A seven star certificate is a design score, and very little checks the finished home against it. The national disclosure framework moves the measurement to the point of sale, and NSW has started.
Every new home in Australia is approved on a promise. The NatHERS certificate that clears a building permit describes how the design should perform. It does not describe the house that gets handed over.
Around 90 per cent of new home designs are assessed through the Nationwide House Energy Rating Scheme. The rating comes from plans, specifications and modelling software. After approval, nothing in the system routinely tests the finished building against that number.
That is starting to change, and not through the building code. Residential changes to the National Construction Code are paused until mid 2029. The shift is coming through home energy rating disclosure, a separate track set by energy ministers, which rates homes again when they are sold or leased.
What does a NatHERS certificate actually measure?
A NatHERS certificate carries two numbers. The star rating, out of 10, covers the building shell. The Whole of Home rating, out of 100, adds fixed appliances, hot water, lighting and any solar or battery. Under NCC 2022 a new house needs seven stars and a Whole of Home score of 60.
Both numbers are calculated before the slab is poured. The Australian Government’s YourHome guide describes NatHERS ratings for new homes as based on their designs.
Most designs are rated to clear the line rather than beat it. Research conducted between 2016 and 2018, cited in the consultation draft of the national disclosure framework, found that 81.7 per cent of new housing was designed to meet only the minimum NatHERS requirement.
How closely do finished homes match their ratings?
The honest answer is that nobody knows for certain, because finished homes are rarely checked.
The most direct test was a pilot run in 2015 under the National Energy Efficient Building Project. Nine councils carried out 86 inspections across 59 new homes against the energy provisions of the code. For glazing, inspectors recorded 18 homes as compliant, 3 as non compliant and 26 as inconclusive. For roof insulation, 28 were compliant, 3 non compliant, 11 inconclusive and 11 could not be inspected at all.
The report’s authors cautioned that the sample was too small to generalise. Its clearer finding was about verification. Inspections often fell too early or too late to see insulation and glazing, and approval documents frequently lacked the detail needed to check against.
Are new homes as leaky as their reputation?
On air tightness, the evidence has moved in the industry’s favour.
In 2024 CSIRO tested 233 new dwellings, 105 apartments and 128 houses built within the previous four years, across Melbourne, Sydney, Brisbane, Canberra and Adelaide. Average air permeability was 6.86 cubic metres per hour per square metre at 50 pascals. CSIRO’s 2015 study of 129 new homes averaged 15.4 air changes per hour at the same pressure, a different but broadly comparable measure. Apartments were tightest at 5.80 on average, single storey houses averaged 6.77 and two storey houses 8.55.
For the 13 houses where CSIRO had the original NatHERS files, the air tightness assumed in the model and the result measured on site differed by 0.01 on average. For the 8 apartments with files, the finished homes were tighter than modelled.
That is a small sample. But it does not support the idea that new houses are routinely far leakier than their ratings assume.
Where are finished homes losing performance?
The same study shows where the gaps sit, and most of them fall between trades. Testers found poor or missing door seals in 65 per cent of houses and leaks at bath fans in 63 per cent of dwellings. Cavity sliding doors leaked in 49 per cent of houses, sliding glass doors in 48 per cent and kitchen cabinetry penetrations in 45 per cent.
Star ratings did not predict any of this. CSIRO found no correlation between a dwelling’s star rating and its air tightness.
Ducted heating and cooling was the weakest point. None of the 11 duct systems tested met the leakage limit in the 2021 International Energy Conservation Code. In the five systems tested for it, between 79 and 93 per cent of duct leakage went to unconditioned space. NatHERS does not count duct leakage while systems are switched off.
The opposite problem appeared too. About 26 per cent of dwellings tested below 5 cubic metres per hour per square metre, the level at which the code requires continuous mechanical ventilation. None had it, because none had been tested.
