BASIX and alterations and additions (December 2025)

State: NSW

Explainer – Is a BASIX certificate always required for alterations and additions?

NSW planning regulations require a BASIX certificate for all alterations and additions to an existing BASIX building (such as residential premises) that cost $50,000 or more. This applies regardless of the nature of the alterations.

The online BASIX tool can be used to do the assessment and create a BASIX certificate. The initial part of the assessment requires you to answer a series of ‘yes’ / ‘no’ questions about the scope of the alterations (for example, are you installing a new hot water system or installing any new or altered lighting fixtures, floors, walls, ceilings, windows or skylights). It also asks you to provide the existing and proposed floor area.

If you answer ‘no’ to all of the questions and the floor area is unchanged, you will generate a BASIX certificate that has no BASIX commitments. Project examples where this may apply include verandahs, covered unenclosed outdoor areas, or brickwork repairs.

However, in most cases, you will answer 'yes' to one or more of these questions. The BASIX tool then directs you to provide further details, and the BASIX certificate you generate will include some BASIX commitments relating to these details.

 By completing the BASIX assessment and answering these questions for every alteration and addition costing $50,000 or more, it ensures that the development is assessed correctly.

Contact BASIX directly with any enquiries 

To ensure that the BASIX team receives all your enquiries, please always include ‘BASIX’ in the subject line when emailing us.

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