BASIX and Heritage NSW 2026: Alternative Assessments When Heritage Controls Conflict With BASIX Commitments

Answer first: If your NSW home is a heritage item or sits in a heritage conservation area and a heritage control directly conflicts with a BASIX commitment, you can apply for a BASIX heritage alternative assessment. The council must confirm the conflict, and only the conflicting commitments are removed or revised. There is no blanket BASIX exemption for heritage homes.

By: giantA Pty Ltd · Updated 5 November 2026

What is a BASIX alternative assessment?

An alternative assessment is the Department of Planning’s way of dealing with designs the online BASIX tool cannot fairly assess. The NSW Planning Portal’s alternative assessments page says it is appropriate in two situations:

• Heritage — the development is subject to specific heritage controls that conflict with BASIX requirements.
• New technology — the design includes a technology that saves energy or water but is not reflected in the BASIX tool.

For most homeowners the heritage pathway is the relevant one. It typically comes up with renovations and additions to Federation, Victorian and inter-war houses in conservation areas across the Inner West, North Shore and Eastern Suburbs. In these projects the BASIX tool’s usual answer to a thermal shortfall, such as external shading, tinted or performance glazing or a roof-mounted system facing the street, can be exactly what the council heritage officer will not support.

The rest of this guide explains who is eligible, how the process works step by step, what the Department will and will not do, and how to keep a heritage project moving while the application is assessed.

Does BASIX apply to heritage homes at all?

Usually yes. Being heritage-listed does not take a house out of BASIX by itself. Under the definitions in the Environmental Planning and Assessment Regulation 2021 (Schedule 7, Dictionary), BASIX development includes building a new dwelling, a change of use that turns a building into a dwelling, alterations to a dwelling where the estimated development cost is $50,000 or more, and a pool or spa serving one dwelling with a capacity of 40,000 litres or more. The Planning Portal’s alterations and additions page uses the same $50,000 threshold.

There is one important heritage exception. The Regulation’s list of BASIX excluded development includes development that involves the alteration of a building listed on the State Heritage Register under the Heritage Act 1977. The Planning Portal’s BASIX legislation summary lists the same exclusion, although that summary still refers to the older 2000 Regulation. So it matters which kind of heritage listing applies:

How do the different heritage situations compare for BASIX?

Sources: EP&A Regulation 2021, Schedule 7; Planning Portal BASIX legislation, alterations and heritage pages. Confirm the in-force wording before relying on it for a specific project.

Two other exclusions often appear in heritage renovations. Development only for a garage, storeroom, carport, gazebo, verandah or awning is excluded. So are alterations that create a space that cannot be fully enclosed, such as an open or screened verandah. If those elements are part of a larger addition, though, the cost of the whole project still counts towards the $50,000 test. See our guide to when renovations trigger BASIX and why you still need a certificate over $50k.

Who is eligible for a BASIX heritage alternative assessment?

According to the Planning Portal’s heritage alternative assessment page, you may be eligible if:

• the proposed development is on a statutory heritage list or in a statutory heritage conservation area, and
• the heritage control directly conflicts with a BASIX commitment.

The Department’s Heritage Alternative Assessment instructions describe this as a building listed as a heritage item on a statutory list, or in a heritage conservation area identified by an environmental planning instrument (such as the council’s LEP) or a development control plan. A general preference for a traditional look is not enough: there has to be a statutory heritage control, and the BASIX commitment has to clash with it.

The Portal gives two typical examples of conflict:

• shading needed to pass BASIX conflicts with a requirement to design a heritage-affected façade without shading
• the orientation of solar panels conflicts with heritage controls that say they may not be visible from the street.

The instructions give another: BASIX might require shading or dark-tinted performance glass that is not consistent with the heritage façade or the existing windows.

What will the Department remove and what will it not?

This is where heritage clients are often surprised. The Portal is explicit: “no complete exemptions from BASIX will be granted”. Only the commitments that clash with heritage controls are removed, so that a certificate can be issued. The instructions say the Department will remove or revise the conflicting commitments from that dwelling’s certificate. They also say that a complete exemption for the entire development will not be given.

In practice that means:

• water commitments, such as WELS-rated fixtures, usually still apply
• energy commitments, such as hot water and lighting, usually still apply
• thermal commitments that do not conflict with heritage (for example ceiling insulation that cannot be seen) still apply
• if a “heritage-compatible” shading or glazing option can satisfy both BASIX and the heritage control, you are expected to use it. The instructions say that commitment “should be made”.

