Updated context: This article refers to a NatHERS Technical Note update from 2019. NatHERS requirements, software tools and residential energy efficiency settings have continued to evolve since then, including the later shift toward 7 Star NatHERS and Whole of Home energy performance under NCC 2022. For current NatHERS assessment guidance, start with our NatHERS Knowledge Hub.
The 2019 NatHERS Technical Note update introduced more detailed modelling requirements for property developers, builders, assessors and designers. At the time, the update raised an important question: would the new requirements support clearer residential energy assessments, or create additional pressure during the building design process?
Since its introduction in 1993, the Nationwide House Energy Rating Scheme, commonly known as NatHERS, has played an important role in assessing the thermal performance of new homes in Australia. NatHERS has continued to evolve over time, with one notable update taking effect from 1 June 2019.
The 2019 NatHERS Technical Note update included changes and clarifications relating to:
- window opening percentages
- roof colour specification
- glazed verandas and winter gardens
- ceiling penetrations
- mandatory document requirements
- protected trees
These changes placed greater emphasis on accurate modelling and clearer documentation. For designers, builders and assessors, this meant that some assumptions previously handled through judgement or common practice needed to be modelled more consistently.
One of the most significant changes related to window opening percentages. Under the 2019 Technical Note, certain window types, including awnings, casements and louvres, had to be modelled with a smaller assumed opening percentage than before. This affected how natural ventilation and cooling potential were represented in NatHERS modelling.
For homes with large amounts of operable glazing, this change could influence the cooling load and overall rating outcome. In warmer climates, the reduced assumed ventilation benefit could make it harder for some homes to meet cooling targets without changes to glazing, shading, orientation or building fabric.
In cooler climates, the effect could be different. Window operation assumptions, heat loss, winter performance and climate zone all interact in a NatHERS assessment. This is why NatHERS results are always project-specific rather than based on one design feature alone.
Another important update related to roof colour. Builders and designers were required to provide clearer roof colour information as part of the project documentation. Where roof colour was not specified, assessors could need to consider more conservative or worst-case assumptions in the modelling process.
Roof colour can influence thermal performance, especially in warmer climates or on exposed sites. However, it should not be treated in isolation. The final NatHERS result is shaped by the combined effect of roof construction, insulation, ceiling design, ventilation, solar exposure and the broader building fabric.
The Technical Note also provided clearer guidance for glazed verandas, balconies, winter gardens and similar spaces. These elements can affect shading, solar access and the way adjacent rooms are modelled. The update helped assessors apply more consistent modelling assumptions to these spaces.
Overall, the 2019 NatHERS Technical Note was part of a broader move toward more detailed and consistent residential energy assessments. Since then, the NatHERS framework has continued to develop, including the later shift toward 7 Star NatHERS and Whole of Home energy performance.
For current projects, the main lesson remains the same: NatHERS outcomes are easier to manage when energy performance is considered early. Glazing, orientation, shading, roof colour, insulation, ventilation and documentation all influence the final assessment pathway.
Certified Energy can review your residential project documentation and advise whether NatHERS, BASIX, Whole of Home or another residential energy compliance pathway applies.
Read the current NatHERS Knowledge Hub
