IFC, Revit and You

In Australia and likely elsewhere, a lot of people believe that BIM = Revit, however this is certainly not the case; there are many other software packages out there and if you need to collaborate with these software packages, chances are you will need to use IFC files.

IFC stands for Industry Foundation Class, it is a platform neutral file format that is not controlled by any of the software vendors.

For those that haven’t worked with IFC files before, there are a few things you need to keep in mind before you jump headlong into working on a project where IFC is used for collaboration. I will specifically be talking about my experiences working with IFC outputs from ArchiCAD.

You need time

Depending on the size of the project, the process of importing and IFC file into Revit could take a very long time. IFC imports can be anywhere from almost instant to a few days. You need to make sure that you clearly communicate this not just with your engineering team but with your architecture design team as well.

It’s very important to keep an open line of communication with your architect. Pick up the phone.. or more importantly answer the phone! Don’t let problems go unsolved sitting in someone’s inbox. 5 or 10 minutes spent on the phone with the architect might save hours of time for both of you down the track. They will be able to split large projects into smaller chunks or limit what elements are being exported from ArchiCAD so that the heavy lifting your hardware needs to perform is more manageable.

In all my testing, Revit appears to use 2 cores at most when importing IFC files. If you have a fast multi-core machine, you can set more than one file to import at a time. I highly recommend selecting each instance of Revit that you have open and setting the CPU affinity in task manager. This forces windows to spread the load across your CPU, maybe I’m imagining it but I found that if I didn’t do this all Revit processes seemed to share the same few cores; without doing this my 6 core/12 thread Xeon CPU sat at around 12% utilisation where as if I forced each instance of Revit to use certain cores I could push my CPU usage towards 80% utilisation. The problem you will face though is RAM. On some IFC files even 32gb is not enough.

For the Revit users on the team, push for the use of 2015 or newer; there really is no reason to dilly-dally in the comfort of older versions of the software. Revit 2015 brings to the table more efficient IFC imports through the Link IFC option. It is not a true IFC link, Revit actually converts the file to an RVT on the fly, in my testing using IFC Link instead of the open IFC method saves up to 60% on import times. The first iteration of architecture I received for the most recent project I’ve been working on took just on 3.5hrs to import a 286mb IFC file using Open -> Open IFC where as using Link IFC on the same file took only 24mins.

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With some helpful splitting of models by the architecture team you can improve your workflows significantly.

I have worked on two hospital projects authored in ArchiCAD and we split the FF&E from the building fabric. The building fabric was always imported first and the FF&E flowed on afterward. We always requested up to date DWG exports of the floor plans that could be overlayed to reflect the FF&E as well.

You need DWG files

DWG files will play a very important role when working with IFC files, they will allow you to keep up to date quickly with furniture layouts but they’ll also help speed up your model. ArchiCAD seems to be able to handle higher polygon counts far better than Revit can which leads to glorious, highly detailed furniture models, trying to run a model with the 3D furniture models loaded in is going to slow you and your team down to a crawl. You don’t need to coordinate in 3D with a chair, but you may need to know where it is so you can place power and data outlets or other equipment. DWGs are the best way to do this.

Make sure you follow all the usual rules about DWG files. Keep them clean. Link them into their own host model, don’t insert. Never link or load them into your live model where possible. There is an article in the June 2015 AUGI magazine which goes into detail on best practice. Something they suggest that I’ve never tried before is to insert the DWG files into an *.RFA file and then stack the *.RFA files in the host model. If it means that it will be less problematic, go for it.

I2015-07-16_9-44-57FC files do not carry ceiling tile information

Don’t worry though, you asked for DWG files remember? Depending on what you want to show on your plans, you may need to link the DWG at certain heights so that they fall within the view range of your ceiling plan.

Again, follow best practice with linking in DWG files to a host model. Do not locate your RCP DWGs in your working model.

You need to understand coordinates

And you need to understand them well. When working with IFC exports from ArchiCAD, you will be working at the architect’s origin location, not shared coordinates. As much as it has probably been drummed into you to “always use shared coordinates” there is nothing actually wrong with using an origin to origin system.

In fact when importing an IFC file you don’t get a choice of how to bring the file in, Revit will automatically import at origin to origin. This poses a problem if you’re also collaborating with a civil team, but this is pretty easy to overcome, you just need to make sure that it’s part of your workflow.

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You can’t host families to an imported IFC

Unless you’re going to draw hundreds or potentially thousands of reference plane, forget about using those face hosted families that you’ve become so accustomed to.

As you’re probably aware, all elements in Revit have a unique identifier, also known as an element id or global unique identifier (GUID). For whatever reason, Revit does not have a consistent way of applying GUIDs to imported IFC elements. This means that today the wall on ground level at grid intersection D5 might have an element id of 654321 and next week, it could be 751155 and as a result your hosted families will become orphaned. Or worse yet, maybe now a different wall from level 10 has picked up that original 654321 identifier and now your data outlets have been automatically moved to that new location by Revit.

At least this was the case in earlier versions of Revit. In newer versions of Revit you simply are not even allowed to host a family on an imported IFC face at all.

My advice would be to develop a suite of unhosted families. IFC is going to become more prevalent in the future especially as some governments around the world are mandating the use of IFC so you’re going to have to deal with it more in the future, you might as well be prepared.

Never ask the architect “Can’t you just do it in Revit?”

Unless you want the architect to ask “Well can’t you just do it in ArchiCAD MEP?” then don’t; and yes in case you were wondering there is an ArchiCAD MEP. Seriously, show a little respect. Sure Revit has a larger market share than ArchiCAD but that is not the point. BIM shouldn’t be and is not restricted to a single piece of software.

At the end of the day it’s not actually that hard to work with IFC files. Sure you have to think about things a little more but that’s OK because how boring would life be if every day was exactly the same? The most important thing if you’re on your way to higher levels of BIM is to make sure you get the rooms imported from the IFC file, that way you can still create MEP spaces and in turn perform all your MEP calcuations quite successfully. Otherwise if you’re still finding your feet in BIM and Revit is primarily a 3D documentation and coordination tool, working with IFC isn’t as hard as you might think it is.

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