If you are planning a new home in Perth, you will come across the NatHERS star rating. Most people know that more stars means better energy performance. But what the numbers actually represent, and what the difference between a 7-star and a 9-star home feels like in practice, is less obvious. This guide explains the system in plain language so you can make an informed decision about what to aim for.

What NatHERS measures

NatHERS stands for the Nationwide House Energy Rating Scheme. It is the standard used across Australia to rate the thermal performance of residential buildings.

The rating measures one specific thing: the predicted heating and cooling energy needed to keep a home comfortable throughout the year. This is expressed in megajoules per square metre per year (MJ/m²/yr). The lower the number, the less energy the home needs, and the higher the star rating.

The scale runs from 0 to 10 stars. A 10-star home needs virtually no mechanical heating or cooling to stay comfortable. A 0-star home has no thermal performance at all.

What the assessment considers

What it does not measure

NatHERS rates the building envelope only. It does not account for appliance energy use, hot water systems, lighting, solar panels or the way you actually live in the home. Two identical homes with the same star rating could have very different electricity bills depending on the occupants. The rating tells you how the building itself performs, independent of lifestyle.

What each star range means in practice

The star rating scale is not linear. The jump from 6 to 7 stars requires more design effort than the jump from 2 to 3. At the higher end, every half-star represents a meaningful improvement in comfort and energy use.

Here is what each range typically means for a home in Perth.

Rating What it means Maximum heating and cooling load (MJ/m²/yr) Energy saved against 7 stars
5 stars Below the current standard. Relies heavily on mechanical heating and cooling, particularly through Perth's long summer. Typical of homes built before energy standards tightened. 89 71 per cent more energy
6 stars The previous code minimum, superseded in Western Australia in May 2024. 70 35 per cent more energy
7 stars The current minimum for new homes in Western Australia. Compliant, but still noticeable discomfort through peak summer and winter weeks. 52 the baseline
8 stars A meaningful step up. Noticeably more comfortable year-round with reduced reliance on air conditioning. This is where passive solar design starts to make a real difference. 34 35 per cent less
9 stars High-performance range. Minimal mechanical heating or cooling needed. Stable, comfortable indoor temperature year-round. This is the range Norde Homes consistently achieves. 17 67 per cent less
10 stars Essentially no mechanical heating or cooling required. The building does the work itself. 4 92 per cent less

These are the official NatHERS thresholds for Perth, which is climate zone 13. The figure is a load, not a bill: it is the heating and cooling energy the building itself is predicted to need per square metre per year. What you actually pay depends on your tariff, and on how efficient your heating and cooling equipment is. A reverse-cycle system delivers roughly three units of heating or cooling per unit of electricity, so the electricity you buy is a fraction of the load shown here.

The scale is not linear, and it steepens as you climb. Each additional star removes a larger share of what is left: 35 per cent from 7 to 8, 50 per cent from 8 to 9, and 76 per cent from 9 to 10. That is why the jump from the code minimum to a genuinely high-performing home is so large. Moving from 7 stars to 9 removes two thirds of the heating and cooling the building needs.

Why 7 stars is not enough

Western Australia has enforced a 7-star minimum for new building permits since May 2024, raised from the 6 stars required under the previous National Construction Code. Seven stars is now the floor, not the benchmark.

Most volume builders in Perth design to exactly that floor. They treat the NatHERS rating as a compliance hurdle rather than a performance target. The result is a home that passes code but still needs significant air conditioning to stay comfortable through a Perth summer.

The gap between the minimum and a high-performance home is larger than most people realise. Consider the numbers above: a 7-star home in Perth is allowed 52 MJ/m²/yr of heating and cooling, a 9-star home just 17. That is two thirds less energy for the same comfort, every year, for the life of the building. Energy is only part of the picture, though. The comfort difference is what most owners notice first. A 9-star home holds its temperature overnight and through the hottest part of the day without the air conditioner running constantly.

If you are building a new home in Perth, the question is not whether you can afford to go above the minimum. It is whether you can afford not to.

How the rating is calculated

NatHERS assessments are performed using accredited software tools such as AccuRate, BERS Pro and FirstRate5. These programs model the thermal performance of a building based on its design drawings and construction specifications.

What the software needs

Perth is climate zone 13 of the 69 NatHERS climate zones. The software uses a Reference Meteorological Year for that zone, compiled from decades of Bureau of Meteorology records, and simulates the indoor temperature of every room for all 8,760 hours of a year.

What "comfortable" actually means

It is worth being precise here, because the rating is often misread as an average temperature. It is not an average. It is a set of comfort thresholds that change by room and by hour, and the software counts only the energy needed to hold the space inside them.

For living areas, the heating threshold is 20 degrees, maintained from 7am to midnight. For bedrooms it is 18 degrees during waking hours and drops to 15 degrees overnight, because occupants are assumed to be under bedding. The cooling threshold is set per climate zone rather than nationally, so Perth occupants are modelled as acclimatised to Perth rather than to Hobart, and it shifts room by room to account for air movement and humidity.

