Integration: BIM design

Building information modeling (BIM) is used frequently when working across multiple disciplines, including mechanical, electrical, plumbing, and fire protection engineering, and also with other stakeholders such as architects and contractors.

By Ed Paul, Arup, Los Angeles March 19, 2015

Learning objectives

  • Understand the requirements for a BIM model.
  • Learn the key components of a BIM execution plan.
  • Understand the nuances of smart data, content, and other details within a model.

Is it possible for BIM to be done correctly for mechanical, electrical, plumbing, and fire protection (MEP/FP) design? Numerous factors come into play when integrating BIM into the MEP/FP engineering and design process. It is up to the design team to take the best from each variation of modeling and apply the appropriate elements to create a successful process.

Expectations are never the same on any engineering project. Everyone has various ideas of how BIM will be incorporated, and quite a few of them are unrealistic. The MEP/FP engineering team needs to set appropriate expectations with the architect and owner at the onset of the project. Before defining these expectations, we need to understand why divergent expectations exist.

When we say or hear BIM, it is often interpreted to mean 3-D modeling using Autodesk Revit. While other platforms are available, most architects use Revit, which sets the expectation that MEP/FP models will also use Revit. The main concern is related to the detail and accuracy that an architect or owner might expect because he or she doesn’t completely understand the MEP/FP software or process. Architectural models are detailed and dimensioned to a high level of accuracy, and it is expected that MEP/FP models will match that accuracy, an attitude also shared by the client/owner. This sets the precedence in architectural and structural models, which are required to provide dimensional control for the contractor as an element of design. MEP/FP design work rarely, if ever, has the same level of detailing. However, as MEP modeling software became mature enough to be used on major projects, expectations were already set for similarly detailed MEP/FP models.

Contractors have also become accustomed to using architectural/structural models directly to create their 3-D coordination models; increasingly, they expect the MEP/FP models to have the same detail and accuracy. For example, a general contractor was completely surprised by my "negative" response when he asked about modeling all the conduit runs in the electrical model. MEP/FP design models are created primarily to show design intent. While support modeling and constructability are secondary drivers, they are still important, as the subcontractors make a substantial investment in the trade coordination exercises and rely on that information from the design models.

Keeping this in mind, the MEP/FP models should focus on overall dimensional accuracy of equipment,ducts, pipes, and other items that will require coordination with other disciplines. This virtual coordination for physical location must satisfy everyone’s needs, including those of the facility engineers who will eventually maintain the equipment and facility. These expectations should be clarified in meetings with the various teams when collaborating to create a joint BIM execution plan (JBEP).

Creating the JBEP

Collaboration to create the JBEP is another key factor for a successful project. Quite often the request for proposal (RFP) for a potential project is accompanied by the client’s BIM requirements. The JBEP is simply a response to the requirements, defining the plan and processes that will be used throughout the length of the project to meet the goals. If the RFP or the client does not have any BIM requirements, it is still in the best interest of the project team to create a JBEP so that all members understand what is created and delivered to each other-and finally to the client at turnover. Without an agreed-upon JBEP,teams often move forward with their own definition of BIM goals, which results in misaligned expectations,at times allowing the architect and/or contractor to continually ask the MEP/FP engineers and designers for small changes in the model’s detail or accuracy that may add up to a significant amount of work beyond the contractual scope.

When creating the JBEP the MEP/FP team needs to pay special attention to topics like roles and responsibilities, BIM uses, model organization/setup, models exchange, level of development (LOD),modeling matrix, software used, and data export. Quite often Construction-Operations Building Information Exchange (COBie) is required as a data deliverable, though it is not always clear how it will be used by the owner. While all the elements of the JBEP are important, the topics noted above are the core working parts of a well-defined BIM execution plan. Once these topics are defined in the plan, effort must be maintained to stay within the bounds of the JBEP. For projects within the U.S. the following documents provide good references for creating the JBEP:

It is important to keep the JBEP simple; the goal is to create a virtual building before the contractors start working on the real building. Contractor input for constructability is necessary to create the virtual building, which defines the necessity to model major items in 3-D. The LOD matrix identifies the development of objects in the model, which should be used to populate the modeling matrix, identifying MEP/FP systems and element authors.

The modeling matrix is an excellent place to start identifying which items will be modeled at the agreed-upon LOD. Accept the fact that certain elements will always be at LOD 300 and continue to add such elements to your content library. Elements like pumps, fans, chillers, panelboards, transformers, ducts,pipes, and cable trays should always be shown in 3-D, in the correct X, Y, and Z location with respect to the architectural model.

