30 September 2016

Making BIM Work: Quality Models

BIM processes only work if there is something those processes can act upon.
No BIM models, no process.
And quality matters: without good quality models no matter how good BIM processes or standards are it will be extremely difficult for anyone to do anything useful.

Pretty basic stuff, but all too often ignored.

Ignored because to ensure these thing happen action has to occur at the very, very, beginning of a project. When each design consultant is signed up, because they are the BIM authors, the ones who will be creating the BIM models.
Ignored because owners assume BIM authors will produce adequate BIM models as part of their normal service, even when the contract deliverables are only drawings, schedules and specifications.

Now, one day this will hopefully change. Consultant agreements will by default contain common, widely understood BIM requirements. Consultants themselves will be familiar and comfortable with BIM software and what is necessary for quality BIM models.

But at present, pretty much everywhere, this is not the case. And it is not going to change if we don't start addressing this issue directly.

Why is there a Problem with Models?

The reason it is so difficult to get quality BIM models from design consultants is that they think their job is, for architects, to produce drawings, for engineers, to produce diagrams. So they use their software, whether BIM or not, to only produce drawings. Also they generally don't use their BIM software to produce schedules. As they see it their deliverable is a paper schedule, maybe an Excel spreadsheet. So why use your drawing software?

All this is because drawings have traditionally been their tangible deliverable, and is still the main contractual deliverable even in notionally "BIM" projects. Due in part because the reality is that drawings are still the legal documents that contractors use to construct from.
Mind you there are good reasons why drawings are used for legal evidence. All information on drawings is visible and unchangeable. Explanatory text can be included, status, revision sequence and issued date are all clearly displayed. It is very hard for someone to say "I didn't see it".
One day BIM models may be able to do these things, or things that achieve the same outcomes. There are examples around that do some of these things, or something similar, like Bentley's 'Hypermodel' functionality, or the open source BIM Collaboration Format (BCF).

But presently there are no common, robust, methods that match the certainty of drawings.
So are architects and engineers justified in using their BIM software to just produce drawings?

BIM Software is Designed to produce Drawings

The softwares we use today to do BIM were not originally designed to do BIM. They were designed to produce drawings.
When ArchiCAD came out in 1987 the way it worked was that the building was modelled in 3D up to a point. Once it was decided to move to drawings, plans, elevations and sections were created as separate files from the model and worked over to turn them into drawings.
This is a common approach. SketchUp does the same with its separate LayOut program.
Revit came out in 2000 with a similar functionality, except that plans, elevations and sections remained live. Everything was in the one file, so changes in the 3D model instantly appeared in all views created for drawings. But the purpose of Revit was still to create drawings.
Other software now used for BIM started life as CAD programs, with gradual 3D functionality added to assist drawing production (e.g. Bentley, and the now defunct AutoDesk Architecture).

BIM as we know it today came from the realisation that the integrated 3D model that these softwares produced could be used for other purposes. In practical terms BIM is what these softwares are capable of doing, despite the efforts to extend BIM into the realm of fantasy by the standards wonks and BIM evangelists (see my previous post on standards).

So if you use BIM software as it is intended to be used it will produce drawings for you. There is no need to "take shortcuts" to produce convincing looking drawings. And if you use the software properly it will be BIM ready, it will not "take more time" to do BIM.

The Benefits of BIM to Authors

Much is made of using BIM models for 4D (construction sequencing), 5D (quantity measuring), 6D (life-cycle management), and other 'D's. They can also be used for analysis and simulations, particularly in engineering - structural analysis, power circuits, mechanical systems etc.

What is often not appreciated is that a BIM model can also be used for quality assurance (QA) purposes. Checks can be utilised that minimise design errors, that ensure the model is in fact a quality BIM model and an accurate representation of what is to be built.
If all you produce are drawings and separate schedules, you can only check drawings and schedules.
If your BIM models are created properly you can use the model to do the checking.

If your walls contain their fire rating as data in a parameter you can colour code those walls, the same for fire rated doors, fire rated dampers etc. Which makes checking that the correct walls and doors are in the right place much quicker than trawling through multiple drawings and cross referencing schedules.

If your doors contain size data you can run a model check for doors with heights or widths below minimum required values. Check concrete walls required to be fire rated to ensure their thickness achieves their rating. You get the idea, the list is endless.

