to run parallel to an exterior CMU wall, but is in fact modeled so that it resides partially into the wall, will not show up as a clash if you have ruled out pipes and exterior CMU walls.

Figure 2: Use Rules to trim your clash list.

Organize Clash Groups

Grouping is your next weapon in the fight against chaos.  When you group clashes, they instantly become more manageable for you and more understandable for your team.  Because of the way Navisworks creates, displays, and thinks about objects, there will be many times when what looks like a single clash between two components, such as a duct and a fire sprinkler head, will generate multiple clashes—perhaps 10 or more.  These clashes presented for your resolution will most likely not be listed together.  They might be clash numbers 6, 7, 8, 11, 14, 15, 16, 17, 29, 42, etc.  So instead of taking the time in your coordination meeting to find and show each micro view of the same clash, create a folder in your clash detective results list.  Give it a name that is short but descriptive.  I like to begin with the number of the first incidence of the clash.  Then drag and drop all of the other views of the clash into the folder.  Voila—many become one. 

Another good use of clash groups is to combine all clashes with the same status.  Approved or resolved clashes have already been dealt with, and just get in the way of your productivity.  Your active clash list will be long enough without sifting through these, as well.  Make a folder for each and simplify your work by cleaning up the clutter.  By grouping, you can also save time, because when you change the status of a folder, say from active to resolved, the status of all clashes contained in that folder changes. Figure 3 shows some folders used to make large numbers of clashes manageable.

Figure 3: Group clashes to save time and brain cells.

Use Viewpoints for Freedom

Viewpoints are valuable tools you can use in your coordination effort.  They are snapshots of scenes you feel are important that can be named and saved.  You can add text, dimensions, clouds, etc. in order to further clarify a particular situation.  An even more important reason to use viewpoints is that there is a good possibility that all of the people who will have the need to view your coordination file will not have access to a full featured version of Navisworks.  Some of them will be using Navisworks Freedom, the viewer provided by Autodesk at no charge. 

While Freedom has many excellent features and is an amazing piece of software for free, it cannot see the clash detective or any clashes contained in it.  It does, however, allow the user to see all saved viewpoints.  Pick the best view in each group-o-clashes, then save it as a viewpoint.

Viewpoints are also a great way to quickly jump between different project views and conditions.  If there's an area of the project that you know will be discussed, take your time to get the right view angle and scene composition then create a viewpoint.  Like clashes, they can also be organized in a logical folder and file structure to make your life easier.  And isn't an easier life almost always a good thing? 

Stay tuned for further tips on how to become a Superstar BIM Project Coordinator.

John Segler has been working in Mechanical and Architectural Design, with AutoCAD since release 9.  Revit and Navisworks have become his weapons of choice for 3D Modeling and BIM Coordination, since their 2009 release.  He is the BIM Manager for Create 3Ds in Las Vegas, Nevada.  John is also a Licensed General Contractor and can be reached via

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