Retain and Subdivide in Adelaide: Managing Existing Eaves and Boundary Clearances

The Retain-and-Subdivide Conundrum: When Eaves Meet Proposed Boundaries

Across established middle and inner suburbs in Adelaide, the “retain and subdivide” model is a commonly used urban infill strategy. By keeping an existing front dwelling to preserve rental yield or capital value while dividing off the surplus backyard for rear development, property owners can unlock value from their land. However, when licensed surveyors arrive on site to peg the proposed allotment boundaries, developers frequently encounter a difficult legal and physical issue: the eaves, gutters or timber fascias of the existing home project too close to, or hang directly across, the proposed new boundary line.

Under the Planning, Development and Infrastructure Act 2016 (PDI Act) and the Planning, Development and Infrastructure (General) Regulations 2017, each new allotment must satisfy the planning requirements for area and frontage, and the retained dwelling must also meet the planning setback and building code (NCC) requirements once the new boundary exists. If eaves or similar elements are too close to the new boundary, rectification or additional assessment may be needed, which can affect how the land division application progresses.

Planning Code Setbacks vs NCC Fire Separation: Two Distinct Compliance Hurdles

Addressing the distance between an existing eave and a new allotment boundary requires managing two distinct technical regimes: the South Australian Planning and Design Code, and the National Construction Code (NCC).

1. Statutory Setbacks under the Planning and Design Code

The Planning and Design Code includes specific requirements for land division that retains an existing dwelling: where new allotments are created in conjunction with the retention of an existing dwelling, the site of the existing dwelling should remain fit for purpose. The specific criteria (such as site area, frontage, private open space and setbacks to the new boundary) are set by the DTS/DPF of the relevant zone. If the new boundary leaves the retained building closer to the boundary than the criteria allow, the application may not be able to follow the Deemed-to-Satisfy pathway, and may move to the Performance Assessed pathway, or the assessing authority may ask for the plan to be redesigned. How eaves and gutters are measured for setback purposes under the Code should be confirmed with your planning consultant.

2. Fire Separation and Stormwater under the NCC

More specific limits commonly come from Part 9.2 of the NCC 2022 Volume Two and the ABCB Housing Provisions, which govern fire separation of external walls for Class 1a residential buildings. When an allotment is split, the newly surveyed boundary becomes an allotment boundary for the purposes of the building code. South Australia’s current Building Code is based on NCC 2022 with South Australian variations, which should be confirmed with your certifier. The main requirements include:

• External Wall Fire Separation: Where an external wall of a Class 1 building is less than 900 mm from an allotment boundary (other than a boundary adjoining a road or other public space), or less than 1.8 m from another building on the same allotment, it must be of fire-resisting construction (for example FRL 60/60/60, or masonry veneer with an outer leaf of at least 90 mm, or masonry at least 90 mm thick), extending to the underside of a non-combustible roof covering or non-combustible eaves lining. Openings within that zone are also restricted.

• Eaves and Projections: Within 900 mm of the boundary, the permitted projections are subject to material and distance conditions, for example non-combustible fascias, gutters and downpipes, and eaves with non-combustible roof cladding and non-combustible eaves lining; combustible fascias, gutters and downpipes generally must not be closer than 450 mm to the boundary (see Housing Provisions 9.2.9). An eave that extends directly across the new boundary line is an encroachment and raises a property title issue.

• Stormwater Drainage: Roof water from an existing building generally needs to be collected and discharged within the same allotment. An overhanging eave or gutter above the new boundary can cause stormwater to run onto the newly created parcel, requiring a redesigned drainage layout or a legally registered stormwater easement.

Engineering and Legal Remedies: Modification, Easements, and Boundary Realignment

Where the eaves of an existing dwelling are too close to the proposed boundary, developers commonly weigh three remedies, based on site viability, structural cost and resale liquidity:

1. Boundary Realignment / Plan Redesign

Where the rear allotment has surplus width or depth, a fairly direct solution is to adjust the proposed survey plan before the application is finalised. By incorporating a step, dog-leg or lateral shift into the proposed boundary, the surveyor may be able to create compliant separation for both the external wall and the roof projections.
Limitation: This approach may not be viable if the shift causes the rear allotment to fall below the Code’s minimum area, frontage or driveway width requirements.

2. Structural Modification (Eave Cut-Back)

If the boundary geometry cannot be altered without breaching planning requirements for the rear allotment, the structure of the retained home may need to be modified. Measures may include:

• Cutting back the depth of timber rafters and eaves lining so that the fascia line sits within compliant clearance limits;

• Replacing projecting eaves with parapet flashing or vertical concealed gutters;

• Installing non-combustible eave soffit lining (for example compressed fibre cement sheet), together with a non-combustible roof covering, to meet the NCC requirements near the boundary.

Heritage Note: If the existing building is a State or Local Heritage Place, or sits within a historic area, changes to external elements will generally need development approval and may involve heritage referral or assessment, so the original character should not be altered before approval is obtained.

3. Registering an Eaves Easement

In legal theory, where one owner holds both proposed parcels, an easement for eaves and gutters encroachment could be registered over the new parcel through the Registrar-General (via Land Services SA), allowing the roof line of the front dwelling to project over the rear property’s airspace. In practice, however, this approach is not common in residential development in Adelaide, and advice should first be obtained from the certifier, a lawyer and the lender, for the following reasons:

• A registered easement resolves the title encroachment but does not automatically remove the NCC fire separation requirements;

• Encumbrances of this kind may affect buyer acceptance or lending approval when the rear lot is resold.

Due Diligence Workflow for South Australian Property Owners

To avoid costly redesigns mid-project, landowners intending to retain an existing dwelling should carry out a disciplined pre-lodgement review:

• Commission a Detail and Contour Survey: Do not rely on historical certificates of title or aerial imagery alone. Instruct the licensed surveyor to pinpoint both the external wall line and the outermost edge of the gutter or fascia (the eave extent).

• Consult a Private Building Certifier Early: Before finalising the subdivision plan, have the certifier confirm whether the proposed boundary requires any additional fire protection to the existing home’s walls, openings and eaves under the NCC.

• Audit Roof Drainage Routes: Check the existing downpipe and gutter routes, so that roof water from the retained dwelling does not discharge across the newly divided land without a legally registered stormwater arrangement.

Disclaimer: The setbacks, building clearances and technical standards discussed in this article are provided for practical industry discussion only. The compliance requirements for a specific site should be determined from reports by a licensed surveyor, planning consultant and registered building certifier, based on the actual site conditions.

Sources

• Guide to the Planning and Design Code | PlanSA

• Part 9.2 Fire separation of external walls | NCC 2022 ABCB Housing Provisions

• Part H3 Fire safety | NCC 2022 Volume Two

• Planning, Development and Infrastructure (General) Regulations 2017

• Heritage and character | PlanSA

Illustrative image only — not a photograph of a Cyberate PM project. Photo by Ron Lach on Pexels.