Revit Warnings

These checks can be manual (e.g. use Filters in Revit or the free add-in Color Splasher to color-code  views by object parameter), or automated (e.g. Revit's inbuilt Warnings,  Autodesk Model Checker for Revit, Solibri IFC model checker).

And because drawings and schedules come directly from the model they will be correct if the model is correct.

When I say correct, I mean correct information. Letting software create your drawings and schedules means forgoing some control over graphic representation. But then BIM authors are architects and engineers, not graphic artists. The question they need to ask is not does this drawing look "neat", but can it be misinterpreted? Will the contractor build the wall using the wrong material or in the wrong place because the lineweight is not exactly right, the hatch pattern doesn't align perfectly? Will they mistake a grid for something else because its head doesn't perfectly align with other grids?

The bottom line is that it is possible to be much more thorough when checking a model as compared to checking drawings and schedules. It can also be done much quicker, especially if standardised automated model checking processes are implemented alongside manual checking. All this leads to less errors in documents, meaning less time wasted dealing with mistakes, both internally and on site.

Looks OK in 2D plans and elevations, but an on-site mistake waiting to happen
There is no real excuse for design consultants to NOT produce good quality BIM models. They should be doing as part of their normal duty of care.

Why won't People Share?

Producing good quality BIM Models is one thing, but if these models are not shared BIM processes will fail.

The comments above about checking the model instead of drawings and schedules extends to other people's work. It is much easier and quicker to see if structure is aligning with architecture if both models are linked together and viewed in 3D. And there are softwares that can automate this checking. Revit has a built-in clash detection ability, Naviworks and Solibiri are specialised software for doing this type of checking.

Design consultants, particularly architects, generally don't like giving their native models to anyone (a topic I covered in my post IP - it is not all yours, get used to it). They see them as their property. The justification is that their contractual deliverables are completed drawings, schedules and specifications. BIM models are their "internal working documents".
Design professionals are also generally paranoid about having their ideas stolen, which they extend to the documents they produce.
And some have this view that as initial author of BIM models they have the right to total control of that model including getting paid whenever anyone makes use of it.

None of these justifications are valid. They just need to get over the fact that in the 21st Century drawings are no longer their only deliverable, and that current legal protections easily extend to cover other deliverables.

However there is a mistaken belief (and not just by design consultants) that handing over models means providing an untouched copy of the model, still containing all its housekeeping and drawing creation setup. None of this is required for BIM Uses. It should be removed - as a requirement. No-one wants to trawl through someone else's rubbish, and allowing people to recreate the drawings of others is a legal minefield.

What is a Quality Model?

In simple terms by quality model I mean a model that is:
  • Fully modelled in 3D.
  • Is modelled as it will be constructed.
  • Uses correct categories and types.
  • All objects contain data about themselves.
  • Data is consistent and coherent.
and taking into consideration the fact that drawings and schedules are contractual deliverables:
  • The model must match issued drawings.
  • Data in the model must match issued schedules.

It is not so much about WHAT information is in the model (which most standards seem to concentrate on, including LOD descriptions like the BIMforum LOD Specification), but that the information that is there is complete and can be relied upon.

This is where discussion of BIM becomes confused. Many believe BIM is about extra work and extra data. It is not. It is about data that is produced for normal purposes being in a consistent format.
The final format doesn't even matter. If data is consistent it can be converted from one format to another. If data required for COBie exists in a model it can be converted to COBie format on export. It doesn't have to exist in the model in COBie format.

If someone wants data that is not usually created as part of your normal service then it is an extra cost. An architect may put minimum warrantee requirements in their specification, but if the owner wants the manufacturer's actual warrantee information in the architect's model that is work they would not normally do and so is an extra.

In short a quality BIM Model is one that has been created by people doing what they normally do and using their BIM software the way it was designed to be used.

Not such a big ask.

How to Obtain Quality Models

As explained above it can't be left solely to design consultants to initiate quality models. To be fair that is not all design consultants, there are some who are very good. And not yet, one day it will become standard practice, but for now owners have to be proactive.

There are two places requirements can be spelt out: - consultant engagement agreements and a project's BIM Brief.

Consultant engagement agreements are better because they are contractually binding, whereas a BIM Brief may or may not be, depending on what is in consultant engagement agreements. Also the BIM Brief may not be completed before consultants are engaged (particularly if those consultants are expected to participate in creating the BIM Brief).

