Planning an extension is one of the most exciting decisions a homeowner can make. More space, better flow, a home that actually works for how you live.
But it is also one of the most misunderstood processes in residential construction. The mistakes that cost homeowners the most time, money, and stress rarely happen during the build. They happen well before a slab is poured, often before a designer is even engaged.
Here are the five most common planning mistakes we see, and what to do instead.
1. Underestimating the Approvals Process
This one catches more homeowners off guard than almost anything else.
Extensions in Australia are subject to council planning controls, building regulations, and in some cases, overlays that restrict what can be built, how high, how close to boundaries, and in what materials. What looks straightforward on paper can involve multiple rounds of documentation, referrals, and waiting periods before a single thing gets built.
Many homeowners assume that because a neighbour built something similar, their approval will be quick and simple. Site conditions, zoning, and even the orientation of your block can change the outcome significantly.
What to do instead: Get clarity on your planning controls before you invest in design. A good builder or building designer can help you understand what is likely to be permitted on your specific site before you spend money on drawings that may need to be redesigned.
2. Setting a Budget Based on a Best-Case Scenario
Extensions routinely cost more than homeowners initially expect. Not because builders are cutting corners on quoting, but because early conversations often happen before the full scope is understood.
Rough figures from a friend, a quick online search, or a rate-per-square-metre from an unrelated project become the mental budget. Then when a proper quote comes in, the gap between expectation and reality can feel like a shock.
The reality is that extensions involve more complexity than a straightforward new build. Tying into an existing structure, working around live services, managing access, and dealing with what is already there all adds cost and time that a simple rate per square metre will not capture.
What to do instead: Build a contingency of at least 10 to 15% into your budget from day one. Treat early figures as a directional guide, not a commitment. Move through the feasibility and estimate stages properly before locking in expectations.
3. Assuming Reusing Materials Saves Money
It seems logical. The existing home has brickwork, timber, or roofing that could carry into the extension. Why not reuse it and cut costs?
The reality is more nuanced. Salvaging and reusing materials from an existing structure is rarely straightforward. It requires careful removal, cleaning, sorting, and often significant labour to make reclaimed materials workable in a new context. In many cases, the cost of doing that properly exceeds the cost of using new materials.
That said, there is a genuinely compelling reason to reuse materials in extensions and it has nothing to do with saving money. When done well, it is about look, feel, and honouring the character of the original home.
Matching a heritage brick, continuing a timber floor, or carrying through original weatherboards into a new addition creates continuity. It makes the extension feel like it belongs rather than like something that was added on. For older homes with historic or architectural character, this approach can be the difference between a result that feels cohesive and one that feels like a compromise.
At AVK Homes, we do reuse materials in extensions, but we do it intentionally and with realistic expectations about what it involves. The decision is driven by the outcome we are trying to achieve, not by the hope that it will reduce the budget.
What to do instead: If material continuity matters to your project, raise it early with your builder. Understand what is actually salvageable, what the labour cost looks like, and what the visual outcome will be. Go in with clear eyes rather than assumptions.
4. Getting the Layout Wrong from the Start
An extension that adds square metres but disrupts the flow of the existing home is one of the most common and frustrating outcomes in residential construction.
This happens when layout decisions are made based on what is easiest to build or cheapest to draw rather than how the household actually lives. The connection between old and new matters as much as the new space itself. Where the junction happens, how natural light moves through, where doors and windows land, all of it shapes whether the finished result feels like a considered home or a compromise.
Homeowners often underestimate how much thought needs to go into the relationship between the extension and the existing structure. It is not just about adding rooms. It is about how those rooms connect to the rest of the house.
What to do instead: Before finalising any layout, walk through how you use your home today. Think about morning light, where people gather, how traffic flows through the house, and what you actually want to change. Share that context with your designer and builder early. The best layouts come from understanding how a family lives, not just how many square metres they want.
5. Engaging a Builder Too Late in the Process
Many homeowners complete design and documentation before speaking to a builder. The logic makes sense: get the design right, then get it priced.
The problem is that design decisions made without builder input can create significant cost, buildability, or compliance issues that are expensive to unwind by the time a quote comes back. A structural approach that looked clean on plan may be difficult or costly to execute. A material specified by a designer may have long lead times or require specialist trades. A siting decision may create site access challenges that affect the entire programme.
Getting a builder involved early does not mean handing over creative control. It means adding a layer of practical, construction-level thinking to the design process before those decisions become locked in.
What to do instead: Bring a builder into the conversation at the feasibility or early design stage. Even an initial conversation about site conditions, structural approach, and likely cost ranges can save significant time and money before documentation is finalised.
How AVK Homes Approaches Extensions
Extensions are one of our core areas of work at AVK Homes. We work with homeowners across Albury-Wodonga on projects that range from modest additions to significant whole-home transformations.
Our approach is builder-led from the start. That means Alex is involved early in the process, not just at the quoting stage. We work through feasibility, help homeowners understand their constraints before they invest in design, and stay across the project at every stage.
If you are in the early stages of thinking about an extension and want a realistic view of what is involved, we are happy to have that conversation.
Get in touch with AVK Homes to start the process the right way.
