A Site-Based,
Evidence-Driven Assessment
Millions of Australian homes were built before modern energy efficiency standards existed. As a result, many older dwellings are poorly insulated, inefficient to heat and cool, and costly to run. The NatHERS for Existing Homes program is designed to change that — giving homeowners, property professionals and policymakers a standardised, nationally recognised way to assess and improve the energy performance of homes already built.
Understanding Your Home's Thermal Performance
A NatHERS assessment measures how well a home’s building fabric- its walls, roof, floor, windows and orientation- retains heat in winter and resists heat in summer. The result is a star rating from 0 to 10.
Whole of Home Energy Picture
Beyond the building shell,NatHERS for existing homes program also measures the energy use and generation of major fixed appliances- heating, cooling, hot water, solar PV and batteries- to produce a Whole of Home score out of 100.
A Pathway to Smarter Upgrades
The NatHERS certificate produced through a NatHERS for existing homes assessment identifies specific areas where improvements would have the greatest impact, giving homeowners a clear, evidence-based starting point for retrofits and renovations.
This Service Is
For You If…
NatHERS for Existing Homes is relevant to a broadrange of stakeholders across Australia
- Homeowners wanting to understand their home’s current energy efficiency and identify practical, cost-effective upgrades.
- Property sellers and buyers seeking a transparent, objective energy rating ahead of a transaction.
- Landlords and property managers looking to demonstrate the energy performance of rental properties to prospective tenants.
- Households applying for green home finance; many lenders now request a NatHERS rating to support loan applications for energy-efficient upgrades..
- Architects, builders and renovation consultants using an existing-homes rating as a documented baseline before designing retrofit works
- Property developers and investors aiming to improve asset performance and market appeal
What Is NatHERS for Existing Homes?
NatHERS— the Nationwide House Energy Rating Scheme is Australia’s nationally recognised framework for rating the energy performance of residential buildings. The NatHERS program is administered by the Australian Government’s Department of Climate Change, Energy, the Environment and Water (DCCEEW). Traditionally, NatHERS has been used to rate new residential buildings at the design stage. From mid-2025, the scheme was formally expanded to include homes that have already been built — allowing the NatHERS for existing homes program to extend credible energy rating capability to the vast majority of Australia’s existing housing stock.
Program Status — Currently in Trial Phase
As of 2025, NatHERS for Existing Homes is in its trial and early rollout phase across Australia. Stage 1 of the NatHERS for existing homes program commenced from mid-2025. A broader Stage 2 rollout is expected from mid-2026, subject to government review and confirmation. NatHERS for existing homes assessment is not yet mandatory for existing homes under the National Construction Code (NCC). Homeowners and property professionals should check the latest updates from DCCEEW at nathers.gov.au for the current status in their state or territory.
The Two Key Outputs
Star Rating and Whole of Home Score
A NatHERS for Existing Homes assessment produces two complementary ratings, both
issued on a single Home Energy Rating Certificate:
Thermal Star Rating (0–10)
Measures the thermal performance of the building shell, based on:
- Building orientation and floor plan layout
- Wall, roof and floor construction and materials
- Insulation levels — ceiling, wall and underfloor
- Window glazing type, size, frame and placement
- External shading — eaves, screens, vegetation
- Local climate zone data
A 10-star home requires minimal or no artificial heating and cooling year-round. A 1–2 star home is likely to be uncomfortable and costly to condition.
Thermal Star Rating (0–10)
Estimates annual energy consumption and generation from major fixed appliances and on-site systems, including:
- Space heating and cooling systems
- Hot water systems (gas, electric, heat pump or solar)
- Fixed lighting
- Rooftop solar PV generation
- Battery storage systems
The Whole of Home score complements the thermal star rating, providing a broader view of a home’s total energy footprint.
