NatHERS Existing Homes is more than a new assessment category. It represents a wider shift in how Australia understands the energy performance of homes that have already been built, occupied, renovated, altered and lived in over time.
For many years, NatHERS has been closely associated with new homes, where energy performance can be assessed from plans, specifications and proposed construction details. Existing homes are different. They require assessment methods that can respond to real buildings, real conditions, observable construction features and the practical limitations of working with homes that are already occupied.
As NatHERS expands to cover existing homes, the next challenge is not only technical accuracy. It is practical delivery.
Home energy ratings need to be reliable, consistent and useful. They also need to be delivered in a way that can work across many different property types, locations, household situations and assessment pathways.
A new home energy assessment usually begins with design documentation. The assessor reviews drawings, specifications, glazing, insulation, construction systems, orientation and other design inputs before the home is built.
An existing home assessment begins in a different place.
The assessor is working with a dwelling that already exists. Some information may be available from plans or previous documentation, but much of the assessment depends on what can be observed, measured, verified and modelled from the current condition of the home.
This may include the dwelling’s age, construction type, window systems, shading, insulation, ventilation, air leakage, heating and cooling systems, orientation, renovation history and other features that influence thermal performance.
That makes existing-home assessments practically more complex. Two homes that appear similar from the street may perform very differently depending on past upgrades, construction quality, glazing, insulation and the way the building has changed over time.
The value of NatHERS Existing Homes will depend on more than the rating itself.
For homeowners, a rating should help explain how a home performs and where upgrades may have the greatest impact. For property professionals, it may become part of a broader shift toward clearer energy performance information in the housing market. For governments and industry, it may help support better decisions around residential energy efficiency, disclosure, housing quality and retrofit programs.
But for this to work, the assessment process needs to be practical.
It needs to be clear enough for homeowners to understand, robust enough for industry to trust and consistent enough to support broader use across the property market.
This is why delivery models matter. A technically sound rating system still needs reliable workflows, trained assessors, data collection processes, quality assurance and systems that can support assessment at scale.
The NatHERS Existing Homes trial was designed to test what works in practice and what needs strengthening to support a staged rollout of existing home energy ratings. NatHERS has stated that the trial found the scheme to be viable and fit for purpose, with a staged release intended to help manage workforce scale-up, capacity building and process improvement.
Home energy rating disclosure is also part of the broader context.
Disclosure means that a home energy rating may be shared publicly with prospective buyers or renters, such as in sale or lease advertising. NatHERS notes that the NSW and Australian governments have trialled how a Home Energy Rating could be used and shared during the sale or lease of a property.
If energy performance information becomes more visible in the property market, consistency will become even more important.
A rating will need to be more than a private technical report. It may become part of how homes are understood, compared and improved. This creates a higher need for assessment pathways that are practical, trusted and capable of supporting larger volumes of homes over time.
Scaling existing-home assessments is not as simple as applying new-home assessment workflows to older dwellings.
Existing housing stock is varied. Homes may have incomplete documentation, multiple renovation stages, mixed construction types, unknown insulation levels, ageing glazing systems, draughts, additions, enclosed verandahs, altered roof spaces or services that have been upgraded over time.
Assessors need to work with real-world information. They need to collect data efficiently, model the home accurately and provide results that are meaningful to the homeowner or property stakeholder.
At larger scale, this becomes a systems challenge.
The industry needs practical ways to manage property information, assessment inputs, photographic evidence, modelling workflows, certificate generation, quality assurance and upgrade guidance. NatHERS’ delivery model for existing homes includes accredited assessors entering homes to collect data for NatHERS tools, producing certificates and ratings that include thermal performance and Whole of Home information, along with upgrade advice.
Certified Energy has been involved in NatHERS Existing Homes assessment work through national trial programs and real-world assessment workflows.
This experience matters because existing-home ratings sit at the intersection of technical modelling, building knowledge and practical delivery.
Assessors need to understand building fabric, glazing, insulation, thermal comfort, climate response and residential energy systems. But they also need to work within a process that can be delivered clearly and consistently for homeowners, property professionals and larger housing programs.
That practical layer is important.
A rating is only useful if it can be trusted, explained and acted upon.
Certified Energy is collaborating with Cotality Australia to explore how NatHERS Existing Homes assessments can be delivered practically, consistently and at scale as the market moves toward broader home energy rating disclosure.
Cotality brings property data and workflow capability across the Australian housing market, while Certified Energy contributes practical NatHERS assessment experience, thermal performance knowledge and residential energy compliance expertise.
Cotality has publicly described the challenge of existing-home ratings as one of scale, consistency and trust, and has noted its collaboration with Certified Energy to explore practical, high-volume delivery as the market moves toward mandatory disclosure.
This type of collaboration is important because NatHERS Existing Homes will not be successful through technical assessment alone. It will also require delivery systems that can operate reliably across real homes, real property data and real assessment conditions.
For homeowners, NatHERS Existing Homes assessments may provide a clearer understanding of how a home performs and where future upgrades may have the greatest impact.
This can be useful for improving comfort, reducing heating and cooling demand, planning renovations or understanding the practical energy performance of an existing dwelling.
For property professionals, the growth of home energy ratings may create a new layer of information in the residential property market. Energy performance could become more visible in conversations around sale, lease, renovation, finance, retrofit planning and housing quality.
For governments and program designers, practical delivery models will be important for any broader rollout. A rating system needs to be technically credible, but it also needs to be workable in the field.
NatHERS Existing Homes is not only about producing ratings. It is about helping Australia understand and improve the performance of the homes people already live in.
That requires more than software, certificates or assessment rules.
It requires trained assessors, reliable workflows, useful property data, quality assurance and practical upgrade guidance. It also requires collaboration between technical assessors, data providers, industry organisations, government programs and property market participants.
The future of existing-home energy ratings will depend on whether the industry can make the process both credible and usable.
That is why practical delivery matters.
Learn more about Certified Energy’s NatHERS Existing Homes assessments.