BASIX Tool Update May 2026: Passive House Pathway, v4.04 and What Changed

On 1 May 2026 the NSW Government rolled out a significant round of upgrades to the BASIX tool – the online system every NSW dwelling application passes through. Most homeowners will never open the tool themselves, but three of the changes flow directly into how homes are designed, documented and certified. Here is what changed and what it means for your project.

The headline: Passive House is now a recognised pathway

The biggest change is formal recognition of the Passive House Standard as an approved pathway for BASIX thermal performance compliance. Until now, the thermal comfort section of BASIX has been satisfied through NatHERS star-rating simulation (or the older DIY method for simple projects). Homes designed and certified to the international Passive House standard can now use that certification as their thermal compliance route.

In practice this matters for a small but growing group of projects. Passive House targets airtightness, continuous insulation, thermal-bridge-free construction and mechanical ventilation with heat recovery – a more demanding regime than a 7-star NatHERS result. If you are already committed to Passive House, NSW no longer makes you model the same building twice in two systems. For everyone else, NatHERS simulation remains the standard route, and for most homes the most cost-effective one.

Ventilation: no more exhausting into the roof space

From v4.04 of the BASIX standards, bathroom, kitchen and laundry exhaust systems can no longer be specified as discharging into the roof space. Exhaust air now needs to be ducted to the outside. This closes off a shortcut that was always questionable building science – dumping warm, moist air into a roof cavity invites condensation, mould and insulation damage, and it undermines the airtightness that modern energy ratings reward.

If your plans or your builder’s standard details still show ceiling exhaust fans venting into the roof, they need updating before your next BASIX certificate is generated.

A declaration of accuracy

The tool now requires the person generating a certificate to declare that all information entered is accurate. It sounds procedural, but it sharpens accountability: the specifications behind your certificate are formally attested, and casual guesswork in the inputs carries more weight than it used to. It is one more reason to have a registered assessor prepare the inputs from your actual drawings rather than approximations.

What this means for current projects

• Certificates already issued remain valid – the changes apply to new certificates generated after the update.
• Projects mid-design should check exhaust ventilation details now, before documentation is finalised.
• Passive House projects should talk to their certifier about using the new pathway rather than parallel NatHERS modelling.
• Everyone else: nothing about your targets changed in this round – the 7-star thermal requirement and energy and water targets carry on as before.

Frequently asked questions

Does my existing BASIX certificate need re-issuing? No. Certificates generated before the update stay valid for their normal life. The new rules apply when a new or amended certificate is generated.

Is Passive House now required? No – it is an optional alternative pathway. NatHERS star-rating simulation remains the standard and usually the most economical route.

My plans show fans venting to the roof space. What now? Update the detail to ducted-to-outside before your certificate is generated – we can flag exactly which rooms are affected when we review your plans.

Sources: NSW Planning Portal – BASIX tool upgrades. Building in NSW? Send us your plans for a fixed-fee quote within one business day.