A building information model is, by definition, a model of intent - what the design team intended each system to look like, where it intended each duct, conduit, and pipe run to sit, before a single trade has mobilized to the field. The gap between that model and what actually gets built is not a flaw in the model; it's simply the distance between design and construction that every project has to close.
The problem isn't that the gap exists. The problem is how many projects treat the as-designed model as a static artifact - accurate at issuance, then effectively frozen while the field proceeds to deviate from it in ways nobody is tracking in real time.
Why the Gap Widens During Construction
Field conditions force changes that never make their way back into the model: a conduit run gets rerouted around an unexpected structural element, a mechanical contractor adjusts equipment placement for maintenance clearance, a subcontractor substitutes a component with different physical dimensions. Each change is reasonable on its own. Collectively, and left undocumented, they turn the model into a historical snapshot rather than a current representation of the facility.
BIM and VDC exist specifically to close this gap before it becomes expensive - clash detection during design and pre-construction catches conflicts between systems while they're still lines in a model, not pipes and conduit already installed. But that value only holds if the model keeps getting updated as field conditions evolve, rather than being treated as complete once design is issued for construction.
What an Unreconciled Gap Costs an Owner
An owner who takes over a facility with a model that no longer reflects as-built conditions inherits a documentation problem that outlives the construction phase. Every future renovation, tenant improvement, or system expansion starts by rediscovering what's actually behind the wall, because the model that was supposed to answer that question stopped being trustworthy partway through construction.
It also undermines the facility team's ability to operate the building day to day - troubleshooting a system is harder when the reference documentation doesn't match the equipment actually installed, and that mismatch tends to surface at the worst possible time, mid-incident rather than during a planned review.
Frequently Asked Questions
Is it realistic to expect a model to stay perfectly current through construction?
Perfectly current isn't the standard - reliably reconciled is. The goal is a disciplined process for capturing field deviations and updating the model at defined intervals, not an assumption that the model updates itself.
Who is responsible for keeping the model current during construction?
Responsibility should be assigned explicitly as part of the BIM execution plan, typically involving the design team, trade contractors documenting field changes, and a VDC function coordinating updates - left ambiguous, no single party ends up owning it.
What's the difference between clash detection and as-built reconciliation?
Clash detection identifies conflicts between systems before construction, using the as-designed model. As-built reconciliation is the ongoing process of updating that model to reflect what actually gets installed in the field, including changes made after clash detection was complete.
Closing the Gap Is a Process, Not a Final Deliverable
An as-built model handed over at the end of a project is only as good as the discipline that maintained it throughout construction. Owners who ask for that discipline explicitly - defined update intervals, clear ownership of field-change documentation, reconciliation built into the schedule - end up with a model they can actually trust at handover.
The alternative is a model that looks complete on the day it's delivered and starts losing credibility the first time someone in facilities opens a wall and finds something different from what the drawing shows.
