NSW Residential Compliance Guide
BASIX is the NSW residential sustainability framework. Where the BASIX Simulation method applies, NatHERS modelling can be used to demonstrate the dwelling’s thermal-performance outcome against the applicable BASIX targets.
BASIX and NatHERS are often discussed together on NSW residential projects, but they are not interchangeable systems. BASIX is the state-based assessment and submission framework. NatHERS is a national residential energy-rating framework that can be used within one of the BASIX thermal-performance methods.
Under the Simulation method, an accredited assessor models the proposed dwelling using approved NatHERS software. The resulting star rating and heating and cooling loads are then used to support completion of the BASIX thermal-performance section.
This guide focuses specifically on how the BASIX thermal pathway and the 7 Star NatHERS benchmark relate. For the complete NSW submission process, certificate requirements and wider water, energy and materials commitments, see the BASIX submission guide.
In Brief
BASIX
The NSW assessment and certification framework covering residential water, energy and thermal performance, together with applicable materials reporting.
NatHERS Simulation
One method for demonstrating thermal performance within BASIX using accredited modelling, a star rating and calculated heating and cooling loads.
7 Star Target
The higher thermal benchmark applying to many NSW homes using the Simulation method, subject to dwelling type, climate zone and applicable BASIX provisions.
A NatHERS result can support the BASIX thermal-performance section, but it does not replace the BASIX Certificate or demonstrate every BASIX commitment applying to the development.
Framework Ownership
BASIX forms part of the NSW development assessment process for residential projects within its scope. The BASIX tool records project information and assesses the proposed development against the applicable state standards.
The assessment is broader than a NatHERS thermal rating. Depending on the project, BASIX addresses water use, thermal performance, operational energy and information relating to building materials.
The resulting BASIX Certificate records commitments that must be reflected in the development documentation and, where applicable, carried through into construction. These may include insulation, glazing, shading, fixtures, hot-water systems, heating and cooling equipment, solar generation and other project selections.
NatHERS modelling therefore sits within a wider NSW compliance pathway. It supplies thermal-performance information where the Simulation method is selected, but BASIX remains the governing assessment and submission framework for the project.
Simulation Pathway
NatHERS is used when the project follows the BASIX Simulation method for thermal performance. An accredited assessor creates a model of the proposed dwelling using approved NatHERS software and the documented project information.
The model produces a thermal star rating together with calculated heating and cooling loads. These results are reviewed against the applicable BASIX targets and entered into the BASIX assessment using the required assessor documentation.
The star rating provides a high-level expression of thermal performance. BASIX also checks the underlying heating and cooling loads against separate limits for the climate and dwelling type.
For broader information about NatHERS software, modelling inputs and certificates outside the BASIX relationship, see the NatHERS Knowledge Hub.
Thermal-Performance Options
Simplified Pathway
A web-based Deemed-to-Satisfy method for eligible single dwellings using common construction methods. It estimates heating and cooling loads through BASIX inputs and does not produce a NatHERS star-rating certificate.
Modelled Pathway
A detailed thermal assessment completed by an accredited assessor using approved NatHERS software. It can address a wider range of materials, complex designs and multi-dwelling developments.
Alternative Standard
A pathway for eligible single dwellings designed and constructed in accordance with the Passive House standard using the required specialist modelling and certification process.
A project using the DIY or Passive House method should not be described as having achieved a 7 Star NatHERS rating unless a separate NatHERS simulation has actually produced that result. Each BASIX method has its own assessment basis and documentation requirements.
Requirement Boundaries
No. A 7 Star NatHERS rating is relevant where the project uses the Simulation method and the applicable BASIX thermal target requires that result.
A single dwelling may instead use the DIY method where it satisfies the method’s eligibility limitations. A qualifying single dwelling designed to the Passive House standard may use the separate Passive House method.
