How to Plan a Home Extension in Queensland: Feasibility, Design, Approvals and Build, in Order

House extension design ideas

Most extensions are one of five types. Each solves a different problem, and each has its own catch:

• Rear extension. New living space opening to the yard, often an open-plan kitchen and family room. Find the sewer line and any easements first, because they often cross the back of the block.
• Second storey. Bedrooms upstairs without losing yard. The existing footings and frame have to carry the new floor, and the stair takes space out of the rooms below.
• Building in underneath. New rooms under a raised house, without a new roof. Ceiling height and any flood level set what's possible.
• Side extension. Works on wider blocks, but side setbacks often limit how wide it can go. See Building near the boundary below.
• Pavilion and link. A separate wing joined to the house by a short glazed link. It leaves the original house mostly untouched, which suits character homes.

Whichever type you choose, the join between new and old is where measuring the existing house pays off first.

Most extension budgets don't blow out during the build. They blow out earlier, when a design drawn from old plans meets the house as it actually is, or when an overlay nobody checked adds a council application halfway through design. The order you do things in matters as much as the design itself.

This guide sets out how to plan a home extension in Queensland, stage by stage: feasibility, the brief, measuring the existing house, design, the building approval process, the contract, the build and handover. It's written for owners who have decided to extend and want to know what comes next, and who does it.

The home extension roadmap, in order

An extension runs through eight stages: feasibility, brief, measure, design, approvals, contract, build and handover. Each one has its own people, its own decisions and one thing that most often goes wrong. Skipping a stage rarely saves time; it usually moves the problem to a point where it costs more to fix.

Pick the stage you're at in the roadmap below. It shows what to do now, who does it, what to watch for, and the step that moves you to the next stage.

Feasibility: what your site allows

Before paying for design, find out what the planning rules allow on your block. Look up the property in your council's planning scheme for its zone and any overlays, such as character, heritage or flood. Then check the siting rules: how far the extension has to sit from each boundary, how much of the site can be covered, and the height limit.

Check the title for easements, and find the sewer line and any other services you can't build over or near. Then set a budget range. A rough number at this stage tells your designer what to aim for, and which ideas to drop early.

Designing a house extension that fits the house

Write a brief before anyone draws: the rooms you need, their sizes, how you'll use them, and which items are must-haves rather than nice-to-haves. Then choose who designs it: a registered architect or a QBCC-licensed building designer.

The best house extension design ideas start from what the existing house does well. A few decisions shape most designs:

• Out, up or under. A ground-floor extension uses yard space; a second storey keeps it but needs the existing structure checked; building in under a raised house adds rooms without a new roof.
• Where new meets old. Floor levels, ceiling heights, rooflines and the wall where the two join decide whether the extension feels part of the house or bolted on.
• Light and orientation. An extension can take light from the rooms behind it. Check which rooms lose windows or northern light.
• Services. Moving a kitchen or bathroom means moving water, waste and power, so look at where they run now before choosing where they'll go.

Old Queenslanders and character homes have their own rules on all of this; our Queenslander guide covers raising and building in underneath.

Measure the house before anyone designs

Old plans rarely match a house that's been renovated over decades: walls have moved, ceilings have been lowered, floors fall, and services have been rerouted. A design drawn from those plans is where the on-site surprises start.

Capture the existing house where the extension joins it: the rooms, levels, roof space and subfloor. A 3D capture gives your designer a point cloud or Revit model of the house as it stands, before concept design starts. It's an architectural-grade record for design, not a survey, so add a registered surveyor if you need boundaries or levels tied to a survey datum. The scan-to-BIM brief template sets out what to ask for.

The two kinds of approval: planning and building

The building approval process in Queensland usually involves a building certifier, and sometimes the council as well. They're two different checks.

• Building approval. Almost every extension needs it. A building certifier assesses the design against the building rules and issues the approval before work starts. The engineer's design for footings, beams and bracing goes in with it.
• Siting. The Queensland Development Code sets boundary setbacks for houses (MP 1.1 for lots under 450 m², MP 1.2 for larger lots). If the design doesn't meet them, the certifier needs the council's referral response first.
• Planning approval. If the design doesn't meet the planning scheme's rules, or an overlay applies, you may need a planning application to council before building approval. In Brisbane, for example, some extensions to houses built in 1946 or earlier need one.
• Plumbing. Work that moves drainage or adds plumbing can need its own approval, arranged by a licensed plumber.

Rules differ between councils, so ask a certifier or the council early, while the design is still easy to change.

Building near the boundary

Extensions often push towards a side or rear boundary, and excavation for footings, a slab or retaining can sit close to the neighbour's house. Since 1 August 2025, section 179 of the Property Law Act 2023 (Qld) has set a duty of care between neighbours for the support of land, so the condition of the house next door before your work starts matters.

A dated record of the neighbouring home, captured with their consent before any excavation, gives both sides something to check against if cracks appear later. Our guide to pre-construction condition surveys covers what to capture and when. This is general information, not legal advice.

Contract, build and handover

Get quotes on the same drawings and specification so you're comparing like with like, and read the stage, variation and delay clauses before you sign. Our building contract guide goes through them, and disputing a progress claim or variation covers what to do if a claim doesn't match the work.

During the build, the join between new and old is where most defects start. Protect the existing house, keep every variation in writing, pay only for stages that are done, and record the frame before the plasterboard goes on. At handover, walk the extension with the builder, list the defects, and collect the final inspection certificate and trade certificates. Our practical completion guide has a room-by-room checklist.

Planning a home extension in Queensland: FAQs