Commissioning vs Retro-Commissioning: The Complete Explainer

Building owners, project managers, and facility directors encounter the terms “commissioning” and “retro-commissioning” repeatedly in the course of California construction and operations. They are related concepts — both apply a systematic verification process to building systems — but they serve different purposes, apply at different points in a building’s life, and produce different kinds of value.

The confusion is understandable. Both terms describe processes that verify whether building systems are performing as intended. Both involve functional testing of HVAC, controls, and electrical systems. Both produce a commissioning report documenting findings and deficiencies. The difference lies in when they are applied and what the baseline for comparison is.

Budlong maintains an in-house commissioning team that delivers both new construction commissioning and retro-commissioning for existing buildings across California. This explainer clarifies the distinction, describes what each process involves, and helps building owners determine which is appropriate for their situation.

What Is Building Commissioning?

Building commissioning (Cx) is a quality assurance process applied to new construction or major renovation projects. Its purpose is to verify that building systems — primarily HVAC, controls, electrical, and plumbing — are designed, installed, tested, and operating in accordance with the owner’s project requirements (OPR), the basis of design (BOD), and the contract documents.

Commissioning begins during design, not at construction completion. An effective commissioning process involves the commissioning authority (CxA) reviewing design documents against the OPR, identifying potential performance gaps before construction begins. This design-phase engagement is what distinguishes commissioning from post-construction testing and balancing (TAB) — commissioning verifies design intent as well as installation quality.

A complete new construction commissioning scope includes: OPR and BOD development, commissioning plan preparation, construction document review, construction-phase site observations, functional performance testing of commissioned systems, deficiency documentation and resolution tracking, a commissioning report, operator training, and (for enhanced commissioning) a post-occupancy review. The commissioning authority may be a member of the design team (for smaller projects) or an independent firm retained directly by the owner (for larger or LEED-enhanced commissioning requirements).

What Is Retro-Commissioning?

Retro-commissioning (RCx) applies the systematic investigation and verification methodology of commissioning to existing buildings. It is used when a building was never commissioned during original construction, when building systems have drifted from their designed performance over years of operation and maintenance, or when occupancy, use patterns, or schedules have changed significantly since the building was designed.

Building systems do not maintain peak performance indefinitely. Control sequences drift as setpoints are changed for comfort complaints and never restored. Damper actuators fail in fixed positions. Economizers are disabled during a fault condition and never re-enabled. Variable frequency drives are locked out during a hot summer and left at full speed. Over time, a building that was once well-performing accumulates these small degradations until energy use is significantly higher than it should be, occupant comfort complaints multiply, and maintenance costs escalate.

Retro-commissioning identifies these degradations systematically and restores systems to their design intent — or to an improved design intent appropriate to the building’s current occupancy and use — without requiring capital equipment replacement. The Lawrence Berkeley National Laboratory has found that retro-commissioning of commercial buildings delivers median energy savings of approximately 16 percent, with typical simple payback periods of 1 to 3 years.

Commissioning vs. Retro-Commissioning: Side-by-Side Comparison

The Commissioning Scope: What Systems Are Involved?

The systems covered by commissioning are defined in the commissioning plan and agreed upon with the owner at the start of the project. The scope varies by building type and project goals.

For most nonresidential commercial buildings, the commissioning scope includes: central air handling units and terminal units (VAV boxes, fan coil units, VRF indoor units); chillers, cooling towers, and chilled water pumping systems; boilers and hot water distribution systems; building automation systems and control sequences; electrical distribution and emergency power systems; and lighting controls including occupancy sensors, daylighting controls, and demand response capability.

For healthcare facilities subject to HCAI review, the commissioning scope expands to include medical gas systems, emergency power systems (generators, transfer switches, critical and equipment branches), and the HVAC systems serving each clinical space type with verification against ASHRAE 170 air change rates and pressure relationships. For education buildings subject to DSA review, the commissioning scope must align with DSA’s project closeout documentation requirements.

The Retro-Commissioning Process: How It Works

A retro-commissioning project follows a defined investigation methodology that systematically identifies performance deficiencies and develops a prioritized remediation plan.

Phase 1: Planning and Investigation

The RCx team reviews all available documentation — original design drawings, equipment manuals, TAB reports, BAS trend data, energy bills, and maintenance records. Where documentation is incomplete (as is common in older buildings), the team conducts field surveys to establish a baseline picture of existing system configuration and control sequences. Energy benchmarking data — often using ENERGY STAR Portfolio Manager or the EPA ENERGY STAR program — establishes how the building’s energy use compares to peers of similar type and climate zone.

