NSW Residential Compliance Guide
A project that does not initially meet its applicable BASIX requirements is not automatically rejected, but a BASIX Certificate cannot yet be finalised for lodgement.
The phrase failing BASIX is commonly used when a residential assessment has not yet achieved the water, energy or thermal performance requirements applying to the project. It may also refer more broadly to an incomplete assessment that cannot yet generate a Certificate.
In most cases, this is a design and documentation stage rather than a final refusal. The assessor reviews the result, identifies the part of the assessment requiring attention and determines whether the issue comes from incorrect information, an unresolved specification or a genuine performance shortfall.
This guide explains what happens next. For a broader explanation of BASIX targets, documentation and the NSW submission pathway, visit the BASIX Knowledge Hub.
In Brief
Certificate Paused
The BASIX Certificate cannot be generated until the applicable targets and mandatory information requirements have been satisfied.
Cause Reviewed
The assessor checks whether the issue relates to project information, water, energy, heating performance, cooling performance or documentation.
Project Refined
Practical changes are tested, agreed with the project team and incorporated into the assessment and supporting documents.
Once the applicable requirements are met, the commitments can be reviewed and the BASIX Certificate can proceed. The aim is not simply to create a passing number, but to establish a solution that can be approved, documented, procured and built.
Understanding the Result
Usually, no. Before a BASIX Certificate has been generated, a result below the required standard means the assessment is still in progress. It does not ordinarily represent a council refusal or a determination that the development can never proceed.
The BASIX Tool calculates the project outcome from the information entered. Where the applicable standard is not achieved, the project remains unable to generate the Certificate needed for the relevant approval package.
The next step is therefore not to restart the entire project automatically. It is to establish:
A council or registered certifier may still raise separate planning or construction matters. Those issues should not be confused with an assessment that has not yet reached its BASIX requirements.
Assessment Pathway
A new-home BASIX assessment and an alterations-and-additions assessment do not use identical pathways. The assessor should interpret the result according to the dwelling type, project scope and standards applying to that particular application.
For new residential development, the principal performance requirements include:
The alterations-and-additions pathway uses a different assessment structure and should not automatically be described using the same new-home score thresholds.
Project type therefore matters. A result that appears straightforward in a detached new home may require a different interpretation for a renovation, pool, secondary dwelling or multi-dwelling development.
Certificate Status
The BASIX Certificate records the development and the commitments made to achieve the applicable requirements. It should not be generated while the entered project remains below those requirements or while essential information is missing.
Certificate generation generally depends on three conditions:
Applicable requirements have been achieved. The project must reach the targets or standards applying to its assessment pathway.
Mandatory fields are complete. Missing project details, construction information or required declarations can prevent finalisation even where the displayed scores appear adequate.
The certificate fee has been paid. Payment and generation occur after the assessment and commitment review have been completed.
Until these steps are complete, the project may still use an assessment report or in-progress result for design coordination. That document should not be confused with the final BASIX Certificate required for lodgement.
Review Pathway
The assessor should first review the assessment rather than immediately prescribing a list of upgrades. The project may be affected by incorrect data, an unresolved design decision or a genuine performance constraint.
Recheck the project information. Confirm that the assessment reflects the current plans, schedules, dwelling configuration and selected systems.
Identify the unresolved requirement. Separate a water or energy shortfall from heating, cooling, missing information or another pathway-specific issue.
Locate the influential inputs. Establish which parts of the design or specification are materially affecting that particular outcome.
Test realistic options. Compare adjustments that can be documented, sourced and delivered without unnecessary disruption to the project.
Agree on the preferred solution. The owner, designer, builder and relevant consultants may need to confirm cost, design and technical consequences.
Recalculate and coordinate. Update the BASIX assessment and ensure the plans and specifications reflect the resulting commitments.
Cause of the Result
Information Issue
The assessment may contain superseded window sizes, incorrect construction data, missing shading or systems that no longer match the project.
