How Much Does a Home Extension Cost in Sydney? (2026 Breakdown)
How Much Does a Home Extension Cost in Sydney? (2026 Breakdown)
It is the very first question every homeowner asks: “How much is this going to cost?”
If you are planning a home extension in Sydney in 2025, you might have heard horror stories about rising construction prices. While it’s true that costs have stabilised since the post-COVID peaks, budgeting for a renovation can still feel like guessing the length of a piece of string.
While no blog post can give you an exact quote, we can give you the realistic ranges you need to start planning. This guide breaks down the typical costs per square metre for ground-floor and second-storey extensions in Sydney, and highlights the “hidden” costs you must budget for.
The “Per Square Metre” Rule of Thumb
Builders often use a “per square metre” rate to give rough estimates. In Sydney for 2025, here are the realistic ranges for a quality custom build:
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Ground Floor Extensions: $3,000 – $4,500 per m²
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Example: Adding a simple open-plan living room (40m²) might cost between $120,000 and $180,000.
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Second Storey Additions: $4,000 – $5,500+ per m²
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Example: Adding a new level with 2 bedrooms and a bathroom (60m²) might cost between $240,000 and $330,000+.
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Wet Areas (Bathrooms & Kitchens): Significantly Higher
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Because of the tiling, plumbing, waterproofing, and cabinetry, these rooms are much more expensive than empty bedrooms. You typically budget these as “lump sums” (e.g., $30k for a bathroom, $50k for a kitchen) on top of the structural shell.
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Note: These are construction costs only. They do not include professional fees, council fees, or GST.
Why Is It So Expensive? (The 4 Cost Drivers)
Why does one extension cost $150k and another cost $300k? It usually comes down to four factors:
1. Ground vs. Second Storey Going up is almost always more expensive than going out. It requires scaffolding, crane hire to lift materials, removing the existing roof, and significant structural steel to hold the new weight. (Read our Pros and Cons guide here to learn more).
2. Site Access & Slope If your block is flat and has a wide side driveway for trucks, your price will be lower. If your block is steep, or if builders have to hand-carry materials through the front door because there is no side access, your labour costs will skyrocket.
3. Finishes & Fittings This is where the budget can blow out. Are you choosing standard aluminium windows or architectural timber glazing? Are you buying $30/m² tiles or $150/m² natural stone? The “bones” of the house cost the same, but the “skin” can double the price.
4. Hazardous Materials If your home was built before the late 80s, you may encounter asbestos. Removing this safely requires licensed specialists and can add unexpected costs to the demolition phase.
Don’t Forget the “Hidden” Costs (The Soft Costs)
A common mistake is budgeting only for the builder. You typically need to set aside an additional 15-20% of your budget for “soft costs” before you even start building.
These include:
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Drafting & Design: (That’s us!) You need professional plans for approval and construction.
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Consultants: Structural Engineer, Surveyor, Basix Consultant, Stormwater Engineer.
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Council Fees: DA or CDC lodgement fees, Long Service Levy, and Section 7.11/7.12 Development Contributions (a tax paid to council for local infrastructure).
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Private Certifier Fees: For approving the Construction Certificate and inspecting the build.
How to Keep Your Budget Under Control
The most expensive words in construction are: “Can we just change that?”
Changing your mind once the builder has started is the fastest way to blow your budget. The secret to staying on budget is detailed planning before you build.
This is where JJ Drafting adds value.
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We design to your budget: If you tell us you have $200k, we won’t design a $500k monument.
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We provide clarity: Our detailed construction drawings leave less room for interpretation. When the drawings are clear, the builder can quote accurately, meaning fewer “variations” and surprises later.
Get a Quote based on FACTS, not Guesses
You can’t get a real price from a builder until you have a plan. They need to know exactly what they are quoting on—how many windows, how much steel, what type of roof.
The best first step is to get a concept design drafted. This gives you a document you can show to builders to get preliminary estimates, allowing you to adjust the size or scope before you commit to the full project.
Worried about the cost of your extension? Start with a clear plan. Contact JJ Drafting today for a design consultation on 0414 71 75 41 or jjdrafting.com.au, and let’s create a project that fits your lifestyle and your budget.