Project location also matters. The higher thermal standards were not applied as a 7 Star requirement in NatHERS climate zones 9, 10 and 11. Projects in these areas remain subject to the applicable BASIX thermal standards rather than automatically being assessed against a 7 Star target.
The applicable BASIX version, project type, climate zone, approval history and selected thermal method should therefore be confirmed before treating seven stars as the required outcome.
Detached and Attached Homes
For detached and attached houses subject to the higher BASIX standards and using the Simulation method, the thermal-performance target is generally a minimum 7 Star NatHERS result together with compliance with the applicable heating and cooling caps.
The star result is produced from the complete dwelling model. It reflects the interaction between climate, orientation, building form, room layout, glazing, external shading, insulation, thermal mass and documented construction.
Reaching seven stars does not remove the need to check the separate load limits. A dwelling may reach the headline star target while still requiring further work if its heating or cooling demand exceeds a relevant BASIX cap.
For a detailed explanation of what the thermal benchmark means outside the NSW submission relationship, see the 7 Star NatHERS requirements guide.
Multi-Dwelling Developments
For apartment developments subject to the higher standards, the 7 Star target is generally assessed across the building rather than applied as an identical rating to every apartment.
Building Average
The rated apartments must collectively achieve the applicable average thermal star result across the development.
Individual Minimum
A stronger rating elsewhere in the building cannot be used to offset an individual apartment falling below the applicable minimum.
Apartment orientation, level, external exposure and glazing can create substantial differences between dwellings in the same building. Corner apartments, upper levels and highly exposed façades may require different design responses from more protected apartments.
The development must also address the applicable average heating and cooling caps and the maximum caps applying to individual apartments. The building average should therefore be reviewed alongside the performance of each dwelling.
Beyond the Star Number
The NatHERS star rating combines heating and cooling performance into one overall result. BASIX also applies separate limits to prevent a dwelling from relying on very strong performance in one season to compensate for excessive demand in the other.
Heating Load
The modelled energy required to maintain the prescribed indoor conditions during colder periods must remain within the relevant BASIX limit.
Cooling Load
The modelled energy required during warmer periods must also remain below the applicable BASIX cap for the climate and dwelling type.
A project can therefore need design refinement even after reaching the nominated star rating. Excessive western glazing may create a cooling problem, while poor insulation or difficult winter solar access may cause the heating cap to be exceeded.
The assessment should be reviewed as a set of related outcomes: overall star rating, heating load, cooling load and, for apartments, building-average and individual-dwelling results.
Connected BASIX Sections
The BASIX thermal-performance and energy sections assess different aspects of the project, but they are connected. The heating and cooling loads established through the thermal pathway are combined with the selected heating and cooling equipment in the Energy section.
Lower thermal loads can reduce the modelled energy associated with maintaining indoor conditions and may help the project achieve its BASIX Energy target. The final Energy outcome will also depend on household systems and other project selections entered into BASIX.
Thermal Performance
Establishes the dwelling’s modelled heating and cooling loads through the selected BASIX thermal method.
Energy Systems
Records the relevant heating, cooling, hot-water, lighting, cooking, solar and other energy-related selections.
BASIX Energy Result
Combines the applicable inputs within the NSW BASIX calculation to determine whether the project satisfies its Energy target.
A 7 Star thermal result does not, by itself, demonstrate that the BASIX Energy section will pass. The building fabric and household energy selections must both be coordinated within the wider BASIX assessment.
Assessment Documentation
NSW Submission Document
Thermal Assessment Evidence
The documents should be treated as connected but distinct. A NatHERS thermal result does not replace the BASIX Certificate, and a BASIX Certificate does not remove the need for the supporting assessor documentation where Simulation has been used.
Project Coordination
The NatHERS model, BASIX assessment and architectural documentation should describe the same proposed development. Differences between them can create approval questions, certification issues or the need for reassessment.
Building Fabric
Wall, roof, ceiling and floor systems should match the construction types and insulation values represented in the thermal model and BASIX commitments.
