Achieving As-Built Net Zero Performance

About this course.

Finished buildings frequently underperform their design ratings because a rating describes an intended building under assumed conditions, while the real building is only as good as it is actually constructed, commissioned and operated. The gap between the two — often called the performance gap — arises from a chain of small and large discrepancies: materials and details substituted or installed differently from the design, insulation left with gaps, air leakage far greater than assumed, services that are present but never properly commissioned, renewables that generate less than expected, and occupants who use the building differently from the modelling assumptions. Each link can erode performance, and because they compound, a building that was designed to an excellent standard can end up using substantially more energy than predicted. Closing the gap means attending deliberately to every link.

It helps to understand what a design rating actually is. An energy rating or assessment predicts how a building should perform based on its design — its orientation, envelope, glazing, insulation, services and so on — evaluated under standardised assumptions about climate, occupancy and use. This is exactly what it needs to be for its purpose: a consistent, comparable measure of the design's intended performance, used for compliance and comparison. But by its nature it is a prediction about an idealised version of the building operated in a standard way. It is not a measurement of the finished building, and it does not, and cannot, guarantee that the building as built and used will match the prediction. The rating is a promise about the design; delivering on that promise is a separate task. The ABCB's energy-efficiency and assessment frameworks, described here in general terms, provide these design-stage measures; the point of this course is what happens between that design promise and the operating building.