NatHERS Assessment Pathways
NatHERS is becoming part of two related but different conversations in Australian housing.
For many years, NatHERS has been most commonly understood as a new-home energy rating pathway. Architects, builders, certifiers and energy assessors use NatHERS software to assess the thermal performance of proposed homes before they are built.
Now, NatHERS for existing homes is expanding this framework into dwellings that have already been built.
The two pathways are connected, but they should not be treated as the same thing. A new home NatHERS assessment usually supports design-stage compliance. A NatHERS existing homes assessment is more focused on real built performance, current dwelling condition and upgrade potential.
Quick Answer
A new home NatHERS assessment is usually completed before construction. It assesses a proposed residential design using approved software and helps demonstrate energy efficiency compliance for a new dwelling or major renovation.
A NatHERS existing homes assessment is different. It looks at a home that has already been built and helps describe its current energy performance, comfort and improvement potential.
The key difference is purpose. New home NatHERS is mostly about proposed design compliance. NatHERS for existing homes is about assessing the real dwelling as it stands and helping owners, buyers, renters or project teams understand performance and possible upgrades.
Both pathways use the broader NatHERS framework, but they answer different questions.
A new home NatHERS assessment is an energy rating assessment for a proposed dwelling. It is commonly used for new houses, townhouses, apartments and major residential renovations.
The assessor works from documentation such as architectural drawings, elevations, sections, construction details, glazing schedules, insulation specifications and other design information. The home is modelled in approved NatHERS software to assess how well the proposed design is expected to perform thermally.
The output is generally used to support building approval, planning, certification or construction documentation.
In simple terms, a new home NatHERS assessment asks: how well is this proposed home expected to perform if it is built as designed?
New home NatHERS focuses heavily on the thermal performance of the building shell.
It considers elements such as:
Under NCC 2022, new homes are also subject to higher energy efficiency expectations, including a stronger connection between thermal performance and Whole of Home energy use. This is where 7 Star Energy Rating requirements become important for new residential design.
NatHERS for existing homes is the expansion of the NatHERS framework into homes that have already been built.
Instead of modelling a proposed design from architectural plans alone, an existing homes assessment responds to the real dwelling. It considers the home’s current construction, systems, condition, comfort and upgrade opportunities.
In simple terms, NatHERS Existing Homes asks: how does this actual home perform now, and what could improve it?
An existing homes assessment needs to deal with the realities of a built dwelling.
Depending on the assessment pathway and available information, it may consider:
The assessment is not simply a new-home rating copied onto an older dwelling. Existing homes often contain unknowns. Plans may be missing. Renovations may have changed the building over time. Insulation may be incomplete or uncertain. Installed systems may be old, inefficient or poorly matched to the dwelling.
The most important distinction is this: new home NatHERS assesses a proposed design. NatHERS existing homes assesses an actual dwelling.
This difference affects almost everything else: the documentation, the assumptions, the purpose, the audience, the timing and the way results are used.
A new home assessment is usually completed before construction. It helps answer whether the proposed home can meet energy efficiency requirements before it is approved and built.
An existing home assessment happens after the home exists. It is more concerned with what the building is doing now and how it could be improved.
This is the semantic difference Certified Energy should make very clear: new home NatHERS is a design compliance pathway. NatHERS existing homes is a built performance and upgrade pathway.
For new homes, the assessor usually relies on design documentation. The model is based on what is specified to be built.
Common inputs include:
For existing homes, the input process is different. The assessor may need to use available drawings, homeowner information, site observations, photos, installed system details, utility context and reasonable assumptions where documentation is incomplete.
A new home NatHERS assessment usually supports compliance documentation. Its result may be used by builders, designers, certifiers, developers and approval authorities.
An existing homes assessment is more likely to support understanding, disclosure, upgrade planning or future program requirements.
The output may help a homeowner understand:
Both pathways can produce energy performance information, but the decision context is different.
Timing is one of the clearest differences.
A new home NatHERS assessment is usually carried out during design or documentation. Ideally, it happens early enough to influence design decisions before the project is locked in. This allows the team to adjust glazing, shading, insulation, orientation, construction systems or layout before building approval or construction.
