Openings with multiple hosts

IFC5 schema change request

There are cases when a single opening element cuts more than one wall. E.g. in staircases, corner windows or stacked walls. Now it is impossible to export the IfcOpeningElement with more than one hosts.

image

Current schema:
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Proposal:

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+1 to this

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There are 2 openings here, on in the left and one the right wall.
They have different Qto_OpeningElementBaseQuantities thus they are 2 different entities.
They may share IfcRepresentationItem used for Boolean difference from walls.

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Hi Igor!

Why do you think they are two separate openings? Based on the inputs of architects and other users there should be only one single opening entity in the model, in the listing and everywhere in the ecosystem/workflows. Moreover, in normal cases there should be only one wall in the model, but because of the modelling capabilities of the authoring tool it is modelled with two separate walls to have different coverings.

this depends on how the model is being generated. I see here two ways:

  • Two walls with composite structures. In this case your suggestion makes sense.
  • One load bearing wall with two finishin layers. In this case you cut only one wall (the load bearing), since the finishing layers don’t need an opening. Here the one OpeningElement fulfills the needs.

when the openingElement is placed on one of the above situation, it must have the intelligence to define the relationship to either one or two walls.

I agree with you @agron, there is only one IfcOpeningElement with the possibility to have single or multiple relations with walls to cut.

I understand opening volume as volume of material subtracted from host element.
One volume is substructed from left brick wall, another from right concrete wall.
Thus I would prefer 2 opening elements each with own quantity set.

I agree, here may be another view, and also have doubt is it a real case in building construction.

Anyway this case is open issue for IFC because one or two opening but obviously it may be filled with one window.

related: Allow IfcRelVoidsElement to be a one to many relationship. · Issue #87 · buildingSMART/NextGen-IFC · GitHub