Existing fabric matters too. The instructions note that existing construction that does not meet BASIX’s definition of “new or altered construction” does not need to be described on the certificate, and so does not need an alternative assessment. The Portal’s new or altered construction help notes explain when a wall or ceiling counts as altered. For example, a wall is treated as altered if removing its lining reveals framing. Repainting, or fixing sheeting directly over existing lining, does not count. Getting this right in the BASIX inputs can sometimes remove the apparent heritage conflict altogether.

How does the BASIX heritage alternative assessment process work?

The process below combines the Planning Portal’s alternative assessment page and the Department’s heritage instructions.

1. Enter the dwelling in BASIX and genuinely try to pass. Complete all sections and test a range of compliance strategies that do not conflict with the heritage controls. If you are using the Simulation method for a new dwelling, your accredited NatHERS assessor can help. If you can pass without any heritage conflict, no alternative assessment is needed.
2. If you cannot pass, generate a BASIX Report, not a certificate. The report lists the commitments that can be made. Do not generate a BASIX certificate at this stage.
3. Talk to the council’s heritage officer or advisor. The consent authority must form the opinion that the heritage limits on the building conflict with one or more commitments in the BASIX Report.
4. Complete the Heritage Alternative Assessment form. The form asks for the heritage listing and its statutory basis, the heritage controls that may conflict, and the commitments on the BASIX Report that conflict with them. It must be signed on behalf of the council or consent authority by the heritage officer. Attach the BASIX Report and documentation of the alternative compliance strategies you explored.
5. Apply in the BASIX tool. Log back into the project and apply for an alternative assessment on the Certificate page, selecting “Thermal Comfort (Heritage)” as the application type. Send the signed form as directed. The Portal’s BASIX forms page notes that the form needs signatures before it is sent.
6. Department review. The Department makes an initial assessment of whether an alternative assessment is appropriate and contacts you within 3 working days. It may request further information. If it accepts the application, the turnaround is at least 20 working days from the date of the application, and an additional cost applies.
7. Certificate issued with commitments removed or revised. If the dwelling cannot comply through a reasonable alternative method, the Department may issue a certificate with the conflicting commitments removed or revised.
8. Lodge with your DA or CDC. Submit the certificate with the development application. The Portal says the conflicting commitments are removed and you can then proceed with the development application process.

The Portal does not publish the additional fee on the alternative assessments page. It points to its BASIX certificate cost information, and you should confirm the current amount with the BASIX team before you budget for it.

How long does a heritage alternative assessment add to a DA?

Allow for it in the programme. The published timeframes are an initial response within 3 working days and at least 20 working days from application if accepted. On top of that comes the time to secure a council heritage officer’s signature, which depends on the council. Two practical consequences follow.

• Watch the 3-month window. A BASIX certificate must be lodged within 3 months of being issued (see the Portal’s certificate validity page and our guide to the 3-month lodgement window). Line up the alternative assessment with your DA lodgement date.
• Use the BASIX Report function while the design is moving. The Portal recommends using reports until the design is final, to avoid paying for new certificates.

When you lodge through the Planning Portal, you will enter the certificate number and the Portal will validate it. If the address on the certificate does not match the application, see our BASIX certificate validation guide.

What happens if the design changes after the alternative assessment?

Normally, revising a valid, lodged BASIX certificate for the same property and project costs nothing. Alternative assessment certificates work differently. The instructions say you will need to obtain modified certificates from the Department through the alternative assessment process if the design or specification changes. However, you will not need further council consent if the affected heritage aspect has not changed.

In practice, lock in the heritage-sensitive elements (street-facing glazing, shading, roof-visible equipment) before you apply. Treat later changes to those elements as a new heritage conversation with council, not just a BASIX re-run. Any change still has to flow through to the construction certificate drawings, and finally to the BASIX completion receipt before the occupation certificate.

What heritage-compatible options should you test before applying?

The Department expects a genuine and reasonable attempt to comply, and asks for documentation of the strategies you explored. In our design reviews, the options worth testing in the BASIX tool before claiming a conflict usually include:

• Glazing selections that keep the heritage look. Since the May 2026 tool upgrade, alterations and additions have more glazing options with low solar heat gain coefficient values. See our May 2026 BASIX tool upgrade guide. Ask your heritage advisor whether a clear-looking low-SHGC product in a traditional frame is acceptable.
• Moving the thermal work out of sight. Insulation in new or altered walls, floors and ceilings, and well-designed rear additions, can do much of the work without touching the street elevation.
• Shading that reads as part of the building. Rear pergolas, deep eaves on new work or internal-looking solutions may be acceptable where façade shading is not.
• Switching to the Simulation method where it is available. For alterations, see when NatHERS modelling is allowed over $50k. For new homes, see our comparison of DIY, Simulation and Passive House.
• Locating solar panels on non-street-facing roof planes before concluding that panels conflict with heritage controls.

