15 November 2013

Minimum Modelling Requirements

The basis of BIM as a process is that information created by a participant for their purposes can be reused by others to assist them with their purposes.
For this to work 3 things have to happen:
  1. The information has to be there at the time it is required (i.e. is actually generated).
  2. It needs to be in a form useful to others (i.e. they don't need to re-create it)
  3. It needs to be reliable (at least for the purposes others will use it for).
The last is covered by LOD, the middle one is covered by designating software, or use of standards (like IFC), and the first is covered by Minimum Modelling Requirements.

The first requirement is the most important - the others have no meaning if the information doesn't exist - yet it is the least discussed and tackled by industry bodies. There is endless discussion and work being done on openBIM, COBie and the like; LOD is becoming mature and is now appearing in agreements and contracts.

But where is the clear definition of Minimum Modelling Requirements? Certainly many owner groups have tackled this issue and come up with their own solution - they have to, they operate in the real world where results are a necessity. But where are all the bureaucrats, academics and standards junkies?

Am I being unfair? - probably. I don't really believe the issue is being totally ignored. But the reality is where do I go to get practical advice on Minimum Modelling Requirements? Surely there is a better way than just referring to publicly available owner's attempts at solving the issue (and I say attempts because there is no way to assess how successful they have been).

Like all things BIM different participants have different views on what Minimum Modelling Requirements means. From owners who think it is just about ensuring they have a BIM based FM system at the end of the project to BIM mangers trying to get their team to model consistently.

Delineating Minimum Modelling Requirements

So let's start by trying to list what Minimum Modelling Requirements could include.


Who are Minimum Modelling Requirements directed at:
  • others so they can meet their own Minimum Modelling Requirements 
  • others documentation needs 
  • others analysis needs
  • construction needs (clash, sequencing)
  • costing 
  • FM 
  • your own needs (like documentation, analysis etc)


What are the types of information Minimum Modelling Requirements applies to:
  • element categories 
  • element geometry 
  • degree of detail (how much)
  • degree of precision (how small)
  • data (parameters)


What are (some of) the possible ways to define Minimum Modelling Requirements:
  • text description 
  • table / matrix 
  • no definition, just suitable for end use


How might Minimum Modelling Requirements be enforced:
  • contract deliverable (forced)
  • scope of works in agreements (offered)
  • included in BIM Execution Plan (agreed)
  • industry expectation ("reasonable professional" would provide)


Once Minimum Modelling Requirements have been established how might they be checked for compliance:
  • human sign off
  • computer checking
  • fit for purpose

Note that these lists are not all unique methods, some are alternatives that on the surface seem to have the same purposes. Nor exclusive; more than one may be utilized. But of course different methods will have different outcomes.

Different participants will use different methods to achieve what they believe are their aims. Owners like using end use / fit for purpose type methods as it shifts their responsibilities onto others. BIM managers like using highly specific software dependant requirements that can be computer checked because it makes their job easier (and they like using computers).

Current Examples

A comprehensive analysis of all attempts at Minimum Modelling Requirements would be a PHD in itself, and be out of date before it was finished. But I'll endeavour to show examples of different approaches to the issue.

MPS - VICO Software (US commercial)

VICO is an example of a number of commercial firms providing BIM planning services. They call their Minimum Modelling Requirements product Model Progression Specification (MPS). They also offer many other services around this so it is not a matter of simply purchasing a copy and using it.
I can't go into the specifics about their MPS as I have never used it, but it seems to be an elaboration of the [US]AIA E209 Document LOD table (the E209 document is actually based on VICO's MPS).
Commercial firms effectively make you pay to utilise their experience. But they also offer a service - they do some of the work someone in the team would otherwise would have to do. It is therefore hard to say if their success is due to the experience they bring or the extra manpower. I suspect it is both.

M3 - USACE (US government body)

The USACE (U.S. Army Corps of Engineers) Minimum Modelling Matrix (M3) is used by the US military to manage BIM construction projects. It is an example of owner created Minimum Modelling Requirements. It is freely available at their BIM web portal (with free registration).