The model also assumes people behave sensibly before reaching for a switch. Windows and blinds are opened and closed first, then ceiling fans, and only then is mechanical heating or cooling counted. So the load is what remains after a reasonable occupant has already done the free things.

The result is an energy load in MJ/m²/yr, which is then read against the star band table for that zone. In Perth, a 7-star home is allowed up to 52 MJ/m²/yr of heating and cooling. A 9-star home is allowed 17, and a 10-star home just 4.

One more adjustment matters. Because a small home has more external wall and roof per square metre of floor, it would otherwise be harder to rate well. NatHERS applies an area correction factor so that homes of different sizes can be compared fairly, which is why the rating is a genuine measure of design quality rather than a reward for building large.

What affects your rating most

Not every design decision has the same impact on your NatHERS rating. In Perth's climate, some factors carry far more weight than others. Here are the most influential, ranked roughly by their effect on the final rating.

  1. Orientation. Positioning living areas to face north is the single most impactful factor. It determines how much winter sun enters the home and how effectively summer sun can be excluded with passive shading. Getting this right costs nothing, but it has to be considered from the very start of the design process.
  2. Wall construction method. Standard double brick, the default in Perth, stores heat during the day and releases it into the home at night. Reverse brick veneer places the thermal mass on the inside and the insulation on the outside, which works with Perth's climate rather than against it.
  3. Glazing. Double-glazed windows with low-E coatings and thermally broken frames significantly reduce heat gain in summer and heat loss in winter. Window size, placement and orientation all matter.
  4. Insulation. A continuous insulation envelope with minimal thermal bridges is essential. Gaps in insulation, particularly around window frames and at wall-to-roof junctions, undermine the performance of the whole building.
  5. Shading. Well-designed eaves, pergolas and louvres keep direct summer sun off north and west-facing glazing. Fixed shading is more reliable than adjustable systems that depend on occupant behaviour.
  6. Ventilation strategy. Cross-flow ventilation through carefully placed operable windows allows cool evening air to flush heat from the building. This is particularly effective in Perth where evening temperatures drop reliably through most of the year.

These factors are interconnected. Good passive solar design addresses all of them as a system, not as isolated upgrades bolted onto a standard plan.

Wondering what star rating is achievable on your block? Start a conversation and we will give you an honest estimate.

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NatHERS and resale value

Energy performance is becoming a more visible factor in the property market. As regulatory minimums continue to rise, homes built to today's minimum will look increasingly dated compared to those designed for genuine performance.

Buyers are more educated about energy costs than they were five years ago. A home with a documented 9 or 10-star NatHERS rating offers a measurable advantage over the surrounding housing stock. It is not a vague marketing claim. It is a number produced by accredited software that can be verified and compared.

The NCC trajectory suggests that minimum standards will continue to increase. A home built to 9 or 10 stars today will remain well above the regulatory minimum for years to come. A home built to the current minimum will not.

There is also a practical consideration. A high-performing building envelope holds its value regardless of what happens to energy prices. Whether electricity costs rise, fall or stay flat, a home that needs very little heating or cooling to stay comfortable will always be cheaper and more pleasant to live in than one that does not.

Norde Homes and NatHERS

Norde Homes consistently achieves NatHERS ratings between 8 and 10 stars. This is not a theoretical target. It is a documented outcome across completed projects.

Some recent examples:

These results come from a combination of passive solar design, thermal mass and high-performance glazing. Every project is modelled during the design phase and the NatHERS assessment guides decisions about orientation, window sizing, insulation detailing and shading.

You can see completed projects and their specifications on our projects page.

Frequently asked questions

Is a 10-star rating worth the extra cost?

It depends on your priorities and budget. The cost gap between an 8-star and a 10-star home is typically smaller than the gap between a 7-star and an 8-star home, because most of the heavy lifting has already been done through good orientation and construction method. For many clients, the incremental cost of going from 8 to 10 stars is modest relative to the overall build cost and the long-term return in comfort and energy savings.

Can I get a NatHERS rating for my existing home?

Yes. An accredited assessor can model an existing home and produce a NatHERS rating. However, older homes typically rate quite low, often between 1 and 4 stars, because they were built before meaningful energy standards existed. The rating can be useful for understanding the baseline performance and for comparing renovation options.

Does a higher NatHERS rating mean I do not need air conditioning?

Not necessarily. Even a 10-star home may benefit from some mechanical cooling during Perth's hottest weeks. The difference is how often and how long you need to run it. In a 9 or 10-star home, the air conditioner is a backup for extreme days rather than something that runs constantly from November to March.

Are solar panels included in the NatHERS rating?

No. NatHERS rates the building envelope only. Solar panels, battery storage, hot water systems and appliances are assessed separately under other frameworks such as the Whole-of-Home rating. A high NatHERS rating combined with solar generation is a strong combination, but they are measured independently.