PR: Qto values Net Area, and Gross Area of IfcSpace is exporting same values from Revit

[ArunSanthosh98]

Problem Description

The Qto_SpaceBaseQuantities GrossFloorArea and Qto_SpaceBaseQuantities NetFloorArea values are same in Ifc as shown below. And when space boundary set to wall core center the the GrossVolume and NetVolume export different values.

Revit Version

2024.0.x

IFC for Revit Addon Version

24.x.x

Windows Version

11 22H2

[parrela]

I can reproduce this in Dev. Seems funny it hasn't been seen before : REVIT-219275

[ArunSanthosh98]

I can reproduce this in Dev. Seems funny it hasn't been seen before : REVIT-219275

am using Revit 2024 and Ifc4 @parrela

[AngelVelezSosa]

Looking at the above, I see inconsistencies but I am not sure what's actually incorrect. Gross vs. net area is intended to subtract out elements in the space. Is it the case that the gross area should not include the walls? Or is it just that the net volume calculation isn't right? I would think that gross and net area should be the same as each other, regardless of the computation method, and should change for core center vs. finish calculations. Is that correct?

[ArunSanthosh98]

@AngelVelezSosa
The gross area includes walls and columns, but the net area doesn't include walls and columns. if room boundary is the wall center, then the gross area should be the total area including walls and columns and the net area excluding walls and columns.

[o-babii]

It is worth paying attention to the fact that from the point of view of IFC, we export the IFCSpace entity, and if you check with Qto_SpaceBaseQuantities (https://standards.buildingsmart.org/IFC/DEV/IFC4_2/FINAL/HTML/schema/ifcproductextension/qset/qto_spacebasequantities.htm), there is no area of the room itself or space area. Instead, there are:

GrossFloorArea - Sum of all floor areas covered by the space. It includes the area covered by elements inside the space (columns, inner walls, etc.) and excludes the area covered by wall cladding.

NetFloorArea - Sum of all usable floor areas covered by the space. It excludes the area covered by elements inside the space (columns, inner walls, built-in's etc.), slab openings, or other protruding elements. Varying heights are not taking into account (i.e. no reduction for areas under a minimum headroom).

In case we are using "At wall finish" option the exported model looks OK.

In the case of using "At wall core center" option we can see that the room boundary is changed in Revit (also an area parameter is recalculated)
After export, we can see that room geometry is the same as for "At wall finish" option, but area quantities are bigger, which is incorrect because the actual geometry area is 25 square meters.

So, based on Qto_SpaceBaseQuantities, I think that exported GrossFloorArea/NetFloorArea values are related to the exported IfcSpace element. And right values should be 25 square meters, for any room area computation option. Since exported geometry has the actual 25m area, and has no columns or other inner elements.

I think if you want to export Area of the room calculated with "At wall core center" option it is better to use user-defined property sets.

@ArunSanthosh98 , What is your opinion on the behavior described above?

[ArunSanthosh98]

hi @o-babii thank you for the comment. I was studying the behavior of these two options: the wall center and wall finish boundary. I also want to know how to export GA and NA areas of spaces without adding a custom property set. If we add a custom property set, then we have to manually fill in the Net Area, and it's not practical to calculate the area for all spaces in a project manually.