What the Home Energy Rating Certificate Includes
What the Home Energy Rating Certificate Includes Once an assessment is complete, a qualified NatHERS assessor issues an official Home Energy Rating Certificate. The certificate typically includes:
- A thermal star rating from 0 to 10
- A Whole of Home score from 0 to 100
- Heating and cooling load figures in megajoules per square metre per year
- Estimated annual energy consumption and greenhouse gas emissions
- A summary of the home’s key assessed construction details and inputs
This certificate is recognised by Australian banks and lenders as supporting documentation for green home loans and renovation finance. It can also support property disclosure requirements and provide a credible baseline for planning retrofit or renovation works.
Is a NatHERS Assessment Mandatory for Existing Homes?
A ‘NatHERS for Existing Homes assessment’ is not currently mandatory under the National Construction Code (NCC). The program is still in its trial and early rollout phase. However, assessments are increasingly relevant — and in some cases required — in specific circumstances:
- Green home finance — many lenders require a NatHERS rating to approve loans for energy-efficient home upgrades or green mortgages
- Property transactions — some states are piloting or considering mandatory energy disclosure requirements at the point of sale or lease (refer to your state or territory authority for current requirements)
- Renovation and retrofit projects — an existing-homes NatHERS rating provides a documented, objective baseline from which upgrade impacts can be measured
- Government incentive programs — some federal and state rebate or upgrade programs use NatHERS ratings as eligibility criteria
Note: The ACT operates a separate Energy Efficiency Rating (EER) Disclosure Scheme, which is not currently compatible with the national NatHERS for Existing Homes program. Homeowners in the ACT should refer to the ACT Government’s specific requirements.
How Existing Homes Assessments Differ from New-Home Ratings
- An accredited NatHERS assessor must visit the property in person to gather evidence of the home’s construction, materials and installed systems
- The assessor collects all necessary data on-site
- Accredited software (AccuRate Enterprise, existing homes mode) is used to model thermal performance and calculate the Whole of Home score
- Where specific construction details cannot be directly observed or documented, the assessor applies conservative default values as prescribed in the NatHERS Technical Note published by DCCEEW
How a NatHERS for Existing Homes Assessment Works
Booking an Assessment
An accredited NatHERS assessor is contacted and the property visit is arranged. At this stage, homeowners are encouraged to gather any available documentation — building plans, insulation records, appliance specifications or renovation records — to assist with accurate data collection.
On-Site Data Collection
The qualified assessor visits the property in person. They systematically measure rooms and openings inspect accessible roof and sub-floor spaces for insulation, identify glazing and frame types, record wall and ceiling construction, and note details of heating, cooling, hot water and other fixed appliances. Most residential assessments take between one and two hours on-site.
Thermal Modelling
All collected data is entered into AccuRate Enterprise — the NatHERS-accredited software used to conduct NatHERS for existing homes assessments . developed by CSIRO. The software models the home’s thermal performance using the Chenath physics engine and calculates Whole of Home energy use based on the appliance and system data gathered. Where specific details could not be directly observed or documented, conservative default values prescribed by the NatHERS Technical Note are applied.
Certificate Issuance
An official NatHERS Home Energy Rating Certificate is generated and provided to the homeowner. The certificate includes the thermal star rating, Whole of Home score, energy and emissions data, construction input summary, and tailored upgrade recommendations.
How to Prepare for Your NatHERS
Existing Homes Assessment
Access and Documentation
Access
- Access to all rooms in the dwelling
- Access to roof space or attic — this allows the assessor to confirm ceiling insulation type and thickness
- Access to sub-floor or underfloor areas, where applicable
Documentation
- Original building plans or council-approved drawings, if available
- Records or invoices for any insulation installed — product name, R-value and location
- Details of any renovation or upgrade works carried out since the original build
- Appliance specifications or WELS/MEPS labels for heating, cooling, hot water systems and solar
- Any previous energy assessments or audit reports for the property
The more documented evidence provided to the assessor, the fewer conservative default values need to be applied — which typically results in a more accurate and potentially higher rating. Where evidence is unavailable, the assessor applies defaults in accordance with the NatHERS Technical Note.
