Dual occupancy projects in NSW generally need BASIX as part of the residential approval pathway. A dual occupancy may be attached or detached, and it may involve two dwellings on one lot, future subdivision, shared services or separate dwelling arrangements. Because there is more than one dwelling involved, the BASIX assessment often needs more careful coordination than a single dwelling project.
The NSW Planning Portal describes multi-dwelling housing as more than one dwelling on a single lot, including townhouses, villa units and dual occupancy. This means a dual occupancy can fall within the multi-dwelling housing pathway depending on the project structure, site arrangement and approval documentation.
A dual occupancy in NSW will generally need BASIX because it is residential development. BASIX needs to account for both dwellings, including their layouts, glazing, orientation, insulation, hot water, rainwater, solar, garden areas and any shared services. The certificate should match the approval plans for the attached or detached dual occupancy design.
A dual occupancy is generally a development with two dwellings on one lot of land. The dwellings may be attached, such as two homes sharing a common wall, or detached, such as two separate dwellings on the same site. NSW Planning describes dual occupancy attached as two dwellings on one lot that are attached to each other, and dual occupancy detached as two detached dwellings on one lot.
For BASIX, the important question is how the project is classified and how many dwellings are being assessed. A dual occupancy is not the same as a secondary dwelling or granny flat, and it should be entered and reviewed according to the actual project type and approval pathway.
BASIX project type selection matters. NSW Planning explains that BASIX has project type options including one dwelling and two or more dwellings. For multi-dwelling housing, users enter the number of dwellings where there is more than one dwelling on a single lot, including townhouses, villa units and dual occupancy. :contentReference[oaicite:0]{index=0}
This means the assessor needs to understand whether the project is one dwelling per lot, two dwellings on one lot, multiple dwellings on one lot or a project connected to subdivision. Selecting the wrong pathway can lead to incorrect inputs, missing information or a certificate that does not reflect the approval documents.
Attached and detached dual occupancies may have similar BASIX categories, but they can perform differently. Attached dual occupancies may share walls, roof forms, party wall conditions, services or common elements. Detached dual occupancies may have separate orientations, different glazing exposure, separate roof areas, separate garden areas and different service locations.
These differences matter because BASIX and NatHERS outcomes are affected by the actual design. One dwelling may have better orientation than the other. One may have more west-facing glazing. One may have different shading or roof exposure. Both dwellings need to be assessed in a way that reflects the drawings.
For new dwellings, NSW Planning states that the applicant must submit with the development application one BASIX Certificate covering all dwellings. In some cases, the consent authority may allow a project to be split and accept separate BASIX Certificates covering different parts of the project. :contentReference[oaicite:1]{index=1}
For a dual occupancy, this means the project team should not automatically assume each dwelling will have a separate certificate. The correct approach should be confirmed based on the BASIX pathway, the approval documentation and any advice from council, the certifier or consent authority.
Dual occupancy BASIX can take longer than a simple single dwelling assessment because the assessor may need to review two dwellings, two layouts, two sets of window exposure, separate or shared systems and a more complex site arrangement. If NatHERS modelling is required, each dwelling may need to be modelled according to its own orientation, glazing, insulation and construction conditions.
The assessment can move more efficiently when the plans clearly show each dwelling, all elevations, sections, window schedules, floor areas, roof plans, garden areas, shared services and any proposed subdivision or common property arrangement.
BASIX still assesses water, energy use and thermal performance. For dual occupancies, those areas may need to be considered for each dwelling and for any shared systems. For example, the project may include separate hot water systems, a shared rainwater tank, separate solar systems, shared outdoor areas or different garden areas allocated to each dwelling.
The assessment may include:
Garden and landscape areas can matter in BASIX water assessment. NSW Planning explains that BASIX requires the total area of lawn or garden to be measured directly from the development application plans, and that all lawn and garden areas included in the development must be shown on those plans. :contentReference[oaicite:2]{index=2}
For dual occupancies, the site may include private open space for each dwelling, shared landscape areas or future subdivision boundaries. These areas should be clearly shown so the BASIX assessment can allocate water uses and landscaping assumptions correctly.
Dual occupancy projects often run into BASIX issues when the documentation does not clearly separate the two dwellings or explain shared systems. This can lead to uncertainty about project type, floor areas, roof catchments, private open space, window orientation, hot water systems, solar allocation or rainwater commitments.
Common issues include:
Some dual occupancy projects may use shared systems, while others may use separate systems for each dwelling. Shared systems could include rainwater tanks, stormwater infrastructure, solar PV, hot water systems or common landscape irrigation. The BASIX assessment needs to reflect the actual design and the way systems are allocated.
If shared systems are proposed, they should be clearly shown in the plans or specifications. The project team should also consider whether future subdivision, ownership or maintenance arrangements affect how realistic those shared commitments are.
For a dual occupancy BASIX assessment, the assessor needs enough information to assess both dwellings and any shared site commitments. The more clearly the documentation separates the dwellings, the easier it is to prepare the certificate accurately.
Useful documents and details include:
Certified Energy prepares BASIX Certificates and NatHERS assessments for dual occupancy projects across NSW. Our team can review the plans, confirm the likely BASIX pathway, identify missing information and coordinate the assessment for both attached and detached dual occupancy designs.
This is especially useful where the project includes shared systems, different dwelling orientations, future subdivision, complex glazing, tight thermal comfort requirements or multiple design revisions before lodgement.
Send your dual occupancy plans to Certified Energy and our team can review the BASIX pathway, missing information and likely assessment requirements.
Request a ReviewYes. A dual occupancy is a residential development type in NSW and will generally need BASIX as part of the approval pathway. BASIX may treat dual occupancy dwellings as multi-dwelling housing when there is more than one dwelling on a single lot.
The NSW Planning Portal describes multi-dwelling housing as more than one dwelling on a single lot, including townhouses, villa units and dual occupancy. Dual occupancy can therefore sit within the multi-dwelling housing pathway depending on how the project is structured.
Attached and detached dual occupancies may need similar core BASIX information, but the assessment must reflect the actual design. Attached dwellings may share walls, roof forms or services, while detached dwellings may have separate orientations, glazing, roof areas, gardens and service arrangements.
An assessor usually needs the project address, site plan, floor plans, elevations, sections, roof plan, dwelling layouts, window details, construction and insulation details, garden areas, hot water, rainwater, solar, pool or spa information and any shared services or common property details.