Commercial property is entering a new phase of accountability. Increasingly, investors, occupiers and regulators are looking beyond design-stage predictions and asking a more important question: how does a building actually perform once it is occupied?

A building can comply with regulations, achieve an impressive sustainability certification, yet still consume considerably more energy than anticipated. Owners do not pay theoretical energy bills. They pay real ones.

This disconnect, often referred to as the performance gap, is becoming increasingly difficult to ignore. For investors, occupiers and asset managers, operational performance is becoming a defining measure of asset quality, resilience and long-term value.

That is precisely why frameworks such as NABERS UK are attracting increasing attention. Rather than concentrating solely on design intent, they encourage project teams to set credible operational targets, design and commission buildings around them, and ultimately demonstrate performance through real-world outcomes.

Why design intent is no longer enough

A building is not sustainable simply because it was designed to be. It has to demonstrate that performance every day it is occupied.

Predicted energy models are essential for comparing options and establishing targets before completion. But a model is not an operational result.

Actual energy use is influenced by controls, commissioning, occupancy, operating hours, maintenance and the way systems interact. A well-specified building can underperform if its services are difficult to operate, poorly integrated or inadequately commissioned.

For example, two office buildings may achieve similar EPC ratings at completion, yet one can consume considerably more energy in operation because poorly commissioned controls, ineffective system integration or changes in occupancy prevent the building from performing as intended.

For owners and investors, that can mean:

• higher running costs;
• greater exposure toenergy-price volatility;
• weaker progress against carbonand ESG commitments;
• occupant comfort complaints;
• premature plant replacement orretrofit; and
• uncertainty over long-termmarketability.

Compliance may establish a minimum standard. It does not guarantee an efficient building in use. The Better Buildings Partnership has identified the UK's historic emphasis on theoretical, modelled performance rather than measured outcomes as a central cause of the commercial-office performance gap.

What NABERS UK adds

NABERS (National Australian Built EnvironmentRating System) originated in Australia more than 25 years ago and is now recognised internationally as one of the leading operational building-performance rating systems. The UK version was launched in 2020 and is administered by CIBSE.

NABERS UK Design for Performance helps developers and owners set an operational energy target for a new office or major refurbishment and embed it through design, construction, commissioning and operation. NABERS UK Energy for Offices subsequently assesses efficiency using actual operational data.

• EPCs indicate theoretical energy efficiency.
• BREEAM considers sustainability across design and construction.
• NABERS UK places operational energy performance at the centre of the process and provides a route towards real-world verification.

These approaches are not interchangeable. The significance of NABERS is that it asks the question commercial property increasingly needs answered: how efficiently does the building actually operate?

Evidence is becoming commercially important

Measured performance is no longer simply an environmental metric. Increasingly, it is becoming a commercial indicator ofasset quality, investment resilience and long-term value.

Reliable operational data gives owners a stronger basis for investment decisions. It can expose controls and commissioning issues while demonstrating whether improvement measures are delivering the intended return.

For occupiers, efficient operation can support lower service charges and a more comfortable workplace. For investors and landlords, credible evidence can strengthen ESG reporting, reduce transition risk and provide confidence that an asset will remain competitive as expectations continue to rise.

A building that performs well only in a design report carries uncertainty. A building whose performance can be measured, managed and improved provides evidence.

Delivering performance throughout the project lifecycle

No single technology creates an operationally efficient building. Performance depends on decisions made from the initial brief through to day-to-day management.

Integrated building services design - Heating, cooling, ventilation, lighting, metering and controls should be designed as one operational system, based on realistic occupancy, load profiles and operating conditions.

Controls that people can use - Complexity does not necessarily create intelligence. Controls should provide flexibility and insight without making the building difficult for facilities teams or occupiers to operate.‍

Commissioning and seasonal tuning - Commissioning should verify sequences, set points, sensors, metering and system interaction, not merely confirm that equipment switches on. Performance should then be reviewed as occupancy settles and seasonal conditions change.

‍Collaboration and a shared objective - Clients, consultants, contractors, controls specialists, commissioning teams and facilities managers all need a shared definition of success. An operational target gives every member of the project team something more meaningful to work towards than practical completion alone.

Refurbishment is not a barrier to high performance

Much of the commercial property sector's carbon and cost challenge lies within existing assets.

Refurbishment brings constraints, including inherited fabric, retained structures and limited service routes. Yet it also creates an opportunity to rethink how a building operates.

That matters because the vast majority of the buildings that will exist in 2050 have already been built. Improving operational performance across existing commercial building stock will have a greater impact than focusing solely on new developments.

The refurbishment of Trinity College CambridgeScience Park demonstrates what can be achieved when building services are considered strategically. Green Building Design designed and coordinated the mechanical and electrical services for the £9.5 million transformation of the40,000 sq ft office building, including a new central core and CAT A fit-out.

The project achieved a 5.5 Star NABERS UK Design for Performance rating. It was the first building in Cambridge to reach thatlevel, one of only nine UK projects to do so and one of only five refurbishment projects nationally.

Its significance extends well beyond the rating itself. It demonstrates that ambitious operational performance is achievable inrefurbishment projects when engineering decisions, intelligent controls and performance objectives are integrated from the earliest stages of design.

From compliance to accountability

EPCs, MEES, BREEAM, the emerging UK Net Zero CarbonBuildings Standard and NABERS all form part of a broader shift across the commercial property market: Compliance establishes the baseline; design intent defines the ambition; measured performance provides the evidence.

That does not make predictive modelling or design certification less important. It makes follow-through more important. Targets must influence specification, controls, commissioning, handover and ongoing operation.

Increasingly, investors, occupiers and regulators expect evidence rather than assumptions. Buildings that can demonstrate operational performance are likely to enjoy a growing competitive advantage over those that rely solely on predicted outcomes.

For owners planning a development or major refurbishment, the practical question is no longer simply, "What ratingcan this design achieve?" It is, "What performance will this buildingdeliver, how will we measure it and who will remain accountable?"

Buildings that answer those questions convincingly are more likely to control costs, meet carbon commitments, support occupants and retain value over the long term. As expectations continue to evolve, involving building services engineers early in the design process can help ensure ambitious operational targets translate into measurable outcomes.

 At Green Building Design, we help clients create commercially viable building services solutions that deliver lasting operational performance, not simply design intent.

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