House Energy Ratings Explained


Housing Energy Ratings: Problems and Pitfalls

Did you know that while Australian houses are growing in size, they are also becoming more energy efficient? That’s good news as we try and tackle climate change, and it also bodes well for homeowners, because energy efficient homes cost less to keep comfortable all year round. 

We can thank government regulation for driving this improvement: The National Construction Code introduced minimum performance standards for new homes – to reduce energy consumption by 20-25% over previous norms – in May 2012 in WA.

I recently set out to improve my own understanding of this rather confusing topic – so I can better explain it to our clients – by asking colleagues and consultants about the various pathways we can use to demonstrate compliance with energy efficiency provisions. I reasoned that if I found this a difficult area to navigate – and I’m in the industry – consumers might also feel confused and overwhelmed by options and be unsure about how to get the best outcome on their new home project.

Here’s what I found out – and please bear with me as we wade through some acronyms! There are several ways that architects. designers and builders can demonstrate compliance with the performance-based requirements of the National Construction Code (NCC), as follows:

  • the Deemed to Satisfy (DTS) provisions, using accredited energy rating tools under the Nationwide House Energy Rating Scheme (NatHERS), which provides a star-rating (the current minimum standard is 6-stars);
  • Elemental Provisions, which provide a ‘checklist’ to assess individual elements – such as windows, doors, roofs and insulation – against the requirements outlined in Volume Two of the NCC; 
  • Verification Using a Reference Building (VURB) assessment – an alternative method that demonstrates compliance outcome for designs against Performance Requirements; and
  • Using Expert Judgement.

The new bespoke homes that architects design are generally assessed using energy rating tools or VURB. Many of the project homes being marketed in Perth are also assessed using VURB, rather than NatHERS or other rating tools. 

According to the CSIRO, which tracks energy efficiency assessments, about 15-20% of those houses using NatHERS in WA fail to achieve 6-stars, compared with just 1.5% of submissions nationally. The reasons for this failure are varied and not yet well-understood. 

It’s worth nothing that only designs that have been assessed using NatHERS can achieve a star-rating, because DTS and VURB don’t generate star-ratings, because these methods are not directly comparable although all three are acceptable under the minimum standard of the National construction code. Also, there is currently no provision to ensure that new houses are built to the stated design standard, so consumers have to do their own homework to make sure they get what they paid for (a building surveyor can monitor this for you).

So, if you plan to buy a house that’s been marketed as a 6-star design (the current minimum), ask to see the NatHERS certificate, or the report that verifies the rating achieved. 

It’s also worth remembering that energy efficiency goes beyond design and material selections: it is strongly influenced by user behavior. Essentially, you could have a 10-star house – the highest possible NatHERS rating – and still rack up huge energy bills if you ran the air conditioner or heater around-the-clock, with the windows and doors wide open. And you definitely can improve your efficiency with smart window treatment selections, landscaping choices, and putting on that extra layer indoors in the cooler months!

If you’re interested in finding out more about the various assessment pathways, or to see what types of houses, materials and designs have been built in your neighbourhood since the new provisions came into force, visit the CSIRO’s Australian Housing Database, at