What Consultants Do You Actually Need for a Dual Occupancy Development in Australia

Dual occupancy developments are one of the most common project types across Australian cities right now. Two dwellings on one lot, either side by side or one behind the other, are an efficient way to add housing supply and generate strong returns on well-located suburban land. But first-time developers are often caught off guard by how many consultants are involved before a single brick gets laid. Here's a straightforward guide to who you actually need, what they do, and roughly when you need them.

Town Planner

The first call you should make is to a town planner, not an architect. Before you spend money on design, you need to know what the planning controls on your site actually allow. Your town planner will look at the zoning, overlays, council requirements, and neighbourhood character provisions and tell you what's realistically achievable. In Victoria this is essential — the planning permit process for a dual occupancy can take anywhere from three months to well over a year depending on the council and the proposal. In NSW, some dual occupancies can go through as complying development which is faster, but only if the site and design meet the code. Budget roughly $3,000 to $8,000 for a town planner on a standard dual occupancy planning permit application, depending on complexity.

Private Certifier or Building Surveyor

Once you have planning approval, or if your project qualifies as complying development, a private certifier or building surveyor issues your building permit and carries out statutory inspections. In NSW they can also issue the CDC if you're going down the complying development path. In Victoria they issue the building permit after planning is sorted. Engage your building surveyor early — they can flag building code issues with your design before you finalise drawings and save you costly amendments later.

Hydraulic Engineer

Most councils require a hydraulic report as part of the DA or building permit documentation. The hydraulic engineer designs your stormwater management system — how water drains from the site, any detention or retention requirements, and connections to council infrastructure. If your site has any drainage constraints or sits in a flood-affected area this report becomes even more important. Don't leave this until the last minute. Hydraulic reports can take two to four weeks to produce and councils won't grant approval without one.

Geotechnical Engineer

If you're in an area with reactive or unstable soils — common in many parts of Melbourne, Brisbane, and coastal NSW — your building surveyor or engineer will require a geotechnical report to classify the site and determine appropriate footing design. This is a soil test and report, usually completed in a day on site with a written report to follow. Not every project needs one, but it's better to find out early than to discover reactive soil when your slab is already designed. Structural Engineer Your structural engineer works with your architect or building designer to design the structural elements of the buildings — slabs, frames, beams, and connections. They produce the structural drawings your builder prices from and your building surveyor needs to issue the permit.

Land Surveyor

You'll need a land surveyor at two key points. First, a feature and level survey at the start — this gives your architect an accurate picture of the site boundaries, levels, and existing structures to design from. Second, a re-establishment survey before construction to peg the boundaries so your builder knows exactly where to build. In Victoria a plan of subdivision is also required if you're subdividing the lots after construction, which is another land surveyor engagement.

Building Designer or Architect

You need someone to actually design the dwellings. A registered architect or building designer produces the drawings that go to council, your certifier, your structural engineer, and ultimately your builder. Choose someone with experience in dual occupancy design in your specific council area — they'll know what gets approved and what gets knocked back. The order of all this Town planner first. Then architect. Then hydraulic engineer and geotechnical engineer in parallel with the design. Then structural engineer once the design is locked. Building surveyor engaged early and issuing the permit once everything else is in place. Land surveyor at the start for the feature survey and at the end for subdivision. Get that sequence right and you avoid the most common cause of delays — waiting on one consultant's report before another can start their work. If you need to find any of these consultants in your state, lodgepath.com lets you search by discipline and availability and see who's actually taking on new work right now.