Ask any estimator who has worked a healthcare or data center project about VFDs. You will hear the same story, told with different numbers and different subs.
The mechanical sub installs the air handling unit. The electrical sub runs power to the panel. Somewhere between those two scopes lives a variable frequency drive, a motor starter, and a disconnect switch. Neither sub included them. Both assumed the other would. The GC absorbs the cost.
This is not a rare edge case. According to Provision's research across 200+ GC interviews, generator field conditioning and MEP equipment boundaries are among the most frequently cited recurring scope gaps on commercial and ICI projects. The dollar amounts are rarely small.
A 2018 PlanGrid and FMI study found that $31.3 billion in U.S. construction rework was tied to miscommunication and bad project data. That figure is from 2018, but the root cause has not changed. Scope boundaries that are never written down produce disputes that repeat across every project.
These three components sit at the intersection of two trade divisions. That is the problem.
The confusion compounds when the equipment supplier for the HVAC unit offers a factory-mounted starter as an option. If nobody confirms whether that option was exercised, the electrical sub prices a standalone starter that is already included in the mechanical sub's equipment quote.
The spec language rarely resolves this cleanly. Here is what you will typically find:
The spec tells you what the designer intended. It does not tell you what the subs included in their number. Those are two different things.
It starts at bid day. The electrical sub scopes the project, sees the VFD called out in Division 23, and excludes it. The mechanical sub sees "VFD by electrical" in a note on the mechanical drawings, and excludes it too. Both exclusions are buried in clarification lists.
The GC receives bid packages, compares numbers, and selects the low trades. Nobody reconciles the exclusion language against the spec. The scope letters go out with generic language like "per plans and specifications" and both trades sign.
As one Pre-Construction Lead at a Top-ENR Canadian GC described it: "If you miss anything, they'll bill it." That quote applies directly here. By the time the VFD question surfaces in the field, the GC owns the dispute.
This is one of the anti-patterns documented in The Scope Gap Playbook's trade-specific chapter: "as per plans and specs" is the most-cited anti-pattern in GC scope practice, precisely because it passes ambiguity downstream without resolving it.
This gap is not new. But it is getting bigger.
Data center specs run 1,500 to 2,500 pages. Healthcare projects carry dense Division 23/26 interplay, particularly around medical gas compressors, chiller plants, and air handling units. The number of VFD-driven motors on a single project can run into the hundreds.
When spec density increases, the probability that something is assigned in one division and silently excluded in another goes up. Estimators reading a 2,200-page spec set over two or three days will not catch every cross-reference. That is not a performance problem. It is a volume problem.
The $300K lead-lined glass gap documented in The Scope Gap Playbook followed the same logic: a specialty item sat at a trade boundary, the GC absorbed it under "readily inferable" language, and nobody caught it at buyout. The dollar amount was not exceptional. The pattern was.
You cannot rely on the spec to resolve trade boundaries for you. That is the job of your scope letter.
Here is a framework for MEP boundary assignments. Use this as a starting point, then tailor it to what the spec actually says.
For every motor-driven piece of equipment, write out who furnishes the VFD or starter and who installs it. Do not combine them into one line. Combined lines create room for each trade to claim the other side.
Specify which trade provides and installs the disconnect switch at each motor location. Reference the section or drawing that shows it. If the electrical drawings show it, it goes in the electrical scope letter with a section cite.
Before the scope letter goes out, confirm with the mechanical sub whether their equipment quote includes factory-mounted starters or VFDs. Get it in writing. If the answer is yes, exclude it from the electrical scope letter and document the confirmation.
Low-voltage control wiring is a consistent source of finger-pointing. Assign it by circuit type: who runs conduit from the BAS panel to the VFD, who terminates at both ends, and who is responsible for point-to-point verification.
Before scope letters go to the trades, review MEP sections side by side. Look for items that appear in both Division 23 and Division 26 without a named trade. This is Habit 8 from The Scope Gap Playbook: the pre-issue scope review checkpoint. It takes 90 minutes and prevents weeks of field disputes.
As an Estimating Manager at a Canadian ICI GC noted: "We have fewer subs who just rely on a gentleman's agreement. They've become more quick to clarify that they're not including that one piece of scope." The subs are protecting themselves. The GC needs to keep pace.
Compare these two approaches:
Weak: "Electrical sub to include all items per Division 26 plans and specifications."
