What is LOD (Level of Detail) ?

There still seems to be some confusion about what LOD means, and how they should be used. I must say I have difficulty relating what I do and what I need whenever confronted with filling in an LOD table. If they are this difficult why are we using them? Are they really useful, or just a waste of our time?  

HISTORY OF LOD
From what I can gather LOD was developed by Vicosoftware, a software company that produces construction costing software. They saw the advantages of costing straight from a BIM model, but had a problem. How do you tell how accurate, or how definitive, the model elements you are connecting to in the model are?

Traditional methods of costing have a human between what was being measured and the way it was being measured. But automatic take off from the BIM model doesn't.

So they developed the concept they call "Level of Detail". A measure of how definitive an element is in terms of costing it. So LOD 100 meant not very definitive, an area or volume rate is accurate enough, LOD 200 you can assume the number of items in the model is correct, but use an estimate for each, LOD 300 items are identified and actual cost can be used, LOD 400 is a measure what has actually been supplied so can be used to assess payments.

   Sounds very sensible, very precise. But then the AIA (American Institute of Architects) decided that this system would be a good one to apply to all uses of a BIM model, from energy analysis to 5D programming. They sensibly renamed it "Level of Development" because "Level of Detail" could get confused with the amount of information, rather than the decisiveness of the information. Although both still have an acronym of LOD so the two continue get confused (more on that later).

 Others have taken up the concept, and today it has become one of few common BIM concepts that is kind of understood by all  (more on that later).

WHAT EXACTLY IS LEVEL OF DEVELOPMENT
LOD, as in "Level of Development", is a measure of how seriously you take the information represented by a BIM element. It is not necessarily a measure of the amount of information, although obviously there must be enough information to satisfy the LOD level it is at. It is also not a measure of the amount or accuracy of graphical information. The appearance of a BIM element is only one piece of information about that object, and usually the least important. A contractor doesn't need to know what a desk looks like to order it, nor to place it in the building. But they do need to know what the manufacturer and model number is. Others may need to know its dimensions to coordinate with things around it, but they too do not necessarily need to know what it exactly looks like.

Therefore LOD levels for a chair might go:
LOD 100 = there is a chair
LOD 200 = there is a chair that has nominal space requirement of 500x500
LOD 300 = there is a chair with arm rests and wheels
LOD 400 = manufacturer and model number.
LOD 500 = manufacturer and model number, supplier, date purchased

 or in general terms:
LOD 100 = there is a thing
LOD 200 = there is a thing about this size
LOD 300 = there is a thing with these functions and options
LOD 400 = it is this particular thing.
LOD 500 = this particular thing provided by this person on this date.
LOD is also a measure of progress. At LOD 100 there is obviously more work to do to reach LOD 300. In that sense it is like the traditional percentage complete of drawings. Assuming LOD 500 is 100%, then LOD 100 = 20%, LOD 200 = 40%, LOD 300 = 60% etc.

 Except LOD contains more information. It tells you how decisive each element is, not just how complete its representation is on a drawing. It is more useful to know that on a plan the floor is 60% complete (LOD 300), the walls are 50% complete (LOD 250) and the service ducts are 40% complete (LOD 200), rather than the whole drawing is 50% complete (the average of all elements).
Article provided by Antony McPhee:  Antony has been a registered architect since 1986, he has been a project architect on projects ranging from large commercial and cultural developments to house extensions. Developing CAD systems since 1988, involved in BIM since 2001.