Openings
Opening dimensions, locations, frame types, glass performance and operability should remain consistent across plans, schedules and assessment inputs.
Solar Control
Modelled shading should be supported by clearly documented dimensions, projections and locations in the architectural information.
Energy Commitments
Heating, cooling, hot-water and solar selections should remain aligned with the BASIX Energy inputs and final project specifications.
Where the design changes after the assessments have been completed, the affected NatHERS inputs and BASIX commitments should be reviewed before the existing documentation is relied upon.
Common Misunderstandings
BASIX is not another name for NatHERS. BASIX is the wider NSW framework; NatHERS can support its Simulation method.
Not every BASIX project needs a NatHERS certificate. Eligible single dwellings may use the DIY or Passive House thermal method.
Seven stars is not the only thermal check. Heating and cooling loads must also satisfy the applicable BASIX caps.
Every apartment does not necessarily need 7 Stars. The higher standard uses a building average with a separate individual minimum.
A NatHERS result does not replace the BASIX Certificate. The BASIX Certificate records the broader state-based assessment and project commitments.
Seven stars does not automatically pass BASIX Energy. Household systems and other energy-related inputs still affect the BASIX Energy result.
The same target does not apply in every NSW climate zone. The applicable BASIX standard should be confirmed for the project location.
Thermal Design Review
Where the model falls below the required star outcome or exceeds a heating or cooling cap, the proposed design will usually need to be reviewed before the Simulation results can support a passing BASIX thermal assessment.
The required response depends on what is driving the result. Potential changes may involve glazing, external shading, insulation, construction, ceiling fans, window area or the performance of a particular room or apartment.
The BASIX relationship determines which result must be achieved. The detailed design methodology for improving the NatHERS model belongs to a separate design question.
For practical design guidance, see How to Design a 7 Star NatHERS Home.
Frequently Asked Questions
No. BASIX is the NSW residential sustainability assessment and submission framework. NatHERS is a national energy-rating framework used within the BASIX Simulation method to establish thermal-performance results.
Does every BASIX project require a NatHERS assessment?No. BASIX provides the DIY, Simulation and Passive House thermal-performance methods. NatHERS modelling is required where the Simulation method is selected or required for the development.
Do all NSW houses need to achieve 7 Stars?Seven stars is the applicable Simulation benchmark for many houses subject to the higher BASIX standards. The actual requirement depends on the project’s climate zone, BASIX version, dwelling type, approval circumstances and selected thermal method.
Does every apartment need to achieve 7 Stars?No. Under the higher standard, apartment developments generally need an average 7 Star result across the building, with no individual apartment below 6 Stars. Average and individual heating and cooling caps also apply.
Can a dwelling achieve 7 Stars and still fail BASIX thermal performance?Potentially. BASIX also checks separate heating and cooling caps. A dwelling may reach the overall star target while exceeding one of the applicable seasonal load limits.
Does a 7 Star result automatically pass the BASIX Energy section?No. The thermal loads contribute to the Energy calculation, but the Energy result also depends on the household systems and other project inputs recorded in BASIX.
Does the NatHERS certificate replace the BASIX Certificate?No. The NatHERS and assessor documentation supports the Simulation results. The BASIX Certificate remains the NSW document recording the wider assessment outcome and project commitments.
Can the BASIX DIY method produce a NatHERS star rating?No. The DIY method estimates heating and cooling loads from the information entered into BASIX. A certified NatHERS star rating is produced through accredited simulation software.
What happens if the plans change after BASIX and NatHERS are completed?Changes to glazing, shading, insulation, construction, dwelling layout or fixed systems may affect one or both assessments. Relevant changes should be reviewed before the existing certificates and commitments are relied upon.
Related Guidance
NSW Residential Assessment
Certified Energy can review the available plans, project location and construction information to help confirm the relevant BASIX pathway, thermal assessment requirements and documentation needed for the proposed development.
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