NatHERS vs BASIX: What's the Difference and Which Do You Need? (2026)
NatHERS measures thermal performance. BASIX is the NSW planning certificate that uses NatHERS results. Most NSW homes need both — here's why.
Taylor M
NatHERS & Home Energy Specialist
The short answer
NatHERS and BASIX are not competitors — they work together. NatHERS rates how well a home's building envelope performs thermally on a 0–10 star scale. BASIX is a NSW Government planning certificate that uses NatHERS data (alongside water and energy targets) to prove your home meets minimum sustainability standards before council will approve construction.
If you're building or renovating in NSW, you almost certainly need a BASIX certificate, and that BASIX certificate will rely on a NatHERS thermal assessment. Outside NSW, you only need NatHERS — BASIX doesn't apply.
What is NatHERS?
NatHERS (Nationwide House Energy Rating Scheme) is the national framework for measuring residential thermal performance. An accredited NatHERS assessor models your home using software like FirstRate5, BERS Pro or AccuRate, then issues an official certificate showing a 0–10 star rating.
NatHERS applies Australia-wide and is used for new builds (mandatory NCC 7-star minimum), renovations, voluntary existing-home assessments, and increasingly for property sales under state mandatory disclosure schemes.
What is BASIX?
BASIX (Building Sustainability Index) is a NSW Government planning tool, mandatory for all new residential developments and major alterations in New South Wales. It sets minimum targets for thermal comfort, energy use and water efficiency.
BASIX issues a single certificate that must be submitted with your DA or CDC. The thermal-comfort component of BASIX is satisfied either by a simple DTS (Deemed-to-Satisfy) check or — for most modern designs — by an underlying NatHERS rating from an accredited assessor.
NatHERS vs. BASIX: side by side
| Attribute | NatHERS | BASIX |
|---|---|---|
| What it measures | Thermal performance only (0–10 stars) | Thermal comfort + energy + water targets |
| Where it applies | Australia-wide | NSW only |
| Who issues it | Accredited NatHERS assessor | BASIX assessor (often the same person) |
| Required for | All new builds nationally; some sales | All NSW new builds + major reno |
| Typical cost | $300–$600 existing / $200–$400 new | $150–$350 (often bundled with NatHERS) |
| Output | Star rating + report | Pass/fail certificate for council |
| Software | FirstRate5, BERS Pro, AccuRate | BASIX online tool (planningportal.nsw.gov.au) |
| Replaces the other? | No — feeds into BASIX in NSW | No — needs NatHERS data for thermal |
When you need NatHERS
- • Building a new home anywhere in Australia (mandatory under NCC 2022/2025)
- • Renovating or extending — to model 'before vs. after' star ratings
- • Selling in states moving to mandatory disclosure (ACT now, NSW pending)
- • Voluntary assessment to identify upgrade opportunities for existing homes
- • Applying for state rebates (VEU, REPS) that require a star rating
When you need BASIX
- • Lodging a DA or CDC for a new home in NSW
- • Major NSW renovations or extensions over $50k that change building fabric
- • Adding a new pool or large landscaping in NSW
- • Subdividing or building dual occupancies in NSW
- • Anything that needs NSW council approval for residential work
Which one do you actually need?
If you're in NSW: you need BASIX, and your BASIX certificate will almost always be backed by a NatHERS thermal assessment. Most assessors offer a combined NatHERS + BASIX package — typically $450–$750 total — which is cheaper than commissioning each separately.
If you're anywhere else in Australia: BASIX doesn't apply to you. You only need NatHERS, costing $300–$600 for an existing home or $200–$400 for a new build from plans.
There's no scenario where BASIX replaces NatHERS or vice versa — they cover different things and BASIX literally depends on NatHERS data to assess thermal comfort.
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Frequently asked questions
Is BASIX the same as NatHERS?
No. NatHERS measures only thermal performance (heating and cooling needs) and produces a 0–10 star rating. BASIX is a broader NSW planning certificate covering thermal comfort, energy use and water efficiency. BASIX uses NatHERS data to assess the thermal-comfort component but adds energy and water targets on top.
Do I need both NatHERS and BASIX in NSW?
For most new builds and major renovations in NSW, yes. Your BASIX certificate is mandatory for council approval, and the thermal-comfort section of BASIX is almost always satisfied by an underlying NatHERS rating from an accredited assessor. Some very simple projects can use BASIX's DTS (Deemed-to-Satisfy) pathway without a full NatHERS rating.
How much does BASIX cost compared to NatHERS?
A standalone BASIX certificate typically costs $150–$350 for a single dwelling. A NatHERS assessment costs $300–$600 for existing homes or $200–$400 for new builds. Most NSW assessors offer a combined NatHERS + BASIX package for $450–$750 total — cheaper than getting them separately.
Does BASIX apply outside NSW?
No. BASIX is a New South Wales scheme administered through the NSW Planning Portal. Other states use their own equivalents — Victoria has BAVA-style requirements through council, Queensland uses QDC 4.1, the ACT uses NatHERS plus mandatory disclosure on sale. NatHERS is the common thread nationally.
Will BASIX be replaced by NatHERS?
No. NSW has been integrating BASIX more tightly with NatHERS (the BASIX 2022 update raised thermal-comfort thresholds in line with NCC 7-star), but BASIX remains the regulatory certificate while NatHERS provides the thermal data. They're complementary, not competing.
Can the same assessor do both NatHERS and BASIX?
Yes — and most NSW assessors do. Combining them into one engagement is faster, cheaper, and avoids inconsistency between the two certificates. When booking, ask specifically for a 'NatHERS + BASIX package'.
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