3-D modeling surges ahead

3-D modeling continues to improve the overall design and construction process, saving time and money.


Figure 1: This fully coordinated model shows HVAC ductwork and piping in a mechanical room space. Courtesy: Ring & DuChateauIn today’s world of building engineering and construction, 3-D modeling has become increasingly popular as a means for owners, architects, engineers, and contractors to design and coordinate building systems, such as HVAC systems. This valuable tool can save time and money. While the use of 3-D modeling is expanding, it is still used to varying degrees to achieve a variety of different outcomes. For example, some engineers are using 3-D modeling simply to produce construction documents, while others are using BIM for clash detection or to input specific parameters such as specifications, electrical characteristics, and sizing criteria.

The purpose of this article is to clarify what 3-D modeling really means to avoid misguiding clients, engineers, and contractors; identify what each group expects of a model; explain the benefits of clash detection with common engineering software; and show how using 3-D modeling can save time and money in the process.

Modeling expectations

It is important to have a clear understanding of what all parties expect from the use of 3-D modeling because each person in the design and construction process expects something different. Modeling a building with computer software is the first step in producing construction documents. Construction documents today use 3-D modeling software to model real-time changes and design within the building. The following is an overview of the general expectations of the major parties in the design and construction of a project.

Owners expect the most efficient use of their money during the construction process to ensure accurate results and minimal waste of time and resources. The owner can use the model with its teams during design for many purposes, including review of room layouts and finishes as rendered by architects, operations and maintenance (O&M) staff can review mechanical rooms to observe space available for service, and users can get a feel for building layout prior to construction. Today, a building fly-through can be an eye-opening experience for owners as they can see their space and plan prior to construction. It also allows the O&M personnel to become more involved in the design process based on their input to service and maintain the building, not only within mechanical rooms but also in occupied spaces. A 3-D model is a great means to saving time and money because it shows owners what they will receive when construction is completed.

Architects expect everything in the 3-D model to be as accurate as possible to maximize useable building space. This starts by modeling equipment at its actual physical size and location so the 3-D relationship of all equipment can be seen. It also must show equipment clearances and maintenance spaces, as building design will be completed using this information to maximize ceiling heights, space finishes, and useable floor space. Because the architect is ultimately responsible for a design of the physical space, a 3-D model can be used to confirm room sizes are adequate based on the function of the space.

MEP engineers expect the 3-D model to be a method to communicate design intent. The ability to review a 3-D model and clearly observe design intent is superior to using the 2-D approach, and a model in 3-D can be continuously updated in real time. 3-D modeling also presents a new set of responsibilities, however. Increasingly, engineers are expected to draw/design with the intent of making sure more detailed coordination is shared in the design phase so the contractor’s field coordination can follow a more streamlined approach.

Mechanical contractors, like architects, expect everything in the model to be as accurate as possible. The mechanical contractor's main question about a 3-D model is: “Is the model coordinated?” The contractor spends a lot of time and effort to take a completed set of engineering drawings and convert them for use with fabrication software and field construction practices. By spending time during design to coordinate, many issues can be identified and resolved earlier in the process to reduce construction-related issues. Mechanical contractors also are interested in the content of the material within the model as some contractors can use the model to develop a bill of materials for the project and produce cost estimates.

Coordination between engineers, contractors

The value of 3-D modeling becomes more apparent when one examines the coordination process between engineers and contractors. In this phase, 3-D modeling can be used not only as a means for increased collaboration, but also as a method to eliminate any waste and redundancy in the construction process.

It is very common these days to have discussions in the construction phase around sharing engineering drawings and/or 3-D models with the mechanical contractor. Some engineers believe the contractor should create shop drawings without the use of the engineer’s CAD drawings, while others believe in the value of sharing the knowledge and complete understanding of what the project entails. Engineers should ask: If the project is a team effort, why would we want to exclude the contractor from information that will make the project a success?

Factoring into the answer is the engineer’s errors and omissions professional liability insurance, particularly letting the contractor use the documents without the proper liability safeguards in place. The issue revolves around communicating design intent; if the model shows something that isn’t exactly as it must be installed, who becomes responsible? Furthermore, if additional changes are required with cost impact between the design intent and practical field construction practices, does it open the door to change orders from the contractor?

