NatHERS Assessment Process
What Happens If a Home Fails NatHERS?
If a home does not meet the required NatHERS rating, the design is not automatically abandoned. It usually means the project team needs to understand what is holding the rating back and adjust the design or specifications before final documentation.
Low NatHERS ratings in brief
If a home does not achieve the required NatHERS rating, the assessment result needs to be reviewed. The assessor and project team can usually identify which parts of the design are increasing heating or cooling demand. Improvements may include glazing changes, better shading, insulation upgrades, roof colour changes, floor insulation, construction detail updates or other design refinements.
What “failing NatHERS” really means
When people say a home has “failed NatHERS”, they usually mean the modelled star rating is below the performance level required for the project’s compliance pathway. It does not mean the home cannot be built. It means the thermal performance pathway needs to be resolved before the assessment can be finalised.
The NatHERS result reflects how much heating and cooling the home is predicted to need in its local climate. If the rating is too low, the model is showing that the home is expected to need more heating or cooling than the required pathway allows.
The next step is to identify why. A low result may come from one major issue or from several smaller issues across glazing, shading, insulation, orientation, roof colour, floor construction or building form.
A low rating does not always mean a bad design
A low NatHERS rating does not automatically mean the home is poorly designed. Sometimes the design intent is strong, but the thermal performance details are not yet aligned. A beautiful home can still have thermal pressure points that need to be resolved.
For example, the home may have large areas of unshaded glazing, a dark roof in a hot climate, exposed floors, limited insulation depth, poor solar control or a challenging orientation. These features may be part of the architectural design, but they still need to work within the thermal performance pathway.
In many cases, the solution is not to redesign the whole home. It is to adjust the specific elements that are affecting the rating most.
The practical point
A low NatHERS result is a design signal.
It shows where the home may need refinement so the final design can meet the required thermal performance pathway.
What happens after the first result is too low?
If the first NatHERS result is below the required level, the assessor will usually review the model and identify the main factors affecting performance. This may involve checking glazing, shading, insulation, roof colour, floor construction, orientation and climate response.
The project team can then consider possible improvements. Some changes may be simple, such as increasing ceiling insulation or adjusting roof colour. Others may require more design coordination, such as changing window sizes, adding external shading or reviewing floor construction.
Once agreed changes are made, the home can be re modelled to confirm whether the updated design reaches the required rating.
Common ways to improve a low NatHERS result
• Improve glazing performance or frame type
• Reduce or adjust difficult window areas
• Add or improve external shading
• Increase insulation where it has the strongest effect
• Review roof colour, floor construction or exposed floors
• Coordinate thermal mass, solar access and climate response
Glazing is often a key pressure point
Windows and glazed doors can strongly affect NatHERS ratings. Large areas of glass, poor glazing performance or difficult orientations can increase heating or cooling demand.
A low rating may improve if the project uses better glazing performance, different frame systems, reduced glass areas or more suitable window placement. The best response depends on whether the home is losing too much heat, gaining too much heat or both.
For more detail, see our guide to how window design affects NatHERS ratings.
Shading can change the result
Shading can be one of the most effective ways to reduce unwanted heat gain. This is especially true where the home has exposed glazing, large windows or east and west facing façades that receive low angle sun.
Good shading should respond to orientation. A shading strategy that works well on a north facing window may not work on a west facing window. External shading is usually more effective than relying only on internal blinds because it can reduce heat before it reaches the glass.
For more detail, see our guide to shading and solar heat gain.
Common misunderstanding
Improving a failed NatHERS result does not always mean choosing the most expensive windows or adding maximum insulation everywhere.
A targeted change that addresses the actual thermal issue is usually more useful than a generic upgrade.
Insulation may need review
Insulation can help improve a low NatHERS rating when heat transfer through the ceiling, roof, walls or floor is affecting the result. The impact depends on where the insulation is located and whether it matches the actual construction system.
Increasing insulation may be useful, but it is not always the only answer. If overheating is caused by unshaded glazing, for example, improving shading or glazing may be more effective than only increasing insulation.
