Ontario Building Code Article 1.2.2.2, the general review clause in Division C, Part 1 of the OBC, requires the designer to carry out general reviews of construction and to form a professional opinion on whether the work is in general conformity with the documents that formed the basis for the permit. A companion piece establishes that the clause binds every discipline whose design required a sealed permit drawing, not only structural. This piece applies that obligation to one of those disciplines specifically: mechanical.
The mechanical engineer who sealed the HVAC permit drawings is a designer within the meaning of the clause. The obligation to general-review the mechanical construction follows the seal on those drawings, exactly as it does for the structural engineer who sealed the framing drawings. What changes for mechanical work is not whether the obligation applies, but the character of the review, the standards it is measured against, and the kind of evidence a defensible report has to carry. Each of those shifts away from the structural template, and a mechanical firm that has borrowed a structural firm's documentation without adapting it carries a durability gap into every report.
Who the clause binds in mechanical work
The clause speaks to the "designer," which is a functional description, not a job title. It means the person who prepared the design for a part of the work. On a multi-discipline building project the mechanical engineer who designed the HVAC, hydronic, and life-safety mechanical systems, and who sealed the permit drawings for that scope, is the designer of the mechanical work. No other discipline can stand in for that. A structural firm cannot general-review the mechanical installation because the structural firm did not design it and cannot form a professional opinion on its conformity.
Regulation 941 section 53, rewritten by O. Reg. 837/21 and in force in its current form since 2021, reinforces this at the sealing level. A practitioner shall sign and seal an engineering document where the practitioner prepared the engineering content or otherwise assumes responsibility for it. The seal is an assumption of responsibility scoped to the engineer's own discipline. A mechanical seal on the permit drawings is a statement that the sealing engineer assumed responsibility for the mechanical design; the general review obligation under Article 1.2.2.2 is the field-stage continuation of that same responsibility. The two are not separable. An engineer who sealed the design and then treated field review as someone else's problem has assumed the responsibility without performing the obligation that comes with it.
What mechanical general review actually looks like
General review is not exhaustive inspection. It is periodic, professional-judgment review for general conformity, and the clause has never asked for continuous or guaranteeing examination of every fitting and every metre of duct. That much is discipline-neutral. What distinguishes mechanical general review is the nature of the observations that carry information.
Structural observations are largely dimensional and geometric: bar spacing, concrete cover, connection geometry, plumb and level. A structural reviewer can frequently confirm conformity by looking, measuring, and photographing. Mechanical observations are frequently instrumental. Whether an HVAC system conforms is often a question the eye cannot answer, because the relevant fact is a pressure, a flow rate, a temperature differential, or a commissioning result rather than a position in space. A reviewer can see that a variable-air-volume box is installed; whether it has been commissioned and is modulating to its design setpoint is a reading, not a sight. A reviewer can see that ductwork is hung; whether it holds pressure to the specified leakage class is a test.
That instrumental character runs through the typical mechanical scope. HVAC ductwork installation and sealing, diffuser and return-register placement, refrigerant piping, chillers, boilers, pumps, and terminal-unit connections are the visible elements. Pressure tests, flow rates, temperature differentials, and commissioning status are the readings that tell the reviewer whether those elements actually perform as designed. A mechanical field review that records only what was visible, and omits the readings, has documented the easy half of the work and left the half that mattered to professional judgment unrecorded.
Writing to mechanical standards, not borrowed ones
A finding of general conformity is conformity with something, and the reference the finding names has to belong to the discipline. Structural reviews cite the concrete and steel standards that govern structural work. A mechanical review has to shift its references to the mechanical and HVAC installation codes that apply in Ontario, and to CSA B149 for natural-gas installations where gas-fired equipment is in scope. A boiler commissioning, a gas-train installation, a refrigerant pressure test: each is measured against a mechanical standard, and the report has to say which one.
