LOD = LOD + LOI | Evolve-Consultancy

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27/11/15, 0004LOD = LOD + LOI | Evolve-Consultancy

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UK convention US convention Description

LOD 1 Brief: a model communicating the performance requirements and site constraints.

Building models would be block models only.

LOD 2 LOD 100 Concept: a conceptual or massing model intended for whole building studies

including basic areas & volumes, orientation, cost.

e.g. for an HVAC system, this might include block models of the plantroom

locations and distribution risers.

LOD 3 LOD 200 A design development model, "generalized systems with approximate quantities,

size, shape, location and orientation."

e.g. for an HVAC system, this would be more what the architect above expected:

duct runs modelled to approximate routes, but at an accurate overall size to

LOD = LOD + LOI

If youre struggling to cope with the excessive use of TLAs (Three Letter Acronyms) in BIM circles, then you may

throw your hands up in the air when faced with the above formula. You might argue it is mathematically incorrect,

unless LOI = 0; or you might suggest it is completely nonsensical presented as it is. And that last point I will concede.

So many aspects of BIM, or at least the definitions or implementation of BIM, make very little sense. Anyone would

think its another language entirely, invented just to bemuse the majority and keep so-called BIM experts safe in their

black arts.

If you do a Google search for BIM LOD, you will get a number, a plethora even, of hits for Level Of Development of a

BIM model. The AIA (not a BIM-specific acronym, but referring to the American Institute of Architects) has publicisedthis term in its 2008 publication AIA E202-2008: Building Information Modeling Protocol Exhibit to help define,

essentially, the content of any part of a BIM project. The UK also uses LOD, but here it is defined as Level of

Definition. What does either actually mean? First let me explain the problem LOD is trying to resolve!

Expectations and understanding of what BIM is varies greatly. While a common consensus is obvious to those in the

know, the majority of the construction industry is still fighting to comprehend what it is they will produce, issue and

receive. Even for those who had begun work on BIM projects, it was still a matter of subjective opinion what would be

included in the model. In the example of an air conditioning system, a structural engineer might be expecting to

receive dimensionally accurate ducting layouts to ensure their structural openings would be an adequate size, an

architect may only need an approximation of zoning in order to work up their circulation layouts and minimum

headroom, while the reality is that the services engineer is only working on 2D schematics oblivious to the others

expectations. This lack of communication and common perspective leads to delays, friction and in many cases error.

The CIC BIM protocols in the UK detail a Model Production and Delivery Table, more commonly referred to as a

Responsibility Matrix, to clarify what information is going to be produced at any stage and by who. Simply put, you

assign an LOD code against each building component or system at each progressive stage of the project so the

complete team knows what to expect. The basic codes differ between the US and UK conventions, which only serves

to further confuse the issue:
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include maximum potential sizes without detail of flanges or accurate radii of

bends.

LOD 4 LOD 300 Production, or pre-construction, design intent model representing the end of the

design stages. Modelled elements are accurate and coordinated, suitable for cost

estimation and regulatory compliance checks.

This LOD would typically be a model suitable for production of traditional

construction documents and shop drawings.

e.g. for an HVAC system, this is what the structural engineer was hoping for:

accurate duct sizes & locations.

LOD 5 LOD 400 Installation: an accurate model of the construction requirements and specific

building components, including specialist sub-contract geometry and data.

This model would be considered to be suitable for fabrication and assembly.

Architects or engineers would rarely produce objects at this level.

e.g. for an HVAC system, the cut lengths of duct runs, fixings; a CAM model.

LOD 6 LOD 500 An as built model showing the project as it has been constructed. The model and

associated data is suitable for maintenance and operations of the facility.

LOD 7 Asset Information Model used for ongoing operations, maintenance and

performance monitorin

The UK convention can be better visualised as:

The problem with a single LOD code is that not all objects graphical representation relate directly to the information

they need to contain. It is a simplification of intent that does not allow for the iterative design stages when modelling a

visually accurate object might actually be counter-productive and overload a model with unnecessary detail. Take the

simple example of a door: while the architect may prefer to see visually correct detail (including vision panels,

recessing, handles and hinges) none of that is needed for LOD 4 / 300, a model suitable for production of traditional

construction documents. All you need for that is a location, an accurate width and two rectangles joined by a line andarc to denote swing direction. Without a doubt, to be able to produce accurate quantities and schedule the items


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correctly, that data is going to need to be included. An electrical lighting system may never need to be modelled at

LOD 4 / 300 level, as the locations of switches and fittings might be totally symbolic; their data would be anything but.

Conversely, at earlier stages it may be critical to develop geometry to a high level of visual development in order, for

example, to resolve complex details or clash detection purposes when little is yet known about the performance or

exact specification of any objects.These definitions can be found in numerous places on the web. What isnt

specifically stated is the amount of non-graphical data contained in any of the components or systems. In both the AIA

and UK definitions it is implied by the allowable uses of each LOD model; the data contained in or linked by an

object reflects the analytical use. For LOD 2 / 100, basic attributes would be included: cost per metre (or footdepending on your location). Continuing with the HVAC example LOD 3 / 200 would see that increased to include flow

rates, expected dimensions which would extend into more accurate data through LOD 4 / 300. By LOD 5 / 400, the

object might include its constituent materials, accurate cost or performance specification. LOD 6 / 500 would have

maintenance schedules, safety monitoring, and so on.

A better approach to this, and one designated in a number of example BIM Execution Plans from around the world

and the AEC (UK) BIM Protocols, is to define graphical and non-graphical attributes separately.

Coding for graphical representations, the Level Of Detail, is easy enough. The AEC (UK) BIM Protocols define the

graphical appearance as:

G0Symbolic. Not to scale, merely a suggestion of where the object will exist. In terms of doors, this might simply bea black rectangle in a 2D wall.

G1Placeholder. While it may be to scale, the object may not represent the appearance of the final component. In

terms of doors this would be a simple, plain object without frames, vision panels or hardware.

G2Suitable for construction. This is where you would provide geometry representative of the final component. It may

still not include hardware (as this would typically be specified separately) but could be a manufacturers downloaded

object.

G3High resolution, fully detailed object. Typically only used for visualisation, or in fact, manufacturing.

Visual representation has always been understood and is easy to group into basic expectations (although architects

will still insist on G3 objects when G1 would serve perfectly well). An alternative method is to specify LOD as therelated drawing scale the graphics will be presented at. This is a much easier to understand approach, inherent in

many designers thinking. The difference between a door at 1:100 and 1:20 is simple to visualise. LOD defined as

drawing scale leave much less room for ambiguity.

The Level Of Information is harder to codify as each project might be drastically different, and will vary greatly per

component or system throughout the work stages. As outlined in last months BIM Brief, the most accurate way to

deal with what attributes will be included is to list them in a tabular format. It should be a fairly easy task to identify

what information will be needed at any stage, as this would be the contractual information you would normally

produce. It doesnt mean that the other stakeholders in the BIM project would need that data (none of the engineers

would ever care about vision panels) but it does help rationalise in your own minds what information you need to

deliver and when. As you prepare for BIM production, its always worth remembering that you dont need to includethe data just because you can; more often than not it is better to simplify.

At any stage then, the Level Of Definition less confusingly becoming referred to as LOMD, Level Of Model Definition

in the UK of each component or system is totally explicit and can be as flexible as necessary. The Level Of Model

Definition is a combination of graphical Level Of Detail, and non-graphical Level Of Information. The formula

should now be clear:

LOMD = LOD + LOI

QED

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LOD = LOD + LOI | Evolve-Consultancy