Alterations and additions can introduce current residential energy-efficiency requirements into a building that was designed and constructed under an earlier regulatory framework.
An extension may include new external walls, roofing, floors, glazing and insulation, while the retained dwelling may contain older construction systems that are difficult to verify or upgrade.
The resulting compliance scope is not identical for every renovation. It depends on the proposed work, building classification, jurisdiction, applicable NCC edition and approval pathway.
The central question is usually not whether the whole existing house meets today’s standards, but which new, altered or affected parts must be addressed for the proposed work.
In Brief
Current NCC requirements will commonly become relevant where an extension, conversion or substantial alteration requires building approval and introduces new or modified building work.
In most cases, the whole retained dwelling is not automatically required to satisfy every current NCC provision merely because an addition is proposed.
The new and altered work may nevertheless need to comply, while some existing elements may also need to be considered because of jurisdictional rules, the selected assessment method or the way the old and new construction interact.
Residential elemental DTS may provide a direct pathway where the relevant glazing, insulation, construction and sealing provisions can be applied clearly to the project scope.
Where elemental DTS is unavailable or impractical, the project team may need to consider whether BASIX, NatHERS, an available reference-building method or another appropriately documented pathway applies.
Scope and jurisdiction note: The treatment of alterations and additions is administered through state and territory building and planning legislation. The applicable NCC edition, local variations, approval requirements and assessment pathway should be confirmed before the energy-compliance scope is finalised.
The NCC generally becomes relevant where building approval is required for new or altered building work.
For residential alterations and additions, this may include projects involving:
Minor cosmetic work, routine maintenance or internal finishes may not create the same NCC energy-efficiency scope, particularly where the building envelope is not being altered.
An internal reconfiguration is therefore not automatically an energy-assessment trigger simply because an open-plan layout is being created. The relevant issue is whether approval is required and whether the work changes or introduces building elements covered by the applicable provisions.
The certifier, building surveyor, council or other approval authority should confirm the formal scope where the status of the work is uncertain.
A renovation project often contains three different conditions:
Entirely new walls, roofs, floors, windows and other construction introduced through the addition.
Existing construction that is opened, replaced, extended or materially changed as part of the project.
Parts of the existing dwelling that remain substantially unchanged by the proposed building work.
Current requirements will commonly be most directly relevant to the new and altered portions of the building.
That does not mean retained construction can always be ignored. An existing wall, roof, room or window may influence the assessment where it forms part of the altered thermal envelope, connects directly with the addition or is included by the selected assessment method.
State or territory legislation may also permit or require the approval authority to consider upgrades to existing elements in particular circumstances.
The assessment scope should therefore distinguish clearly between what is being physically upgraded, what is being included in calculations and what is remaining unchanged.
New South Wales has a specific BASIX pathway for qualifying residential alterations and additions.
A BASIX Certificate is generally required where alterations or additions to an existing residential building have an estimated development cost of $50,000 or more. BASIX can also apply to relevant swimming pool and spa projects.
The alterations-and-additions assessment differs from the pathway used for a completely new dwelling. The information and commitments generated depend on the actual scope of the proposed work.
Depending on the project, the BASIX assessment may consider new or altered:
A conversion or secondary-dwelling project may require a different BASIX application type where it creates a new separate dwelling rather than merely enlarging the existing home.
For the wider NSW framework, visit the BASIX Knowledge Hub.
The junction between retained and proposed construction is often more difficult to resolve than the centre of the new addition.
Typical interfaces may include:
These conditions can affect insulation continuity, sealing, moisture management, thermal bridging and the accuracy of the project documentation.
Existing construction may also be concealed. Original plans may be unavailable, or the installed insulation may differ from what earlier documents describe.
The assessor may therefore need available drawings, photographs, site information, builder confirmation or clearly recorded assumptions to understand the junction.
Where the existing condition cannot be verified, the design and approval team should agree on an appropriate and defensible way to document it rather than relying on an unsupported assumption.
Residential additions frequently introduce large sliding doors, garden-facing windows, skylights, clerestory glazing or double-height openings.
These features can be assessed successfully, but their size, orientation, shading and total-system performance need to be coordinated with the applicable compliance method.
