Dual occupancy is one of the most viable infill development types in Brisbane, but the rules are unforgiving. Whether a dual occupancy can be developed on a particular lot depends on the zone, the lot size, the frontage, the applicable overlays, and the proposed building height. Get any of these wrong and the application moves from a relatively quick code-assessable process into impact assessment, with public notification and substantially higher risk.
What dual occupancy means
Under Brisbane City Plan and most Queensland planning schemes, dual occupancy is the residential use of premises containing two dwellings on one lot, whether attached or detached, or two dwellings on separate lots that share common property. The colloquial terms duplex and dual occupancy are essentially interchangeable.
Dual occupancy is distinct from a secondary dwelling (granny flat), which is a smaller subordinate dwelling capped at 80m² and clearly secondary to the main house. The two are assessed under different parts of the planning scheme and have different feasibility implications.
Lot size and frontage
In Brisbane, the minimum lot size to support a dual occupancy is generally 400m² per dwelling. For a typical pair of attached dwellings, that means a minimum lot of 800m². To qualify as accepted development, meaning no planning application is required at all, the lot must usually have a minimum 800m² area and a frontage of at least 20 metres, plus meet every other accepted development requirement.
Where the lot is below the threshold, or the proposal does not meet accepted development standards, a development application is required. Whether that application is code or impact assessable depends on the zone and the extent of departure from the relevant codes.
Zone and overlay considerations
Dual occupancy is generally supported in the Low–medium density residential, Medium density residential and Character residential zones, subject to compliance with the relevant codes. In the Low density residential zone, dual occupancy is typically not supported as code assessable, meaning any application is likely to attract impact assessment with public notification, and a significant prospect of refusal.
Overlays add another layer. Traditional Building Character, heritage, flood, bushfire and biodiversity overlays each impose specific requirements that may modify the assessment level or impose design constraints. Reviewing the property report and planning scheme overlays is the first step in any feasibility assessment.
Height, setbacks and design response
Building height for dual occupancy in Brisbane is typically capped at two storeys / 9.5 metres in lower-density precincts, with three storey / 11.5 metre limits in some medium-density zone precincts. Setback requirements vary by zone but commonly require 6 metres front, 1.5 metres side and 6 metres rear.
Beyond the numeric standards, dual occupancy applications are assessed on design response, does the building present appropriately to the street, does it integrate with the existing streetscape, is the bulk and form sympathetic to neighbouring buildings? In character zones particularly, the design response is often the deciding factor.
Dual occupancy can be a strong development outcome on the right site, but the difference between a viable code-assessable proposal and an impact-assessable risk often comes down to lot dimensions, zone, and design. A site-specific preliminary review is the correct starting point before any design work begins.