An existing homes assessment happens after the home has been built. It cannot change the original design, but it can help inform upgrade decisions. This may include retrofit planning, insulation improvements, system replacement, draught sealing, solar, electrification or future renovation works.
The earlier a new-home assessment happens, the more design influence it can have. The clearer an existing-home assessment is, the more useful it becomes for staged upgrades.
New home NatHERS is often connected to compliance.
In many jurisdictions, new residential development must demonstrate that it meets energy efficiency requirements. NatHERS is one of the major pathways used to support this. Recent NCC changes increased the minimum star rating or equivalent for new homes and introduced an annual energy use budget for the entire home, including major fixed appliances, solar and batteries.
Existing homes are currently in a different position. NatHERS for existing homes is part of a developing national pathway, including trials, staged rollout and future disclosure possibilities. It should not be presented as identical to new-home compliance.
In NSW, BASIX is a critical part of residential development compliance.
BASIX applies to new residential development in NSW and some renovations, and covers water, energy use and thermal performance.
This means a new residential project in NSW may involve BASIX and NatHERS depending on the project type and pathway.
An existing homes rating is different. It is not simply a BASIX certificate for an old house. It is a performance assessment pathway for a dwelling that already exists.
The 7 Star Energy Rating shift is mainly connected to new home energy efficiency standards under NCC 2022 and state implementation.
For new homes, 7 Star requirements influence design, modelling and compliance documentation. Design teams may need to improve glazing, shading, insulation, thermal mass, ventilation and overall building fabric performance to reach the required outcome.
For existing homes, the conversation is different. A home energy rating may still use a star-based language to explain performance, but the purpose is not the same as proving a proposed new dwelling meets current new-home code requirements.
VURB, or Verification Using a Reference Building, is a separate compliance method used in certain new residential design situations.
It is not the standard comparison point for existing home ratings. However, it may be relevant when discussing the range of pathways available for new residential compliance, especially where a proposed design needs to be assessed against a reference building approach.
For this article, VURB assessment pathways should only be understood in the context of new-home compliance. It should not be framed as an existing homes rating pathway.
A homeowner with an established dwelling may need an existing homes assessment if they want to understand comfort, running costs, upgrade priorities or future disclosure readiness.
A person building a new home may need a new home NatHERS assessment to support design compliance, approval or certification.
An architect or building designer may need new home NatHERS advice during design development to avoid costly late-stage changes.
A renovator may need both forms of thinking. If the project is a major renovation, there may be compliance requirements connected to the proposed works. But the existing dwelling’s current condition may also need to be understood before deciding what upgrades make sense.
A real estate or property professional may increasingly need to understand existing home ratings as disclosure pathways develop.
One misunderstanding is that NatHERS always means the same thing. It does not. A NatHERS assessment for a proposed new dwelling serves a different role from an assessment of an established home.
Another misunderstanding is that existing home ratings are only about energy bills. Energy bills matter, but they are affected by household behaviour, tariffs and occupancy. A rating can help explain the dwelling’s performance more directly.
A third misunderstanding is that a 7 Star new home and a rated existing home should be compared as if they are part of the same compliance process. They are related through energy performance language, but the policy and project context is different.
A fourth misunderstanding is that BASIX, NatHERS, VURB and existing home ratings are interchangeable. They are not. Each pathway has a different purpose, jurisdictional context and documentation role.
For new homes, NatHERS should be considered early. If the rating is left too late, the design team may need to make rushed changes to glazing, insulation, shading or construction systems.
For existing homes, the assessment is most useful when it is connected to real decisions. This may include whether to insulate, replace windows, install solar, electrify appliances, improve airtightness, upgrade hot water or stage renovation works.
For NSW projects, the distinction between BASIX, new home NatHERS and existing home ratings should be made clearly. A new dwelling may need BASIX and NatHERS as part of approval. An established home may need an existing homes assessment for advice, disclosure readiness or upgrade planning.
For consultants, the opportunity is to help clients understand the right pathway before the wrong type of assessment is requested.
Assessment Pathway Advice
Certified Energy can assist with both new-home NatHERS and emerging existing-home assessment pathways.