The M3 relies on Uniformat 2010 codes being associated with every element. Uniformat 2010 is a hierarchical classification system that includes 'headings' that apply to multiple elements. The M3 has designated Levels 1 to 3 to these headings, with only Level 4 applying to individual elements.
As an example:
  • Level 1 is all equipment and furnishings (E);
  • Level 2 is equipment (E10) and furnishings (E20);
  • Level 3 is Commercial Equipment (E1030);
  • Level 4 is individual equipment type like Hospitality Equipment (E1030.50).
The M3 has a separate table for Levels 1 and 2 where general text descriptions of what is required are listed against each element 'heading'.

USACE M3 level descriptions

The other table has all Levels in a tabular format. Levels 1, 2 and 3 are just headings with little information against them, Level 4 is for elements, with a range of columns against them.

USACE M3 example

In terms of  Minimum Modelling Requirements the columns for LOD and Grade are of interest.
LOD means what we now expect it to mean - it indicates the level of certainty required of that element and is defined in terms of the [US]AIA E209 document. But only LOD 100 to 300 are given a definition, and in this table LOD is not associated with a milestone. Yet the other column of interest, Grade, is. But only for Construction Documents and As-Builts.

Grade sets how elements are to be graphically represented:
A   3D + facility data
B   2D + facility data
C   2D only (drafting, linework, text and or part of an assembly)
+   original grade modified
-    not included or tied to the BIM model (however is still required in the deliverable)
●   Refer to the other Levels 1 & 2 table, or is a heading (Level 3).

M3 definitions reflect strongly back to documentation. Many Level 1 and 2 requirements include
"... elements shall be depicted with necessary intelligence to produce plans, sections, elevations and schedules ...". LOD 300 includes "Accurate to the degree dimensioned or indicated on contract documents".
Other types of description are also found, although not consistently across all definitions. Things like "Small diameter (less than 1-1/2” NPS) field-routed piping is not required to be depicted in the Model", and "Slabs shall be developed in the structural model and then referenced by the architectural model".

So the M3 defines:

  • General modelling requirements (using text)
  • Type of graphic (2D or 3D) and whether data included. (using a table)
  • LOD (sort of, surely LOD changes between Construction and Record models)

As you can see it is really quite a mish-mash not only of methods, but also mixes documentation with BIM requirements.

Despite this the USACE M3 is often quoted as one of the best examples of Minimum Modelling Requirements freely available. From a practical sense I tend to agree. They are making a good attempt at encouraging BIM in an industry not yet geared up to provide it. Which is its Achilles heal when it comes to taking lessons from it. The M3 is not necessarily best practice for BIM proficient participants. In fact I believe it has the potential to hinder BIM use. But it is (so far) an evolving document and well worth keeping an eye on for future developments.

LOD Specification - BIMforum (US industry group)

BIMforum is a US based non-profit industry group. There are many of these, but BIMforum is worth a mention because they have recently released an LOD Specification.
This document was created in response to the [US]AIA E209 document and directly uses its definitions.

It lists elements using the Uniformat classification system, and against each element there is a list under the title of   "Element modeling to include:"
Like the USACE M3 it is hierarchical, but simpler. Higher order classifications contain descriptions that are typical referenced back to by lower order classification that don't require further modeling (typically for LOD100 & LOD200). Further, if an element has the same requirements as another, it references back to that earlier element rather than repeat the same information.

BIMforum LOD Specification Example

Strictly speaking I shouldn't include BIMforum's LOD Specification in a discussion on Minimum Modeling Requirements. LOD is supposed to be about what information can be used with certainty - not what information exists.

But one way to define what can be used with certainty is to describe the minimum amount of information required to meet that certainty. This method becomes a de-facto description of Minimum Modeling Requirements: if you do no more than meet the LOD Specification requirements you will have met your LOD obligations; if you have done more than that, others can only reliably use what the LOD Specification describes for that LOD.  

But BIMforum admit their LOD Specification is not intended to be for Minimum Modeling Requirements. In the LOD Definitions sections it list two examples of areas not covered: Size Thresholds and Clearances,  inferring there are others also not covered.

LOD is often mistaken for, or assumed it can be used for, Minimum Modeling Requirements. An instance of which I discussed in my last post.
That said they both make use of the same information - descriptions of element modeling. There may be a way to leverage this to reduce the amount of information necessary to define Minimum Modeling Requirements.
But I believe it is important to remember that LOD by itself is not enough to define Minimum Modeling Requirements.

