BASIX Certificate, NatHERS and Section J for Developers

Energy compliance is one of the few design inputs that is fixed by regulation, priced in the building fabric, and checked twice by someone who can stop your job. It decides your glazing specification, your insulation build-up, your hot water plant, and increasingly whether you are buying a solar array you had not budgeted for. None of that is negotiable at construction stage, which is why the numbers need to be in the cost plan at design stage rather than discovered at tender.

Three separate instruments do this work in Australia. A Building Sustainability Index (BASIX) certificate is a New South Wales planning document. A Nationwide House Energy Rating Scheme (NatHERS) rating is the national method for rating the thermal performance of a home. Section J is the energy efficiency part of Volume One of the National Construction Code (NCC), and it applies to commercial and multi-residential buildings. They overlap, they are frequently confused, and which of them you need depends on your building class and your state.

The people who hold the answers are your accredited energy assessor, your Environmentally Sustainable Design (ESD) consultant, and your building surveyor or certifier. The assessor produces the rating, the Environmentally Sustainable Design (ESD) consultant produces the Section J report, and the certifier is the one who decides whether what you built matches what was rated. The architect draws it, but the assessor’s model is what the specification has to follow.

Figures, section numbers and adoption dates in this guide were current at the date of writing, and they move. Each rule links to its primary source, which is where to confirm the position on your own project.

What is a BASIX certificate, and when do you need one?

A Building Sustainability Index (BASIX) certificate is a New South Wales planning document that records the water, energy and thermal performance commitments a residential development has to meet. It is generated through the state’s online tool and it is the only one of the three instruments that is a planning requirement rather than a building code requirement.

The standards it enforces sit in State Environmental Planning Policy (Sustainable Buildings) 2022, which commenced on 1 October 2023 and repealed the earlier 2004 policy. The State Environmental Planning Policy (SEPP) sets three things: a percentage reduction in greenhouse gas emissions per occupant against a published baseline, a percentage reduction in mains-supplied potable water use, and a cap on the energy needed to heat and cool the dwelling, expressed in megajoules per square metre of conditioned floor area per year.

All three vary by climate zone and by dwelling type. Schedule 1 of the policy runs separate tables for houses and duplexes under 110 square metres, houses over 110 square metres, apartment buildings up to three storeys, four to five storeys, six to twenty storeys, and twenty-one storeys and above. In climate zone 17, for instance, a house over 110 square metres has to beat the emissions baseline by 72 per cent, while a six-storey-plus apartment in the same zone has to beat it by 63 per cent. A developer working across two council areas in different climate zones may find the same standard drawing produces two different results.

The certificate is required at two points. It accompanies the Development Application (DA) or complying development certificate application, and it has to be produced again at construction certificate stage. Under section 10 of the Environmental Planning and Assessment (Development Certification and Fire Safety) Regulation 2021, a construction certificate application for BASIX development must be accompanied by either “a BASIX certificate that applied to the development when the development consent was granted” or “another BASIX certificate issued no earlier than 3 months before the application is made”. Where the work alters a building containing more than one dwelling, the same section requires “a separate BASIX certificate for each dwelling”.

That three-month window is the detail most often missed. A certificate that sits unlodged while a design is being resolved may expire, and the version that binds you is the one attached to the consent, not the one your assessor produced last week.

What is a NatHERS rating, and how is it different?

A Nationwide House Energy Rating Scheme (NatHERS) rating is a modelled star rating out of ten describing the thermal performance of a dwelling’s building shell: roof, walls, windows and floors. It measures how much heating and cooling energy the design needs, not how the building is used and not what appliances go in it.

Since the 2022 edition of the National Construction Code (NCC), the scheme has also produced a second number. The Whole of Home score runs from 0 to 100 and covers the energy used by major fixed appliances, including heating and cooling systems, hot water, lighting and pool and spa pumps, less any energy generated on site by solar photovoltaic systems. The scheme’s own guidance describes a score of 100 as “a net zero energy value home”, and notes that “ratings above 100 are possible” where a dwelling generates more than it uses.

So the star rating and the Whole of Home score answer different questions. The star rating is a fabric number. The Whole of Home score is a plant and appliance number that a solar array can move. A design that struggles on orientation can often recover its Whole of Home score by upgrading the hot water system or adding panels, which is a materially cheaper lever than reworking the glazing schedule. That trade-off is the single most useful thing a developer can understand about the scheme.