Common Upgrades
That Can Improve a NatHERS Rating
Following a NatHERS for Existing Homes assessment, the certificate will include tailored
recommendations. Across Australia’s existing housing stock, the highest-impact improvements
typically fall into three categories:
Booking an Assessment
An accredited NatHERS assessor is contacted and the property visit is arranged. At this stage, homeowners are encouraged to gather any available documentation — building plans, insulation records, appliance specifications or renovation records — to assist with accurate data collection.
Windows & Glazing
Replacing single-glazed windows with double-glazed or thermally broken systems, adding external shading devices such as eaves, screens or awnings, and installing insulating window furnishings all reduce heat gain and heat loss significantly.
Appliances & Systems
High-efficiency reverse-cycle air conditioning, heat pump hot water systems, rooftop solar PV, battery storage and LED lighting all contribute to a better Whole of Home score. Switching from gas to efficient electric systems is increasingly recommended.
Have some Questions
What is NatHERS for Existing Homes?
NatHERS for Existing Homes is an extension of the Nationwide House Energy Rating Scheme (NatHERS), designed to evaluate the energy performance of homes that have already been built. An accredited assessor visits the property, collects data on its construction and systems, and uses NatHERS-approved software to produce a Home Energy Rating Certificate that includes a thermal star rating (0–10) and a Whole of Home score (0–100).
Is the program currently available across Australia?
The ‘NatHERS for existing homes assessments’ program entered Stage 1 of its rollout from mid-2025. A broader Stage 2 rollout is expected from mid-2026. It is available in all states and territories except the ACT, which operates a separate Energy Efficiency Rating (EER) Disclosure Scheme. Homeowners should check nathers.gov.au for the most current availability and program updates.
Is a NatHERS for Existing Homes assessment mandatory?
No – A NatHERS for existing homes assessment is not currently mandatory at this stage. The program is still in its trial and early rollout phase. An assessment is not currently required under the National Construction Code (NCC) for existing homes that are not undergoing major renovation or change of use. However, it may be required for certain green finance products, and some states are exploring mandatory energy disclosure requirements for property transactions.
Do you need building plans to get an assessment?
No. Unlike NatHERS assessments for new homes — which are conducted from architectural plans — existing homes assessments are based entirely on data gathered during an on-site visit by a qualified assessor. Building plans can be helpful if available, but are not required.
What happens during the on-site visit?
A qualified and accredited NatHERS assessor visits the property to measure rooms and openings, inspect accessible roof and sub-floor spaces for insulation, identify window and glazing types, record wall and ceiling construction materials, and note the details of heating, cooling, hot water and other fixed appliances. The visit typically takes one to two hours for a standard residential dwelling.
What software is used for the assessment?
Existing homes assessments use AccuRate Enterprise in its NatHERS for existing homes mode — a CSIRO-developed, cloud-based energy rating tool that is the primary software accredited for this program. It uses the Chenath thermal physics engine and additional appliance modules to model both the thermal star rating and the Whole of Home score.
How long does it take to receive the certificate?
Turnaround times vary by assessor and company. Certificates are typically issued within 3–5 business days following the on-site visit, once all data has been processed and modelled.
Can a NatHERS certificate help with a green home loan?
Yes. Many Australian banks and lenders accept a NatHERS Home Energy Rating Certificate as supporting documentation for green home finance products, including loans for energy-efficient renovations and upgrades. The certificate provides lenders with an objective, government-backed record of the home’s current energy performance.
What can homeowners do to improve their rating?
Common improvements include upgrading ceiling and underfloor insulation, sealing draught gaps, replacing single-glazed windows, adding external shading, and installing high-efficiency reverse-cycle heating and cooling, heat pump hot water systems, rooftop solar PV and battery storage. A qualified assessor’s certificate will include tailored recommendations specific to the property.
Can a home be re-assessed after upgrades are made?
Yes. A follow-up assessment can be conducted by an accredited assessor after upgrades are completed. This produces an updated Home Energy Rating Certificate that reflects the improved performance — which can be used for property listings, updated finance applications or tracking progress against sustainability goals.
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