A BASIX certificate has two costs: a small fee charged by the NSW Planning Portal, and the professional fee for the person who assesses your plans. Most of what people call “the cost of BASIX” is the second one. Then there is a third cost that nobody quotes: the construction upgrades needed if the design fails.
The government fee
The Planning Portal charges a fee to generate each BASIX certificate, currently $50 for a new dwelling, and the NatHERS certificate carries its own fee of $44 plus GST per dwelling. Both are paid when the certificates are issued. Most assessors, including us, build them into the quote.
That fee pays for the certificate, not for the work. It doesn’t cover reading the plans, working out window areas and insulation, running a NatHERS simulation or checking that the commitments match the drawings.
Typical assessor fees by project
These are the ranges you’ll see across Sydney assessors’ published prices in 2026, before GST. Where a price falls in the range depends mostly on design complexity and whether a NatHERS simulation is needed.
| Project | Typical range | What drives it |
|---|---|---|
| Alterations & additions | $200 – $450 | Size of the extension, amount of new glazing, pool |
| Granny flat | $350 – $600 | Usually simple, but still a full dwelling assessment |
| New house, BASIX + NatHERS | $450 – $900 | Floor area, levels, voids, raked ceilings, glazing |
| Dual occupancy | $800 – $1,600 | Two dwellings, two models, two certificates |
| Townhouses / apartments | Quoted | Number of units, repeated layouts, common areas |
Our own starting prices are on the pricing page: from $400 for alterations and additions and $750 for a new single-storey home with NatHERS, ex GST, certificate fees included.
Why quotes vary so much
DIY method vs simulation
The thermal section can be done with the DIY method, which is a fixed set of insulation and glazing rules, or with a NatHERS simulation of the whole dwelling. Simulation costs more because it’s a full 3D model. For most new homes it’s still the cheaper option overall, because it credits good orientation and shading instead of forcing blanket upgrades.
Design complexity
A single-storey rectangle with standard ceilings is quick to model. Split levels, voids, raked ceilings, curved walls, skylights and a dozen window types all add time.
Quality of the drawings
Dimensioned plans, sections and a window schedule make the take-off fast. Missing ceiling heights, no north point or no sections mean questions, delays and sometimes assumptions you won’t want.
The costs no one quotes
A cheap certificate on a design that barely passes can cost you far more at construction. Common examples:
- Glazing upgrades: switching to double glazing or low-e glass across the house to make up for a big west-facing window.
- Insulation beyond standard: higher R-value batts, insulation under a suspended timber floor, or foil and blanket under the roof.
- Revisions: change a window after the certificate is issued and you need a revised certificate, and sometimes a new NatHERS certificate too.
- Delays: an expired or mismatched certificate can hold up a DA, CDC or CC.
The best time to spend money on BASIX is at concept design. A quick early model shows whether the design passes before the drawings are finished, when changes still cost nothing.
How to keep the cost down
- Send complete drawings: site plan with north point, floor plans, elevations and sections.
- Lock in the window layout first. Glazing drives the thermal result more than anything else.
- Decide on services early: hot water system, air-conditioning, rainwater tank and solar PV all affect the energy score.
- Ask for upgrade options, not just a pass, so you can choose the cheapest way through.
- Use one practice for drafting and assessment where possible, so changes don’t bounce between consultants.
The bottom line
Expect to pay a few hundred dollars for a renovation and roughly $450–$900 for a new house with NatHERS. Compare quotes on what’s included, such as stamped plans, revisions and upgrade advice, not just the headline price.
Get a fixed BASIX price for your plans
Assessments prepared from your drawings, anywhere in NSW. Turnaround is confirmed in your quote and starts once all required information is received.
General information only, current at the date above. Requirements change and every project is different, so confirm the rules that apply to your project with your certifier or council.