IFC Export Roofs problem

[Anonymous]

Hi everyone !

I have problem with export to IFC.

I am looking at my exported file in Bim Vision and there is one problem. Roofs are imported in two ways.

1. Roof in one part

2. Roof divided into two pieces, which are not classified as a roof, but as a slab. So instead of roof I have two slabs.

Roofs were made in identical way in Revit.

Could anyone help me to solve te problem?

[ToanDN]

When I export 2 identical roofs to IFC, they all become separate panes. I cannot get one to show up as a gable roof like you show. Granted I am only able to view the IFC by linked it back in Revit, not via another IFC viewer.

[Anonymous]

I just checked one more time. I think have an idea, when I made symmetric roof it is exported in two pieces, but when I made asymmetrical roof it was exported in one piece. Still there is an issue, one of them is treated as a slab, another as a roof. Where can I change this before exporting to IFC?

[ToanDN]

Spot on finding!!

Can you take a look at the IFC export options see if you can change anything?

[Anonymous]

I am thinking all day what makes these roof different, so finally ! 

Yes, I was looking for something in IFC options and I tried many different solutions, but I can't find something that will change this IFC type. I will keep trying

[RDAOU · Accepted solution]

Hello @Anonymous ... 🙂 @ToanDN

when you exported the IFC, you saved in a folder...in that folder a new REVIT file is created with the extension .ifc.rvt

1. Open that file
2. Select the roof elements which are not define or which you want to redefine
3. on the Properties Pallete, select from the drop down menu the IFC definition you need Example IfcSLAB.Roof

Now you need to note that symmetrical roofs will be exported as two slabs+ 1 complete element (i.e.: 3 IFC elements) and that's perfectly normal...asymmetrical roofs will go as 1 element ... In total 4 elements.

we usually keep the two elements from the symmetrical roof and delet the extra 3rd complete .... And in case or asymmetrical roof we convert to parts before exporting in order to obtain two elements in IFC as it is supposed to be)

same for multi layered walls and floors (provides better detail when working 5D)

i will upload screencast once it's on the server

[RDAOU · Accepted solution]

Can't edit previous post to add screencast...so here it goes 

[Anonymous]

This works great. Thanks a lot !

[JoepFIM · Accepted solution]

I am probably a little late with my answer but coincidentally I also experienced the same problem this week. I also experienced an additional problem with IfcRoofs. It seems that it is impossible to get the correct volume from an IfcRoof and when you look at the underlying IfcSlabs they show the total volume (of the IfcRoof) giving you double or more amounts of roof. BIG fail.

My solution for this turned out to be to export the roof as an IfcSlab.ROOF using the IfcExportAs parameter. Hereby I neatly get 1 roof with the correct volume values.