NatHERS 2022 Star Bands
In 2022, the Nationwide House Energy Rating Scheme (NatHERS) climate files will be updated with more recent and more accurate weather data. As the energy performance of a home is dependent on the local weather conditions, the climate file update has the potential to impact NatHERS ratings inconsistently across Australia.
To minimise the potential impacts of the new climate files on NatHERS star ratings, new star bands will be implemented at the same time. The new star bands 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 star bands 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 star band 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 star bands, 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 star band 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 Star Bands.
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 star bands (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 tables from the analysis plot the average changes between the current and new (2022) star bands for capital cities across all states and territories.
*The Australian Building Codes Board (ABCB) has used these new star bands and climate files to conduct analysis for the National Construction Code 2022 changes.