9 May 2026 by SON Architects
Dual Occupancy vs. Secondary Dwellings - The Differences
Dual occupancy allows land subdivision and separate sales titles, while secondary dwellings stay on one title with simpler approvals for family or rental use. Explore the constraints and how architects could support you maximise your investment opportunity.
The Architectural Design Challenges
Navigating complexities of each design
Adding a second home to an existing allotment requires balancing density with livability. Residential architects navigate complex spatial and microclimatic factors to ensure both dwellings maintain high levels of amenity, functionality, and long-term value. While both typologies increase site density, their fundamental differences in title, size, and council regulation create distinct architectural challenges
Private Open Space (POS) Allocation
- Dual Occupancy: Requires strictly divided, policy-compliant Secluded Private Open Space (SPOS) for both homes. Architects must design two fully independent, private yards on a single lot, which often forces multi-storey solutions to preserve ground-level outdoor areas.
- Secondary Dwelling: Shares the overall site green space more flexibly. Because the secondary home is smaller (often capped at 60sqm), architects can preserve the main home’s dominant backyard while integrating a compact, dedicated patio for the secondary residence.
Solar Access & Overshadowing Dynamics
- Dual Occupancy: Involves two full-scale, often two-storey structures. Architects must use 3D solar modelling to prevent the new, larger mass from blocking northern light to both the existing residence and neighbouring properties.
- Secondary Dwelling: Being single-storey or low-profile, the overshadowing impact is easier to mitigate. The challenge shifts to positioning the secondary dwelling so the larger primary home doesn't cast it in permanent shadow.
Overlooking & On-Site Privacy
- Dual Occupancy: Designed for two independent owners or tenants who expect complete separation. Architects must manage 9-meter sightlines between two full-sized, often facing living zones using screening, offset windows, and strategic floor plans.
- Secondary Dwelling: Frequently houses family members or intergenerational relatives. While privacy remains important, line-of-sight rules are often less rigid in layout design, allowing for shared garden views or courtyard outlooks.
Driveways, Parking & Site Circulation
- Dual Occupancy: Councils usually require dedicated off-street parking and independent vehicle access (or compliant turning circles) for both homes, which can create a dominant concrete footprint if not carefully integrated.
- Secondary Dwelling: Parking requirements are significantly relaxed under streamlined rules (often requiring no additional parking spot), allowing architects to prioritize pedestrian paths and green landscaping over asphalt.