Design rating versus existing home rating
A NatHERS new home rating is calculated from plans and specifications before construction and is used to approve the build. A NatHERS existing home rating is based on an on site assessment of the finished home by an accredited assessor, covering the building shell, fixed appliances and any solar or battery. Under the consultation draft of the national disclosure framework, the existing home rating is what is disclosed when an occupied home is sold or leased.
What changes when a home is sold or leased?
In December 2024 energy ministers agreed version 2 of the Home Energy Ratings Disclosure Framework, a national approach to giving buyers and renters an energy rating at the point of sale or lease. NatHERS underpins ratings for houses and apartments. NABERS covers the shared services of larger apartment buildings.
The draft released for consultation sets out how that applies to new homes. A home sold off the plan can disclose its NatHERS design certificate. Once a home has been occupied, the rating disclosed is a NatHERS existing home rating, based on an on site assessment by an accredited assessor. A rating stays valid for disclosure for up to 10 years unless building work or appliance changes affect it.
NatHERS for existing homes is still scaling up. Its first stage opened accreditation to a limited pool of assessors, and NatHERS has said the second stage, with a new tool and open accreditation, was expected from mid 2026.
The ACT has required an energy rating to be disclosed at sale since 1999. NSW started a voluntary rollout from mid 2026, after trials that began in September 2025, and says it will move to mandatory disclosure once the market is ready. No date has been set.
The rating that approves a build and the rating that may follow it to market are becoming two different instruments, prepared at different times and potentially by different assessors.
The rating that approves a build and the rating that may follow it to market are becoming two different instruments
Will a second rating match the first?
No one has published data comparing existing home ratings of recent new homes with their original design certificates. The answer is untested.
A second rating could differ for reasons that have nothing to do with workmanship. An existing home assessment is done on site, and assessors follow set guidance where elements such as wall insulation cannot be seen. The Whole of Home score also moves with appliances, and owners change appliances.
It could also pick up changes made between approval and handover. The 2015 pilot recorded roof colours, insulation and glazing that did not match the specification, and in one home timber window frames had been swapped for aluminium. Changes of that kind are visible to an assessor standing in a finished house in a way they are not on a set of plans.
Why does this matter while the code is paused?
With the residential code fixed until mid 2029, regulation will not lift energy requirements for new homes in the next few years. Disclosure works differently. It does not change what a builder must deliver. It changes what a buyer can see, and when.
THE GOOD BUILDER TAKE
For most of the past two decades, the energy rating on a new home has been a design document whose working life ended at the building permit. Disclosure gives it a second life at sale, and a second assessment.
The evidence so far says new homes are tighter than their reputation. The weak points are the details between trades and the changes made after approval, and the second of those is what an on site rating records.
Frequently asked questions
No. A NatHERS certificate for a new home is calculated from plans and specifications before construction and is used to show the design meets the energy requirements of the National Construction Code. Nothing in the system routinely tests the finished home against it.
The ACT has required an energy rating to be disclosed at sale since 1999. NSW began a voluntary rollout from mid 2026 and says it will move to mandatory disclosure once the market is ready, with no date set. The national framework agreed by energy ministers in December 2024 leaves each state and territory to decide whether and when to make disclosure mandatory.
Under the consultation draft of the national framework, a home sold off the plan can disclose its NatHERS design certificate, but once a home has been occupied the disclosed rating is a NatHERS existing home rating from an on site assessment. A rating stays valid for disclosure for up to 10 years unless building work or appliance changes affect it.
CSIRO tested 233 dwellings built within four years and found an average air permeability of 6.86 cubic metres per hour per square metre at 50 pascals. Its 2015 study of 129 new homes averaged 15.4 air changes per hour at the same pressure, a broadly comparable measure.
No. The pause covers changes to the National Construction Code until mid 2029. Disclosure is a separate track set by energy ministers and implemented by each state and territory.
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Last updated: 12 October 2026. NatHERS, NSW and disclosure framework status current at that date.
General Information Only: This article provides general information only and does not constitute legal, technical or professional advice. Energy rating and disclosure requirements vary by state and territory and are subject to change. Builders should confirm current obligations with their building surveyor, energy assessor or the relevant state regulator.
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