These questions are complex and will likely be worked through on a project-by-project basis. More importantly, how the 3-D model should be used in the construction documentation should be addressed. During the bidding period for a design-bid-build job, the contractor should bid on what is shown on the engineer's plans. The plans are made from the 3-D model and represent the engineer's design intent. The engineer should provide plan views, sections, isometrics, schematics, details, and schedules in order for the contractor to fully understand the design intent. The 3-D model would provide minimal benefit to the contractor at this point in the process. Once a contractor is awarded the project, however, there are great benefits to allowing the contractor having access to the 3-D model. If this is the case, the engineer should note in the construction documents, most likely the specifications, that the successful contractor will receive the model for reference during its coordination and fabrication process.

Some of the benefits to providing the 3-D model to the contractor are:

  • It saves time and effort between the engineer and contractor. There will be fewer questions and issues for the engineer to work out with coordination. Similarly, there will be less work for the contractor to create redundant drawings for fabrication and field construction.
  • Requests for information (RFIs) are reduced due to the ability to review the model.
  • The contractor can use the same 3-D model as a basis for its work. There should be a design model and a construction model, but both models should be open to each trade. With two sets of ”eyes” to view the 3-D model and subsequent plans, the contractor can become familiar with changes made by the engineer after the bid process via construction bulletins, allowing a better understanding of design intent. In a perfect process a single model would be used by both the engineer and the contractor, but for typical design-bid-build jobs, this process still appears to be in the future.
  • It means fewer field visits for coordination efforts. The contractor and engineer can review troubled areas by reviewing the shared model.
  • The owner should receive a more accurate 3-D model and as-built plans. When both the engineers and contractors work from similar 3-D models, both parties can react to real-world building issues prior to fabrication and construction. This also benefits future projects as contractors and engineers have more accurate plans to use for remodeling projects. 

Aside from the coordination and communication benefits of sharing the 3-D model, a major issue that engineers and contractors face is a willingness to change. The engineer needs to design systems that are fully coordinated and able to fit within the spaces allocated. At the same time, the contractor should trust and use the 3-D model it received as a starting point for its work.

Clash detection

A powerful tool that emerges from 3-D modeling is basic clash detection. Clash detection is the ability to find conflicts between two items in a 3-D realm. Previously, drawings were produced in 2-D and the clash detection was the contractor’s responsibility during construction—which for major clashes was too late, resulting in costly change orders. Many engineering and architectural firms are now taking on the responsibility of running clash detection and finding coordination conflicts prior to sending out a project, which is a great advancement in the project delivery process. The caveat to being able to run clash detection is understanding how to use this tool efficiently and wisely; just because clash detection can occur at schematic design doesn’t necessarily make it appropriate. This also shouldn’t relieve the contractor of all coordination, since depending on the project delivery method they are ultimately responsible for final coordination with all trades.

Figures 2 and 3: Image of coordinated drawings for 35% based on standard 2-D CAD (Figure 2) versus 3-D modeling (Figure 3). Courtesy: Ring & DuChateauFigures 2 and 3: Image of coordinated drawings for 35% based on standard 2-D CAD (Figure 2) versus 3-D modeling (Figure 3). Courtesy: Ring & DuChateau

Today, Autodesk Navisworks is a clash detection software commonly used by contractors; similar clash detection can be completed using the software program Autodesk Revit, which many consulting engineering firms currently use as their 3-D modeling software. This eliminates the need for engineers to purchase a separate software package to run their own simplified, independent clash detection. Clash detection in Revit is an effective way to eliminate trouble spots before the 3-D model is sent for project coordination review and can be completed with the 3-D model and any other linked Revit model used by the design team. The following is a brief description on how to conduct a simple clash detection using Revit.

The gateway to clash detection in Revit is through a process called Interference Check, which allows the user to run clash detection based on any models that are linked into the users file. After running the clash detection, Revit will populate a list of all the reported clashes in the model and provide a transaction ID that can be used to find any piece within the Revit model. Similarly, outside software programs such as Navisworks also produce transaction IDs that can be used interchangeably with the respective software programs to find the clashes within models. Based on transaction IDs, engineers and contractors can quickly identify and locate clashes within their software program of choice during design and construction.

Saving time, money

Probably the most convincing reason to use 3-D modeling for many companies is the significant savings of time and money that can result. Drafting using 3-D modeling is more efficient than using standard 2-D CAD and even most existing 3-D CAD software programs. 3-D modeling allows the design team to manage and organize building information in real-time geometry and provide building relationships in a variety of views to convey the design intent more clearly. By defining these objects parametrically, when an object is modified, it is modified accordingly in all aspects and views, saving valuable time and effort.

Second, 3-D modeling allows engineers to share the model with the architects, owners, and contractors and show design concepts clearly in 3-D to identify the design intent and the spatial impact of equipment by transferring files. This can reduce time needed for hand sketches as the model can be used to show the intent.

