PERTH7-star NatHERS and Whole-of-Home: the new energy rule for WA homes
NatHERS energy ratings for new WA homes: the 6-to-7-star lift from 1 May 2025, the new Whole-of-Home requirement, NCC 2022 Spec 42
If you are building or buying a new home in Western Australia, the energy rating attached to it changed significantly in 2025. New houses now have to hit a higher star rating, and for the first time the rules look at the whole home rather than just the shell. Here is what that means, and what it is worth to a buyer.
What NatHERS actually measures
NatHERS is the Nationwide House Energy Rating Scheme, and it rates a home's thermal performance on a scale of 0 to 10 stars. It measures the building shell — the walls, roof, floor, windows and how they work with the local climate to hold a comfortable temperature without much mechanical heating or cooling. A higher star rating means the house needs less energy to stay comfortable, which in Perth mostly means staying cool through summer.
Building and Energy's Industry Bulletin 44 clarified how NatHERS-accredited software is used to demonstrate energy-efficiency compliance, and the software is how the rating on your plans is generated.
What changed in 2025
Under the National Construction Code 2022, adopted for new WA homes from 1 May 2025, two things changed together.
The minimum thermal performance rose from 6 stars to 7 stars. That is a real lift in the building fabric — more insulation, better glazing, and construction detailed to reduce heat gain and loss.
And a new Whole-of-Home requirement was added. For the first time the rules assess a home's actual energy use across its heating and cooling, hot water, cooking, lighting, and pool or spa pumps, against an annual budget, with a Whole-of-Home score of at least 60 required. Rooftop solar and batteries are not mandatory, but they can be counted toward the budget. Previously the assessment stopped at the shell; now it looks at the whole house working.
The detail sits in the NCC: the additional requirements for houses are in Specification 42 of Volume Two, and for apartments in Section J of Volume One. For apartments the 7-star average with a 5-star minimum per unit applied from the same period.
What it means when you are buying
For a new build, the NatHERS certificate is part of the compliance documentation, and it is worth asking for. It tells you what the house was rated to achieve, and a home built to 7 stars with a solid Whole-of-Home score costs meaningfully less to run than the 6-star stock beside it — a genuine difference in a Perth summer.
The important honesty here is the gap between rating and reality. A NatHERS rating is a modelled prediction from the plans, not a measurement of the finished house. If the insulation was skimped, the glazing substituted, or the sealing done poorly, the house can fall short of the number on its certificate. That gap is exactly the kind of thing worth checking, which is why energy-efficiency features — insulation coverage, glazing, draught sealing — are worth verifying at staged inspections and practical completion rather than taken on trust.
Renovations
The 7-star and Whole-of-Home requirements primarily target new builds. A renovation can trigger them where it crosses certain thresholds, typically a substantial addition or work affecting a large share of the existing home, and WA has an Alterations and Additions Protocol as a compliance pathway for existing houses. If you are planning a major renovation on a Perth home, whether it triggers the current energy provisions is a question worth putting to your building surveyor early. On any purchase, a pre-purchase inspection reports the visible state of the things that drive comfort and running cost, whatever the certificate says.
What a star rating actually buys you
The NatHERS star rating measures the thermal performance of a home's design, how well the building itself keeps its occupants comfortable without mechanical heating and cooling, by modelling how it responds to the climate it sits in. A higher rating means the building fabric does more of the work: it holds warmth in winter and keeps heat out in summer through its orientation, insulation, glazing, and construction, so that less energy has to be spent making up the difference. The move to a higher minimum standard for new homes is, at its heart, a move to build homes that are cheaper and more comfortable to live in, because a well-rated house needs less running of the air conditioner and the heater to stay comfortable, and that shows up directly in the energy bills and the comfort of the occupants year after year.
It is worth being clear about what the rating is and is not. It is a measure of the design's thermal performance, modelled, not a measure of how the house was actually built or how it will perform if the construction did not match the design. A house designed to a high rating but built with insulation missing, gaps in the building envelope, or glazing that does not match the specification will not perform as rated, which is one of the places where the gap between the paperwork and the physical building matters. The rating describes the intent. It is a model, not a measurement. whether the house delivers it depends on the construction being faithful to the design, which is a matter for the build quality rather than the certificate.
Why the standard rose, and what it means to build to it
The lift in the minimum energy-efficiency standard for new homes reflects a broader direction: building homes that perform better thermally, cost less to run, and place less demand on energy for heating and cooling. For someone building a new house, the higher standard shapes real decisions in the design and construction, the orientation of the house on the block, the amount and placement of glazing, the insulation, the construction of the walls and roof, the details that determine how the building envelope performs. Meeting the standard is not a matter of adding a feature at the end; it is designed into the house from the start, which is why it is worth understanding early if you are building rather than discovering late that the design does not meet the requirement.
For a buyer of a new or near-new home built to the current standard, the higher rating is a genuine benefit, a house that should be more comfortable and cheaper to run than an equivalent older home, provided it was built to match its design. This is where the connection to construction quality matters: the rating is only delivered if the insulation is actually there and complete, the envelope is actually sealed, and the glazing is as specified. A staged inspection during construction, checking that the insulation and the building envelope are built as designed, is one way the gap between the rated design and the delivered house is kept small.
Where it fits an existing home and a renovation
For an existing older home, the energy-efficiency standards that apply to new construction are not retrospective, so an older house is not deficient for having been built to the standards of its era. But the thermal performance of an older home is a real factor in the cost and comfort of living in it, and it is worth understanding what you are buying: an older Perth home with little insulation, large areas of unshaded west-facing glass, and a leaky envelope will cost more to keep comfortable than a well-designed modern one, and that is a running cost that continues for as long as you own it. None of that is a defect, but it is a characteristic worth factoring into the decision and the budget.
Renovations and additions can bring the energy-efficiency requirements into play for the work being done, depending on its scope, so an owner planning significant work should expect the current standards to apply to the new parts and should factor that into the design. The broader point for a buyer is that energy efficiency is one of the quieter aspects of a home that affects the cost and comfort of living in it for years, invisible on a walk-through. It is real in every bill, and worth understanding as part of the picture of what a given house will actually be like to own, rather than treating it as a technicality that lives only on a certificate.
Common questions
What energy rating do new WA homes need?
From 1 May 2025, new WA homes must meet a minimum 7-star NatHERS rating (up from 6) plus a Whole-of-Home requirement, under NCC 2022. The detail is in Specification 42 of Volume Two for houses.
What is Whole-of-Home?
A new NCC 2022 requirement that assesses a home's actual energy use across heating and cooling, hot water, cooking, lighting and pool pumps against an annual budget, with a score of at least 60 required. Solar and batteries can count toward it.
Is a NatHERS rating a guarantee?
No. It is a modelled prediction from the plans, not a measurement of the finished house. Skimped insulation, substituted glazing or poor sealing can make a home fall short of its certificate.
This comes up on every building stage inspections and pre-purchase building inspection we carry out.
Read next: home indemnity insurance: your protection if the builder fails and ventilation, condensation and mould: the moisture a house can't get rid of.
Sources
Read rather than recalled. Summarised here; the documents themselves are Crown copyright and are linked rather than reproduced.