NSW Residential Compliance Guide
BASIX is required for most new residential development in New South Wales, as well as qualifying alterations, additions, swimming pools and spas.
Determining whether BASIX applies is one of the first residential compliance questions to resolve before lodging a Development Application or Complying Development Certificate application in NSW.
The requirement is not based only on whether a project appears large or whether it changes the thermal performance of the home. BASIX applicability is established through defined development types, cost thresholds and pool or spa capacity thresholds.
This guide focuses specifically on when a BASIX Certificate is required. For a broader explanation of BASIX targets, commitments and the assessment process, visit the BASIX Knowledge Hub.
In Brief
New Residential Development
BASIX generally applies when a new residential dwelling or residential development is being constructed.
Alterations and Additions
BASIX generally becomes mandatory where the estimated development cost is $50,000 or more.
Pools and Spas
A pool, spa or combined pool and spa capacity of 40,000 litres or more can trigger BASIX where it serves one dwelling.
BASIX may apply under either a Development Application or Complying Development Certificate pathway. The approval pathway does not, by itself, determine whether BASIX is required.
Applicability
BASIX forms part of the NSW planning and approval framework for residential development. It commonly applies where a project creates a new dwelling, changes an existing building so that it becomes a dwelling, or alters an existing residential building above the applicable cost threshold.
Projects that commonly require a BASIX Certificate include:
The correct BASIX application type depends on the development configuration. A detached dwelling, multi-dwelling project and alteration to an existing home do not necessarily follow the same assessment pathway.
New Residential Development
A new residential dwelling in NSW will generally require a BASIX Certificate. This includes a single house on a vacant lot as well as residential projects containing two or more dwellings.
Common examples include:
Where a development contains multiple dwellings, the BASIX Certificate will generally address the development as a coordinated project rather than treating each dwelling as an unrelated application.
Existing Homes
Mandatory BASIX
An alteration or addition to an existing BASIX building generally requires a BASIX Certificate where the estimated development cost is $50,000 or more.
Optional BASIX
Work below the threshold may be BASIX optional rather than mandatory, provided another BASIX trigger or statutory exclusion does not change the position.
Separate Trigger
A project that creates a new dwelling should not be treated as an ordinary below-threshold renovation simply because the construction scope is relatively small.
Combined Scope
A pool or spa can create a separate BASIX trigger even where the remaining alteration and addition works are below $50,000.
Development Cost
For alterations and additions, the relevant trigger is the estimated development cost. A project costing exactly $50,000 is therefore within the mandatory threshold because the requirement applies at $50,000 or more.
The test is not limited to work that directly affects glazing, insulation or thermal performance. An internal renovation, building extension or combined package of residential work may still require BASIX when the complete estimated development cost reaches the threshold.
Projects commonly affected by the threshold can include:
The estimated cost used for the approval application should reflect the project being submitted. Separating individual elements from a coordinated development does not necessarily remove the broader BASIX obligation.
Granny Flats and Secondary Dwellings
A project that creates a new secondary dwelling will generally require BASIX, even where the dwelling is relatively small or forms part of a wider alteration to an existing home.
The appropriate BASIX application type depends on how the secondary dwelling is being created. Relevant configurations include:
Because these configurations can use different BASIX application pathways, the project description and existing building arrangement should be reviewed before the assessment is started.
Water Features
A swimming pool, spa or combination of pools and spas generally requires BASIX where it serves one dwelling and has a capacity, or combined capacity, of 40,000 litres or more.
Exactly 40,000 litres is included. The threshold applies at 40,000 litres or more, not only when the volume exceeds 40,000 litres.
Combined capacity may matter. Where a project includes both a pool and spa, or several relevant water bodies, the combined capacity should be considered.
Below-threshold pools may be optional. A smaller pool or spa may be BASIX optional when assessed by itself and when no other mandatory trigger applies.
The wider project still matters. Alterations and additions costing $50,000 or more can independently trigger BASIX even where the pool or spa remains below 40,000 litres.
Approval Pathways
BASIX can apply where a project proceeds through either a Development Application or a Complying Development Certificate application.
