Most people know roughly what they want when they start thinking about a house extension, whether that’s more space, a better layout, room for the kids or a home office. What’s harder to picture is what the actual process looks like between the initial conversation and the day the work is done.
Extensions are one of the more involved projects a homeowner can take on, and the experience tends to go better when you know what’s coming. Here’s a realistic walkthrough of what the process looks like for Brisbane homeowners, based on how we typically work through these projects.
The design phase comes before anything else
Before anyone picks up a tool, the project needs a design. This is where you work out exactly what you’re building, where the extension sits on the block, how it connects to the existing house, what the internal layout looks like, and what finishes you’re after.
For most home extensions in Brisbane, you’ll need to engage a draftsperson or architect to prepare plans. If structural work is involved (and for most extensions, it is), you’ll also need an engineer to assess the existing structure and design the new elements.
This phase takes longer than most people expect. Getting plans drawn, reviewed, revised, and finalised can take anywhere from four to eight weeks depending on complexity and how quickly decisions get made. The time spent here is worth it though, as good documentation up front means fewer surprises during construction.
Council approval and certifiers
Once you have plans, you need approval before construction starts. In Queensland, this usually involves a building certifier rather than going directly through council, though some projects do require a development application (DA) depending on your property’s zoning, size of the extension, or proximity to boundaries.
A certifier checks that your plans comply with the Building Code of Australia and Queensland Development Code. If your project doesn’t trigger a DA, this process is typically faster than council approval, only a few weeks rather than a few months. Your builder or draftsperson can usually advise on which pathway applies to your specific site.
One thing that catches people off guard: if you’re in a flood-affected area, bushfire zone, or heritage overlay, there may be additional requirements that affect the design or materials. Worth checking early.
Preparing the site
Once approvals are in place, work can begin. The first stage is usually site preparation, which might involve demolishing part of the existing structure, excavating, or making good the area where the extension will connect.
For Queenslander extensions or work on older homes, this stage can sometimes turn up surprises: subfloor issues, older materials that need careful handling, or services in unexpected places. A good builder flags these early and works through them with you rather than letting them become problems mid-build.
The construction sequence
The general sequence for a house extension goes: slab or subfloor, frame, roof, lock-up (windows and doors in), fit-out (internal linings, joinery, plumbing, electrical), then finishes (painting, tiling, flooring).
Each stage has to be completed and inspected before the next one starts, which is part of why extensions take the time they do. The inspection process exists for good reason, it’s how defects get caught early rather than buried behind walls.
At the lock-up stage, the structure is weathertight and the project starts to look like something. This is usually when homeowners feel the project turns a corner. Fit-out is detailed and slower than the structural work, so be prepared for the last 20% of the work to feel like it takes longer than expected. It usually does.
How long does a house extension take?
For a typical home extension in Brisbane, like adding one or two rooms, a bathroom, and a deck, construction usually takes somewhere between three and five months once you’re on site. Larger projects, or those involving significant renovation to the existing home alongside the extension, will take longer.
The full timeline from first conversation to handover, including design and approvals, is realistically six to twelve months for most projects. Some move faster, some take longer depending on council processing times, material lead times, and how complex the scope is.
We know that’s a long time to live around a renovation. If you’re staying in the home during the project, it’s worth talking to your builder upfront about staging, as sometimes it’s possible to sequence the work so the most disruptive parts are done first.
What decisions you’ll need to make along the way
Extensions involve a lot of choices, and some of them have lead times. For example, tiles, fixtures, joinery, and windows, need to be selected before they’re needed on site, not the week before installation. Your builder should give you a schedule of when decisions are needed so you’re not being rushed.
The other thing worth knowing is that changes during construction cost more than changes made on paper. If you want to move a door or add a window after framing has started, it’s usually possible, but it comes with a variation cost and potentially a delay. Making decisions early and sticking to them is one of the most practical things you can do to keep your project on budget.
Getting to handover
At the end of the project, your certifier will issue a final inspection certificate confirming the work meets the approved plans and relevant codes. This is an important document, so make sure to keep it. You’ll need it if you sell the property.
Your builder should also do a walkthrough with you before handover to work through any defect items. Minor things sometimes come up. It’s normal, and a good builder will sort them out promptly.
The defects liability period under Queensland law is typically six months from practical completion for residential work. During that time, you can call out any defects that arise and the builder is obliged to fix them. At JM Homes, we have a 12 month defects policy to give you peace of mind.
Where to start
If you’re considering a home extension in Brisbane, it’s worth having plans drawn up before you approach a builder for pricing. A rough idea of what you want is a good starting point, but a builder can give you a much more accurate picture of cost once there’s something on paper to work from.
If you don’t have a designer yet, that’s fine too. We work closely with a number of trusted designers and architects we’ve built solid working relationships with over the years, and we’re happy to point you in the right direction.
Once your plans are ready, we’d love to hear about your project. We’ve completed home extensions across Brisbane and South East Queensland, including Queenslander extensions, room additions, and full renovation and extension combinations. Reach out to the JM Homes team to get the conversation started.
