NatHERS and BASIX
NatHERS vs BASIX: What Is the Difference?
NatHERS and BASIX are closely connected in NSW residential projects, but they are not the same thing. NatHERS focuses on thermal performance. BASIX is a broader NSW sustainability requirement.
The difference in brief
NatHERS is a national framework for assessing the thermal performance of homes. It produces a star rating that reflects the predicted heating and cooling needs of the design. BASIX is a NSW planning requirement that applies to residential development and covers water, energy and thermal performance commitments. In many NSW projects, NatHERS modelling helps support the thermal performance part of BASIX.
What NatHERS assesses
NatHERS stands for the Nationwide House Energy Rating Scheme. It assesses the thermal performance of a home design and produces a star rating out of 10. The rating estimates how much heating and cooling the home may need to stay comfortable in its local climate.
A NatHERS assessment looks closely at the building fabric. This includes orientation, room layout, insulation, glazing, shading, roof colour, floor construction, wall and roof systems, thermal mass and local climate data.
In simple terms, NatHERS helps answer the question: how well is this home expected to manage heat and cold before relying on mechanical heating or cooling?
What BASIX assesses
BASIX stands for the Building Sustainability Index. It is specific to NSW and forms part of the development approval process for many residential projects. BASIX is broader than NatHERS because it considers several sustainability commitments, not only thermal performance.
A BASIX certificate can include requirements and commitments relating to water efficiency, energy use and thermal performance. Depending on the project, it may also record details such as fixtures, appliances, hot water systems, heating and cooling systems, insulation, glazing and other commitments that need to be carried through the design and construction documentation.
In simple terms, BASIX helps answer a broader NSW planning question: does this residential project meet the required sustainability standards for approval?
The practical distinction
NatHERS: thermal modelling and star rating for the home’s building fabric.
BASIX: NSW sustainability certificate covering water, energy and thermal performance commitments.
How NatHERS and BASIX work together
In NSW, NatHERS and BASIX often appear together because NatHERS modelling can be used to support the thermal performance component of a BASIX assessment. The NatHERS result helps demonstrate how the building fabric performs, while the BASIX certificate records the broader project commitments required for NSW approval.
This means the two are connected, but they do different jobs. NatHERS provides the thermal rating. BASIX translates the project’s sustainability pathway into commitments that must be reflected in the documentation and carried through the approval process.
For project teams, the important point is coordination. A change to glazing, insulation, shading, roof colour, hot water or heating and cooling systems may affect the BASIX certificate, the NatHERS result or both.
Do you need NatHERS, BASIX or both?
For NSW residential projects, BASIX is often the required approval document. NatHERS may be used as part of the pathway to demonstrate thermal performance, depending on the project type and assessment method.
For residential projects outside NSW, BASIX generally does not apply, but NatHERS may still be relevant as part of the applicable state, territory or National Construction Code energy efficiency pathway.
Because requirements can depend on location, building class, approval pathway and project scope, it is worth confirming the right pathway before assuming that one document replaces the other.
A useful way to think about it
If the question is about the thermal star rating of the home, you are usually talking about NatHERS.
If the question is about the NSW sustainability certificate needed for approval, you are usually talking about BASIX.
If the project is in NSW, there is a strong chance the two need to be considered together.
Common points of confusion
One common misunderstanding is that a NatHERS certificate and a BASIX certificate are interchangeable. They are not. A NatHERS result may support part of the BASIX pathway, but BASIX has its own certificate, commitments and approval role in NSW.
Another common issue is treating BASIX as a final formality. Because BASIX commitments can affect plans, specifications and construction documents, it is better to consider BASIX and NatHERS before the design is fully locked in.
A third point of confusion is assuming that solar panels or efficient appliances will automatically solve thermal performance issues. They may help with broader energy outcomes, but the NatHERS star rating is still strongly shaped by the building fabric itself.
Design considerations for NSW homes
For NSW homes, NatHERS and BASIX should be considered as connected parts of the same design and approval process. Thermal performance can influence BASIX outcomes, while BASIX commitments can influence the documentation that builders, certifiers and project teams rely on.
The most common pressure points are glazing, insulation, shading, roof colour, heating and cooling systems, hot water and water fixtures. Changes to these items after a certificate is prepared can create inconsistencies or require updates.
For smoother approvals, the best time to resolve the pathway is before final documentation. This allows the design, NatHERS modelling and BASIX commitments to align clearly.
Working with Certified Energy
Certified Energy prepares NatHERS assessments and BASIX documentation for residential projects across NSW. Our team reviews the plans, models the thermal performance pathway and helps align the required commitments with the project documentation.
Where relevant, we can also help connect the project with related requirements such as NatHERS, BASIX, 7 Star Rating and Whole of Home.
For a broader explanation of NatHERS and residential thermal performance, visit our NatHERS Knowledge Hub. For NSW specific guidance, visit our BASIX Knowledge Hub.
FAQ
Are NatHERS and BASIX the same thing?
No. NatHERS is a national thermal performance rating framework. BASIX is a NSW sustainability requirement that covers water, energy and thermal performance for residential development.
Does BASIX use NatHERS?
In many NSW residential projects, NatHERS modelling is used to support the thermal performance component of BASIX. The BASIX certificate then records the broader project commitments.
Do I need BASIX outside NSW?
BASIX is specific to NSW. Residential projects outside NSW may still need NatHERS or other energy efficiency documentation, depending on the relevant state, territory and approval pathway.
Can NatHERS change the BASIX outcome?
Yes, where NatHERS is used for the thermal performance pathway, the modelling result can affect the BASIX thermal performance outcome and the commitments recorded in the certificate.
Which should be done first, NatHERS or BASIX?
They are best considered together. The NatHERS result can inform the BASIX thermal pathway, while BASIX commitments need to be reflected in the project documentation for approval and construction.