Generally best practice is to include generic BIM model requirements in consultant engagement agreements, with specific requirements, and perhaps specific examples of good modelling practice, in the BIM Brief.

It is also best practice to embed BIM requirements within consultant engagement agreements and not simply have a separate "BIM Addendum" or "Exhibit", which can lead to contradictions and perpetuates the belief that using BIM is a separate service.

A good approach is to include BIM requirements in a consultant's project scope. This has the advantage of being easier to understand as a lawyer is less likely to have authored it, and can be tailored to a specific project. Consultant scope is also more likely to be available to those actually working on the project, whereas consultant engagement agreements tend to be withheld as they contain sensitive commercial information.

Current BIM Engagement Documents

A number of organisations have produced contract addendums for BIM.
In the US there is the AIA Document E203-2013, BIM and Digital Data Exhibit by the American Institute of Architects, and in the UK the CIC/BIM Protocol by the Construction Industry Council.
There are also commercial documents available like the US Consensus Docs BIM Addendum.

None of these documents adequately address the issue of model quality. Some are better at addressing model sharing than others, but then introduce unnecessary complications. And some are simply impenetrable for normal humans, those who have to implement them.

The AIA E203-2013 is more like a BIM Brief, or BIM Execution Plan, it describes BIM processes rather than modelling requirements.

The CIC/BIM Protocol is mainly about sharing of models and delivery. That is if you can understand it. You would think by the 21st Century lawyers would have learnt to write understandable English. There is one sentence of 130 words with the only commas dividing up lists of items.
It also has other issues that conflict with standard head consultant engagement agreements; like diluting duty of care, and adding things that may not be in it; like assuming the owner has taken ownership of everyone's IP. Read more on the limitations of the CIC/BIM Protocol in the research paper by Kings college London, Enabling BIM through Procurement and Contracts.

I'm not saying these documents are useless or dangerous (although I'd be careful of using the CIC/BIM Protocol), but they are not enough to ensure quality BIM models.

What to put in Model Author Agreements

By Model Authors I mean anyone who is going to create BIM models. This may include design consultants, sub-contractors, construction consultants, and possibly FM consultants.

I've only discussed model sharing and model quality above, but there are other issues that should be covered within contractual agreements. The minimum that an agreement should cover includes:
  • participation in BIM planning
  • provision of adequate resources to achieve BIM
  • model sharing
  • model quality
  • model use

Some examples:

BIM Planning

The Project BIM Briefing Plan forms part of the building brief and must be complied with.
When requested the Consultant will participate in the process to develop and update all project BIM Management Plans and will comply with these plans.
When requested the Consultant will attend BIM Planning meetings, Coordination and Clash resolution meetings.


The consultant will provide, at their own cost, all software, hardware and training required to comply with their project BIM requirements and responsibilities.
A person experienced in use of the Consultant’s main documentation software will be appointed Discipline Model Manager and be available to attend BIM meetings and address BIM and software related issues raised by other project participants.

Model Sharing

All models the Consultant creates for the project, and all exports from those models, shall be made available without restriction to all other project participants.
The consultant may, and is expected to, remove all elements, options, views, imports etc. that do not contribute to issued drawings and schedules from models before issuing them. They may also remove all titleblocks, sheets and layouts used to create issued drawings.
It is acknowledged that the Consultant retains Copyright of their authored models.
The Consultant will respect the rights of authors of models issued to them and will not use those models, or parts of those models, for purposes not directly required by the project.
The Consultant will not provide to third parties models issued to them by others without the consent of the model author.
The Consultant will not print or export contract drawings or schedules from models provided to them by others. If drawings or schedules are required they must be requested from the original model author.

Model Quality

The Consultant will ensure the information in issued BIM Models exactly matches information issued as drawings, schedules and other related documents. This requirement only extends to information that has been modelled or placed as parameters in model objects. (i.e. excludes 2D details and data linked to the model then used in schedules).

Model Use

The Consultant accepts that models issued by them will be used by others as a source of information for work the Consultant is responsible for.
The Consultant will make reasonable endeavours to ensure their models are adequate for purposes others may want to use their model for. However the Consultant can reserve the right to seek compensation from others if it involves work additional to their normal service.

Example Model Quality Requirements

To be really clear specific modelling requirements can be spelt out. They don't necessarily have to be contractual requirements, they can be presented as expectations, or examples of acceptable modelling practice. After all, we are talking about good modelling practice, things that should be done by competent professionals anyway.

