What is the most important thing in BIM? At least everyone agrees on this question - it's about the Iinformation that is assigned to the components. In order to make this information understandable for everyone in the openBIM process, buildingSMART has also defined corresponding property sets in the IFC schema for each class, which describe the essential properties of this component. This ensures that any software in which this IFC is read out can find these properties straight away.
These properties are defined as Common Property Sets and are also exported by default during IFC export from Revit, whereby it should be noted that
Not all properties from the IFC schema are available in Revit by default!
The reason for this is simple - many of these properties are probably only relevant for a few projects and having them available by default in Revit would overwhelm the user.
But let's look at this in detail using the example of a wall:
Link to the current IFC 4 documentation
Here we can see exactly which properties are contained in the Pset_WallCommon. For the export, it is important that the following option always remains activated:
Export of standard properties available in Revit
If we now export a wall from Revit, we see the following:
This means that the following parameters are automatically mapped in the case of a wall:
Pset_WallCommon
ExtendToStructure = Top edge is fixed. (Yes/No)
IsExternal = Function (External = Yes, Internal = No)
LoadBearing = Load-bearing structure (Yes/No)
Reference = Type name
ThermalTransmittance = Thermal transmission coefficient (U)
FireRating - missing
Combustible - missing
SurfaceSpreadOfFlame - missing
Comparmentation - missing
Status - missing
There are two ways to describe the missing parameters:
- either parameters with exactly the same name and data type are created and filled in Revit
- or values of other Revit parameters are mapped to these parameters (prerequisite: the same data type)
Add IFC properties in Revit
In this case, it is easiest to use the shared parameter files supplied with the Revit IFC plugin, as you do not have to worry about the data type in this case.
The following path applies for Revit 2021:
C:\ProgramData\Autodesk\ApplicationPlugins\IFC 2021.bundle\Contents\2021\IFC Shared Parameters-RevitIFCBuiltIn_ALL.txt
- Free choice of type and specimen
- Grouping is not decisive, but IFC parameters are recommended for a better overview
- Important: select the correct categories in the right-hand window
- The parameters do not necessarily HAVE to be shared, but it is recommended as part of good BIM management
All IFC parameters that you create and fill in this way (note: parameters with empty values are not exported!) are also automatically added to the PSet_WallCommon.
Unfortunately, the disadvantage of this method is that you have terms such as Combustible in your Revit project and therefore the requirement is that the employees understand all these terms and can assign them correctly. For this reason, parameter mapping tends to be used in practice.
Mapping of Revit properties to IFC properties
To map your own Revit properties to the IFC properties, use a parameter mapping table - this is a simple text file with the following syntax:
A text file prepared in this way can then be selected in the IFC Exporter and causes the values of the Revit properties to be transferred to the corresponding IFC values:
One final note: it is not intended to assign properties other than those already defined in the IFC schema to the standard property sets, as they would lose their universal character.
However, additional properties can be defined in the form of user-defined property sets - more on this in the next article!
Hello Lejla, with Revit ifc export, nested families, i.e. an assembly with several individual parts, are dissolved and only the individual parts are displayed in ifc. The parent family with all the information disappears in the ifc. I know that I can declare the individual parts as not shared in Revit, but that would destroy my parts list in Revit. Is there a way to export such a Revit model to ifc so that the parent families with all BIM information appear in ifc?
Greetings
Hello Zeljko, unfortunately I am not aware of any other way than the one you describe - although of course I can understand that this is not always desirable in the Revit project itself. In any case, it's an interesting question - I'll ask the development team about it!
Greetings, Lejla
Hey Leijla, your posts are really very helpful and have a very good quality in terms of content. Thank you very much for that!
But I have a question regarding Revit and IFC.
How can I define my own types for a component and export them under this name?
Example: Wall has the predefined types according to IFC: MOVABLE, PARAPET, ELEMENTEDWALL etc.. However, I would like to define a type for the component via IfcExportType that does not exist in the data structure.
How can I do this in Revit?
Best regards
Oguzhan
Hello Oguzhan,
thank you for the nice comment, it's always nice to hear that someone is reading along here and appreciates the content!
Predefined types are defined in the IFC schema, and in your case you would have to use the predefined type USERDEFINED here and then set the value via ObjectType - in the current IFC manual you can also find this on page 16 including screenshots - here is the link to the manual if you don't have it yet: https://www.autodesk.de/industry/bim/interoperability/ifc
Best regards,
Lejla
Hello Leijla,
Thank you very much for your interesting contributions. I am currently facing a problem for which I have not yet found a solution. I have created a shared parameter that I have assigned to the Material category. I can therefore fill this parameter in the material browser. Unfortunately, I have not yet managed to export it to an IFC file. Do you perhaps have a solution?
Best regards,
Julia
Hello Julia,
unfortunately this is not yet possible - but it is already on the Revit roadmap: https://trello.com/c/yRJcgVDd
Best regards,
Lejla
Hello Lejla,
First of all, thank you for this column! It has been helping me for weeks with the introduction of BIM in my office.
I have a question about the mapping of Specific Psets - e.g. for a wall. I would like to assign parameters such as maintenance (truth value), maintenance interval (positive integer), construction costs (positive number) to the components. The parameters exist in Revit and have a value. I export with user-defined property sets in whose table I have entered the new parameters. However, they do not come out in my IFC viewer.
Do you know what the problem could be?
Kind regards,
Antoni
Hello Lejla!
I have a question, we are only at the beginning and are just taking the last steps towards BIM certification.
My question would be how it works with the non-standard parameters such as fire resistance, sound
how these look when exported.
LG
Julian
Hello Lejla,
Can you create a new IFC class? In other words, an IfcElementProxy in any IFC class of your own devising. Like IfcBimMeUp, for example?
Thank you and best regards
What do I have to consider if I want to export type and element parameters of a component into a user-defined property set? I always get one property set for the type and one for the element. But everything should be displayed in one set. Thank you!
Wie kann ich Fassadensysteme als “IfcWindow” statt “IfcCurtainWall” aus Revit exportieren?
Ich habe in den Exporteigenschaften alle Fassadensysteme zu “IfcWindow” übersetzen lassen, jedoch in der exportierten Datei wird jedes Fassadensystem übergeordnet als IfcEntity “IfcCurtainWall” bezeichnet.