NatHERS 2022 Starbands
The Nationwide House Energy Rating Scheme (NatHERS) climate files have been updated with more recent and more accurate weather data. As the energy performance of a home is dependent on the local weather conditions, the recent climate file update has the potential to impact NatHERS ratings inconsistently across Australia.
To minimise the potential impacts on star ratings, new starbands have been implemented. They have been adjusted so that no particular home type or design will be overly impacted by the new climate files.
Analysis conducted on the impacts of the new starbands using a representative sample of home types demonstrated that the majority of dwellings will have on average, a zero-star rating change. Individual dwellings may show a small increase or decrease to their existing star rating.
NatHERS starband analysis
A detailed 2019 analysis considered the impacts the new climate files would have on NatHERS ratings. The study proposed two options to adjusting the starbands, either a ‘limited change’ (increase or decrease of 0.2 stars) or ‘zero average change’ for the majority of dwellings. The NatHERS Steering Committee decided the ‘zero average change’ was the best approach.
A diverse sample of 18 dwelling designs were rated in all 69 NatHERS climate zones using the current benchmark software and starband levels at 1, 5, 6, 7 and 9 stars. The 18 dwellings were then re-rated in all 69 climate zones using a version of the benchmark software with the new climate files. A correlation was derived using the current star rating levels with the energy loads from ratings using the new climate files. For each climate zone, the current star rating and new energy loads were plotted on a graph and a ‘curve of best fit’ was obtained. The equation of the curve was used to develop the new NatHERS Starbands.
Under the new approach, the 6-star energy level has, on average, been maintained at current levels. Higher star levels will have slightly higher energy values (i.e., greater MJ/m2 will define star bands above 6). This will make the performance of high starbands (greater than 6) slightly lower than the current settings but will make them easier to achieve. The new 10-star rating levels will still represent an aspirational, yet achievable, high energy-efficiency rating.
The following graphs from the analysis plot the average changes between the current and new (2022) starbands for capital cities across all states and territories.
*The Australian Building Codes Board (ABCB) has used these new starbands and climate files to conduct analysis for the National Construction Code 2022 changes.
