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What is the right IFC entity for water outlet into a structural IFC model

It is for Structural engineers vital to dimension large roof opening / water outlets to prevent flat-roof collaps on heavy rain and clogged rain drains. At least in the Netherlands there have been circa 20 roof collapses because of this problem.

we had the same case, not just with these openings on roof but in general all openings in structural and non structural components. In IFC2x3 i was not able to find a proper entity for this matter, except the IfcRelVoidElement, therefore we used IfcBuildingElementProxy with a defined NAME and set some custom P_Sets. You must take care that nothing else in the Model has this entity. And it worked perfectly.

In IFC4 ADD1 so far what I have seen is that IfcBuildingElementProxy has an Enumeration for PROVISIONFORVOID.

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Would IfcWasteTerminal.PredefinedType=’.ROOFDRAIN.’ fit this? Here the link to the description:

Is the “provisionforvoid” the opening itself or rather a reservation for the opening (a request from e.g. the MEP engineer to make room through a structural element)?

I see it as the reservation for an opening that has to be defined by the MEP egineer.
The opening itself would probably be the relation between the wall and the cutting element (Proxy)

As a standalone element (here I see the physical element (not the hole itself)) I would see IfcDiscreteAccessory as the best fit. If it is connected to a flow system, also an IfcFlowTerminal (inlet/outlet of a distribution flow - here water) would fit.

Hi, I am using IfcBuildingElementProxy for something similar and almost in an identical way as you did, but would you explain what do you mean by this?

We tend to use IfcBuildingElementProxy.PROVISIONFORVOID for the opening reservation. Like this:

Since the drain is not directly connected to a flow system, but is mainly used to drain excess water collected on the roof, I think @sergej is on the right track. Though I am not 100% sure.

If it is the word ‘noodoverstort’ you are looking for, perhaps the English term ‘scupper’ might help?

What I mean is that the model should not have other components (such as lighting fixtures, walls, slabs, pipes) that are defined as IfcBuildingElementProxy, because this allows the attachment of your defined P_Sets to those other elements. So everything in the model should have an appropriate classification and just your openings the IfcBuildingElementProxy.
I know it is a hard task, but worth to try :wink:

Hi Agron, now I get you, we used the IfcBuildingElementProxy to represent some boreholes as openings in the construction soil, but we used it also to represent some objects related to our companies business and it works just fine, but we do take care of linking the Psets to the appropriate IfcBuildingElementProxy.
Happy to hear of other use cases of IfcBuildingElementProxy :smiley:

I think in IFC2x3 is one of the most used enteties beside IfcWall for either correct or in most cases incorrect uses :smiley:

I have read through the thread briefly and am not sure if I have understood your request correctly, but for such openings in an structural IFC model we always use the IfcOpeningElement entity. Further you can choose between the Predefined Type OPENING or RECESS in IFC4. In my opinion, this entity meets the necessary needs for an opening. Or did I misunderstand something?

ps: IfcBuildingElementProxy PROVISIONFORVOID should normally be used by the MEP engineer for opening requests and not for the opening itself.