Duplexes and townhouses are common forms of residential development across Australia, but their energy-efficiency compliance requirements are not determined by their marketing or planning descriptions alone. The relevant National Construction Code building classification, building configuration and applicable compliance provisions must first be established.
Some duplexes and townhouse developments comprise Class 1a dwellings, for which the residential energy-efficiency provisions of NCC Volume Two may be relevant. Other residential developments may fall within Class 2 or another classification and require a different regulatory assessment framework.
For architects, building designers, builders and developers, understanding these distinctions early can help determine whether an elemental Deemed-to-Satisfy assessment is appropriate and what documentation will be needed for the proposed development.
A duplex or townhouse may be suitable for an elemental residential DTS assessment, but the correct pathway depends on the building classification and the provisions applying to the particular development.
In Brief
Yes, some duplexes and townhouse developments may be assessed using applicable elemental residential DTS energy-efficiency provisions.
Where individual dwellings are classified as Class 1a, the relevant NCC Volume Two and Housing Provisions requirements may provide an available compliance pathway.
However, not every development described as a duplex or townhouse has the same NCC classification. The building arrangement, separation between dwellings, access configuration and other classification considerations must be reviewed.
Class 2 residential developments are subject to a different NCC framework and should not automatically be assessed using the Class 1 elemental provisions.
For a broader explanation of the elemental compliance pathway, visit the Residential DTS Knowledge Hub.
NCC classification and jurisdiction note: This article discusses the suitability of duplex and townhouse developments for residential elemental DTS energy-efficiency assessments, using NCC 2022 as a reference framework. Building classification must be established under the applicable NCC provisions. The adopted NCC edition, state or territory variations, building configuration and approval circumstances may affect the available compliance pathways. A planning description such as duplex or townhouse does not, by itself, establish the NCC building classification.
The National Construction Code classifies buildings according to their use and relevant physical characteristics. These classifications help determine which technical provisions and compliance requirements apply.
For residential development, the distinction between Class 1 and Class 2 buildings is particularly important when considering energy-efficiency compliance pathways.
A detached dwelling and a row of attached townhouses may both involve Class 1a buildings, depending on their configuration. A residential apartment building, by contrast, commonly falls within Class 2.
Classification influences matters such as:
The development's planning terminology does not necessarily determine its NCC classification.
For example, two developments may both be marketed as townhouses while having different building arrangements and regulatory considerations.
Before selecting an elemental DTS pathway, the project team should confirm the building classification with reference to the applicable NCC definitions and approval framework.
Under the NCC, Class 1a includes a single dwelling that is either a detached house or one of a group of attached dwellings, with each dwelling separated by the required fire-resisting wall arrangement.
This means a duplex or row of townhouses may comprise individual Class 1a dwellings where the relevant classification conditions are satisfied.
The number of dwellings alone does not determine the classification. Their physical relationship, separation and overall building arrangement must also be considered.
Relevant project characteristics may include:
A conventional side-by-side duplex may have a different classification outcome from a development involving vertically stacked dwellings.
Likewise, a row of attached townhouses should not automatically be classified as Class 2 merely because several dwellings are constructed on the same development site.
The classification should be confirmed from the actual design rather than inferred from the number of dwellings, lot arrangement or development description.
Class 2 buildings contain two or more sole-occupancy units, each being a separate dwelling, within a building arrangement that falls under the relevant NCC Class 2 definition.
Apartment buildings are a common example, although classification should always be determined from the particular building configuration.
Class 2 developments are generally addressed under NCC Volume One rather than the Class 1 Housing Provisions framework in Volume Two.
This distinction matters because the energy-efficiency provisions, assessment methods and documentation requirements are not necessarily identical.
For a Class 2 development, the project team may need to consider:
The existence of DTS provisions within NCC Volume One does not mean that the same elemental assessment used for a Class 1 dwelling can simply be applied to a Class 2 development.
Equally, a Class 2 classification does not mean that all Deemed-to-Satisfy compliance options are unavailable.
The appropriate pathway must be established using the requirements applicable to the actual building classification.
For a duplex or townhouse development comprising Class 1a dwellings, the applicable elemental residential DTS energy-efficiency provisions may provide a recognised compliance approach.
Under NCC 2022 Volume Two and the associated Housing Provisions, elemental energy-efficiency requirements address relevant aspects of the building fabric and construction.
The provisions must be applied according to the relevant building classification, climate zone, construction system and assessment conditions.
Depending on the project, the review may consider:
The availability of an elemental pathway does not mean that every proposed design will satisfy its requirements without changes.
Each applicable requirement must be addressed in accordance with the relevant provisions. An improvement to one unrelated building element should not be assumed to compensate for another requirement that is not satisfied.
For the broader assessment framework, see the Residential DTS Knowledge Hub.
Two developments with the same NCC classification may have different practical outcomes when assessed against the applicable elemental DTS provisions.
Building form, orientation, glazing configuration and construction specifications can influence how readily the proposed design satisfies the prescribed requirements.
Townhouse developments may present particular coordination considerations because individual dwellings can have different external wall exposure, roof arrangements, glazing orientations and shading conditions.