Selection Issue
Hot-water systems, glazing, fixtures, insulation or rainwater arrangements may not yet have been selected with enough certainty to complete the assessment.
Performance Issue
The entered project may be accurate and complete but still require changes to achieve its applicable water, energy or thermal requirements.
This distinction matters. Correcting an error is not the same as redesigning the building, while selecting an unresolved system is different from responding to a modelled heating or cooling problem.
Water Requirement
Where an applicable water standard has not been achieved, the assessor reviews the demand and water-saving inputs represented in the project.
The review may consider:
A larger rainwater tank is not automatically the correct solution. The tank must have a credible catchment and practical reuse arrangement. Similarly, efficient fixtures should represent products that can realistically be supplied and installed.
Once the revised water strategy has been agreed, its commitments should remain consistent with the site plan, roof drainage concept, hydraulic documentation and landscape information.
Energy Requirement
An energy shortfall is reviewed through the operational systems and services nominated for the project. It is not necessarily resolved by changing the walls, windows or thermal model.
Depending on the dwelling type and applicable pathway, relevant items may include:
The selected response should suit the dwelling, site infrastructure, electrical capacity, owner requirements and construction scope. A system should not be nominated purely to improve the assessment if the project team does not intend to install it.
An efficient mechanical system may improve the energy component, but it does not automatically correct a separate thermal comfort shortfall in the building design.
Thermal Performance
A thermal comfort shortfall means the proposed building design has not yet achieved the applicable heating, cooling or combined performance requirement.
The assessor should first determine whether the problem is principally related to winter heat loss, summer heat gain or a combination of both. These conditions can require different responses.
Glazing may be reviewed. Window area, orientation, frame type, U-value and solar heat gain characteristics can all influence the result.
Insulation may be reviewed. Roof, ceiling, wall and floor construction should be considered against the particular heating or cooling issue identified.
Shading may be refined. Eaves, screens, balconies and recesses can alter summer solar gain and useful winter sunlight.
Sensitive rooms may be targeted. One highly exposed room or elevation may be driving the result rather than the entire dwelling.
Geometry may require review. Where specification changes are insufficient, the project team may consider window size, room arrangement, roof form or other design elements.
The appropriate response should come from the modelled cause. Adding insulation indiscriminately may not resolve excessive summer solar gain, while reducing all solar access may increase winter heating demand.
Materials Index
The BASIX Materials Index calculates and records the embodied emissions associated with nominated building materials. It should not currently be described as a fourth performance score with an embodied-emissions limit that the project must pass.
However, the required materials information still needs to be completed accurately. Missing mandatory fields or inconsistent construction details may prevent the overall assessment from being finalised.
Where construction systems change during thermal optimisation, the materials information should also be reviewed so both parts of the BASIX application continue to describe the same walls, floors and roofs.
Selecting the Response
The answer depends on the unresolved requirement.
A water or energy issue may sometimes be addressed through realistic fixture, hot-water, rainwater or system selections. A thermal comfort issue is more likely to require review of glazing, shading, insulation, construction or building geometry.
The decision should consider:
The preferred solution is usually the least disruptive credible change that resolves the actual shortfall without transferring an unreasonable burden to another part of the project.
Documentation
A successful recalculation is not the final step. The revised inputs become project commitments and should be coordinated with the documents used for approval and construction.
Depending on the change, this may involve updating:
A Certificate that relies on specifications absent from the plans can create approval, procurement and construction problems later. BASIX, NatHERS and architectural documentation should describe one consistent development.
Approval Timing
Yes. Where a BASIX Certificate is required for the proposed development, an unresolved assessment can delay completion of the Development Application or Complying Development Certificate package.
The delay can extend beyond the Certificate itself where the agreed solution requires:
For this reason, BASIX should be reviewed before the intended lodgement date rather than treated as a final administrative task after every other document has been completed.
After Certificate Issue
A project that changes after Certificate issue presents a different situation from an initial assessment that has not yet achieved its requirements.
