What Is Pre-Commissioning? Checks, Responsibilities & How It Differs from Commissioning

Pre-commissioning means something quite different depending on which industry you are in. If you work in building construction or MEP, most of what you will find written about it covers oil and gas, EPC projects, and industrial piping systems – a different scope, a different regulatory framework, and a different set of documents entirely. This article covers pre-commissioning in the building and MEP context: commercial, hospitality, hospital and data centre facilities.

The Short Answer – What Pre-Commissioning Is

Pre-commissioning in commercial, hospitality, hospital and data centre construction projects is the stage during which systems are inspected and verified as correctly installed before energisation and full functional performance testing begins. Per ASHRAE Guideline 0, ‘pre-commissioning’ is noted as ‘pre-functional checks’ (PFCs) and within data centres they would be covered under ‘Level 2’ – all are static inspections completed by the installing contractor and witnessed by the commissioning engineer. All pre-functional checks must be completed before any equipment and systems are energised and then operated under load.

The terminology varies by region and project type. On North American projects you will see pre-Cx or pre-functional testing used interchangeably. In UK building services, the same activity sits within the pre-commissioning phase of the commissioning programme. The intent is the same across all of them.

Building Pre-Commissioning vs Industrial Pre-Commissioning

The term “pre-commissioning” carries very different meanings depending on the industry, and applying the wrong framework to a building project creates real confusion on site.

In building and MEP commissioning, pre-commissioning refers specifically to pre-functional checks: static inspections and installation verification completed before functional performance testing begins. The governing standard is ASHRAE Guideline 0; for testing scope and witnessing obligations, SSPC 300 Annex 10 applies. The output is Pre-Functional Checklists [PFCs] – a visual and physical inspection against approved project documents [specifications, drawings].

“Is this AHU installed in the correct orientation? Are the pipework connections correct? Is the BMS point-to-point wiring verified? Has the pressure testing been completed? What about the flushing and cleaning of the pipework?”

In oil and gas / EPC projects [Engineering, Procurement, and Construction], “pre-commissioning” describes a much broader phase that includes mechanical completion, piping flushing, chemical cleaning, pressure testing to ASME B31.3, and leak testing. The procedural framework is entirely different, governed by project-specific PTW [Permit to Work] systems and process safety protocols. The PSSR [Pre-Startup Safety Review] – an OSHA/process safety requirement for industrial facilities – is sometimes encountered in this context. The building commissioning equivalent is the CxA’s systems readiness sign-off prior to functional testing, but the two are not the same document.

Building professionals should not apply industrial pre-commissioning frameworks to their projects. The terminology overlaps; but the scopes do not.

Pre-Commissioning vs Commissioning – What Changes

This is the question we see most consistently from engineers joining their first commissioning project: if pre-commissioning involves checking the systems, what is commissioning itself doing? The answer sits in the distinction between static inspection and dynamic performance testing. The two phases must happen in sequence, with proper gates between them.

Pre-commissioning is a static phase [the main systems and equipment are not energised or running]. The installing contractor works through a Pre-Functional Checklist item by item, with the commissioning engineer witnessing and recording the result. The question being answered is: has this system been correctly installed and is it ready to be energised and tested?

Commissioning [Functional Performance Testing] is a dynamic phase. Systems are energised, able to be operated under varying load conditions, and measured against the requirements defined in the Owner’s Project Requirements [OPR] and approved testing scripts / method statements. The question being answered here is: does this system actually perform as required and designed? The governing documents shift from Pre-Functional Checklists to Functional Performance Test [FPT] Reports. For a deeper treatment of how these relate, see Testing vs Commissioning: Understanding the Difference.

Skipping or shortcutting pre-commissioning usually has the same outcome: failures during functional testing that trace back to installation deficiencies a PFC would have caught. Those failures extend the commissioning programme, generate rework / remedial costs, and delay handover. The $1:$10:$100 cost escalation principle applies directly – a deficiency caught during a static PFC inspection is orders of magnitude cheaper to resolve than the same deficiency surfacing during a witnessed functional test, just before handover.

**Abbreviation key: **CxA – Commissioning Authority [independent oversight role, typically contracted directly by the Owner]; CxM – Commissioning Manager [programme management, team coordination, reporting]; CxE – Commissioning Engineer [site execution, witnessed inspections, testing]; CxP – Commissioning Provider [umbrella term for the commissioning organisation; on some projects CxP and CxA are the same appointment, on others they are separate]. OPR – Owner’s Project Requirements; PFC – Pre-Functional Checklist; FPT – Functional Performance Test; BMS – Building Management System; GC – General Contractor.

Where Pre-Commissioning Sits in the Project Timeline

Pre-commissioning starts when mechanical completion is achieved – and understanding what mechanical completion means is essential for anyone programming a commissioning sequence.