There is a quality distinction in who produces the rating, and it matters commercially. The scheme publishes certificates in two formats: one carrying the scheme logo, produced by an accredited assessor, and “a non-accredited report without the NatHERS logo and only available in black and white”. Its guidance is direct about the difference, noting that non-accredited assessors “are not required to have any formal qualifications, maintain insurance or undergo quality assurance checks on their ratings”. Accreditation is not compulsory everywhere. On a project where the certifier or a funder wants a verifiable rating, a cheap non-accredited report can turn into a re-rating and a redesign, and the saving disappears.

Where the Building Sustainability Index (BASIX) applies, in New South Wales, the thermal caps in the State Environmental Planning Policy (SEPP) are expressed in megajoules rather than stars, and the assessment is run through the state tool. Everywhere else, the star rating and the Whole of Home score are the direct compliance metric under Volume Two of the National Construction Code (NCC).

What is Section J, and which buildings does it catch?

Section J is the energy efficiency section of Volume One of the National Construction Code (NCC), which is the Building Code of Australia (BCA) for Class 2 to Class 9 buildings. It covers apartment common areas, offices, retail, hotels, warehouses, hospitals and schools. Detached houses and townhouses sit in Volume Two and are dealt with through the star rating and Whole of Home route instead.

Section J is not a rating. It is a set of performance requirements with prescriptive Deemed-to-Satisfy provisions underneath them, plus several verification methods that let you model your way to the same outcome. The Part J1 performance requirements set “the thermal performance properties of building fabric, the energy efficiency of key energy using equipment and the features a building must have to facilitate the future installation of distributed energy resources”.

For a developer, the practical question is which compliance pathway your consultant intends to use, because the pathways cost different amounts and carry different obligations.

The Deemed-to-Satisfy route is the prescriptive one. You meet the tabulated fabric, glazing, lighting and services requirements and you are done. It is the cheapest to document and the least flexible on design.

The J1V3 verification method compares the modelled greenhouse gas emissions of your building against a reference building built to the Deemed-to-Satisfy provisions. If the proposed building does not exceed the reference building, it complies. This is the pathway that lets an architect keep a glazed facade by paying for it elsewhere in the services. The code builds in a guard against pushing that too far, with provisions “designed to protect the thermal performance of the building’s envelope from ‘trading’ off its performance with that of the building services”.

The J1V1 verification method uses the National Australian Built Environment Rating System (NABERS) modelling framework. Under the 2022 edition, a Class 5 office complies where “an energy model of the building design predicts the energy consumption to be less than 67% of 5.5 stars on the NABERS Energy for Offices base-building scale”, which the code notes is “roughly equivalent to a 6-star NABERS Energy rating”. The important commercial point is that this route requires a National Australian Built Environment Rating System (NABERS) Commitment Agreement, which is an undertaking about how the finished building performs in operation rather than only about how it was designed. That is a live obligation running past practical completion, and on a build-to-hold asset it interacts directly with your net operating income assumptions.

The 2022 edition also expanded this route beyond offices to Class 2 buildings other than sole-occupancy units, Class 3 buildings, and Class 6 shopping centres, each with its own threshold.

Which instrument applies to my project?

The short version is that your state decides, and then your building class decides.

An apartment building in Sydney generally needs both. A Building Sustainability Index (BASIX) certificate covers each dwelling, and Section J covers the common areas, the carpark, the lifts and the central plant. Two consultants, two documents, two sets of assumptions that need to agree with each other. Where they disagree, the usual casualty is the facade specification, because the same window can be doing different work in each model.

What do the current standards actually require?

Under the 2022 edition of the National Construction Code (NCC), the headline residential requirement is a 7 star thermal rating plus a Whole of Home score. Queensland’s published position is representative: Business Queensland states that “a new house needs to achieve a minimum Whole of home score of 60 (out of 100) and a new unit apartment needs to achieve at least 50 (out of 100)”, and that new Class 2 buildings “must also achieve an average 7-star energy equivalence rating for all units in the building, with no individual unit to be rated less than 6-stars”.

That averaging rule is worth reading twice on an apartment project. It means south-facing units can sit below the average provided none falls under 6 stars, which gives a designer room to move but also creates a hard floor that a poorly oriented corner unit can breach. Finding that out after the plans are set is expensive.

Queensland then varies the national position through the Queensland Development Code (QDC) 4.1, which allows 5 stars “for eligible small homes of 50 square metres or less”, 6 stars “for eligible houses with raised floor construction”, and “an optional credit of up to 1 star for a compliant outdoor living area” that can count toward the applicable minimum. A developer running the same product across the border should not assume the rating transfers.