Third, from a construction standpoint, running clash detection sooner can save coordination time for engineers and contractors. Initial clashes can be addressed upfront by the engineer before the contractor even sees the design, resulting in fewer RFIs. This will reduce engineering time for responses and save the owner money as it will see fewer change orders to due to incomplete coordination.

Finally, the use of 3-D modeling software can help reduce risk during the design process by creating more complete, accurate construction documents and avoiding errors and omissions. Engineering firms are required to have professional liability insurance for errors and omissions in case a client alleges that the engineer was negligent or failed to perform its professional duties. 3-D modeling can reduce the potential for errors and omissions, and may help reduce insurance rates with your insurance company.

The 3-D modeling process has proven to be a valuable tool in the coordination and completion of construction documents as it improves the overall design and construction process by reducing cost and risk. Today, with the ability to coordinate everything sooner, we should share our work to save duplication of efforts and produce better projects. There are many opportunities for saving time for all parties involved, including simplifying the architectural/engineering relationship, observing building clashes prior to construction, and reducing contactors’ time to complete coordination drawings and RFIs. Ultimately, all of these benefits will help save the project money but, more importantly, result in a well-coordinated design.

Are you ready for 3-D modeling?

Rolling out new software and shifting design processes within a company is never an easy task. The best advice is to jump in head-first and start using the software but—most importantly—provide adequate training. Start using the software on all new projects regardless of their size, as the goal is to become familiar with the software. Remember, training is necessary for the employees who will be using the software regularly, and a core group of employees will need to be devoted to working through the trials and tribulations of the initial phases of using the new software. 3-D modeling software is not the same as 2-D software, so training should come from professionals instead of on-the-job, or lots of time will be wasted without gaining the knowledge. The first few jobs may feel overwhelming and the advantage to 3-D modeling may not seem evident, but over time, the knowledge will be gained and the savings will be observed. 3-D modeling is here to stay and is a valuable technology for your company to implement.

Modeling success stories

To demonstrate how 3-D modeling has improved work flow, two case studies from current projects using traditional 2-D CAD versus 3-D modeling software are described below.

The first case study is for a 90,000-sq-ft office addition, which is adding two floors and a penthouse to an existing 94,700-sq-ft building. The existing building was completed using 2-D drawings whereas the addition work was completed using 3-D modeling. The mechanical systems are identical for the existing and new work, which includes an underfloor air distribution system. The underfloor plenum is an 18-in. raised floor for fan-powered variable air volume (VAV) boxes with hot water heating, branch ductwork, pedestal supports for the floor, electrical cable trays, and electrical distribution conduits. On the addition, the mechanical contractor was required to enter a line item cost for its 3-D modeling and coordination efforts during the bidding process. By understanding the level of detail of 3-D coordination with all disciplines by the design team, the mechanical contractor was able to reduce its cost for coordination by 25% and approximately 150 man hours compared to a building designed without a heavy concentration on design coordination, saving the time during coordination and allowing construction to begin sooner.

The second case study compares design fees and relative percentages of project completion for two projects. One building was designed using 2-D CAD drawings versus a second building designed using 3-D modeling software. Although the functions of the buildings are different, the two buildings are on the same university campus and both use multiple air handling units (AHUs) with single-duct VAV systems with campus steam converted to hot water heat inside each building and campus chilled water. These percentages are presented from the typical engineering design phases and demonstrate that design fees can be saved using 3-D modeling while also producing drawings with similar detail at an earlier phase of the design process.

Table 1 follows very closely the ASHRAE BIM Standard addressing cost versus approximate completion of construction documents. 3-D modeling projects use more time, effort, and money in the initial phases of the project getting the background work set up, starting the project design, and working out space planning efforts. The savings with 3-D modeling is on the back end, where changes are simpler to make and less time is spent addressing issues that required coordination sooner in the process than using a typical 2-D design process. 

Table 1: This is a comparison of design fees for a standard 2-D CAD project versus a 3-D modeling project. Courtesy: Ring & DuChateau

** Fees used do not add up to 100% due to project construction administration costs not included in the percentages.

Table 1: This is a comparison of design fees for a standard 2-D CAD project versus a 3-D modeling project. Courtesy: Ring & DuChateau

Grassl is a mechanical engineer at Ring & DuChateau. He is also an adjunct instructor at the Milwaukee School of Engineering. Venturella is an HVAC drafter and Revit lead at Ring & DuChateau. He has four years of Revit MEP experience and is responsible for HVAC department coordination, implementation, and training of Revit software.

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