These are design judgements, not guarantees. Whether a particular product or layout satisfies both BASIX and the heritage controls depends on the tool’s results and the council’s heritage assessment.

How does this fit with the heritage side of the DA?

The BASIX alternative assessment does not replace the heritage assessment of the DA. Council will still assess the proposal against the LEP heritage clause and the DCP, and will often ask for a Statement of Heritage Impact. Our guides to heritage impact statements and clause 5.10 and renovating in a heritage conservation area cover that process. If you are not sure of a property’s status, Heritage NSW’s heritage listings page explains the levels of listing, and the property’s planning certificate and LEP heritage map are the usual starting points.

It helps to brief the heritage consultant and the BASIX or NatHERS assessor together. The Statement of Heritage Impact can then explain why certain commitments conflict, and the alternative assessment form can point to the same controls.

What about the new technology alternative assessment?

The second type of alternative assessment is for technologies the BASIX tool does not yet recognise. The Planning Portal’s new technology page gives examples such as geothermal heating and renewable energy sources not currently available in the tool. Before a technology can be considered, it must:

• save more than 1% of an average dwelling’s potable water use (2.5 kL a year) or more than 1% of its greenhouse emissions (85 kg CO2-e a year), or both
• have been physically demonstrated, with provable savings from operation over at least 1 year
• comply with the relevant Australian and NSW standards, regulations and guidelines.

Applications are lodged with the Department, which may accept or refuse them at its discretion. If an application succeeds, the Department assigns savings to the technology type, which may lead to changes in the BASIX tool. This pathway is aimed mainly at manufacturers and suppliers. Homeowners should contact the Department before relying on it for a single project.

Where does giantA fit in?

giantA designs alterations, additions and new homes on heritage-affected sites across Sydney and NSW. We test heritage-compatible BASIX strategies at concept stage and coordinate the heritage consultant and NatHERS assessor. Where a genuine conflict remains, we prepare the BASIX Report and alternative assessment documentation for the council heritage officer’s sign-off. See BASIX and NatHERS, BASIX assessment in Sydney or our design and approvals services, or contact giantA for a project review. For the full BASIX process, start with our step-by-step BASIX certificate guide.

Frequently asked questions

Are heritage-listed homes exempt from BASIX in NSW?

Not generally. Only alterations to buildings on the State Heritage Register are BASIX excluded development. Locally listed items and houses in conservation areas still need BASIX where it is triggered, but conflicting commitments can be removed through an alternative assessment.

Does BASIX apply to a renovation in a heritage conservation area?

Yes, if the alteration’s estimated development cost is $50,000 or more (or it includes a pool or spa of 40,000 litres or more serving one dwelling). The heritage alternative assessment deals only with specific conflicting commitments.

Who signs the Heritage Alternative Assessment form?

The applicant signs a declaration, and the form must also be signed on behalf of the council or consent authority by its heritage officer. Without that signature the application is not valid.

How long does a BASIX alternative assessment take?

The Department makes initial contact within 3 working days. If it accepts the application, the turnaround is at least 20 working days from the date of the application, plus the time it takes to get council sign-off.

Is there a fee for a BASIX alternative assessment?

Yes. The Planning Portal says an additional cost applies if the application is accepted. Check the current amount with the BASIX team, as it is not stated on the alternative assessments page.

Can I change my design after the alternative assessment?

Yes, but modified certificates must come through the alternative assessment process. You will not need new council consent for the heritage conflict if the affected heritage aspect has not changed.

Who do I contact about a heritage alternative assessment?

The Department’s instructions direct applications and enquiries to the BASIX team at basix@planning.nsw.gov.au and the BASIX Help Line on 1300 650 908 during business hours.

Preferred sources (verify current versions)

• NSW Planning Portal — BASIX alternative assessments
• NSW Planning Portal — Heritage alternative assessment
• NSW Department of Planning — Applying for a Heritage Alternative Assessment (instructions, PDF)
• NSW Department of Planning — Heritage Alternative Assessment application form (PDF)
• NSW Planning Portal — BASIX forms
• NSW Planning Portal — New technology alternative assessment
• NSW Planning Portal — BASIX legislation summary
• NSW Legislation — Environmental Planning and Assessment Regulation 2021 (Schedule 7, Dictionary)
• NSW Planning Portal — BASIX alterations and additions
• NSW Planning Portal — New or altered construction
• NSW Planning Portal — Certificate validity and changes to the project
• NSW Planning Portal — BASIX tool upgrades now live (May 2026)
• Heritage NSW — Heritage listings
• Heritage NSW — Works approvals for State Heritage Register items