BASIX vs Section J: Which One Applies?

NSW Building Compliance

BASIX vs Section J: Which One Applies to Your Project?

BASIX and Section J both relate to building performance and approval documentation, but they apply to different parts of the Australian building compliance system.

BASIX is the NSW sustainability assessment pathway for residential development. Section J forms part of the National Construction Code and applies to energy efficiency requirements for relevant commercial and other non-residential buildings.

A standard NSW house will generally require BASIX rather than Section J. A commercial building will generally require Section J rather than BASIX. A mixed-use development may require both, with different compliance pathways applying to different parts of the building.

The correct answer depends on the project location, building classification, proposed use, approval pathway and whether the development contains both residential and non-residential areas.

What is BASIX?

BASIX stands for Building Sustainability Index. It is a NSW assessment and certification pathway used for residential development.

The assessment considers how a residential project is expected to perform in relation to:

• water use;
• energy use;
• thermal performance;
• hot-water systems;
• heating and cooling;
• insulation and glazing;
• ventilation;
• solar photovoltaic systems;
• water-efficient fixtures; and
• rainwater tanks, pools and spas where relevant.

The completed BASIX Certificate records the commitments that need to be incorporated into the project documentation and delivered as part of the approved development.

A complete explanation of the pathway, documentation and assessment process is available in the BASIX Knowledge Hub.

When does BASIX usually apply?

BASIX is commonly relevant to residential development in New South Wales.

This may include:

• new detached houses;
• secondary dwellings and granny flats;
• dual occupancies;
• townhouses;
• multi-dwelling residential projects;
• residential flat buildings and apartments;
• alterations and additions over the applicable project-value threshold; and
• swimming pools and spas of 40,000 litres or more.

The specific requirements depend on the project type, proposed work and approval pathway. Where thermal performance modelling forms part of the residential assessment, BASIX may also work alongside a NatHERS assessment.

What is Section J?

Section J is the part of the National Construction Code that addresses energy efficiency requirements for relevant commercial and other non-residential buildings.

Unlike BASIX, Section J is not limited to New South Wales. It sits within the national building compliance framework and applies according to the relevant NCC edition, building classification, project scope and jurisdictional requirements.

A Section J Report may address requirements relating to:

• building fabric;
• walls and glazing;
• roofs and ceilings;
• floors;
• building sealing;
• air-conditioning and ventilation systems;
• artificial lighting;
• heated water systems; and
• energy monitoring provisions.

The Section J Knowledge Hub explains the broader compliance pathway, required documentation and the relationship between prescriptive and performance-based assessment methods.

When does Section J usually apply?

Section J is commonly relevant to commercial and non-residential building work that needs to demonstrate energy efficiency compliance under the NCC.

Projects may include:

• offices;
• retail premises;
• commercial fitouts;
• warehouses and industrial buildings;
• schools and education facilities;
• childcare centres;
• hotels and certain accommodation buildings;
• healthcare facilities;
• community buildings; and
• commercial components within mixed-use developments.

The building classification and scope of work should be confirmed before the assessment is commissioned. A building may appear residential or commercial from its design while being classified differently under the NCC.

BASIX and Section J compared

Can a project need both BASIX and Section J?

Yes. A mixed-use development may require BASIX for its residential components and Section J compliance for its commercial or non-residential components.

For example, a development containing apartments above ground-floor retail premises may require:

• BASIX for the residential apartments; and
• Section J assessment for the retail or other commercial areas.

The design team may need to separate the assessment areas according to their building classifications and uses. A single BASIX Certificate should not be assumed to address the commercial portion of the development, and a Section J Report should not be assumed to replace the residential BASIX requirements.

Early review can establish which areas follow the BASIX pathway and which areas need to be considered under Section J.

Do apartments require BASIX or Section J?

The size of an apartment building does not automatically make it a Section J project.

The residential dwelling component of a NSW apartment development generally follows the applicable residential compliance pathway. This commonly includes BASIX and may also include NatHERS thermal performance modelling.

However, the same development may contain separately classified spaces such as:

• retail premises;
• commercial offices;
• childcare facilities;
• hospitality areas; or
• other non-residential tenancies.

Those areas may require separate Section J assessment. Residential dwellings, common areas and commercial tenancies should therefore be reviewed according to their classification and use rather than being treated as one uniform assessment area.

What about boarding houses, hotels and short-stay accommodation?

Accommodation projects can be more difficult to categorise than standard houses or commercial offices.

The applicable pathway depends on the building classification, intended use, project description and approval documentation. Some accommodation projects may follow residential requirements, while others may need to demonstrate commercial energy efficiency compliance under Section J.

Where a development is not a standard dwelling, the classification should be confirmed before commissioning the assessment. This can prevent the project team from ordering the wrong report or discovering missing documentation later in the approval process.

Why are BASIX and Section J sometimes confused?

The two pathways are often confused because they can address similar building elements.

Both may involve:

• insulation;
• glazing;
• building fabric;
• heating and cooling systems;
• lighting;
• hot-water systems; and
• energy efficiency assumptions.

Both may also be required during the preparation of Development Application, Complying Development Certificate, Construction Certificate or building approval documentation.

The overlap in design inputs does not make the pathways interchangeable. BASIX remains a NSW residential sustainability pathway, while Section J remains part of the NCC commercial and non-residential energy efficiency framework.

Does Section J always mean JV3?

No. Section J is the broader commercial energy efficiency framework. JV3 is one possible performance-based pathway within that framework.

Many commercial projects can demonstrate compliance by following the relevant Deemed-to-Satisfy provisions directly. A JV3 assessment may be considered where a modelling-based Performance Solution is more appropriate for the proposed design.

The choice between DTS and JV3 belongs to the commercial Section J pathway and does not change whether the residential parts of a NSW development require BASIX.

How to determine which pathway applies

Start with the project location, building classification and proposed use.

• For a NSW house, duplex, secondary dwelling or residential renovation, review the BASIX requirements first.
• For a commercial or non-residential building, review the Section J requirements first.
• For apartments, confirm whether the project also contains commercial or separately classified spaces.
• For mixed-use development, assess the residential and non-residential portions separately.
• Where the building classification is unclear, confirm it before ordering the assessment.

The drawings, planning description, class of building and approval requirements will usually provide the information needed to establish whether the project requires BASIX, Section J or both.

What information should be provided for a pathway review?

The project does not need to be fully documented before an initial review can occur.

Useful starting information may include:

• the project address;
• architectural plans;
• elevations and sections;
• the proposed building use;
• the nominated building classification;
• the scope of the proposed work;
• planning or certifier comments; and
• known approval requirements.

Early review is particularly useful for mixed-use, multi-residential, accommodation and adaptive-reuse projects, where the compliance boundaries may not be immediately obvious.

How Certified Energy can help

Certified Energy prepares BASIX Certificates and assessments for NSW residential development and Section J Reports for relevant commercial and non-residential buildings.

Where the correct pathway is unclear, our team can review the available documents and identify whether the project is likely to require:

• BASIX only;
• Section J only;
• both BASIX and Section J; or
• further clarification of the project classification or approval requirements.

You do not need to determine the complete compliance pathway before sending the project documents. An early review can help establish the correct assessment scope before the design and approval process progresses further.

Frequently asked questions