The goal is to build a virtual building, and one similar to a real building. If the structure is not in place,none of the MEP objects can be installed. Every effort should be made to have the right models in place so the most appropriate elevation is given to elements as they are modeled. An important item that needs to be added to the JBEP is the variance in size of objects given that MEP/FP engineers specify equipment with final dimensions by the manufacturers. This entry gives the flexibly needed to design the right system. If you are part of a design-build project, there must be an agreement regarding level of detail necessary from the design team given that the trade contractor’s model will show the elements in greater detail with all the necessary fittings, flanges, hangers, and other details.

Space allocations

The importance of setting the vertical space allocations for each discipline and system is paramount. This information should be shared with all the disciplines before starting any modeling. If the elevations are not established early in the project, either the MEP/FP will be going back and revising their models or the contractors and the subcontractors will take on the challenge and burden the MEP/FP team with a multitude of requests for information (RFI).

Equally important is the allocation of space for required maintenance/service as well as code-required clearances. Whenever possible, the clearances should be included as a subcategory of the Revit families.This helps with coordination during modeling and, if desired, the flexibility to easily turn off subcategories like clearances for printing purposes.


With respect to content in Revit, there are three major categories that we can refer to:

  1. Equipment
  2. Systems
  3. Connector objects.

Items like fans, pumps, water heaters, panelboards, and transformers are equipment objects that are referred to as families (MvParts in AutoCAD MEP). Systems are the supply, exhaust, return, cold water,chilled water supply, and fire main made of components such as duct, pipe, conduit, or cable tray. These are also the connector objects that connect systems to the equipment families. The project template has to define these items correctly for all the pieces to come together and create the right BIM model. The contractor installing the piping has to know when to use black pipe and when to use PVC and which system they will serve. Furthermore, he or she has to know which system connects to which equipment.

Quite often MEP/FP engineers start modeling with a default system of duct or pipe and provide all this information in the specifications or through annotation as in the past. The contractor will miss out on using some of the automatic features that the software offers, such as ability to count fittings, measure pipe sizes/lengths, add value to objects, and perform early and progressive cost estimates. Once the BIM templates are set up correctly, the engineers can quickly get to modeling without having to define systems and associated objects. Retroactively trying to fix multiple instances of errors in incorrect templates will adversely affect the profitability of the project.

Smart data in models

"Information" is the core component for all successful BIM projects. MEP/FP engineers must decide on a standard approach to what information will be contained in a model. Early determination in the JBEP is important when deciding at which phase of the project information will added to model elements. It is often felt that BIM requires significant amount of data in the early phases of the project, though in reality the amount of information available to the engineer progresses as the engineering/design of the project progresses. Planning ahead for this information growth within the families will allow all project team members to easily add detailed information as necessary.

Take a simple pump, for example. In early phases all a team needs to know that it is "P-1" and that it will be located in the mechanical room. Before placing this pump in the model, however, it would be expedient for the long run to create the basic parameter (name, manufacturer, location, size, etc.), default electrical parameters (horsepower, voltage, phase, frequency, etc.), and HVAC specific parameters(gal/min, total head, efficiency, etc.) and incorporate fields for this data into the pump symbol/family.When the pump element P-1 is placed in the mechanical room where a "space" object exists, the software will automatically record the location in the internal database.

As engineers and designers, we can now follow the JBEP and know when certain information will be available and reliable enough to be added to the equipment objects. At the same time the electrical engineer will know when the electrical data is available in the model and can plan the circuiting effort accordingly. The aim is to have information live and correct within the objects and model. When the project is in the construction phase, final modifications should be made within the model, so that the final deliverable "as-designed" or "record" model has captured the latest information. Facility managers will be indebted to the design team when they realize the amount of smart, useful information they are receiving.

Ultimately this is what BIM is about, using the information contained in the models to manage the facility.

Family content

Managing a firm’s content library is a constant maintenance and investment task. While most firms have established a standard library for symbols/families, every new project requires items that don’t exist in the library. When working with BIM objects, the library needs to manage both graphics and property/parameter data. Parameters that tie in with the graphics to control size and shape require special attention.

Every effort should be made to follow the same process each time when creating the families and adding the appropriate parameters. The parameters should be divided into subgroups for management purposes: basic or common, electrical default, sound data, vibration isolation, etc. These subgroups can be added into overall equipment-specific groups like fans, pumps, chillers, transformers, and more, that can share the same subgroup parameters as the base parameters will be consistent. Certain equipment objects like air handling units or fan coil units can have 100 or more parameter fields. Accurately managing this type of content metadata is better handled by add-on utilities than the default functionality offered by the main software package.

Special attention is needed to decide between "type based" and "instance based" parameters. Consider two scenarios:

Scenario 1: Five pumps in a building and they all have the same specifications, three are in the mechanical room level one and two are in the basement. This can be scheduled three different ways.

