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The vision of BIM in the mid-2000s was a single model that followed the building lifecycle from initial inception through design, construction, facilities management, and renovation. The single model would be a platform to share and contribute information across project phases and with multiple stakeholders, promising increased efficiencies and better decision making. This contrasted with the previous state of technology, which was a disparate collection of bespoke software solutions for each phase of the building lifecycle that met the specific needs of the phase stakeholders.

The precise technical definition of Building Information Modeling (BIM) has been well debated and documented. For this practical discussion, BIM simply refers to a three-dimensional model of building elements that include design or fabrication intelligence as contrasted with traditional CAD technology which simply shows building elements in a two-dimensional fashion. Additionally, my viewpoint is from the mechanical and plumbing design and construction perspectives.

The concept of ‘one model’ is rooted in eliminating rework. Everyone can understand the waste associated with the creation of design models that are not leveraged by construction teams who create their models from scratch in an incompatible platform. Today, given advancements in technology and new approaches to collaboration we are closer than ever to achieving the ‘one model’.

How It Started

While articles written in the mid-2000s expounded almost exclusively on the benefits of design BIM, mechanical contractors had quietly integrated BIM into the fabric of their workflow. Three-dimensional modeling with fabrication intelligence created shop-floor work orders and generated CNC code for driving automated manufacturing equipment such as sheet metal plasma cutters. In 2008 and beyond, I gave presentations to dozens of general contractors and engineering firms about the advancing BIM revolution. A highlight of the presentation was standing on the virtual 50-yard line of a stadium. A simple outline of the football field was surrounded by the mechanical systems floating in empty space in all directions. The message was that construction BIM had arrived for mechanical contractors and the time had come for other trades and design teams to catch up.

Like mechanical contractors, architects were early adopters. For architects the product was not physical mechanical and plumbing assemblies but drawing packages. For the MEP engineering community, BIM did not yet cost effectively address their pain points and the primary motivator for their adoption was the pain point created by architects encouraging adoption. Do you remember those days?

Fast forward to today. BIM has widespread adoption. Design and construction teams alike would be unable to function without the BIM software that drives our businesses. However, despite the increasing convergence of technologies, there are still hard decisions to make when determining the optimal workflow due to the differences in design BIM and construction BIM.  

Revit is also a platform that facilitates more complex analysis such as energy modeling. On the drawing production side, Revit is the platform for scheduling equipment and creating views and details. The purpose of design BIM is to communicate design intent while leaving the contractor the flexibility to incorporate manufacturer specific equipment and means and methods.

For many years, construction BIM was performed in platforms outside of Revit. In 2011, Autodesk purchased MAP software, a provider of construction BIM, and over the next several years, Autodesk increased the integration of construction BIM into the Revit platform. Construction BIM replaces design intelligence with construction intelligence. Construction intelligence includes contractor specific labor rates and up-to-date pricing, in addition to all the information required to fabricate the assemblies. The purpose of construction BIM is to price, procure, and fabricate physical assemblies, including defining associated manpower. The downside of the construction intelligence being added is that the design intelligence is lost. This leaves project teams with a conundrum regarding the optimal workflow.

We are closer than ever to living the dream of ‘one model’.  The forefront of innovation will be our ability to collaborate as teams for the best interest of the project.”

Today, engineers use of Revit for design BIM and contractors use of Revit for construction BIM is commonplace. But life is not as simple as asking, “Are you working in Revit?” Design teams will be drawing systems in Revit Families, and the mechanical contractor will be using Revit Fabrication Items – the vestiges of the MAP software.  The approaches, while both in Revit, require either the complete rework of the design model or an extensive mapping of systems by the contractor. This is antithetical to the concept of ‘one model’.

To understand the inherent challenges of ‘one model’, let’s highlight what goes into a construction BIM model referred to as an LOD 400 model. These factors can be anticipated when you focus on the premise that construction BIM needs a precise level of detail for fabrication:

• Specific equipment manufacturers with certified dimensional data.

• Specific valve specification with bolt and gasket sets and handle orientation.

• Specific connection type at each joint. A hybrid welded and grooved system must have each joint uniquely identified based on work packages and sequencing.

• Does the specification allow for copper press systems? The BIM model must be manufacturer specific. Brands A, B, and C have different lay lengths and tooling requirements.

• Optimization for prefabrication, racking, and modular construction.

Revit Fabrication Items were created to address the level of detail that contractors need. I hope that you can see from the above items, that the success of a ‘one model’ approach is dictated both by BIM technology and the way we collaborate as teams.

With rapid advancements in technology, the BIM technology barrier is fading.  The way we collaborate as teams is also progressing. Let’s look at how a ‘one model’ approach can be applied to three common project delivery methodologies: traditional design-bid-build, design-assist, and design-build.

Traditional Design-Bid-Build

Traditional design-bid-build does not have the installing contractor interface with the model until the design is complete. 

Even in this instance it is possible to use the mapping process to convert the design BIM to construction BIM as a starting point. The success of this process is dependent on several factors:

• How close is the design BIM to a fully coordinated construction BIM?

• Does the design BIM take shortcuts such as not modeling vertical risers or equipment connections?

• How much of the design is depicted in the model versus written into the specification?

With traditional design-bid-build, the cost of changes to accommodate contractor input for items like prefabrication, racking, and modularization is at a premium but still may have a return on investment.


Design-assist has many forms and increasingly involves engineer and contractor collaborating on the creation of a single model for permit and construction. There are critical upfront workflow decisions to be made with the design-assist model. Will the basis be Revit Families following the design team workflow or Revit Fabrication Items following the contractor workflow? There was a time when I thought I would not see the day that an engineering firm would take possession of a contractor’s fabrication database to model the systems with the contractor’s workflow. I can now say that I have been involved in multiple large hospital projects in which the engineering firm did just that.

On other projects, there is a handoff of the model lead from engineer to contractor often at the completion of the design development set. The model is converted through the mapping process at the handoff, and then augmented by the contractor.


Design-build offers the greatest opportunity for realizing the dream of ‘one model’. From the start of the estimating process, through design, and coordination, a single model is based on a common fabrication database. The contractor will typically strip proprietary information out of the database such as pricing and labor rates before the model gets handed to the owner as a record model.

The Future of One Model

A true ‘one model’ approach allows the right information to be contributed at the right time by the right stakeholders. This often requires breaking paradigms about what should be included in a design model and varies based on project. Often, earlier contractor input into the model is beneficial so that the design can accommodate items required for the success of prefabrication and phasing.

When construction BIM detail affects other disciplines such as mechanical floor space, shaft space, or phasing boundaries, cost is minimized through earlier incorporation into the project. However, earlier construction BIM detail has factors that need to be weighed. When earlier construction BIM detail requires committing to a brand of a commodity fitting, there may be benefit in delaying that decision so that pricing and availability at the time of purchase can be considered. Another factor is the inherent iterative nature of the design process. When construction detail adds time, it should only be added after backgrounds are locked.

We have come a long way since the mid-2000’s. Technology is still a factor, albeit more of a speed bump than a barrier. This too will smooth out with the “next software update.” We are closer than ever to living the dream of ‘one model’.  The forefront of innovation will be our ability to collaborate as teams for the best interest of the project. Upcoming changes with generative design and artificial intelligence will require us to evolve again, this time rethinking the very roles we play. 

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