For more detail, see our guides to how insulation affects NatHERS ratings and ceiling insulation and NatHERS outcomes.
Roof colour and roof heat gain
Roof colour can affect cooling demand, particularly in warmer climates or homes with large roof exposure. A darker roof can increase heat absorption, which may place more pressure on the ceiling insulation and cooling performance of the home.
Changing roof colour can sometimes be a practical way to improve the result, depending on the climate, roof form, design intent and approval stage. It should still be tested in the model rather than assumed to solve every issue.
Roof colour is one example of a decision that may be simple early in design but harder to change once selections, approvals or estate requirements are fixed.
Floor construction and thermal mass
Floor construction can also affect a low NatHERS result. Suspended floors, exposed floors over external air, slabs, floor coverings and floors over garages can each influence heating and cooling demand.
Thermal mass may support the rating when it is exposed to the interior and coordinated with solar access and shading. But poorly managed solar gain can also cause mass to store unwanted heat.
For more detail, see our guides to floor construction and thermal performance and thermal mass and NatHERS performance.
Questions to ask after a low result
• Is the issue mainly heating demand, cooling demand or both?
• Are windows too large, exposed or low performing?
• Is shading matched to the right orientations?
• Are insulation values and locations clear?
• Is roof colour contributing to heat gain?
• Are floor construction, thermal mass and climate response working together?
Can changes affect the architecture?
Some NatHERS improvements are specification based and may have little visual impact. Others can affect the architecture, especially if they involve window sizes, shading elements, roof colour, façade design or room layout.
This is why early review is helpful. If the rating is checked before the design is fully locked in, the project team has more options to improve performance without compromising the design intent or creating major documentation changes.
Late changes can still work, but they may require more coordination with the architect, builder, client, certifier or developer.
How this connects to compliance
If a home does not meet the required NatHERS rating, the final assessment usually cannot be issued on that basis until the design is improved or another compliant pathway is resolved. This can affect approval timing if the assessment is left late.
For many current projects, this may relate to achieving a 7 Star Rating. In NSW, NatHERS may also connect with the BASIX thermal pathway, so changes need to remain consistent with the certificate and approval documents.
Where broader residential energy requirements apply, the project may also need to consider Whole of Home, which addresses the home’s fixed appliances and energy systems.
Design considerations for Australian homes
Australian homes need to respond to climate, site orientation and building fabric. A low NatHERS result may be telling the project team that the home is not yet well matched to its local conditions.
The best improvement strategy is usually project specific. A home in a cool climate may need a different response from a home in a hot humid, hot dry, coastal or inland climate.
The goal is not just to pass a rating. It is to create a home that is more comfortable, more efficient and more coherent as a thermal design.
Working with Certified Energy
Certified Energy provides NatHERS assessments for new homes, townhouses and multi residential projects across Australia. If a design does not reach the required rating, our team can help identify the main performance pressure points in the model.
Where needed, we can help project teams understand whether the rating is being affected by glazing, shading, insulation, roof colour, floor construction, thermal mass, orientation or climate zone. 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.
FAQ
What happens if a home fails NatHERS?
If a home does not meet the required NatHERS rating, the design or specifications usually need to be reviewed and adjusted before the final assessment can be issued.
Can a low NatHERS rating be improved?
Yes. A low NatHERS rating can often be improved through changes to glazing, shading, insulation, roof colour, floor construction, thermal mass, orientation or other building fabric details.
Does failing NatHERS mean the home design is bad?
Not necessarily. A low NatHERS result may mean that certain parts of the design need refinement to meet the required thermal performance pathway.
What changes usually improve a failed NatHERS result?
Common improvements include better glazing, improved shading, insulation upgrades, roof colour changes, floor construction changes, reduced exposed glazing or better coordination with climate and orientation.
Can a failed NatHERS result delay approval?
It can if the assessment is left late. If the design does not meet the required rating, changes may be needed before the final compliance documentation can be issued.
