Every DA for a new dwelling in NSW, and for alterations and additions costing $50,000 or more, must be lodged with a BASIX certificate under State Environmental Planning Policy (Sustainable Buildings) 2022. The certificate sets water, energy and thermal comfort commitments for the dwelling, and the thermal comfort part is usually produced by a NatHERS assessment that simulates the design and gives it a star rating. What the planner needs from the energy assessor is simple to state and often hard to get: a certificate generated from the same drawings that are being lodged, with every commitment that affects the plans (glazing, insulation, rainwater tank, solar, hot water) shown on those plans. Mismatches between the certificate and the drawings are one of the most common reasons a small residential DA is sent back.
Key takeaways
- A BASIX certificate is required for a new dwelling, a secondary dwelling, alterations and additions of $50,000 or more, and a pool or spa over 40,000 litres, and it must be lodged with the DA or CDC.
- Since 1 October 2023 the BASIX thermal performance standard is equivalent to 7 stars under NatHERS for most new homes, with higher energy targets, so older designs may not pass without changes.
- NatHERS is the simulation tool; BASIX is the certificate. The NatHERS certificate feeds the thermal comfort section of BASIX and both should be lodged.
- The BASIX commitments must appear on the DA plans, and the certifier checks them again at construction certificate and occupation certificate stage.
- Changes to the design after the assessment (windows, orientation, floor area, roof colour) invalidate the certificate and need a re-run before lodgement.
Two documents, two jobs
People use the terms interchangeably and they aren’t. BASIX (the Building Sustainability Index) is a NSW planning requirement administered through the NSW Planning Portal. The certificate lists commitments in three sections: water (fixtures, rainwater tank, landscaping), energy (hot water, lighting, heating and cooling, solar) and thermal comfort. NatHERS (the Nationwide House Energy Rating Scheme) is the national simulation method that models the building envelope in accredited software and produces a star rating with heating and cooling loads. In NSW, the NatHERS result is entered into the thermal comfort section of BASIX, so for most new houses and dual occupancies the two go together. The state’s BASIX page on the Planning Portal sets out when a certificate is needed and what changed in 2023.
The National Construction Code sets the underlying energy efficiency provisions, and NSW applies them through BASIX rather than through the NCC’s own residential energy pathway. The NCC still governs everything else about the building, including the construction requirements a certifier checks.
What triggers BASIX on a residential DA
| Project | BASIX required | NatHERS usually needed |
|---|---|---|
| New house, knock-down rebuild, dual occupancy, townhouses | Yes | Yes, for the thermal comfort section |
| Secondary dwelling (granny flat) | Yes | Yes in most cases; the simpler BASIX DIY method is limited to small works |
| Alterations and additions of $50,000 or more | Yes | Sometimes, depending on the extent of new conditioned floor area |
| Alterations under $50,000 with no pool | No | No |
| Pool or spa over 40,000 litres | Yes | No |
The $50,000 threshold is the estimated cost of the works, the same figure used for the DA fee and any section 7.12 levy, so it can’t be shaded to avoid a certificate.
The 2023 uplift and why old designs fail
From 1 October 2023 the Sustainable Buildings SEPP raised the bar. The thermal performance standard for new houses and low rise dwellings is set at the equivalent of 7 stars under NatHERS (up from a level closer to 5.5 to 6 stars), and the energy targets increased with them. Large apartment and non-residential projects also picked up embodied emissions reporting, which doesn’t affect a duplex but does affect the larger projects we occasionally plan.
The practical effect on house and duplex DAs in South West Sydney, where summer cooling loads dominate, has been real. Designs that passed comfortably at 5.5 stars in 2022 often fail at 7 without changes to glazing, shading, insulation or orientation. A west-facing wall of glass to the alfresco in Gregory Hills or Oran Park is the classic problem. The assessor will usually solve it with better glazing, external shading, higher ceiling insulation and lighter roof colours, and each of those choices has to make it onto the DA plans.
What the planner needs from the assessor, in order
- The final DA drawing set as the input. The assessor models the plans that will be lodged, at the same revision. If the architect issues Revision C after the assessment was run on Revision B, the certificate is wrong.
- The BASIX certificate and the NatHERS certificate together. The NatHERS certificate with the stamped plans is what shows the certifier how the rating was achieved.
- The commitment schedule extracted. A one page list of every commitment that changes a drawing: glazing type by window, insulation R-values by element, rainwater tank size and connections, hot water system, ceiling fans, roof colour and solar absorptance, shading devices, lighting and any fixed appliances.
- The commitments on the plans. Most councils require the BASIX commitments to be annotated on the elevations and the site plan. The window schedule should match the NatHERS glazing schedule exactly.
- The certificate number and date on the DA form. The Portal asks for it. A certificate from a previous scheme or an expired one will be flagged at completeness check.
Our sister firm NatHERS Pro prepares BASIX and NatHERS certificates for the projects we plan, and the workflow above is the one we run with them: assessor works from the frozen DA set, planner checks the commitment schedule against the drawings before anything is uploaded.
Where BASIX goes wrong at council
- Floor area mismatch. The BASIX certificate carries a conditioned floor area and a site area; if the plans show something different, the officer asks why.
- Windows that don’t match. A NatHERS schedule with double glazing to the north and single elsewhere, and elevations that say “as selected”, is an RFI waiting to happen.
- Rainwater tank with no space. A 3,000 litre tank committed on the certificate but no tank shown on the site plan, or a tank in the side setback the DCP requires to stay clear.
- Solar on the wrong roof. A solar array committed for the north roof when the north roof is a hip too small to carry it.
- Two dwellings, one certificate. A dual occupancy needs both dwellings assessed; a single house certificate lodged for a duplex is rejected.
- Design changed after the certificate. A larger alfresco, a moved window or a changed orientation means the certificate no longer describes the building. Re-run before lodgement, not at construction certificate.
Sequencing it into the DA program
The assessment takes a few days once the drawings are frozen, and a redesign for a failed rating can take a week or two of back and forth between architect and assessor. So we lock the plans, run the assessment, resolve any failure, then update the plans with the commitments and only then finish the Statement of Environmental Effects, which references the certificate number and summarises the commitments in its ecologically sustainable development section. On a Camden or Liverpool duplex the whole loop usually fits inside a fortnight if the architect is responsive. Doing it in the other order, SEE first and BASIX last, is how a lodgement slips a month.
Frequently asked questions
Do I need a BASIX certificate for a granny flat in NSW?
Yes. A secondary dwelling is a new dwelling and needs its own BASIX certificate lodged with the DA or CDC, usually with a NatHERS assessment for the thermal comfort section.
What NatHERS star rating do I need in NSW?
Since 1 October 2023 the BASIX thermal performance standard for most new houses and low rise dwellings is equivalent to 7 stars under NatHERS. The BASIX certificate expresses it as heating and cooling load caps rather than a star figure, but 7 stars is the practical target.
Does BASIX need to be done before the DA is lodged?
Yes. The certificate is a mandatory lodgement document and the Planning Portal asks for its number. Council can reject a DA at completeness check without it.
What happens if the plans change after the BASIX certificate is issued?
If the change affects any commitment or the thermal model, the certificate has to be re-run and a revised certificate issued. At construction certificate stage the certifier checks the built design against the certificate, so an out-of-date certificate is caught eventually either way.
Getting the energy assessment into the DA cleanly is part of how our planners prepare a Statement of Environmental Effects, and on a dual occupancy we coordinate both dwellings’ certificates with the architect and the assessor. If you’re planning a rebuild or duplex in Camden, Liverpool or elsewhere in NSW, request a fee proposal and we’ll scope the whole lodgement package.