This list is generic enough to apply to all those who author models and the different BIM authoring software they use. It is by no means exhaustive, and can be augmented by specific requirements.

  • All project participants shall use compatible software to facilitate model exchanges. If a particular software is used by multiple participants all shall use the same version and all shall keep it updated.
  • A control model shall be created for levels, grids and shared coordinates. This shall be used by all model authors to establish common baseline information.
  • Grids shall be to nearest 5mm increment apart to 10 decimal places, and shall be absolutely orthogonal to 10 decimal places, or if not orthogonal at an angle with no more than 2 decimal places (exactly 2000, not 1999.099899, nor 2000.00006789, and 90° not 89.99967°, or 32.45° not 32.453678943°).
  • Correct categories shall be used, or layers / types etc. will be named to identify the type of object. For example, beams must be modelled as beams, or identified as beams, and not as floors.
  • All model elements in authoring models shall be in the authoring BIM software format. Imported geometry of a format different from authoring software shall not be used for parts of the building the consultant is responsible for.
  • Modelling shall, where possible, match construction methods. For example walls go between floor slabs, not through them.
  • All 3D models shall be consistent with issued 2D drawings.
  • All parameter data shall match issued schedules. This includes, but is not limited to, Area schedules, Revisions, FFE, Wall types, Equipment schedules.
  • All tags and identifying marks on drawings shall match parameter data within the objects being tagged or identified.
  • Text notes shall only be used for general noting or where applicable to multiple objects. Where notes refer to individual objects tags shall be used.
  • Deliver 3D models as separate files per discipline with the same base point.
  • All 2D/3D drawings/models used as references in issued drawings shall be provided with the host file. Pathing of linked files shall be relative and not absolute.
  • When requested provide any associated databases with the models that are linked to the unique component identifiers (i.e. such as external databases for door schedules or steel part / assembly numbers). Provide information on how to access these databases.
  • When requested editable 3D geometry and data shall be issued in native authoring formats (e.g. RVT, 12da, .DWG, .DGN, Moss Genio, ASCII etc) as well as published formats (ie. .PDF, .NWC, DWF etc).
  • Regular exports shall use pre-configured settings to ensure consistency of output. For example “Export for Coordination” view / settings to show only the elements that are to be shared for coordination purposes.
  • Ensure that the exported models retain unique element identifiers (i.e. that there is a globally unique identifier associated to each element that will not be duplicated by another element in the model).
  • Ensure that all elements are modelled as individual selectable elements rather than multiple elements modelled as one element (e.g. don't model a row of columns as a single column element). Nesting or grouping where individual elements are still selectable is acceptable.
  • Where appropriate typical groups of elements can be grouped and copied around the model. There should be no groups with only one occurrence. 
  • Elements, including groups and nested components, are not to be mirrored where doing so creates a different product. (e.g. a dishwasher with an outlet on the left is a different product to a dishwasher with an outlet on the right). Mirrored versions are to be a completely separate element, group or nested component than the original.
  • Main construction elements (walls, columns, slab edges etc) and setouts are to be perfectly orthogonal or at angles no greater than 2 decimal points (e.g. 31.65°).
  • All dimension entities must be rounded to the nearest 1 millimetre, no higher (or rounding errors may occur in strings of dimensions). Dimension values shall not be overridden.

For those of you who know how to use your BIM software the things listed above will be seem pretty basic and obvious. Hopefully there is nothing that you are not already doing. But sometimes the simplest thing can prevent models from being used.


  • BIM requires quality BIM models.
  • BIM requires BIM models to be shared.
  • BIM software, if used as intended, will produce quality BIM models.

If you are a consultant or sub-contractor who authors BIM models review how you are using your BIM software. If those using it in your office are treating it as a drawing tool rather than a modelling tool then retrain them and introduce processes that ensure quality models are produced.
Accept others require access to your BIM models, and when providing those models make sure they only contain information you would normally be providing anyway.

If you are an owner, or contractor who engages design consultants and/or sub-contractors, review your engagement agreements and include minimum BIM and modelling requirement, and the obligation to share models. Don't rely on those you engage to do it for you unless you are certain that they will. And if they complain it will cost more find another consultant or sub-contractor that knows how to do their job properly.