Relevant information may include:
An addition with substantial glazing is not automatically unsuitable for elemental DTS. It may, however, require a narrower range of window products or more deliberate shading coordination.
The elemental pathway should not be described as allowing unlimited trade-offs between new glazing and additional insulation elsewhere. Each relevant provision must be resolved through the applicable method.
Glazing should therefore be reviewed before the façade design and supplier package are fully fixed.
The proposed construction system determines how insulation and other energy-efficiency provisions can be applied.
An additions project may include several different assemblies, such as:
Each assembly should be identified clearly on the plans and supported by an appropriate specification.
The design should also provide enough physical space for the nominated insulation. Raked ceilings, shallow roof cavities, structural members, drainage and services can reduce the available depth or interrupt continuity.
Thermal breaks, exposed floor conditions and slab-edge requirements may also become relevant depending on the proposed construction and applicable provisions.
A single generic insulation note may be insufficient where the project contains several distinct existing and proposed construction systems.
Considering an existing element in an assessment is not necessarily the same as requiring that element to be physically upgraded.
Existing areas may need to be included or documented where:
A NatHERS assessment for a major renovation may, for example, require a broader model of the dwelling than a narrowly scoped elemental review.
That modelling scope should not be confused with an automatic requirement to reconstruct every retained wall, window or floor to current new-home standards.
The compliance report should make clear which existing elements were included, what assumptions were used and which physical works are actually required.
A documentation gap should not automatically be treated as a pathway problem. Missing construction details or inconsistent window schedules should first be resolved as project-coordination issues.
A broader pathway review may be appropriate where the actual design remains difficult to resolve through the direct elemental provisions.
Examples may include:
Depending on the project, a NatHERS pathway may be available for a major renovation. An available reference-building method or another appropriately documented solution may also need to be investigated.
NatHERS should not automatically be described as a Performance Solution. It is a recognised residential assessment pathway using accredited house energy rating software.
Reference-building methods have a different compliance structure and are only relevant where the applicable NCC and jurisdictional provisions permit their use.
An early alterations-and-additions review may use:
The project does not need to be fully documented before an initial pathway discussion.
Concept information should, however, distinguish clearly between retained, demolished, altered and new construction so the likely compliance boundary can be understood.
Frequently Asked Questions
Usually not. Current requirements commonly apply to new or altered work rather than automatically requiring the entire retained dwelling to be upgraded. Existing elements may still need to be considered in limited circumstances because of the jurisdiction, approval decision or selected assessment method.
No. The applicable assessment depends on whether approval is required, what building work is proposed and which compliance pathway applies in the relevant jurisdiction. Minor cosmetic work will not necessarily create a residential energy-assessment requirement.
A BASIX Certificate is generally required for alterations or additions to an existing residential building where the estimated development cost is $50,000 or more. BASIX can also apply to certain swimming pool and spa projects. The correct application type should be confirmed before beginning the assessment.
NatHERS can be used for new homes and major renovations, but its regulatory role and modelling scope depend on the state or territory requirements applying to the project. The assessor should confirm whether it is the appropriate compliance pathway before modelling begins.
Not automatically. New or altered windows may need to satisfy the applicable requirements. Retained windows may also need to be considered where they fall within the selected assessment scope, but inclusion in the assessment does not necessarily mean every existing window must be physically replaced.
Not necessarily. Converting a garage into habitable space can change the relevant building and envelope requirements. Creating a separate dwelling may also trigger a different classification, BASIX application type or approval pathway from an alteration to the principal home.
Heritage or planning controls may restrict changes to windows, façades, roofing or other existing fabric. They do not automatically remove energy-efficiency obligations, but they may affect which technical and approval response is practical. Early coordination between the heritage, design, compliance and approval teams is advisable.
Related Knowledge
Understand elemental residential compliance, project suitability, building-fabric provisions and assessment documentation.
Review the NSW sustainability pathway for new homes, qualifying alterations and additions and other residential development.
See how glazing, shading, insulation and construction choices can influence the elemental pathway.
Alterations and Additions Review
Certified Energy can review the existing and proposed drawings, project location, glazing and construction information to help identify the likely residential energy-compliance pathway and the parts of the dwelling that may need to be assessed.
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