The relevant question is whether the proposed work meets a BASIX development trigger. Choosing the CDC pathway does not remove BASIX requirements, and lodging a DA does not automatically mean that every minor residential project requires a BASIX Certificate.
Where BASIX is required, the Certificate should be prepared before the relevant application is submitted. Its commitments should correspond with the architectural drawings and specifications forming part of that application.
Limited Exclusions
Development solely for a garage, storeroom, carport, gazebo, verandah or awning may fall within the BASIX excluded development provisions.
Alterations to a building listed on the State Heritage Register are identified separately within the BASIX excluded development provisions.
Some alterations resulting in a space that cannot be fully enclosed can also fall outside mandatory BASIX requirements.
These exclusions should be applied to the complete development rather than to isolated components. A garage or verandah forming one part of a larger residential extension does not necessarily make the entire project BASIX excluded development.
Internal Alterations
Internal work is not automatically exempt from BASIX. An alteration to an existing residential building may still require a BASIX Certificate where the estimated development cost is $50,000 or more.
The cost trigger applies regardless of whether every component of the work directly changes the external building envelope. This can become relevant for larger internal renovation packages, especially where they form part of wider building alterations.
For minor internal works, the council or registered certifier should confirm the applicable approval pathway and whether the project is BASIX development, BASIX optional development or otherwise excluded.
Before Lodgement
Where BASIX applies, the Certificate should be prepared and coordinated with the design before the relevant DA or CDC application is lodged.
A BASIX Certificate is valid for three months before submission to the council or registered certifier. If it is not lodged within that period, a new Certificate will generally need to be generated.
Once the Certificate has been lodged with the relevant application, its validity is linked to the life of that development approval. This does not remove the need to review the Certificate if the development itself changes.
Preparing BASIX too early can create unnecessary rework where plans are still changing. Preparing it too late can delay lodgement or reveal commitments that have not been reflected in the architectural documentation.
Design Revisions
A replacement or revised BASIX Certificate may be required where the proposed development changes after the original Certificate has been generated.
Relevant changes can include:
The BASIX Certificate, plans and specifications should continue to describe the same proposed development throughout approval and construction documentation.
Project Review
A preliminary applicability review should establish the complete project scope before an assessment pathway is selected.
Is a new dwelling being created? This includes a new house, duplex dwelling, apartment, townhouse or secondary dwelling.
Is an existing residential building being altered? Identify the complete alteration, enlargement or extension scope.
What is the estimated development cost? Alterations and additions generally trigger BASIX at $50,000 or more.
Does the project include a pool or spa? Confirm the individual and combined water capacity.
Does a limited exclusion apply? Review the exclusion against the complete development rather than one isolated component.
Will the project use a DA or CDC pathway? BASIX documentation should be coordinated before the relevant application is lodged.
Frequently Asked Questions
No. Alterations and additions generally become mandatory BASIX development when the estimated development cost is $50,000 or more. A new dwelling or qualifying pool or spa can create a separate trigger.
Is BASIX required for work costing exactly $50,000?Yes. The threshold for alterations to an existing BASIX building is an estimated development cost of $50,000 or more.
Does a granny flat require BASIX?A project creating a new secondary dwelling will generally require BASIX. The correct application type depends on whether it is a new structure, a conversion of non-habitable space or a dwelling created within existing habitable space.
Is BASIX required for a pool of exactly 40,000 litres?Yes. A pool, spa or combined pool and spa capacity of 40,000 litres or more generally triggers BASIX where it serves one dwelling.
Does a CDC project still require BASIX?Yes, where the proposed development meets a BASIX trigger. Using the complying development pathway does not remove the applicable BASIX obligations.
How long is a BASIX Certificate valid before lodgement?A BASIX Certificate is valid for three months before it is submitted to the council or registered certifier. If it is not lodged within that period, a new Certificate will generally be required.
Can a BASIX Certificate need to be updated after lodgement?Yes. Changes to the proposed development should be reviewed where they affect the information or commitments contained in the lodged Certificate.
Related Guidance
BASIX Project Review
Certified Energy can review the available plans, development description, estimated project cost and pool or spa scope to help identify the likely BASIX pathway before assessment or lodgement.
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