The failure mode here is generic borrowing. A mechanical firm that adopted a structural template and never replaced its reference column will produce reports that cite concrete or steel standards under mechanical findings, or that cite no standard at all because none of the inherited ones fit. Either way the finding floats free of any authority the firm can defend. This is a durability gap in the precise sense that it costs nothing on the day the report is written and surfaces only when the report is examined years later, which is exactly the moment the reference was supposed to do its work. The sibling piece on what a defensible field review report carries, element by element, treats the reference element in general; for mechanical the practical instruction is narrow: cite the mechanical standard that actually governs the work in front of you, and confirm with the municipality's building services department where a specific project's permit conditions are unclear.
The report skeleton applied to a mechanical review
The defensible field-review-report skeleton is discipline-neutral. It carries scope identification, observation, finding, reference, recommendation, and signature and seal. None of those elements is structural-specific, and a mechanical firm can adopt the skeleton directly without inventing anything. What fills each element is where the discipline asserts itself.
Scope identification names the date, the location, and the portion of the mechanical work reviewed: the fourth-floor VAV boxes, the penthouse boiler room, the rooftop air-handling unit. Observation records both what was seen and what was read, because for mechanical work the reading is frequently the substantive observation. Finding states whether the work, as observed and measured, is in general conformity with the design and the applicable mechanical standard. Reference names that standard or the mechanical design document the finding is measured against. Recommendation states what the reviewer requires to bring the work into conformity, and where a commissioning result is still pending it says so rather than implying a conformity that has not yet been demonstrated. Signature and seal apply the mechanical engineer's assumption of responsibility under Regulation 941 section 53.
The element most exposed to the instrumental character of mechanical work is observation. A structural entry can often read defensibly as a sentence of description. A mechanical entry frequently cannot, because the description without the reading omits the fact the finding rests on. "The ductwork was installed and supported" is a description; "the ductwork was installed and supported, and a pressure test held at the specified value for the low-pressure supply duct" is an observation a finding of conformity can actually stand on.
The seal as a scoped assumption of responsibility
Because the seal is an assumption of responsibility scoped to the engineer's own discipline, a mechanical engineer's seal on a field review covers the mechanical work that engineer reviewed and nothing more. It does not extend to the structural, electrical, or plumbing work that appears in the same building, even where the mechanical review sits in a consolidated general-review file managed by the general contractor or the lead architect on someone else's letterhead. Administrative consolidation of the paperwork does not consolidate the responsibility. Each discipline's seal reaches as far as that discipline's design and no further.
This matters for mechanical firms in particular, because mechanical scope on a large project is often divided and subcontracted in ways that blur who designed what. Where a specialty subtrade's shop drawings entered the project, the sealing engineer's general review reaches the mechanical design that engineer sealed, and the report should be clear about that boundary. A report whose scope statement and seal agree is one the mechanical engineer can stand behind without qualification.
What mechanical firms should do
The practical response is direct. A mechanical firm that sealed HVAC or other mechanical permit drawings for a building under the OBC should treat Article 1.2.2.2 as binding on its own work and not assume the structural firm or the general contractor has absorbed it. Where a specific project's permit conditions raise any doubt, the municipality's building services department is the authority to confirm with.
Many mechanical and broader MEP firms have less mature field-review documentation than structural firms, which have refined theirs over decades. That maturity gap is not a reason to defer; the skeleton is discipline-neutral and can be adopted directly, then populated with mechanical observations, mechanical readings, and mechanical references. The two changes that matter most are recording the instrumental observations rather than only the visible ones, and citing the mechanical standards that actually govern the work rather than the inherited references of a structural template.
Documentation should be retained for the long horizon the standard of care contemplates, aligned with Ontario's fifteen-year ultimate limitation period under the Limitations Act, 2002. The retained artefacts include the observations and the readings behind them, the commissioning results, the final report, and the record of who sealed it and when. A mechanical firm operating at that standard is doing nothing exotic. It is applying a discipline-neutral skeleton to its own discipline's work, with the readings and the references that mechanical general review has always required, under a seal that means precisely what it has always meant.
