Issue with roof coming from Revit

Cyril

Hi,
I encountered an unusual strange issue I don’t know how to fix. I made a BEM model based on Opening Design Aalseth Residence. When I export to IFC it from Revit, roof became :

• made of thin layers instead of a solid geometry
• roof are wrongly classified as IfcSlab despite

I have no override anywhere. I tried with IFC 2x3 CV2 and IFC 4 RV and got same result. I opened the IFC in XBIMXplorer and Blender with BIM Addon and get same result so it is really an export issue.
As anyone ever encountered this issue ?

This model will be used to showcase BEM analysis I am working on and will be available as Revit file, ArchiCAD file and hopefully when we will found out how to generate IfcRelSpaceBoundary2ndLevel some day as Blender file.

Bedson

If you add a Shared Parameter called IfcExportAs and give it the value of IfcSlab.ROOF then this should correctly classify the element when exported from Revit.

Cyril

@Bedson said:
If you add a Shared Parameter called IfcExportAs and give it the value of IfcSlab.ROOF then this should correctly classify the element when exported from Revit.

According to wiki it is hardcoded : https://wiki.osarch.org/index.php?title=Revit_and_IFC_classes but I missed that the roof is decomposed by 2 slabs while main class is IfcRoof as expected.

The real issue is only on geometry then.

Moult

It's been on my to-do list to finish that somewhat empty table on the wiki page - you'll notice roofs are empty. I want to confirm (i.e. by reading the code) exactly what the behaviour is. For example, curtain walls can be treated as roofs, and I need to check the effect of exportByComponents here.

I'll try and replicate your bug on Monday when I get access to Revit :)

Cyril

Thanks. For info I opened an issue #244 and it include sample files containing the issue.
Edit : apparently actually an IFC4 RV only issue (I probably did something wrong in my previous tests)

Moult

A note that the behaviour for roofs may change when the IFC4 certified version gets released (currently 17 days and counting!)

See this commit: https://github.com/Autodesk/revit-ifc/commit/64786c58fd6a34254cbf0e292966459334599fa8#diff-533e2b27282abd03f34b4bcb24d70fc76015f0c6534c96b45599a5f17be35af4R212-R216 - see how in RoofExporter.cs it can now export just a roof, without being a slab aggregation.

I see similar improvements for other categories, like walls, which from skimming through now seems to be able to be assigned to any IFC class.

This is good news.