In New South Wales, the equivalent uplift came through the planning system rather than the building code. The Department of Planning records that the standards increased on 1 October 2023, lifting the thermal performance standard from an average of between 5.5 and 6 stars to 7 stars on the Nationwide House Energy Rating Scheme (NatHERS), and reducing greenhouse gas emissions “by 7-11% (depending on location and type of residential development proposed)”. The department also notes the increase did not apply everywhere, excluding “homes in climate zones 9, 10 and 11 and apartment buildings up to 5 storeys”.

What changed under National Construction Code 2025, and when does it bite?

For residential work, very little. For commercial work, quite a lot, and the biggest change is a capital item.

The Australian Building Codes Board released the 2025 edition on 1 May 2026 and describes the position plainly: “the most significant technical changes in NCC 2025 apply to new commercial buildings”. The headline item is that the edition “includes new requirements for renewable energy generation for Class 3 and Class 5 to 9 buildings, through mandatory on-site solar photovoltaic systems”.

The detailed change list sets out what that means clause by clause:

• Under J1P1(e), “the regulated energy allowance has been roughly halved, and greenhouse gas emissions are now quantified”.
• J9D5 has been updated “to require buildings to install solar PV, rather than only providing space for future installation”.
• J6D10 and J8 have been updated to support future electrification, so that “buildings must be designed so gas systems can be more easily replaced with electrical capacity, switchboard space, risers, and plant space”.
• J4 strengthens fabric requirements, “including new thermal emittance rules for roofs, and stricter solar admittance criteria for wall-glazing constructions”.
• J1V1 “increases the NABERS star rating targets”, so the National Australian Built Environment Rating System (NABERS) verification route is now a higher bar than it was.

The shift in J9D5 is the one to price. Under the previous edition you provided space and capacity for a future array. Under the 2025 edition you install it. That converts a design allowance into a real line in the cost plan, along with the structural, electrical and switchboard work behind it. There is no published government figure for what that costs across building types, and any single number would be misleading given it scales with roof area and climate zone. A current supplier quote against your actual roof plan is the only honest source, and it should go into total development cost as a certainty with an unknown size, not as contingency.

Adoption is a matter for each jurisdiction, and the positions differ materially. The board’s published adoption table records the following at the date of writing:

The board also warns that “some NCC requirements may apply at different times or not at all due to state or territory variations”. Two developers building the same office tower, one in Melbourne and one in Sydney, are currently designing to different energy requirements, and the Sydney project has roughly a year before the mandatory solar photovoltaic provision reaches it.

How do the states and territories differ on residential energy?

New South Wales runs the Building Sustainability Index (BASIX) through the planning system, so a residential developer there deals with a certificate and megajoule caps rather than a star rating on its own. The state’s building code adoption is separate from that, which is why the 2025 edition date above does not change the residential position.

Victoria applies the 7 star requirement and the Whole of Home score to new homes. The Victorian Government’s published position is that “the new standards have a mandatory commencement date of 1 May 2024”, and that “the changes will not be compulsory for homes that have a building permit issued before 1 May 2024”. The same guidance confirms that solar photovoltaic systems are not mandatory for residential work in Victoria: “the installation of on-site renewables for example solar photovoltaic (PV) systems, can be used to offset any remaining energy use to meet the tailored Whole of Home budget”. Optional, not required, is a useful distinction when the Whole of Home number is short.

Queensland has applied the residential standards since 1 May 2024 through the Queensland Development Code (QDC) 4.1, with the small-home, raised-floor and outdoor-living-area variations described above.

For the remaining jurisdictions, the residential positions have moved more than once and are best confirmed against each state’s own building authority rather than a table like this one. Where a project sits near a state border or a transition date, the certifier is the person who can tell you which edition your building permit or construction certificate will be assessed under, and that answer is worth getting in writing before the cost plan is signed off.

Does non-residential development in New South Wales carry extra obligations?

Yes, above a capital investment value threshold, and the obligations sit in the planning system rather than the building code.

Chapter 3 of the Sustainable Buildings State Environmental Planning Policy (SEPP) applies to non-residential development involving “the erection of a new building, or alterations, enlargement or extension of an existing building, if the development has a capital investment value of $10 million or more”. Several zones are carved out, including rural, environmental conservation and heavy industrial zones, as are residential care facilities.

Two requirements are worth knowing before you lodge.

First, embodied emissions. Section 3.2(2) provides that “development consent must not be granted to non-residential development unless the consent authority is satisfied the embodied emissions attributable to the development have been quantified”. The policy defines those emissions to include extraction of raw materials, transport to manufacture, and the manufacture of the materials themselves. This is a reporting obligation rather than a performance cap, but it is a consent precondition, so an incomplete report is a hold on the determination.

