BASIX Certificates for NSW Development: What They Cover and When You Need One

A BASIX certificate is one of the documents that goes in with a development application for a new home, and it does not stop mattering when consent is granted. Its commitments are written into the plans, checked during construction and confirmed before the occupation certificate. Owners who first meet it as a line in a quote tend to underestimate how much of the design it fixes.

This post sets out what BASIX covers, when it is required and how it is handled across the project. All of it is taken from the NSW Planning Portal's BASIX pages, which are kept up to date by the Department. The costs of a typical project, including the consultants who prepare BASIX, are in our post on dual occupancy build costs.

What is BASIX?

BASIX is the Building Sustainability Index. The Planning Portal describes it as a set of standards for water and energy use and thermal performance that are part of the development application process in NSW. They apply to:

• all new residential dwellings
• alterations and additions to dwellings that cost $50,000 or more
• swimming pools of 40,000 litres or more

To approve such developments, the consent authority needs evidence that the plan meets the standards. That evidence is the BASIX certificate, which also lists the key elements of the design as sustainability commitments. The Portal notes that the standards were increased from 1 October 2023.

What do the sections test?

You complete an assessment in the BASIX tool, which estimates water and energy consumption, thermal performance and the embodied emissions of the building materials from the information you enter. That information includes the floor area, the size, location and type of windows, the type of insulation and the type of hot water system.

• Water. The standards are set in the Water Use Maps in the State Environmental Planning Policy (Sustainable Buildings) 2022 and range from 0% to 40% reduction on a benchmark of 90,340 litres per person per year, which was the average potable water use of a pre-BASIX home. The score is assessed on landscape, fittings and fixtures, alternative water sources, pools and outdoor spas, and central systems.
• Energy. The standards are in Table 1 of Schedule 1 of the same policy, as a percentage reduction in greenhouse gas emissions against a benchmark of 3,292 kilograms of carbon dioxide per person per year. The score looks at hot water systems, heating and cooling, ventilation, lighting, pools and spas, alternative energy sources and other uses.
• Thermal performance. This tests the design and materials that reduce the need for artificial heating and cooling. The applicant picks a method. The do-it-yourself method is a simplified assessment for single dwelling houses with common construction. The simulation method uses accredited NatHERS software and covers more complex designs and multi-dwelling developments such as townhouses and apartments. A Passive House method exists for single dwellings built to that standard.

The thermal loads feed into the energy section, so a better building shell can help an energy pass.

When does it enter the process?

The Portal sets out the sequence. Once the design plans are complete, you run the assessment, generate the certificate and pay the fee. You then submit the development application, or complying development certificate application, with the certificate attached. If the project changes, the certificate must be revised and resubmitted to council, and there is no charge to revise a valid certificate lodged with the consent authority.

If the application is approved, the building must be built to the BASIX commitments. The certificate is attached to the application for the construction certificate, and every commitment must appear on the plans. It is attached again to the application for the occupation certificate, and before the certifier issues that certificate, a BASIX completion receipt must confirm the project was built as certified. The wider certificate sequence is in our post on construction and occupation certificates.

How long is a certificate valid?

A certificate is valid for 3 months before it is lodged with the council or an accredited certifier. After lodgement, it remains valid for the maximum life of the development application. If you do not lodge within 3 months you generate a new one, with additional fees. The Portal suggests using the BASIX report function until the design is finalised and ready to lodge.

One certificate or several?

For new dwellings, the applicant submits one certificate covering all dwellings with the development application. The consent authority can allow separate certificates for different parts of the project, but the applicant has to ask. The Portal lists these examples:

• a subdivision into single Torrens title lots with detached dwellings and no shared services
• strata developments, including villa units, multi-dwelling housing and dual occupancy, where common areas and shared services can be apportioned between the certificates
• staged developments built over time
• large multi-building residential flat developments of more than 600 units

Separate certificates can allow part consent on a staged project and make later revisions easier, because only the affected certificates need to change. Which route suits a dual occupancy depends on how it will be titled, which is covered in Torrens vs strata subdivision.

Where it affects cost and design

BASIX commitments are not a post-approval detail. They set the window sizes and glazing, insulation, hot water system, fixtures and landscape that the builder is held to, and they cannot be traded away through a variation to a development standard, as the exclusions in our clause 4.6 post explain. A design priced before the assessment has been run can change once it is.

• Run the assessment on the near-final design, not the concept.
• Ask the designer which commitments drive cost, such as the hot water system and glazing.
• Keep the certificate's 3 month window in mind when the lodgement date moves.

We include the BASIX consultant and the design changes it tends to drive in the feasibility before a site is committed. Ask us for an assessment and the line items come back with the rest of the numbers.

Common questions

Who needs a BASIX certificate in NSW?

The NSW Planning Portal says BASIX standards apply to all new residential dwellings, to alterations and additions that cost $50,000 or more, and to swimming pools of 40,000 litres or more. The consent authority, usually the council, requires evidence that the plan meets the standards before it approves the development.

What does BASIX assess?

Water use, energy use and thermal performance, and the Planning Portal also describes a materials section that looks at the embodied emissions of building materials. The water standard is set against a pre-BASIX benchmark of 90,340 litres per person per year, and the energy standard against a benchmark of 3,292 kilograms of carbon dioxide per person per year.

How long is a BASIX certificate valid?

A certificate is valid for 3 months before it is lodged with the council or an accredited certifier. Once it is lodged it stays valid for the maximum life of the development application. If it is not lodged within 3 months a new certificate has to be generated, which carries additional fees.

Does a dual occupancy need one BASIX certificate or two?

For new dwellings the applicant submits one certificate covering all of the dwellings with the development application. The consent authority can allow separate certificates for different parts of a project, and the Planning Portal lists strata developments including dual occupancy and staged developments among the cases where an applicant may ask. The request has to be made to the council.