Phase 2: Functional Testing and Diagnostics

The RCx team conducts functional tests of existing systems, comparing actual performance against design intent and optimal performance benchmarks. BAS trend data analysis is a central tool — logging system variables (supply air temperature, discharge air flow, chilled water supply temperature, economizer damper positions) over time reveals patterns of degraded performance that point investigation teams to specific deficiencies. Equipment that is operating inefficiently, controls that are not following their intended sequences, and sensors that have drifted from calibration are identified and documented.

Phase 3: Findings Report and Remediation Recommendations

The RCx team produces a findings report documenting each identified deficiency, its estimated energy and cost impact, and a recommended remediation action. Recommendations are typically low- or no-cost operational changes — resetting control setpoints, re-enabling disabled sequences, recalibrating sensors, repairing failed actuators — rather than capital equipment replacements. The report prioritizes recommendations by payback period and complexity of implementation.

Phase 4: Remediation and Verification

The building operations team implements the approved recommendations, often with technical support from the RCx team. After remediation, functional testing is repeated to verify that deficiencies have been corrected and the performance improvements are sustained. Measurement and verification (M+V) over a defined period confirms the energy savings achieved.

Code and Certification Requirements for Commissioning

Commissioning is no longer simply a best practice in California — it is increasingly a legal requirement. Multiple code and certification pathways mandate commissioning, and the scope of mandatory commissioning has expanded with each code update cycle.

CALGreen nonresidential mandatory measures require commissioning for all new buildings over 10,000 square feet, with enhanced commissioning requirements for buildings over 50,000 square feet. The commissioning must be performed by a commissioning authority with documented qualifications and must be documented in a commissioning report submitted to the local authority having jurisdiction at project closeout. See the CALGreen MEP Guide for the full mandatory commissioning scope.

LEED certification requires Fundamental Commissioning as a mandatory prerequisite (EA Prerequisite) for all certification levels. Enhanced Commissioning (EA Credit) offers up to 6 additional LEED points and requires an independent commissioning authority engaged from schematic design. See LEED Commissioning Requirements for full details.

HCAI healthcare projects have commissioning expectations embedded in HCAI’s technical standards and in the project inspector’s field documentation requirements. LEED for Healthcare Enhanced Commissioning is required for many publicly funded hospital projects seeking LEED Gold or Platinum certification.

The Business Case for Both

The business case for commissioning and retro-commissioning operates on different dimensions and serves different stakeholders.

For new construction commissioning, the primary value is risk reduction and compliance. Commissioning catches design and installation deficiencies before they become warranty claims, occupant complaints, or code compliance failures. It satisfies CALGreen mandatory requirements, LEED prerequisites, and HCAI or DSA project closeout documentation requirements. The commissioning report provides the owner with a documented baseline of system performance at substantial completion — a record that supports future retro-commissioning investigations and equipment replacement decisions.

For retro-commissioning, the primary value is energy savings and operational improvement. Lawrence Berkeley National Laboratory (LBNL) studies of commercial building retro-commissioning have found median simple payback periods of 1.1 years for buildings with existing BAS infrastructure and 2.1 years for buildings without — making retro-commissioning one of the highest-ROI energy improvement strategies available to commercial building owners. California’s energy benchmarking and transparency programs, including AB 1103 disclosure requirements for commercial transactions, make building energy performance increasingly visible to buyers and tenants, creating direct financial incentives for performance improvement.

When to Commission vs. When to Retro-Commission

The decision is straightforward in most cases: commissioning applies to new construction and major renovation projects; retro-commissioning applies to existing buildings. But the decision becomes more nuanced when an existing building is undergoing a significant tenant improvement, major equipment replacement, or occupancy change.

If more than 25 percent of an existing building’s HVAC or electrical systems are being replaced or significantly modified, commissioning the affected systems to the new design intent is appropriate. If the existing systems are largely unchanged but performance has deteriorated, retro-commissioning is the right tool. If an existing building is being substantially renovated with new building systems throughout, new construction commissioning is appropriate — and the commissioning authority should be engaged during design, not at construction completion.

A practical indicator: if you have a set of design documents defining what the systems are supposed to do, you are commissioning against those documents. If you are investigating what the systems are actually doing versus what they should be doing based on physics and occupancy, you are retro-commissioning.

Who Uses Budlong Commissioning Services?

Related Reading

Frequently Asked Questions