If you’re building a new home, adding an extension or completing some alterations, chances are you’ll need to get a NatHERS rating. These are typically organised by your designer, but having your own understanding of what they are and how they work could make a big difference in how you approach your build. Let’s take a look.
WHAT IS A NATHERS RATING?
If you’ve found yourself a bit confused about what a NatHERS rating is and how it might affect your home, you’re far from alone. Spelled out, NatHERS is the Nationwide House Energy Rating Scheme. It uses modelling tools to assess your home’s energy efficiency and will provide two different ratings: a ‘Thermal Star’ rating and a ‘Whole of Home’ rating.
The Thermal Star rating considers how construction methods and materials effect the movement of heat through a building and, therefore, how comfortable the indoor temperatures will be year-round. In doing so, it can predict how much heating and cooling will likely be required. It will consider things like the local climate, layout and orientation of the home, construction methods and materials, shading, and impact of local breezes. Your home will be given a star rating between 0 and 10, with higher ratings indicating that less heating and cooling will be needed—and the lower your energy bills will be.
The Whole of Home rating is a newer rating which considers how much energy will be used throughout the entire home and is given as a number from 0 to 100, where 100 means the home is net-zero. It will consider heating and cooling as well as other areas of energy usage like lighting, hot water systems, appliances and even things like pool or spa pumps. If you have solar panels, the energy generated from these will be taken from your energy usage to improve your rating.
Both of these NatHERS ratings are used to ensure new homes meet the energy efficiency requirements of the National Construction Code (NCC). As of 2025, the NCC requires all new homes to achieve a minimum Thermal Star rating of 7 and a Whole of Home rating of 60. All assessments must be completed by a certified consultant and typically costs around a grand for both a preliminary and official assessment —although this will vary depending on the size of your project.
DO YOU NEED ONE?
The first thing to note here is that NatHERS ratings are only used for residential builds; commercial spaces have different requirements. When it comes to residential projects, however, all new builds are required to get a NatHERS ratings, and you won’t be able to get a building permit until they meet the NCC requirements (as above).
Alterations and additions are a bit more complicated. Generally, it’s best to assume that you will need an assessment, however the required rating will depend on what percent of the home is being renovated.
In our Arundel Street project, we didn’t need to get a NatHERS rating for the existing home, only the extension.
This may seem a little stressful, but keep in mind that your designer should already have a good understanding of NatHERS ratings, and will be the ones to organise an assessment. If your build doesn’t meet the required rating, they can then work with the consultant to find solutions that are within your budget. We, as your builder, can also help in this process as well.
NOT A PERFECT SYSTEM
Despite the benefits of NatHERS, it’s worth noting that the rating system is by no means perfect. This is primarily because, no matter the modelling software that’s used, it’s impossible to consider every variable.
As such, there may be things that affect your home’s performance that NatHERS doesn’t account for. For example, while the modelling will consider your home’s local climate and some of its surrounding area, it could fail to account for a breeze that comes from a park across the street. If it had, you could design your home to utilise this breeze and easily improve your rating. This is where a good designer will make a huge difference as they can consider these factors and implement them into your design. They may not help your NatHERS rating, but they will improve your home’s performance in the long term.
Maldon Way - a prime example of a NatHERS rating that didn’t account for a breeze from the park opposite, in this case Blue Gum Lake.
In the other direction, the software is also unable to account for the quality of your build. While your home may meet a certain NatHERS rating in the modelling, a low-quality build could mean your home doesn’t perform as well as predicted. Take insulation for example. Even if you’ve used high-quality insulation that looks great in the models, if it’s poorly installed with lots of gaps it won’t perform nearly as well as the model predicts. This won’t affect your NatHERS rating, but will affect the performance of your home and how much you spend on heating and cooling in future.
If sustainability is important to you, it’s also worth noting that the NatHERS ratings don’t consider the longevity of the home or carbon footprints of individual materials—it only considers current performance. If you want a home that lasts a long time and has minimal impact on the environment, you’ll be best off sourcing an architect or designer with specific experience in sustainable design.
TIPS FROM THE TRADE
So, you now know all the basics about NatHERS ratings, but how can you make sure you make the most of them?
The most important tip we can give you here, is to get a preliminary assessment early in the design stage. These won’t provide you with an official rating but will give you an opportunity to make necessary adjustments early in the design before it becomes more complicated, and the changes become more costly. On a similar note, choosing your fixed appliances early will ensure these are considered in your Whole of Home rating, and reduce the chances it’ll need to be reassessed.
It’s also good to be aware that some design choices will have a bigger impact on your NatHERS rating than others. Most importantly, take the time to think through your home’s orientation as this can make a huge difference to solar access and shading. If your glazing needs to face the wrong direction - say, to catch a good view - you can still minimise heat transfer with double or triple glazing and good window furnishings. Extensive, high-quality insulation (installed correctly) will also have a big impact on your NatHERS rating. At Arklen, we typically use high-quality Polymax insulation paired with Anticon (a reflective blanket insulation that’s installed under metal roofing) in all projects.
This extensive North/West facing glazing in Banjup is not only reflective glass with commercial framing, it’s further protected from the sun with a huge veranda and window furnishings.
Finally, remember that the quality of your build will have a huge impact on your home’s performance —let alone its longevity. A high-quality builder may be more costly upfront, but will be well-worth it down the line when other homeowners are spending big bucks on repairs and maintenance. If you’d like to chat to us about Arklen being that team, get in touch!