buildingSMART Forums

What exactly is the area measured in Qto_DoorBaseQuantities?

Hello all,

I was investigating an issue where a user stated that an area quantity for a door was incorrect. Looking at the output, the value actually matched the internal Revit value called “Area”, but then I realized that the Revit “Area” might not match the IFC Qto “Area”. The definition of the “Area” quantity for doors is:

“Total area of the outer lining of the door.”

The doesn’t clear things up, unfortunately. For a rectangular door, is area length x width? Is it the total surface area? Is it length x width x 2?


This is bizarre.

First off, the English definitions are missing in IFC4.3. This should probably be fixed. Ping @jwouellette

Secondly, the lining is not the door panel. This is bizarre, since the area of lining is pretty useless. I’d say this is a bug for buildingSMART to fix.

I’m not a door manufacturer, but I think they don’t charge by square metre of the door panel. They usually charge by unit (i.e. the whole door), I believe - so for the purposes of QTO, the area is pretty useless.

… unless the QTO is used for paint. In that case, a good builder’ll paint the door panel top and bottom too, and that should be taken into account - therefore it should be the total surface area.

Again, take with a grain of salt - I’m not a door specialist.

@Evandro @jonm this should be noted for the IFC4.3 schema documentation

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Yes, I can see the English definitions are missing in the published html, seems to be a bug in ifcdoc that I will look at.

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Hi @angel.velez,

if I remember correctly, the QTO Area for doors meant to be the opening area within the wall, the door lining has to fit into. (in German, Rohbauöffnung, if someone can help to translate - (rought opening, shell opening - are some translations I found). Normally the exact height/width of the lining is a little smaller by a tolerance.

So yes, for rectangular doors it is width by height. But I am also not a door specialist.

But I guess the confusion comes from the translation - what is meant is the area, the door lining has to fit into.

I think the key issue here is that an area is a surface measure, while a door is a physical object in three dimensions. As such, any area measure has to be specified against some sort of reference plane. Is it the plane of the opening at the exterior face of the wall? Is it some center reference plane? What about if the wall has some unusual shape (say, horizontally tapered?)

@TLiebich can the documentation be fixed to define it as the “opening area”, with an explicit definition of “Width X Height”?

I’m also curious if somebody as a trained quantity surveyor can explain why this area is useful as a metric. My unqualified gut feel is that doors are best quantified by counting, not per area.

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If I’m reading the current documentation correctly, it is at it should be.

As the Qto is about the door itself, and have lining measurements of the actual door, fit into the OverallHeight and Width of the IfcDoor. So the area would logically refer to the same measurements of the lining.

If anything, it’s the drawings for the door lining properties that could use a bit of clarification.
It’s looks like the QTO of the lining is always equal to the overall size of the IfcDoor. In a curtain wall they are equal, in a regular wall, most often not.

A parameter to describe that planned tolerance between the two, ie. the joint, would be nice.