Second, the operational standards for large commercial development. Section 3.3 provides that consent “must not be granted to large commercial development unless the consent authority is satisfied the development is capable of achieving the standards for energy and water use specified in Schedule 3”, and that capability is established “if there is a NABERS commitment agreement in place to achieve the standard”. Schedule 3 sets those standards as a 5.5 star National Australian Built Environment Rating System (NABERS) energy rating for prescribed office premises, 4 stars for prescribed hotel or motel accommodation and prescribed serviced apartments, and a 3 star National Australian Built Environment Rating System (NABERS) water rating.

The definitions do the work here. “Prescribed office premises” means office premises with a net lettable area of at least 1,000 square metres, and prescribed hotel or motel accommodation means accommodation “with at least 100 rooms”. Below those thresholds the Schedule 3 standards do not apply, though the embodied emissions requirement still does.

A Commitment Agreement is a forward obligation on the operating asset. On a build-to-hold project that is a covenant your future asset manager inherits, and it belongs in the same conversation as your leasing assumptions rather than being treated as a planning form to be signed and forgotten.

What does energy compliance do to build cost and margin?

It shows up as a rate increase spread across trade packages rather than a single line, which is what makes it easy to miss in a high-level estimate and hard to argue about later. Glazing, insulation, hot water plant, and now solar photovoltaic on commercial work.

The most useful published figures are the ones the New South Wales Department of Planning released when it lifted the Building Sustainability Index (BASIX) standards. Its estimate of the upfront cost of that increase was $7,152 more to build an average house in Blacktown, $6,403 more for an average townhouse in Albion Park, and $860 more per apartment for a high-rise in Macquarie Park. Those figures were published around September 2023 and describe one specific regulatory step in one state, so treat them as an order of magnitude rather than a rate to apply.

The ratio between them is the part that generalises. Per dwelling, the same regulatory increase cost a detached house roughly eight times what it cost a high-rise apartment. Fabric-driven requirements land hardest on the product with the most external envelope per dwelling, which is exactly the low-density product with the thinnest margins.

Two worked examples, using those published figures.

A 60-apartment high-rise. Gross realisation of $54,000,000 at an average of $900,000 per apartment. Total development cost of $45,000,000, of which land is $12,000,000 and everything else is $33,000,000. Development profit of $9,000,000, which is a margin on cost of 20.00 per cent. Apply the $860 per apartment uplift and total development cost rises by $51,600 to $45,051,600. Profit falls to $8,948,400 and margin on cost falls to 19.86 per cent. A 14 basis point movement, which most feasibilities would absorb without comment.

A 40-lot detached housing project, same state, same rule change. Gross realisation of $34,000,000 at $850,000 per dwelling. Total development cost of $28,000,000, of which land is $9,000,000 and everything else is $19,000,000. Development profit of $6,000,000, a margin on cost of 21.43 per cent. Apply the $7,152 per dwelling uplift and total development cost rises by $286,080 to $28,286,080. Profit falls to $5,713,920 and margin on cost falls to 20.20 per cent. A 123 basis point movement from the same regulatory change, nearly nine times the effect on the apartment project.

Neither result is catastrophic on its own. The point is that a single national or state-wide “energy compliance allowance” applied across a mixed pipeline will be wrong in both directions, and the direction it is wrong in is the one that matters most on the thinnest deal.

Three practical consequences follow.

Your benchmark rate is probably describing an older code. Any construction cost per square metre figure you are carrying was derived from buildings certified under a particular edition. Benchmarks lag code changes by years. On a commercial project in a jurisdiction that has already adopted the 2025 edition, a rate set on 2022 edition projects has no solar array in it at all.

Your quantity surveyor needs to be told which edition applies. This is a one-line instruction that is easy to forget and expensive to omit, particularly where a project straddles an adoption date and the answer depends on when the building permit or construction certificate issues rather than when the Development Application (DA) was lodged.

Mandatory items are not contingency. A required solar photovoltaic system is a certainty with an unknown size, not a risk. Parking it in construction contingency means competing with genuine risk for the same pool, and contingency gets consumed early.

Where does each instrument sit in the programme?

Earlier than most developers assume, and each one gates a different approval.

The Building Sustainability Index (BASIX) certificate is a Development Application (DA) document. It has to exist before you lodge, which means the assessor has to have modelled a design that is resolved enough to rate. That usually means a fixed glazing schedule and a nominated hot water system at a stage when the architect would rather keep options open.

The Nationwide House Energy Rating Scheme (NatHERS) rating is generally a building approval document outside New South Wales, so it attaches to the building permit or construction certificate. In practice the sensible time to run a preliminary rating is at design development, because a design that fails at permit stage fails after the cost plan is written.

