For years, building owners and engineers have observed a persistent challenge: the energy performance predicted during the design phase often differs significantly from what buildings actually consume once they are occupied.
Research has consistently shown that measured energy use in commercial and institutional buildings can reach up to two-and-a-half times higher than original design-stage energy models. The discrepancy is particularly noticeable in facilities such as schools, university campuses and healthcare buildings, where occupancy patterns and operational requirements are far more complex than standard assumptions.
While this performance gap has been recognized for decades, it is becoming increasingly significant as governments and organizations introduce building standards that require verified operational results rather than projected performance alone.
Across Canada, institutional and public-sector clients are increasingly incorporating measurable energy performance commitments into project requirements through initiatives such as the Canada Green Building Council’s Zero Carbon Building Standard (ZCB), provincial decarbonization programs and municipal green procurement policies. As a result, energy models are no longer simply tools for obtaining permits—they are becoming contractual benchmarks that projects are expected to achieve.
According to Chris Flood, Vice-President, Canada, at global building performance software company IES, three primary factors continue to drive the gap between predicted and actual building performance.
The first is the reliance on generalized modelling assumptions.
Energy models are built using standardized inputs for factors such as occupancy density, operating hours and plug loads. These default values allow projects to be compared consistently but rarely reflect how an individual building will actually operate.
For example, an office building model may assume a traditional weekday schedule, yet the actual tenant could operate around the clock as a call centre or another high-intensity workplace. Even when the building’s design remains unchanged, different operating patterns can produce dramatically different energy consumption.
Flood argues that closer collaboration with building owners during the design phase is essential to accurately understand how facilities are expected to function in practice.
The second factor is occupant behaviour.
How people interact with thermostats, lighting controls, blinds and electrical equipment can have a major effect on energy consumption. Design models frequently assume occupants will follow predictable routines and will not frequently override building controls, but in reality behaviour is far less predictable.
Traditional modeling approaches can’t always capture the increase in energy use associated with higher plug loads, manual lighting adjustments and adjustments to temperature settings.
Rather than modelling extreme scenarios, Flood believes engineers should design systems capable of maintaining efficient performance across a realistic range of occupant behaviours.
The third major contributor is what occurs between project completion and building occupancy.
Even well-designed facilities can underperform if building systems are not properly commissioned. Common issues include unbalanced ventilation systems, improperly configured control sequences and sensors that are not correctly calibrated.
Flood notes that commissioning frequently takes place only at the end of a project, separated from the design and modelling teams that established the building’s performance targets. Without aligning commissioning activities with the original modelling assumptions, there is no effective process to verify that the completed building operates as intended.
Performance can also decline after occupancy as operating schedules change, manual overrides increase and maintenance practices evolve. Ongoing commissioning and post-occupancy monitoring help identify these issues before they become long-term operational problems.
Flood argues that most opportunities to reduce the performance gap occur well before construction begins. Project teams that carefully validate occupancy assumptions, develop realistic energy models and integrate commissioning early in the design process are more likely to deliver buildings that achieve their expected performance targets.
These practices have already become common on projects pursuing Zero Carbon Building (ZCB) certification, where post-occupancy verification is required to confirm that buildings perform as promised.
As Canada’s building sector places greater emphasis on measurable environmental performance, the industry is moving beyond regulatory compliance toward accountability. Energy models are now expected to be able to accurately predict the building behaviour over its full lifecycle and verified building performance has become a vital part of the modern project delivery process for engineers, designers and project teams.
