Commissioning Roles & Definitions: Who Does What on a Cx Project?

Pick up any commissioning project document and you will find at least four or five different titles staring back at you: CxA, CxP, CxM, Commissioning Authority, Third-Party Commissioning Agent, Commissioning Engineer, Commissioning Manager.

Understanding what commissioning roles are, what each one does, and how they differ from one another — including what a commissioning manager does versus what the CxA is accountable for — is one of the foundations for understanding how a commissioning team works. If you are new to the industry or writing a commissioning scope of work for the first time, getting this clear early saves a significant amount of time and confusion later.

If you want the background context on what commissioning is and why it matters before we get into the roles, that is a good place to start.

The Short Answer – It Depends on Who Appointed Them

On a commissioning project, there are several distinct roles. The Commissioning Authority (CxA) or Commissioning Provider (CxP) – contracted directly by the owner, and independent of the design and construction team to avoid conflicts of interest – leads the commissioning process. The Commissioning Manager (CxM) coordinates the overall commissioning program for the owner, or – on the contractor’s side – manages the GC’s or MEP subcontractor’s own commissioning obligations. “Commissioning Manager” and “Senior Commissioning Manager” are also used as internal seniority grades within a CxP firm. The Commissioning Engineer (CxE) performs field testing and verification [ASHRAE Guideline 0-2019; SSPC 300 Annex 21].

The confusion is understandable. CxA and CxM look similar on paper. In practice, they are different appointments with different scopes, different employers, and different accountability lines. The CxM sits in one of two places depending on the project: on the owner’s side, as part of the team managing a broader commissioning program across the CxA contracts; or on the contractor’s side, managing the contractor’s own commissioning obligations and reporting to the GC or MEP lead. Same title, different employer, different accountability line entirely.

The simplest way to separate any commissioning role: ask who appointed the person and what they are accountable for delivering. That question resolves most of the overlap you will encounter on a real project.

The Roles at a Glance – Complete Reference Table

The table below covers the six principal commissioning team members: what they do, who appoints them, and what documents they own or produce.

This table covers a new-build project structure following ASHRAE Guideline 0-2019. On smaller projects, roles may overlap – the CxA may also perform field-level CxE work directly and there may be no owner-side CxM. On large programs, the CxM and CxA are clearly separate appointments.

The Commissioning Authority (CxA / CxP) – The Process Lead

The CxA, or Commissioning Authority, is the independent process lead. The Building Commissioning Association (BCxA) uses the term Commissioning Provider (CxP) for the same role – with ASHRAE from what we understand moving to this terminology. Both describe the same function: the owner-contracted independent professional who leads the entire path from pre-design through to final commissioning report.

The independence requirement is not optional. Per ASHRAE Guideline 0-2019, the CxA must be independent of the design and construction team. The GC cannot be the CxA on their own project. Neither can the mechanical design engineer. Independence is what gives the CxA the authority to issue deficiency notices, challenge designs, and report unresolved issues to the owner without compromise.

For the full breakdown of what the CxA does across the project lifecycle, who qualifies, and how LEED changes the eligibility criteria, see: What Is a Commissioning Authority?

Third-Party Commissioning Agent

“Third-party commissioning agent” is not a separate role.

It describes the contractual relationship: the [CxA] or [CxP] is contracted directly to the owner, separate from the design team and separate from the contractor. The function is identical to the [CxA] / [CxP] scope above, with the label making the independence more explicit.

For a full breakdown of the role, when it is required, and what to check when appointing one, see: What Is a Third-Party Commissioning Agent?

The Commissioning Manager (CxM) – The Owner’s Representative

The CxM, or Commissioning Manager, is an owner-side program role. Where the CxA delivers the commissioning process on a specific project, the CxM manages the overall commissioning program for the owner – typically across multiple projects or a large, complex estate where several CxA contracts are running simultaneously. On a single mid-sized project, you may not see a dedicated CxM at all. On multiple asset build-outs, or a hyper-scale data centre campus, or a multi-site public sector portfolio, the CxM will usually be seen and will be a clearly defined appointment with their own scope, reporting line, and deliverables.

Day-to-day, the owner-side CxM manages the CxA and CxP appointments on the owner’s behalf: reviewing commissioning plans, tracking progress across projects, managing the commissioning budget, and reporting commissioning status to senior leadership. This is a governance and coordination role, not a technical process lead.

What qualifications does a commissioning manager typically need?

Similar to the other roles, there is no single prescribed pathway. Most CxMs come from a mechanical or electrical engineering background, with hands-on experience as a CxE or CxA before stepping into a program management role. See our article What qualifications a commissioning manager typically needs for more information on that.

Contractor as CxM

The same CxM title also appears on the contractor’s side of a project (usually the UK). A contractor-side CxM manages the GC’s or MEP subcontractor’s own commissioning obligations – writing the contractor’s commissioning programme, coordinating pre-functional checks, and reporting to the GC or MEP lead rather than to the owner. The deliverables, the accountability line, and the scope are completely different.

Does the CxA / CxP not employ a CxM?

Within a CxP or commissioning consultancy firm, “Commissioning Manager” and “Senior Commissioning Manager” are career-level titles describing seniority and team leadership within the firm. A person holding that title at a CxP firm is delivering the CxA/CxP scope under that contract; they are not the owner-side program CxM.

If you see “Commissioning Manager” on an org chart, the first question to ask is: which side of the contract are they reporting to, and is this a project-structure appointment or a firm seniority grade?