Relevant design considerations include:
An end townhouse may have a different external envelope configuration from an internal townhouse within the same row.
Likewise, two mirrored duplex dwellings may have different window orientations even when their floor plans are otherwise similar.
These differences should be considered when establishing the assessment inputs and determining whether the same specifications can be used throughout the development.
For further discussion of early design considerations, see How Building Design Decisions Affect Residential DTS Compliance.
The assessment scope for a duplex or townhouse development depends on the building classification, applicable provisions and the design characteristics of the individual dwellings.
A development may be documented within a coordinated compliance package while still requiring the relevant requirements to be demonstrated for each dwelling or building element to which they apply.
It should not be assumed that one dwelling's compliance outcome automatically establishes compliance for every other dwelling in the development.
Differences that may affect assessment inputs include:
Where dwellings share genuinely identical relevant assessment conditions, some information may be suitable for coordinated documentation or repeated use, subject to the applicable assessment method.
However, similarities in appearance or layout should not replace verification of the relevant technical inputs.
The appropriate number and form of assessment documents should be agreed with the assessor and coordinated with the relevant certifier or approval requirements.
Residential energy-efficiency compliance must be considered within the regulatory framework applying to the project location.
In New South Wales, BASIX may apply to eligible duplex and townhouse developments as part of the residential planning and approval process.
BASIX and the NCC serve related but distinct regulatory functions. Establishing the NCC building classification and available DTS provisions does not remove separate BASIX requirements where they apply.
Likewise, a BASIX certificate should not be assumed to establish every NCC compliance matter for a project without considering the relevant statutory framework.
Before confirming the assessment approach, project teams should identify:
The correct compliance approach may therefore differ between otherwise similar townhouse developments in different jurisdictions.
The project team should establish these obligations before assuming that a particular elemental assessment will satisfy the complete approval requirements.
An initial suitability review should establish the building classification and identify the relevant energy-efficiency compliance framework before detailed elemental calculations are undertaken.
The information required will depend on the development, but a coordinated preliminary drawing package can help identify the appropriate assessment approach.
Useful information commonly includes:
The assessor may need additional information where the classification is uncertain or the building configuration includes features not clearly shown on the preliminary drawings.
Where the development includes different dwelling types, the relevant distinctions should be identified rather than assuming one representative dwelling covers the entire project.
For wider documentation considerations, see Preparing Residential DTS Documentation for Certifier Review.
An elemental residential DTS assessment is not necessarily the most appropriate approach for every duplex or townhouse development.
The correct pathway depends on the building classification, the applicable NCC requirements and the design's ability to satisfy the relevant provisions.
Where the proposed development is not within the scope of the relevant Class 1 elemental provisions, the project team must establish the compliance framework that applies to its actual classification.
Where an elemental requirement cannot be satisfied, the design may need revision or another recognised compliance approach may need to be considered, subject to the applicable NCC and jurisdictional requirements.
Other assessment approaches should not be treated as interchangeable. NatHERS-based pathways, reference-building methods and Performance Solutions have their own scope, requirements and supporting evidence.
The appropriate approach should be confirmed before the project team commits to a compliance method or assumes that a particular report will satisfy the approval requirements.
For a more focused comparison of residential assessment methods, see VURB vs DTS: Residential Compliance Pathways.
Frequently Asked Questions
Potentially. A duplex comprising Class 1a dwellings may be eligible for assessment under the applicable residential elemental DTS energy-efficiency provisions. The building classification, relevant NCC requirements and jurisdictional conditions must first be confirmed.
Townhouses may comprise Class 1a dwellings where the relevant NCC classification conditions are satisfied. Other residential configurations may fall within Class 2 or another classification. The term townhouse alone does not determine the classification.
An applicable elemental DTS pathway may be available for some Class 1a developments, but suitability depends on the relevant NCC provisions and jurisdictional requirements. DTS and NatHERS-based approaches should not be assumed to be interchangeable for every project.
The documentation arrangement depends on the development and assessment method. Each applicable dwelling or building element must be adequately addressed, but the information may be presented in a coordinated package where appropriate. One dwelling's result should not automatically be assumed to cover all others.
BASIX may apply to eligible duplex developments in New South Wales. The applicable BASIX and NCC requirements should both be established under the relevant approval framework. Selecting a DTS approach does not automatically remove BASIX obligations.
The project team should confirm the building classification, applicable NCC edition, jurisdiction, climate zone, development configuration and proposed construction systems. Current plans, elevations and relevant specifications help establish whether an elemental assessment is appropriate.
Related Knowledge
Understand the elemental residential compliance pathway, relevant building provisions and project suitability considerations.
Explore the distinction between elemental compliance and a reference-building approach where relevant to the project.
Understand how building form, orientation, glazing and construction choices can influence the elemental assessment.
Learn how the project location influences prescribed insulation, glazing and building sealing requirements.
Residential DTS Assessment
Certified Energy can review the proposed building configuration, architectural documentation and relevant energy-efficiency requirements to help establish whether a residential elemental DTS assessment is appropriate for your project.
Explore Residential DTS Assessment