Mechanical completion is the contractual milestone at which MEP&F [mechanical, electrical, plumbing, and fire protection] installation is complete and the system is ready for pre-commissioning to begin. The contractor issues a Mechanical Completion Certificate [sometimes called an Installation Completion Certificate], which formally hands the system over to the commissioning team for inspection and testing. Pre-commissioning begins immediately after. Mechanical completion is a prerequisite – not a concurrent activity. A system that is still being installed cannot be properly inspected against a Pre-Functional Checklist.

On large or phased projects [data centres, hospitals, large commercial fit-outs], mechanical completion may be achieved system by system, or floor by floor, rather than across the entire building simultaneously. Pre-commissioning for individual systems or zones can therefore begin ahead of overall mechanical completion, allowing the commissioning programme to progress in parallel with remaining installation works. The gate rule still applies: a given system must reach mechanical completion before its pre-commissioning can begin.

What Pre-Commissioning Actually Involves

Pre-commissioning covers three categories of activity, each building on the previous one. They are not interchangeable – you cannot verify startup readiness on a system whose installation has not been checked, and you cannot sign off a PFC until both have been completed.

Static Checks

Static checks are visual inspections of the installation itself. The commissioning engineer or inspector walks the system and verifies: correct equipment installed per specification / drawings, correct location and orientation, correct labelling and identification, maintenance access maintained around plant items, and safety clearances observed. On an AHU installation, this includes checking that filters are correctly seated, access panels are operable, belt tension is within tolerance, drain connections are correct, and damper linkages are free. These checks sound straightforward. In our experience though, they can consistently surface issues – incorrectly oriented pumps, missing isolation valves, access doors blocked by adjacent services – that would not have been caught until functional testing if no PFC process was in place.

Installation Verification

Installation verification moves beyond the visual to check the physical connections between components. For HVAC systems, this means verifying that pipework flow directions are correct and not crossed, pipe connections match the design intent, flexible connections are installed correctly, and ductwork connections are sealed and supported. For electrical systems, cable terminations are checked against schedules, circuit protection is confirmed, earthing is verified, and isolation points are accessible and clearly identified. For BMS and controls, point-to-point wiring checks confirm that every sensor and control output is connected to the correct BMS point – a step that is routinely underestimated in terms of time and that uncovers a disproportionate number of wiring errors. For plumbing systems, connections are verified, water treatment systems are confirmed in place, and flushing is documented. For fire and life safety systems, device installation is checked against design drawings and circuit supervision is confirmed.

Pre-Functional Checks

The Pre-Functional Checklist [PFC] is the structured inspection document that records the result of the static checks and installation verification on a system-by-system basis. Per ASHRAE Guideline 0, PFCs are the formal mechanism for capturing this inspection record. Each item is recorded as pass, fail, or not applicable. Failed items generate entries on the pre-commissioning punch list. A completed PFC – with all items passed or punch list items closed – is the gate document that authorises the system to proceed to functional performance testing.

One point worth making explicitly, because it creates genuine confusion for engineers crossing over from industrial or oil and gas backgrounds: activities like pipework pressure testing, hydrostatic testing, and chemical cleaning do appear within the pre-commissioning scope in the building context – but the responsible party and procedural framework are different from what those engineers will be used to. Per ASHRAE SSPC 300 Annex 10, Section 10.4.5.2, the contractor carries out static tests including pressure testing and hydrostatic testing, and these are witnessed and validated by the CxP. The CxP’s role is physical witnessing and validation – they are present on site when the test is executed, not simply reviewing a certificate after the fact. In oil and gas pre-commissioning, the pre-commissioning team executes pressure testing directly under a Permit to Work [PTW] process, against ASME B31.3. In building commissioning, the contractor executes and the CxP witnesses. The activity looks the same on paper; who picks up the tools, and who holds the pen, are different.

Skipping this stage does not save time. We have seen functional test programmes extended by weeks because installation deficiencies [a chiller with reversed pipework connections, a BMS with 40% of points wired to the wrong addresses] were not caught at the PFC stage. Functional testing will surface problems under live conditions, in front of the client and design team, with rework required before testing can recommence. For a full breakdown of what pre-Cx checks cover across building systems, see What Checks Are Done During Pre-Commissioning?

The Pre-Functional Checklist – What It Is and Why It Matters

The Pre-Functional Checklist [PFC] is a structured inspection document used to record whether each item of plant, equipment, or system has been correctly installed and is ready for functional performance testing. Per ASHRAE Guideline 0, PFCs are typically prepared by the CxA or CxM [or the CxE on their behalf] and completed by the installing contractor or subcontractor, then independently verified by the commissioning engineer before functional testing commences.

PFCs cover three categories of content.