DPoW  - BIM Task Group (UK government)

The BIM Task Group is a government body in the UK with the aim of "helping deliver the objectives of the Government Construction Strategy and the requirement to strengthen the public sector’s capability in BIM implementation".
I came across one of their draft documents while researching this post. Its name "Digital Plan of Work (DPoW)" [follow the links - requires registration] made me think it might be a good candidate for defining Minimum Modeling Requirements. Particularly as it may possibly be an extension of an existing body of work by the RIBA on building design and construction processes (RIBA Plan of Work).

But alas, I was disappointed, not surprised, but disappointed at another lost opportunity.
Admittedly it is a draft, but the problem is with the whole focus of the document, nothing a few tweaks are going to overcome.
Beside some items that probably should be in another document it is dominantly a proposal for computer based checking of COBie data submission.

For a start COBie is no-where near being a way of defining Minimum Modeling Requirements. COBie is only about data, not geometry, not end uses. It is a standard way of structuring data, it actually says nothing about what that data needs to include (see my post for more on COBie).

As a strategy, computer based checking is problematic. To do the checking some-one has to set up a checking system. That system will have its own requirements. So there needs to be Minimum Modeling Requirements Checking Requirements defined. And how is it checked that these Minimum Modeling Requirements Checking Requirements have been met?
Assuming the checking has fewer requirements than the actual requirements, in theory there could be a series of checking levels of reducing complexity, until a level simple enough for a human to grasp in its totality is reached.
But we all know what will happen in the real world. No-one will check the checking requirements. A template will be used from another project without being properly edited, because the person editing is not responsible for the outcome, the person being checked is. It will be left up to the parties being checked to highlight errors in the checking, creating an enormous additional work burden for everyone actually involved in getting the facility built.
Computer based checking has a place, as a tool in a kit of tools, not as a strategy for defining requirements.

The biggest problem is none of it is useful, or even close to being useful. Beside the fact it doesn't actually cover what is required for Minimum Modeling Requirements (or Plan of Works for that matter), it can't be used until the checking software is finished and tested. What does the industry do in the meantime? Keep doing it the old way then suddenly everyone switches at the same time to the new way? Are they serious?

This is a classic example of bureaucrats, academics and standards junkies tackling the Minimum Modeling Requirements problem. I just hope this is not the only attempt the UK government (or the RBIA for that matter) will make at integrating BIM into their Plan of Work concept.


At risk of being compared to bureaucrats, academics and standards junkies, I don't have any practical solution. I just don't think we are there yet.

At the moment I suspect the USACE M3 approach is the most realistic. A customised mish-mash to get the results required.
BIMforum's LOD Specification is new (released August this year) and largely untested. It is not designed to be customised so may or may not work for you. In any case it could only ever be part of a customized mish-mash as it doesn't cover everything required of Minimum Modeling Requirements.
If the money available a commercial provider is a good bet, if for no other reason than to lessen the workload and extra responsibilities a BIM delivery requirement generates for everyone involved.

But in the spirit of being practical I will offer some advice on good practices that should make complying with any Minimum Modeling Requirements easier.


  • Use your software as it was designed to be used - don't use shortcuts purely for the production of documentation.
  • Embed all the data you can into your model - then use it to generate all schedules.
  • Use categories (or their non-Revit equivalents) in consistent and transparent ways.
  • Insist on a robust co-ordinate base point.


  • Make sure all non-BIM and non-project specific elements are identifiable, and if possible remove them before issuing your model.
  • Check your model for consistency before issuing.
  • Provide documentation to others on how your model is structured.
  • Define the degree of precision you model to.
  • Create a table of LOD expectations for selected milestones.

Postscript - What's in a name

I've used the term Minimum Modeling Requirements throughout this post. But is it the best term?

  • Requirements makes it sound like an imposition. Something only the owner controls.
  • Standard? The level everyone is expected to achieve. Perhaps too soon to be meaningful.
  • Provision? The level to be provided. Bit like Requirement.
  • Contribution? The level each participant contributes to the overall BIM.

I like the last. Minimum Modeling Contribution. It can come from anyone, as an offer, or as a request. It is in the spirit of collaboration.

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