Assessing the performance gap in energy rating systems in Australian commercial office buildings

The energy performance gap, defined as the difference between expected and actual building energy performance, has been recognized as a significant obstacle to meeting energy targets in the building sector. In Australia, various policies and private-sector initiatives have been introduced to assist the construction industry in reaching its environmental impact reduction potential. The National Australian Built Environment Rating System (NABERS) and Green Star, two widely adopted building certification systems, have targeted this gap, with Green Star mandating design verification during construction and NABERS monitoring operational performance. This study aims to assess the effectiveness of these certification systems in reducing the performance gap in Australian office buildings by quantifying the predicted and actual performance of certified assets. Predicted energy usage data was collected from Green Star submissions of 176 office buildings and matched and compared with NABERS Energy ratings reporting performance during operation. The results were discussed with a group of building certification specialists, who provided insights on these outcomes and approaches towards narrowing the remaining performance gap. Overall, 65% of the cases achieved or exceeded their predicted NABERS Energy performance targets. The cases increased to 75% when considering the buildings’ highest NABERS Energy rating during the period of analysis and to 94% in cases that included NABERS Commitment Agreements (CA)—where developers are held accountable by contract to meet a specific performance target. These results suggest that the use of certification systems, such as the ones evaluated in this study, can contribute to closing the energy performance gap in Australia by setting buildings up for high-energy performance through design and operation.