If you've spent any time researching building approvals, you've probably seen "NatHERS" and "BASIX" mentioned in the same breath — sometimes even used interchangeably. They're not the same thing, and mixing them up can cost you time at DA stage.
Both deal with how well your home performs thermally. Both involve an accredited assessor and a certificate you'll need before construction. But they're run by different bodies, cover different ground, and apply in different places. Here's the plain-English version.
What is NatHERS?
NatHERS stands for the Nationwide House Energy Rating Scheme. It's a national system — used in every state and territory — that rates the thermal performance of a home's building fabric on a scale of 0 to 10 stars.
A NatHERS assessment looks purely at how well the building shell holds a comfortable temperature without mechanical heating or cooling: wall and ceiling insulation, window glazing and orientation, floor construction, shading, and airflow. An accredited assessor feeds your architectural drawings into approved modelling software, which simulates your home's performance against the local climate zone.
The higher the star rating, the less energy your home needs to stay comfortable year-round. Since the NCC 2022 update, most new homes across Australia need a minimum 7-star NatHERS rating as part of the Whole of Home requirements.
What is BASIX, again?
BASIX — the Building Sustainability Index — is a NSW-specific requirement. It's broader than NatHERS: alongside thermal comfort, it also assesses energy use (appliances, hot water, lighting) and water consumption (fixtures, rainwater tanks, landscaping). We've covered what BASIX is in detail here if you want the full picture.
Where NatHERS produces a star rating, BASIX produces a pass/fail outcome against a set of index targets, generated through the NSW Planning Portal's online tool.
"NatHERS asks: how good is the building itself at staying comfortable? BASIX asks: how sustainably does the whole home operate — energy, water, and comfort combined?"
The key differences at a glance
- Coverage — NatHERS is national. BASIX applies in NSW only.
- Scope — NatHERS measures thermal performance only. BASIX covers thermal comfort, energy, and water together.
- Output — NatHERS gives a star rating (0–10). BASIX gives a pass/fail certificate.
- Governing body — NatHERS is administered federally. BASIX is run by the NSW Government.
- Where they overlap — In NSW, a NatHERS assessment can satisfy the thermal comfort component of your BASIX certificate.
Do you need both?
This depends entirely on where you're building and what you're building.
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1Building in NSW? You'll almost certainly need both. Your BASIX certificate is mandatory for the DA or CDC, and its thermal comfort component is typically satisfied by a NatHERS assessment.
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2Building outside NSW? BASIX doesn't apply — but NatHERS almost certainly does, either directly through your state's planning requirements or as part of the national Whole of Home pathway under NCC 2022.
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3Doing a major renovation in NSW? If the works are valued over the BASIX threshold, you'll need a BASIX certificate, and a NatHERS assessment is often the most flexible way to meet the thermal target.
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4Working on a multi-unit development? Both schemes apply to duplexes, townhouses, and apartment buildings, with targets adjusted for the dwelling type.
How NatHERS and BASIX work together
In practice, most NSW projects run through both processes as a single package. Your assessor models your home's thermal performance once, then uses that output to satisfy the BASIX thermal comfort commitment while also generating your NatHERS star rating certificate for construction compliance.
That means you don't necessarily pay for two separate, disconnected assessments — a good assessor coordinates the two so the same drawings and modelling work do double duty. It also means design changes need to be checked against both outcomes at once: a window swap that helps your NatHERS star rating might affect a BASIX water or energy target, and vice versa.
- Assuming one certificate covers everything — In NSW, BASIX is the mandatory lodgement document. A NatHERS rating alone won't satisfy your DA requirements on its own.
- Getting them from assessors who aren't accredited for both — Not every assessor holds accreditation for both schemes. Confirm before you commission the work.
- Changing plans after certification — Altering windows, insulation, or orientation after either certificate is issued can invalidate both, not just one.
- Assuming interstate rules mirror NSW — Outside NSW, there's no BASIX equivalent — don't budget for a certificate you won't need, but don't skip NatHERS either.
The bottom line
NatHERS and BASIX aren't competing systems — they're different lenses on the same goal: a home that's comfortable to live in and cheaper to run. NatHERS zooms in on the building fabric alone. BASIX zooms out to energy and water use across the whole home, and applies specifically in NSW.
If you're building or renovating in NSW, plan for both from the start rather than treating them as separate hurdles. Get your assessor involved early, and the same set of drawings can carry you through both processes without duplicated work or last-minute redesigns.
At Thermal Nest, we handle NatHERS and BASIX together as standard, coordinating both from the one set of plans. If you've got a project coming up and aren't sure which certificates you need, get in touch — we'll tell you exactly what applies before you commit to anything.
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