The Section J report is a construction certificate or building permit document, produced by the Environmentally Sustainable Design (ESD) consultant once the facade and services design is settled enough to model. Where the J1V1 route is used, the National Australian Built Environment Rating System (NABERS) Commitment Agreement has to be in place before the verification is complete, and that is a separate process with its own timeline.

Then there is the second check, at the other end. The certifier’s job is to confirm the building as constructed matches the rated design. A window substituted during procurement because the specified unit had a twelve-week lead time can invalidate a rating that was correct on the day it was issued. The trap is procurement, not design.

What are the common traps?

Design changes after the certificate issues. The rating models the design as drawn. Changing glazing, insulation, orientation or hot water plant after the fact can put the building outside the rated commitments, and the certifier is entitled to say so. In New South Wales a change significant enough to need a fresh certificate can also mean a section 4.55 modification to the consent, which is its own timeline.

Certificate expiry. The three-month issue window in section 10 of the Development Certification and Fire Safety Regulation catches projects where design resolution takes longer than expected.

Non-accredited ratings. Cheaper, faster, and not quality assured or insured. Where a certifier or a funder wants a verifiable document, the saving reverses.

The apartment averaging floor. The average 7 star requirement with a 6 star minimum per unit means one badly oriented unit can hold up the whole building’s compliance.

Assuming a product transfers across borders. State variations are real. The Queensland Development Code (QDC) 4.1 concessions do not exist in Victoria, and the New South Wales megajoule caps do not exist anywhere else.

Assuming Section J is only about insulation. Under the 2025 edition it is also about a physical solar array, switchboard space, risers and plant space set aside for future electrification, and lighting control systems. Those are services and structural items, and they need to be in the services budget rather than the fabric allowance.

How does New Zealand handle this?

Through clause H1 of the Building Code, which “provides for the efficient use of energy and sets physical conditions for energy performance”. There is no star rating scheme equivalent to the Australian residential system and no planning-level certificate equivalent to the Building Sustainability Index (BASIX). Compliance runs through Acceptable Solutions and Verification Methods published by the Ministry of Business, Innovation and Employment (MBIE).

The current position is a transition. H1/AS1 6th edition and H1/VM1 6th edition took effect on 27 November 2025, with H1/AS2 2nd edition and H1/VM2 2nd edition on the same date. The 5th edition documents remain available “until 26 November 2026”, which means a New Zealand developer currently has a choice of compliance documents, and that choice closes on 27 November 2026.

The Ministry of Business, Innovation and Employment (MBIE) frames the 2025 update as increasing flexibility rather than raising stringency, and has published guidance material on the changes. For a developer with consents in train across that cutover date, the question worth asking the designer is which edition the consent was assessed under and whether the design would still comply under the other one.

What to ask your energy assessor and ESD consultant

• Which instrument does this project actually need, and does it need more than one? On a Sydney apartment building, confirm who is producing the Building Sustainability Index (BASIX) certificates and who is producing the Section J report, and that the two models use the same facade.
• Are you accredited, and will the certificate carry the scheme logo? If not, ask why, and ask whether the certifier and any funder will accept it.
• Which Section J compliance pathway are you proposing, and what does each cost to document? Ask specifically whether the J1V1 route is being used, because it brings a National Australian Built Environment Rating System (NABERS) Commitment Agreement with it.
• What is the cheapest lever if we are short? Ask for the trade-off explicitly: what does one more star of fabric cost against what an upgraded hot water system or an array costs to move the Whole of Home score.
• Which National Construction Code (NCC) edition will this project be certified under, and what changes if the timing slips past the adoption date in this state?
• If the project sits in a jurisdiction that has adopted the 2025 edition, what solar photovoltaic capacity does J9D5 require on this roof, and what structural and electrical work sits behind it?
• What in this design is most likely to change during procurement, and which of those changes would invalidate the rating?

What to ask your quantity surveyor and building surveyor

• Which National Construction Code (NCC) edition is the cost plan priced to, and were the benchmark rates derived from buildings built to that edition?
• Is the solar photovoltaic system a separate line in the cost plan, or is it inside a fabric allowance where nobody will find it?
• What is the difference in total development cost between the two editions, priced as two scenarios rather than as a single allowance?
• At what point does the applicable edition lock in for this project, and is it the Development Application (DA), the construction certificate or building permit, or the commencement of work?
• Which trade packages carry the energy compliance uplift, and are those packages already let?
• What does the certifier need to see at completion to sign off that the building matches the rated design, and who is responsible for producing it?