How VDC and BIM Coordination Catches Engineer and Manufacturer Conflicts Before Hangers Go Up

Every mechanical project has the same kind of surprise waiting in it. The drawing shows a chilled water main running through a space, and the structural beam, the duct and the electrical tray are all in the same place. Or the engineer scheduled a pump with connections on one side, and the pump that was approved has them on the other. Those problems used to be found with a tape measure and a tense phone call. Virtual design and construction, usually shortened to VDC, finds them on a screen instead.

What VDC and BIM actually are

BIM, building information modeling, is a three-dimensional model of the building in which each system is drawn at its real size and location. VDC is the practice of using those models to plan, coordinate and sequence construction before it happens. Each trade builds its own model: mechanical, plumbing, electrical, fire protection, structure. The models are combined, and software highlights where one system occupies the same space as another.

That overlap is a clash. Finding one in the model costs a few minutes of a coordinator's time. Finding the same clash in a ceiling cavity, with pipe already hung, costs a crew, a lift and a delay.

Where engineer and manufacturer conflicts come from

Design drawings are drawn around a basis-of-design piece of equipment. The unit that actually gets bought may be a different model, because of availability, price or an approved equal. Its footprint, weight, service clearances, connection locations and sizes can differ in ways that matter. When the equipment submittal comes in, those differences have to be reconciled with the pipe, duct and structure around it.

Michael Roane, who reviewed Midlands Mechanical on Google, put it plainly: "Occasionally there were oversights from the engineers with my company or with the equipment manufactures, and Doug and Ricky's crew were phenomenal to work with to get the conflicts resolved." That's the honest description of a real project. Oversights happen. What matters is how early they surface and how the contractor handles them.

What good coordination looks like

A model is only useful if the information in it is accurate and the team acts on what it finds. A few habits separate coordination that saves money from coordination that produces a report nobody reads.

• Model the real equipment. Use the manufacturer's dimensional data for the unit being purchased, including service clearance zones and connection points, not a generic placeholder.
• Model supports and insulation thickness. A pipe drawn at its nominal size will clash with a hanger and an insulated surface in the field that the model never showed.
• Coordinate in a regular meeting with the other trades. Clashes get resolved when the people who control the space are in the room and agree who moves.
• Set a priority order. Gravity drain lines, large ducts and main pipes generally get first claim on space, and smaller, flexible runs move around them.
• Lock the model before fabrication. Once pipe is prefabricated from the model, changes are costly, so the coordination needs to finish first.

From model to field

The model pays off most when it flows into the shop and the field. Pipe assemblies can be prefabricated from the coordinated model, with spool drawings that match what the crew will hang. Sleeves and penetrations can be located before concrete is poured or walls are framed. Hanger points can be laid out from the model so that supports land where the structure can carry them.

Estimating benefits as well. Quantities pulled from a model are more reliable than takeoffs from flat drawings, and routing problems that would otherwise be priced as contingency can be priced as real work. Midlands Mechanical lists CAD estimation, CAD, VDC and BIM, design-build and value engineering among its services, and BIM coordination is one of its listed project areas. Josh Merchant leads the company's VDC and BIM work as coordinator manager.

What it asks of the owner and general contractor

Coordination works best when it starts early. If your project is going to a mechanical contractor after the design is complete, ask whether models will be built and when. Ask who is responsible for resolving a clash that involves two trades, and how fast the design team will answer questions. A model that finds a problem in week two is only helpful if the engineer's response doesn't take until week six.

Owners also gain a record. A coordinated model of what was built, where, is a useful tool for maintenance staff years later. When a facilities team needs to find a valve above a ceiling, a good model beats a stack of drawings.

Starting the conversation

Even on smaller retrofit work, a few hours of model time can reveal an obstruction before the crew finds it. If you're planning a project and want to understand how coordination could work for it, call the Omaha office at (402) 571-4258. The Denver office at (303) 650-5990 is the Colorado contact.