BASIX Alterations and Additions: When BASIX Is Required

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BASIX alterations and additions apply to most residential renovations and extensions in New South Wales (NSW) where the construction value is $50,000 or more, or where a swimming pool or spa over 40,000 litres is being installed. While BASIX requirements for alterations and additions differ from those for new homes, compliance is still mandatory for many renovation projects and must be addressed before lodging a Development Application (DA) or Complying Development Certificate (CDC).

This guide explains when BASIX applies to alterations and additions, how the BASIX assessment works for renovation projects, and what homeowners, designers, and builders should expect when preparing a BASIX certificate.

When Does BASIX Apply to Alterations and Additions in NSW?

BASIX applies to alterations and additions in NSW when:

• The estimated construction cost is $50,000 or more, or
• The project involves a swimming pool or outdoor spa with a total water volume greater than 40,000 litres

If the work is below the $50,000 threshold and does not include a pool or spa, BASIX may not apply, however, local councils can still request confirmation. In some cases, optional BASIX certification is recommended even when it is not strictly required.

It’s important to confirm BASIX requirements early, as BASIX certificates must be generated before lodging planning approval applications.

What Are BASIX Alterations and Additions?

BASIX alterations and additions refer to changes made to an existing dwelling rather than the construction of a new home. Common examples include:

• Home extensions (bedrooms, living areas, garages)
• Major internal renovations
• Structural alterations
• Swimming pools and outdoor spas
• Converting existing habitable space

Unlike new dwellings, BASIX assessments for alterations and additions focus on the changed or added components rather than reassessing the entire home.

How BASIX Alterations and Additions Differ From New Dwelling BASIX

BASIX assessments for alterations and additions are completed using a dedicated section of the BASIX tool, which differs from new dwelling assessments in several key ways:

• There are no fixed percentage reduction targets for water and energy
• The assessment focuses on efficiency improvements rather than whole‑of‑home performance
• Only the new or altered works are assessed
• Existing parts of the dwelling are generally not reassessed

This approach recognises that renovation projects should improve efficiency where possible without requiring full upgrades to an existing home.

What BASIX Assesses for Alterations and Additions

For alterations and additions, BASIX typically assesses:

Lighting

A minimum proportion of new light fittings must be high‑efficiency (LED or equivalent)

Plumbing Fixtures

New taps, toilets, and showerheads must meet minimum WELS star ratings

Construction and Insulation

New walls, ceilings, roofs, and floors are reviewed

Insulation upgrades are commonly required where new building elements are introduced

Glazing and Windows

Window size, orientation, shading, and glazing type are assessed

Larger glazing areas can increase energy load and trigger additional requirements

Pools and Spas (if applicable)

Rainwater tanks or pool covers may be required

High‑emission heating systems are restricted

Each project is assessed based on its specific scope rather than a checklist approach.

Common BASIX Issues for Alterations and Additions

Some of the most common compliance issues include:

• Underestimating the construction value and triggering BASIX late
• Increasing window sizes without reassessing BASIX impacts
• Design changes made after the BASIX certificate was generated
• Incomplete information at DA or CDC lodgement

Addressing BASIX early helps avoid assessment delays and certificate revisions.

When Should You Organise BASIX for Alterations and Additions?

BASIX should be addressed:

• Before lodging a DA or CDC
• Once the renovation scope and estimated cost are defined
• Before making major design changes that impact glazing, insulation, or fixtures

Late BASIX assessments often result in compliance surprises that can delay approvals.

Final Thoughts

BASIX alterations and additions are a mandatory consideration for many renovation projects in NSW. While the requirements are more targeted than those for new dwellings, they still play a critical role in reducing long‑term energy and water use and improving comfort.

Understanding when BASIX applies, how the alterations and additions assessment works, and what is typically reviewed helps ensure smoother approvals and fewer compliance issues during construction.

Need a BASIX Compliance Certificate?

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