The Commissioning Engineer (CxE) – The Field Specialist

The Commissioning Engineer, or CxE, is the person doing the hands-on technical work on site. They are employed by the CxA or CxP firm – not by the owner directly – and they report into the CxA Manager or Lead. On larger projects, the CxA Manager / Lead may manage a team of several CxEs, each assigned to specific systems: one covering HVAC and controls, another covering electrical and life safety, a third covering building enclosure.

What does a commissioning engineer actually do?

They write / review the pre-functional checklists that verify installation is complete before testing begins. They develop / review the functional test scripts that define exactly how each system will be witness tested and what is an acceptable result. They conduct the functional performance testing [FPT] in the field, witnessing and documenting each test sequence. When a system fails a test, the CxE raises the deficiency in the issues and resolution log and retests once the contractor has corrected it.

For understanding a Commissioning Engineer and Commissioning Manager – see our article “the difference between a commissioning engineer and a commissioning manager”.

The Owner, the GC, and the Subcontractors

Owner

The owner is the client of the entire commissioning process. They fund it, they set the Owner’s Project Requirements (OPR) that define what the building must deliver, and they receive and formally accept the final commissioning report. What the owner does not do is manage the commissioning process day-to-day – that function belongs to the CxA / CxP [or the CxM, on larger programs]. For a full overview of where the responsibility lays on a project and how those responsibilities are contractually allocated, see our article: “who holds responsibility for commissioning on a project”.

General Contractor

The GC’s commissioning obligation is to install systems correctly, complete pre-functional installation checklists, support the functional testing and correct any deficiencies the CxA identifies. The GC does not lead commissioning.

On a project following ASHRAE Guideline 0-2019, they do not lead the Cx process. Some contractors will argue that their in-house commissioning team satisfies the owner’s requirement for a CxA. It does not. The independence requirement makes this a non-starter.

Subcontractors

Subcontractors – mechanical, electrical, controls, and specialist trades – have their own specific commissioning obligations. They complete equipment-level pre-functional checklists, attend functional performance testing for their scopes, provide technical support during testing, and are responsible for correcting deficiencies that fall within their trade. The commissioning process can’t run without their active participation.

Why the Terminology Varies by Region and Sector

The same role carries two or three different names depending on where in the world you are working and which sector you are in. It just reflects different industry bodies, different commissioning frameworks, and different regional terminology that developed independently.

In the US, CxA [Commissioning Authority] is the dominant term, established through ASHRAE Guideline 0 and reinforced by LEED commissioning requirements. The BCxA [Building Commissioning Association] prefers CxP [Commissioning Provider] for the same role, and that term is gaining ground in US specifications and contracts. LEED Enhanced Commissioning uses CxA as its designator but does not mandate specific title usage beyond the independence requirement.

In the UK, “Commissioning Manager” is the dominant term – and critically, in UK usage it typically describes the process lead role [what ASHRAE calls the CxA], not the owner-side program manager role [what ASHRAE calls the CxM]. This is a genuine source of confusion for engineers who move between UK and US projects. The UK commissioning framework references BSRIA Commissioning Codes rather than ASHRAE Guideline 0, and how UK commissioning terminology differs under BSRIA is a topic we cover separately. CIBSE also publishes guidance that influences terminology in UK building services.

In the data centre sector, you will encounter “Commissioning Authority” used to describe an entire governance function rather than a single individual. Many hyperscale data centre owners use CxM to describe their owner-side program lead, running a structured Levels 0–6 commissioning sequence across multiple vendor and subcontractor packages.

In healthcare, OSHPD [Office of Statewide Health Planning and Development] in California uses “Commissioning Authority” as a specific regulatory designation with defined independence requirements. The term carries regulatory weight in that context that it does not carry in a standard commercial project.

None of these are wrong. How the terminology varies by region and sector is something any commissioning professional working internationally needs to understand early.

When Certification Matters

Commissioning is not a regulated profession in most jurisdictions – and as noted above, there is no single mandatory licence the way there is for structural or civil engineering. In practice, however, certification has become a de facto requirement at the upper end of the market.

The Building Commissioning Professional [BCxP] credential, issued by the ASHRAE, is the leading US certification for the CxA/CxP role. Large sophisticated owners – healthcare networks, hyperscale data centre operators, major REITs – increasingly specify BCxP as a minimum requirement for CxA appointments on projects above a certain value threshold.

The Certified Commissioning Professional [CCP] credential from the Associated Air Balance Council [AABC] is the other widely recognised US certification. LEED Enhanced Commissioning does not require BCxP or CCP specifically, but it does require that the CxA be independent of the design and construction team, references ASHRAE – and evidence of certification is increasingly how sophisticated owners satisfy themselves that independence and competence are both present.

For careers in commissioning see our article: “commissioning career paths and what drives salary“, and for an overview of commissioning qualifications see “What Qualifications Does a Commissioning Manager Need”.

What This Means When You’re New to a Project

If you are new to commissioning, the single most useful thing you can do on day one is establish the commissioning org chart. Find out: who is the CxA on this project? Who appointed them, and are they independent of the design and construction team? Is there a CxM sitting above them on the owner’s side? Who are the CxEs on the CxA’s team, and what systems are they each responsible for?

Those answers give you the real accountability lines – not the org chart version. In our experience, roughly half of the confusion people encounter on a commissioning project traces back to not knowing who has the authority to do what. The CxA issues a deficiency notice. The GC acts on it. The CxA closes it out. If that chain is not clear to everyone from week one, the process slows down.

A few practical questions worth asking early: Has the commissioning plan been issued? Has the owner formally accepted it? Have pre-functional checklists been developed for your systems? Is there an issues and resolution log in place, and who manages it? If the answer to any of these is “I’m not sure,” find out – because why the commissioning process exists in the first place is directly connected to these process structures being in place before testing begins.