Where changes affect the information or commitments contained in the BASIX Certificate, the assessment should be updated and another Certificate generated. Relevant changes may include:
If the original Certificate has already been lodged, the revised Certificate and affected documents may also need to be re-lodged with the consent authority or certifier.
The exact approval process for a post-lodgement design change depends on the nature and extent of the amendment and should be confirmed with the relevant consent authority.
Important Distinction
Before lodgement, a project that has not yet met its BASIX requirements can usually be reviewed and refined within the design process.
After approval, the BASIX commitments form part of the development documentation. Constructing the project with different windows, insulation, water systems or energy systems can create a compliance issue even if the original Certificate was valid.
Where a proposed substitution affects a BASIX commitment, it should be reviewed before installation. The appropriate response may be to:
The certifying authority must ultimately be satisfied that the completed development has been built in accordance with the applicable BASIX commitments before final occupation documentation can proceed.
Common Mistakes
A shortfall may be concentrated in one assessment component, room, elevation, system or missing piece of information.
Water, energy and thermal comfort respond to different measures. An unrelated upgrade may add cost without improving the unresolved result.
A nominal product or system is not a credible solution if it is unavailable, unaffordable or inconsistent with the construction strategy.
Assessment work based on an old layout or window schedule can create recommendations that no longer suit the current development.
A thermal measure that reduces summer heat gain can also reduce useful winter sunlight if the complete modelled response is not reviewed.
The resolved specification must be transferred into the drawings, schedules and consultant documentation used for approval and construction.
Technical Boundary
This article explains the process that follows an unresolved BASIX result. It does not prescribe one universal set of upgrades for every residential project.
Detailed design optimisation is a separate step. It involves testing the particular inputs affecting the result, comparing practical alternatives and coordinating the selected response with the architectural design.
A BASIX assessor also does not replace the architect, hydraulic engineer, mechanical consultant, structural engineer, supplier or consent authority. Where a proposed change affects another technical scope, it should be confirmed with the relevant project consultant.
The assessor’s role is to identify how the proposed project performs within the BASIX pathway and help ensure that the adopted commitments are accurately represented in the assessment.
Frequently Asked Questions
The BASIX Certificate cannot yet be generated. The assessor reviews the project information and identifies which applicable requirement, mandatory field or commitment needs to be resolved before the assessment can proceed.
Does failing BASIX mean the council has rejected my project?Not usually. Before Certificate generation, it generally means the assessment is still in progress and the project has not yet demonstrated that it meets the applicable BASIX requirements.
Can the design be changed to meet BASIX?Yes. Depending on the cause, the response may involve correcting information, changing specifications or refining glazing, insulation, shading, systems, water commitments or selected parts of the design.
Does every BASIX shortfall require a major redesign?No. Some issues result from incorrect information or unresolved specifications. Where performance changes are required, the most effective response may be limited to one system, room, elevation or construction detail.
Can an unresolved BASIX assessment delay lodgement?Yes. Where a BASIX Certificate is required, the DA or CDC documentation may not be ready to lodge until the assessment has been completed and the Certificate has been coordinated with the plans.
What happens if the design changes after the BASIX Certificate is issued?Changes affecting the assessment or commitments should be reviewed. The BASIX assessment may need to be updated and another Certificate generated, with revised documents submitted to the consent authority or certifier where required.
Can a builder substitute a BASIX product after approval?A proposed substitution should be checked against the documented BASIX commitment before installation. Where it changes the assessment outcome or Certificate information, revised documentation or approval may be required.
Can a project fail because the BASIX Materials Index is too high?There is currently no BASIX limit on the embodied emissions reported through the Materials Index. However, the required materials information and other mandatory application fields must still be completed before the Certificate can be generated.
Related Guidance
BASIX Project Review
Certified Energy can review the available plans, assessment inputs and current project result to identify the unresolved requirement and advise on a practical pathway toward certification.
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