• Installation checks confirm that physical installation is correct – equipment is in the right location, correctly oriented with required maintenance space, and connected per the design.
• Startup readiness checks confirm that the system is safe to energise – isolation is in place, electrical protection is correct, and there are no open connections or uncompleted works that would create a safety hazard.
• Pre-functional operational checks confirm basic response on startup – does the pump rotate in the correct direction? Do the AHU dampers respond to a test signal from the BMS? Does the chiller power on without fault codes?

PFCs are system and equipment-specific. An AHU pre-functional checklist covers filter installation, belt condition, drain pan, damper operation, and ductwork connections. A chiller PFC covers pipework connections, refrigerant charge, electrical supply, BMS integration, and safety device confirmation. A BMS PFC covers point-to-point wiring, controller configuration, and network communication. The same form does not work across all systems – and a generic checklist applied across all plant is a sign that the pre-commissioning process is being managed by inexperienced engineers.

There is a secondary benefit to conducting detailed PFCs that is worth noting: pattern detection. When the commissioning team works through PFCs across multiple systems and pieces of equipment, repeated omissions by the same contractor become visible in a way they would not be if checks were done in isolation. Missing temperature and pressure gauges are a consistent example we see on site – specified in the contract documents, paid for by the owner, and quietly left off across a range of equipment. When constantly repeated across a project, it’s not an oversight, it’s a potential cost-saving measure at the owner’s expense. Detailed, system-by-system PFCs are one of the few mechanisms on a project that make this kind of systematic non-compliance visible before handover.

For the full treatment of PFC structure, content, and how to use them on site, see What Is a Pre-Functional Checklist in Commissioning?

Who Does Pre-Commissioning – and Who Signs It Off

Pre-commissioning involves multiple parties, and the boundaries between their roles matter. The most consistent source of confusion we see on site is the assumption that the commissioning team carries out pre-commissioning. They do not – at least not in terms of executing the checks. The installing contractor carries out the physical work; the commissioning team witnesses, records, and signs off.

The PFC documents are prepared by the CxA, CxM, or CxE, depending on the scale and structure of the project. Per ASHRAE Guideline 0, PFC templates are developed during the design phase [typically Schematic Design through Construction Documents] so they are ready for contractor use the moment mechanical completion is achieved. The commissioning team owns the document, defines what needs to be checked, and sets the standard. The installing contractor or specialist subcontractor then works through the PFC item by item, completing each check and recording the result. The commissioning engineer witnesses the checks, verifies the outcomes, and signs the completed PFC. On larger projects, the CxM [or CxA] reviews the completed PFC package and issues the formal proceed-to-test authorisation before functional testing begins.

The point to this process and sequence is that, the contractor cannot sign their own PFC and proceed to functional testing independently – the commissioning team’s independent witness is what gives the PFC process its quality assurance value. A contractor-only pre-commissioning process is contractor self-certification, not commissioning.

For the full picture of the CxM’s role within this structure, see What Is a Commissioning Manager? For a day-to-day view of how the CxE operates on site during this phase, see What Does a Commissioning Engineer Do Day to Day? For the broader question of who holds responsibility across the commissioning programme, see Who Is Responsible for Commissioning on a Construction Project?

Pre-Commissioning Punch Lists and Deficiency Tracking

A pre-commissioning punch list [also called the pre-Cx deficiency list] is the record of items that failed the PFC inspection and require remediation before functional testing can proceed. It grows and shrinks as PFCs are completed and deficiencies are identified and closed.

Each punch list item is assigned to a responsible party [typically the installing contractor or relevant subcontractor], given a target closure date, and flagged with a re-inspection requirement. The item stays open until the deficiency has been remediated and the commissioning engineer has independently re-verified it. Closure is not self-certified by the contractor – the CxE confirms it.

We should note that the ‘pre-commissioning punch list’ and the ‘commissioning issues log’ are different documents tracking different problems at different stages. A punch list item is an installation deficiency [wrong connection, missing label, incorrect component]. An issues log entry is a performance deficiency, based on the owners project requirements [system not achieving design set points, controls sequencing incorrectly, integration failure between systems]. Conflating the two creates a tracking problem and obscures whether the programme is on track. One distinction worth making explicit: both documents are populated dynamically during construction and testing, but the format and procedure for the issues and resolution log is established during pre-design. Per ASHRAE Guideline 0 Section 5.2.5, setting up issues and resolution log procedures is a pre-design activity, and Section 5.2.1.6(m) identifies developing the initial format for issues and resolution logs as a specific CxP responsibility at that stage. The log itself does not exist yet – there are no issues to record – but the structure, categories, escalation rules, and responsible parties are defined before design begins, so the process is ready to run from the moment construction starts generating deficiencies.

On large projects, a system with a short punch list may proceed to functional testing while other systems remain in pre-commissioning – the gate is system-specific, not project-wide. For the full treatment of punch list structure, management, and closure process, see What Is a Pre-Commissioning Punch List and How Is It Used?