NatHERS Assessment Process
The time needed for a NatHERS assessment depends on the project, the quality of the documentation and whether the design already supports the required thermal performance pathway.
A NatHERS assessment can often move quickly when the project documents are clear, the design is straightforward and the thermal pathway is already close to compliance. Timing can increase when plans are incomplete, construction details are unclear, window schedules are missing or the home needs design changes to reach the required star rating.
A NatHERS assessment is based on the specific design of the home. The assessor needs to review the plans, understand the building form, model the rooms and zones, enter construction details, assess glazing and shading and calculate the predicted heating and cooling demand.
A simple detached home with complete plans and clear specifications will usually be faster to assess than a complex project with split levels, multiple dwellings, raked ceilings, large glazing areas, incomplete details or unresolved construction systems.
The timing is also affected by what happens after the first model is run. If the design does not meet the required pathway, the project team may need to review possible changes before the final documentation can be completed.
The process usually begins with the assessor reviewing the project documents. This includes the site plan, floor plans, elevations, sections, construction details, insulation values, glazing information, shading details and roof colour where known.
The home is then modelled in accredited NatHERS software. The assessor enters the dwelling geometry, orientation, room zones, building fabric, windows, doors, shading and other relevant details. The software then calculates the predicted thermal performance of the home in its local climate.
If the result meets the required pathway, the assessment can proceed toward final documentation. If not, the assessor may need to test design or specification changes to help improve the rating.
The assessment itself is only one part of the timing.
Clarifications, missing information and design changes often have a bigger impact on turnaround than the modelling process alone.
A straightforward single dwelling with complete documents is usually easier to assess. If the plans are clear, the window schedule is available and construction details are known, the assessor can model the home with fewer interruptions.
A simple project can still need careful modelling, especially if it has large glazing areas, limited shading, challenging orientation or a rating target that is difficult to reach. But clear documentation usually makes the process more efficient.
For these projects, the biggest timing risk is often not complexity, but missing or inconsistent information.
More complex homes can take longer because they require more modelling judgement and documentation review. Split levels, raked ceilings, voids, exposed floors, multiple roof forms, large glazing areas and unusual construction systems can all add complexity.
Townhouses and apartments can also take longer because each dwelling may need to be considered separately. A middle townhouse, end townhouse, upper apartment and ground floor apartment may all perform differently because of exposure, orientation and shared construction conditions.
This does not mean complex projects are a problem. It simply means they benefit from earlier coordination and clearer information.
• Project size and number of dwellings
• Quality and completeness of drawings
• Window and door schedule availability
• Construction detail clarity
• Insulation, glazing, roof colour and shading information
• Whether design changes are needed to reach the required rating
The most common delays come from missing or unclear information. If the assessor does not have enough detail to model the home accurately, the project may need clarification before the assessment can progress.
Common delay points include incomplete sections, missing window schedules, unclear glazing performance, unresolved insulation values, unknown roof colour, unclear shading dimensions and construction details that do not match across drawings and specifications.
Changes after modelling has started can also affect timing. If window sizes, roof forms, floor construction or insulation values change, the assessment may need to be updated.
If the first NatHERS result does not meet the required pathway, the project team may need to consider changes. These changes could be small or significant, depending on why the rating is low.
Possible improvements may include glazing upgrades, reduced window areas, improved shading, insulation changes, roof colour adjustments, floor insulation or construction detail revisions. The right change depends on what is influencing the model.
This review process can add time, especially if the changes need approval from the architect, builder, client or developer before the final documentation can be issued.
A NatHERS delay is not always caused by the assessor being slow.
Often, timing depends on whether the design is complete, coordinated and already close to the required performance level.
A preliminary NatHERS review can be helpful when the design is still developing. It can show whether the home is generally on track or whether there are likely thermal performance issues that need attention.
This can save time later because major issues can be identified before the plans are fully documented. It is usually easier to adjust orientation, glazing, shading or construction details earlier than after approval drawings are complete.
A preliminary review does not replace the final assessment. The final NatHERS result still needs to be based on confirmed plans and specifications that match the project being approved and built.
The best way to avoid delays is to provide clear, coordinated documentation. The assessor needs to understand the design, construction and performance details without having to guess or repeatedly request missing information.
• Site plan, floor plans, elevations and sections
• Project address and orientation
• Window and door schedules
• Glazing and frame performance where known
• Wall, roof, ceiling and floor construction details
• Insulation values and locations
• Shading, roof colour and floor covering details where relevant
For a more complete checklist, see our guide to what documents are needed for a NatHERS assessment.
NatHERS often supports the residential energy compliance pathway, so timing can affect the approval process. If the assessment is left until the end, the project may discover late that it needs design or specification changes to meet the required performance level.
This is especially important for projects targeting or required to achieve a 7 Star Rating, or for NSW projects where NatHERS may sit within the BASIX pathway.
Early assessment gives the project team time to resolve performance issues without disrupting lodgement, costing or construction documentation.
Australian homes vary widely in climate, site conditions and design complexity. A home with large west facing glazing, limited shading, exposed floors or raked ceilings may need more careful review than a simpler design in a mild climate.
Timing should therefore be considered part of the design process. If the project has known thermal performance pressure points, it is better to identify them early than wait until the documentation is nearly complete.
A well timed NatHERS assessment can help the design stay aligned with comfort, compliance and construction practicality.
Certified Energy provides NatHERS assessments for new homes, townhouses and multi residential projects across Australia. Our team can review your documentation, model the design and help identify whether any design or specification changes may be needed.
Where documentation is still developing, we can help clarify what information is needed to progress the assessment. We can also help connect NatHERS with related requirements such as NatHERS, BASIX, 7 Star Rating and Whole of Home.
For the broader assessment framework, visit our NatHERS Knowledge Hub.
The time needed for a NatHERS assessment depends on project complexity, documentation quality, assessor workload and whether design changes are needed. Simple projects with clear documents are usually faster than complex or incomplete projects.
What can delay a NatHERS assessment?A NatHERS assessment can be delayed by missing plans, unclear construction details, incomplete window schedules, unresolved insulation values, unclear shading or changes to the design after modelling has started.
Can a NatHERS assessment be started early?Yes. A preliminary NatHERS review can often begin before every detail is final, but the final assessment needs confirmed plans and specifications that match the project being approved and built.
Does a failed first result make the assessment take longer?It can. If the first result does not meet the required pathway, the project team may need to review glazing, insulation, shading, roof colour, floor construction or other design changes before the final assessment can be issued.
How can I help the assessment move faster?Provide clear plans, elevations, sections, window schedules, construction details, insulation values, glazing information, shading details and roof colour information where known.