Read Between the Stars

Did you know that a dwelling rated in 2010 at 6 Stars is more than likely rating at 5 Stars in 2023?

6 Star energy efficiency regulation was transitionally introduced into the National Construction Code on May 1st 2010 (BCA2010).?It has been 13 years since the last major increase in minimum energy efficiency requirements for new residential construction was introduced in Australia.?

Moving to 7 Star requirements is definitely overdue and to the average consumer it would look on the surface that nothing has really changed in the last decade as the code hasn’t formally increased in any meaningful way.

But is that really the case??No, in fact it has substantially changed and the goal posts have shifted many times in that period.?What was 6 Stars in 2010 is absolutely not even close to 6 Stars in 2023.

What has changed with the way we calculate data since the introduction of 6 Stars?

The evolution of the Chenath Engine and NatHERS software combined with the introduction of technical notes providing stability and consistency within the industry has been a big driver for these changes.?

NatHERS software has matured over time like any industry and we are definitely better off for it.?Although the National Construction Code never increased from the minimum 6 Star requirement some of the software updates that were introduced over the last 13 years include:

• Wall and Floor builder added which allowed simulations of the actual construction materials within each system.
• Ability to model downlights which included calculations for the percentage reduction in ceiling insulation based on ceiling penetration amounts and sizes.
• Ability to adjust the colour of more materials with increased solar absorptance options beyond 3 choices. (SA = 0.1 – 0.9)
• Functional ability to adjust wing walls throughout the design for additional shading factors.
• Improvements to modelling eaves and how they are now finitely interpreted via the Chenath engine.
• More options for zone types, including a zone type for unconditioned zones and void areas.
• Technical note improvements to include shading obstructions such as fences and neighbouring buildings. (Tech Note 1.1 April 2013)
• Ability to adjust floor height above ground to compensate for different wind forces.
• Waffle-pod R value adjustment reduced all waffle pod slab projects by 0.1 Stars as compensation for thermal bridging of concrete beams was considered.
• Zoning adjustments in tech notes for better occupancy understanding within the modelling.
• Application of AS3999 for reduction in ceiling perimeter insulation to stop condensation and insulation compression.
• Introduction of capped heating and cooling load limits on May 1st 2020.
• Random Chenath engine updates that caused automatic reduction in assessments.

As the software became more developed allowing for complex construction systems to be entered and the increased ability to calculate factors that previously were not being considered energy ratings became more precise and more accurate to reality.

At one point in the early 2010’s each new software update reduced data files by 0.1 Stars every time they were opened and updated to meet the most recent protocols.

Choose your sources of data wisely!

Any study or data collected prior to 2018 is irrelevant when making comparisons to modern NatHERS reports and the perception of what is required specification wise for 6 Star compliance.

The data may have been accurate at the time of release however the variation in data input complexity, style and calculation engine results are so vastly different within legacy files they cannot be used for any meaningful analysis. ?

For example, we picked a random energy efficiency assessment that achieved 6.0 Stars in 2013 using FR5 version 5.1.9c. The same file was then updated to FR5 V5.3.2b including all current technical notes following all current FR5 instructions and when recalculated the results were 5.4 Stars in 2023.

This is a demonstrated 0.6 Star reduction in a certified project between software versions within 10 years. The deviation is even greater when comparing files with a 13 year calculation spread.?

Without knowing the intricacies of the information presented above it would definitely look like 6 Stars has always been 6 Stars since 2010 although it is extremely easy to demonstrate otherwise having been active in the industry for a significant amount of time.

Where we are heading beyond 2023?

Obviously, we all immediately think of mandatory 7 Stars in October however there are other developments within NatHERS software very close to implementation which will cause the same issues as we have already discussed.

The addition of thermal bridging calculations for external walls including the selectable introduction of steel frames will automatically reduce energy rating performance overnight.?

A house that rates at 6.0 Stars one day could very well rate at 5.7 Stars the day after implementation of new software that takes into consideration updated thermal bridging calculations for timber studs and noggins due to a reduction in wall insulation area.

A steel framed house could potentially lose another 0.3 Stars due to thermal bridging of the steel itself when compared to timber. ?In a worst-case scenario, a steel framed house which achieved 6 Stars in 2010 may rate as low as 4.4 Stars when calculated in future updates of NatHERS software.

Conclusion.

Technically the requirements within NCC 3.12 have not changed from 6 Stars since introduction in 2010 however it is disingenuous to say that energy efficiency requirements for residential housing has not increased within the same period.

The energy efficiency of our housing stock has definitely increased over time as modern compliance requires more energy efficiency upgrade specification due to improved data entry stringency to achieve the same numeric Star value.

It would be wise for anyone with a legacy energy efficiency assessment pre 2018 to contact a competent energy assessor to update the data to match current protocol requirements in order to provide a more accurate representation of the design.

If you have any questions please contact Energy Lab on 1300 033 343.

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