Scenario 2: Five pumps in a building and each is a different manufacturer model. Three are in the mechanical room level one and two are in the basement. This can be scheduled only one way.

Type or instance parameters should be created with scenario 2 in mind to allow for maximum flexibility.The "location" parameter has to be instance, though the equipment "type/number" parameters (P-1) can be type or instance based. The automatic tags for equipment are dependent on this being set correctly.When there is a limited number of different pump types, it is not a major concern, but when the count will go up to hundreds or even thousands, it is important to make almost all the parameters type based,including the name/number.

Manufacturers’ content

More and more manufacturers are providing Revit families along with AutoCAD blocks. While this is very useful, care should be taken before using manufacturer content. These objects are very detailed to support the manufacturer’s processes but typically too detailed for design model due to file size. In addition, the objects use parameters and formulas to manage content that is useful to the manufacturer,but that may not always be clear to the designer. Best practice is to use the manufacturers’ content as a starting point and simplify it down to the graphic shape that makes sense to display. Then go through the same steps as above for adding standard parameters to families to meet the design team’s obligation for appropriate detail. These steps will keep all the content in the model to the same standard established for the project.

The automatic generation of schedules and equipment tagging should be a standard approach on all projects. As the models progress, size tags, circuit tags, etc., should be generated from the model. Limit the use of text objects to annotate items that cannot be generated from the model. As the team gets more comfortable with using the model-generated information, the design/engineering accuracy will be reflected in the BIM model.

An unseen and usually forgotten part of the MEP/FP model is the "space" object. It is possible to engineer/design and produce all the drawings needed for construction documents without placing a single space object; however, they are extraordinarily useful at adding sophistication to the BIM process. It is possible to export room size data to run load calculations, to create space schedules to showroom/area/volume within your model, and to track which objects exist within a space to do room/equipment quantity takeoffs. Spaces can be tagged to show room names and numbers from the architect’s model and yet allow the BIM technician to move the tags freely to less congested parts of the room. Space schedules can be exported to spreadsheets and then compared to project program and room data sheets to verify that model objects are placed and accounted for as planned. In addition, they are required to build a COBie compliant BIM model.

Data delivery (COBie)

As more facility owners request design data for facility management software from the MEP/FP engineers, COBie will become a normal part the project deliverable. COBie is standard format for structuring data to allow for data export from models to facility management systems. Providing COBie compliance is a small step on top of what the engineering team is already doing. Models already have assigned the name/numbering, the manufacturer, and/or alternates. The equipment already knows in which space/room it is located and more. The rest of the information that is required for a COBie deliverable comes from the trade contractors during the construction phase as information that is already required in their submittals. The COBie effort is simply to combine that information into one location,either in the Revit model or more commonly in a spreadsheet or an external database. MEP/FP teams should create the necessary fields/parameters in their models so the design engineering parameters can be filled in as the design progresses, while leaving fields available as placeholders that can be exported at predetermined milestones by the contractors.

Several third-party software packages allow much of the data and placeholder fields to be exported to Excel. Once in a spreadsheet, the data can be manipulated in mass, verified, and reimported into the BIM model. Editing the data external to the BIM modeling software also provides opportunities for multiple personnel in a firm to be engaged in the workflow without having to be experts in the BIM software.

Streamlining workflow

This article has discussed some of the topics that MEP/FP engineers and designers should incorporate into the workflow when integrating BIM. Other factors like type of project, project size, complexity, number of systems, number of users, and locations all play a significant role in determining the model setup.Because there is more than one way of setting up the model, it is important to capture all possible information within the JBEP. The JBEP will be the "go to" document to clarify BIM related issues as the project progresses. Model exchange schedule should be established and incorporated in the JBEP. Quite often a bi-weekly exchange works best for schematic design and design development phases; it can switch to weekly when moving into the construction documentation phase. The process for milestones and final delivery of the model should include the file format that will be exported from the models, such as PDF and/or DWG format for all sheets to document design progress. Certain owners are also asking for Industry Foundation Classes (IFC) format models to allow exchange of model objects between BIM software by different vendors, along with models from the authoring software.

The information discussed here includes engineering data shown in equipment schedules, or captured from objects and systems. MEP/FP engineers have the capability to perform simple calculations on this data within the Revit software, or complex calculations on the data after exporting it to spreadsheets. The data can also be exported to databases to tie into facility management solutions. The flexibility of the modeling software and the opportunities it offers to the engineers will continue to grow, and it is in the best interest of MEP/FP engineers to integrate BIM into their design workflow for all projects.

Ed Paul is the BIM manager at Arup’s Los Angeles office. He has more than 20 years’ experience in managing large multi-discipline projects from inception to handover. His experience includes various CAD/BIM software packages along with information systems management.