Strong: "Electrical sub to include: (1) disconnect switch at each motor location per E-201, Specification Section 26 28 23; (2) field wiring from MCC to motor, including conduit and terminations; (3) programming of VFDs at AHU-1 through AHU-6 per Spec Section 26 29 23. VFDs are factory-mounted by mechanical sub on AHU-1 through AHU-4. VFDs for AHU-5 and AHU-6 are field-mounted by electrical sub. Confirm in writing."
That level of detail is what keeps a $60,000 scope gap from becoming a $200,000 change order. The $60.1 million average North America construction dispute value cited in Arcadis's 2024 Global Construction Disputes Report does not start with large ambiguities. It starts with language like "per plans and specs" on a disconnect switch.
Need a starting point? The scope of work template on Provision's site gives you a structure to build from.
The challenge is not knowing what good scope language looks like. Most experienced estimators know. The challenge is reading a 2,000-page spec set, coordinating six to eight trade scopes, and catching every cross-trade boundary item in the time available before bid day.
Scope Agent reads the full project set: drawings, specs, and contracts together. It does not read specs in isolation. It reads Division 23 and Division 26 simultaneously and flags items where supply, installation, and control responsibilities are split across trades without a clear assignment.
It generates a complete scope package per trade in under 60 minutes. That includes flagging items like VFDs where the spec assigns supply to one division and installation or control wiring to another. The output cites the exact spec section and drawing reference, so your scope letter gets written with specific language, not generic incorporation.
Provision has reviewed more than $100 billion in project value and processed 66,000 construction documents. The patterns that surface most often in MEP scopes, including VFD/starter/disconnect boundary disputes, are built into what it looks for.
For contract language questions, Risk Review flags "readily inferable" clauses and similar terms that shift undefined scope onto the GC. It identifies those risks with 99% accuracy, cited to the exact clause. If your subcontract has language that could expose you on a VFD dispute, it will find it.
See how GCs are using these tools in the EllisDon case study and the NAC case study.
VFDs, motor starters, and disconnects are small-dollar line items on any individual sheet. Across a healthcare or data center project, they add up. And when both trades exclude them, the GC pays.
The fix is not complicated. Write specific scope language. Cite the section. Confirm factory vs. field. Run the cross-trade review before the letters go out.
The subs are already doing this. They are protecting their numbers on every bid. The GC's scope letter needs to keep pace.
For a full breakdown of trade-specific scope gaps across MEP, envelope, and structural trades, read The Scope Gap Playbook's trade chapter. It documents the most common boundary disputes by trade, with operator-cited dollar amounts and the language patterns that cause them.
It depends on the spec. Division 23 often assigns VFDs to the mechanical sub as part of HVAC equipment. Division 26 sometimes assigns them to electrical. The critical issue is confirming whether VFDs are factory-mounted in the equipment package or field-supplied separately. Write it down in the scope letter either way.
The most common gap is a factory-mounted starter included in the mechanical sub's equipment quote that the electrical sub also prices as a standalone item, or the reverse: both subs exclude it assuming the other owns it. Confirm factory vs. field-mounted status before scope letters go out.
Name the trade, cite the drawing or spec section, and specify location. For example: "Disconnect switch at each motor location per Drawing E-201 and Specification Section 26 28 23, furnished and installed by electrical sub." Generic language like "per plans and specs" leaves the assignment unresolved.
Spec density. Data center and healthcare specs routinely run 1,500 to 2,500 pages. Division 23 and Division 26 interplay is dense, and the number of motor-driven pieces of equipment is high. Estimators reading under time pressure will miss cross-trade boundary items. The gap is a volume problem, not just a skill problem.
It means the GC may be required to provide something not explicitly shown or specified if a reasonable contractor would have inferred it was required. For VFDs and disconnects, this is a real risk. If the spec requires a code-compliant installation and the disconnect is code-required, a court may find it was "readily inferable" even if no trade included it.
Purpose-built tools can. Generic AI tools lack the construction context to read Division 23 and Division 26 together and identify cross-trade boundary conflicts. Provision's Scope Agent reads the full project set, including drawings and specs together, and flags these gaps with citations to the exact section and drawing reference.
Review the "readily inferable," "work reasonably inferred," and "complete and proper execution" clauses in your subcontract. These are the most common mechanisms that shift undefined scope onto the GC. Risk Review identifies these clauses with 99% accuracy, cited to the exact location in the contract document.
Scope Agent reads Division 23 and 26 together and flags cross-trade gaps before the scope letters go out.
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