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?
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.
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.
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.
From a traditional quantity surveyor’s point of view, a door opening is the work necessary to provide the opening in the wall ready for some later operation. It will have an area which represents a deduction from the overall area of the wall. In addition, there are treatments to the threshold, jambs and head which are necessary to form the opening. In brickwork, this would also imply work to provide and install a lintel, closing the cavity, damp proof courses etc.
Once an opening is formed, we must consider what goes into the opening - an entirely separate question. This may simply involve finishing the threshold, jambs and reveals (plaster, angle beads and paint) or it may involve fitting a timber frame or lining, borrowed lights, a door leaf, glazing and ironmongery all of which may be either measured as separate (length) items and cut/fixed on site or prefabricated delivered and fixed as a finished unit (count). Any work returning the skirting through the opening and painting or polishing the finished work is again, measured separately. All this depends on the design and specification.
It should be clear that the opening in the wall and the door/window which may eventually go in it are two separate things and that the specification, size or area of a door leaf is only loosely connected to the size of the opening and even then, only within the specific context of the design. There is a relationship which is asymmetrical. The existence of a door and frame implies an opening into which it is fixed but the existence of an opening does not imply the existence of a door. This should clarify the distinction between the information which can be derived from the wall and the opening and the information which should be attached to the final treatment of the opening which may or may not include fitting a door.
Consider also that the operations necessary to create a new door opening in an existing wall are different.
Thanks for your insights @PaulBurrows - I do not have any training in quantity surveying, so I defer to you to clarify and check that the quantity sets are useful for surveyors. However, from the perspective of an implementer, as per @angel.velez’s original question I am still confused what the formula is to calculate the area here.
Is it:
width of the lining * height of the lining
width of the lining * height of the lining * 2
total area of the void that the lining fits into, including front, back, top, bottom, and 2 sides
@angel.velez best describes the complications here:
in answer to @PaulBurrows - the main purpose of base quantities was always to have rough alphanumeric values that can be derived directly from the geometry (not making measurement rules into account, as they differ between countries) for the benefit of software applications, that do not have the capacity of a geometry kernel to recalculate them directly from the geometry in an IFC dataset.
Looking back to the qset of ifcdoor vs. the qset of ifcopeningelement that holds the quantities of the opening, in which the door is placed, I would conclude with some of the arguments in this thread. It would be better to use the width and height of the door panel (or door panels) instead of lining (which works fine at least for swing doors).
Thanks @TLiebich , that definition is indeed clear and something we can implement in software. I’ve got no opinion on the correctness of it, as I am not qualified, but it is certainly unambiguous for swing doors.
Is it possible for the documentation then to be updated so that it is clear? Also perhaps for a sanity check on different door types?