How much does a house extension cost per m² in Australia?

House extension costs are a key factor to consider when planning your renovation. Whether you’re adding extra living space or upgrading your layout, understanding these costs is essential for budgeting effectively.

So, how much does a house extension cost? On average, a ground-floor house extension in Australia costs between $160,000 and $320,000 for an 80m² addition — which works out to approximately $2,000 to $4,000 per m². If you’re considering a second-storey extension, be prepared to pay around 50% more than a ground-floor build.

The total cost of your house extension will ultimately depend on factors such as the type of construction, materials, finishes, and inclusions you choose.

In this house extension cost guide, we explore:

• How much does an extension cost?
• Cost of house extension by room type
• Other home extension costs
• What affects the cost of building an extension?
• House extension ideas
• How to get a house extension quote, and more.

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House extension costs in Australia

How much does it cost to extend a house? House extension costs are typically quoted per square metre or as a total project price. On average, you can expect to pay between $1,900 and $4,000 per m², depending on the scope and specifications of your extension.

• Ground-floor extensions generally range from $1,900 to $4,000 per m².
• Second-storey extensions typically cost $3,000 to $3,500 per m², around 50% more than ground-level builds.

While second-storey extensions are often more expensive, they can sometimes be more cost-effective, as they don’t require additional land or extensive excavation. However, factors like wall removals, structural modifications, and renovations can further impact overall costs.

Once your plans are finalised, obtaining detailed quotes from builders will give you a clearer idea of your total extension costs.

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House extension costs by room type

How much does it cost to extend different rooms in your home? The price varies depending on the room type, finishes, and structural work required. While a bathroom extension can cost up to $28,000 for a high-end finish, a laundry, living room, or bedroom extension is generally more affordable and quicker to build.

Estimated Room Extension Costs

• Bathroom/ensuite: $12,000 – $28,000
• Kitchen extension: $15,000 – $40,000
• Laundry: $6,000 – $15,000

If you’re adding a master bedroom with an ensuite, the cost will generally be lower than a full-sized bathroom extension. A small ensuite or budget bathroom may cost $2,500 to $15,000, while adding a brand-new bathroom as part of an extension is often more expensive due to additional plumbing, drainage, and electrical work.

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Cost of 50m² extension in Australia

A 50m² ground-floor extension in Australia typically costs between $50,000 and $70,000, including materials, labour, and council fees. For an upward extension, the price ranges from $70,000 to $100,000 due to added complexity.

Factors Affecting Costs

• Materials – Using brick veneer is more affordable, while rendered finishes increase the cost.
• Location – Prices may vary by region, depending on local labour and material costs.

Council Approval

Council approval is usually required for extensions of this size, with fees ranging from $200 to $2,000 depending on the project.

This is a general estimate, and final costs may vary based on the specifics of your extension.

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Other home extension costs to consider

When planning a home extension, it’s important to factor in additional costs beyond the construction itself. These expenses can significantly impact your overall budget and should be accounted for from the start.

Additional Costs to Budget For:

• Permits and inspections – Required approvals and compliance checks.
• Architect or designer fees – Design and planning costs.
• Project management – Fees for overseeing construction.
• Demolition and site preparation – Clearing space for the extension.
• Plumbing and electrical – Installing new wiring, outlets, and plumbing.
• Materials and finishes – Flooring, countertops, lighting, and fixtures.
• Heating and cooling – Extending or upgrading HVAC systems.
• Furnishings – New furniture, window treatments, and appliances.
• Landscaping and hardscaping – Outdoor modifications post-construction.
• Financing costs – Interest or fees if taking out a loan.

Plan for Unexpected Costs

To avoid budget shortfalls, it’s wise to set aside a contingency fund for unexpected expenses that may arise during construction. A buffer of 10–20% of the total project cost can help cover unforeseen issues and keep your extension on track.

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What affects house extension costs?

Several factors influence the cost of a house extension, with the type of extension being one of the biggest determinants.

Key Cost Factors

• Extension Type – Kitchens and bathrooms tend to have a higher cost per m² due to plumbing, electrical work, and expensive fixtures, while living rooms and bedrooms are generally more affordable.
• Size and Complexity – Larger extensions naturally cost more, but simple conversions (e.g., a garage-to-bedroom conversion) can be a budget-friendly option.
• Single vs. Double Storey – Adding a second storey is typically 50% more expensive than a ground-floor extension due to structural reinforcements.
• Materials and Finishes – High-end fittings, custom cabinetry, and premium flooring significantly increase costs.
• Professional Services – Hiring an architect, engineer, or land surveyor adds to the total price but ensures quality and compliance.
• Permits and Regulations – Building permits and inspections vary by location and can add to overall expenses.
• Site Conditions – Factors like sloping land, accessibility challenges, or difficult terrain may require additional preparation and engineering.
• Demolition and Excavation – Costs can rise if existing structures need to be removed or if extensive groundwork is required.
• Hazardous Material Removal – If your home contains asbestos or other hazardous materials, specialist removal is an added cost.

Understanding these factors can help you plan your budget more effectively and avoid unexpected expenses.

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House extension ideas

Many homeowners in Australia are opting for house extensions to increase their living space and boost property value. Whether you have a small or large home, there are plenty of creative extension ideas to explore. Here are some popular options:

Small House Extension Ideas

• Sunroom – Add natural light and outdoor views with a cosy sunroom at the back of your home.
• Single-story extension – Expand sideways with a simple single-storey addition.
• Garage conversion – Transform an unused garage into a functional living space, like a home office or extra bedroom.
• Small second-story addition – Build a second level above an existing room, such as a bathroom or bedroom.
• Detached structure – Add a backyard studio or home office for more privacy and space.
• Porch or deck – Enhance your home’s entrance or backyard with a small, inviting porch or deck.
• Mudroom or entryway – Create a practical entryway at the side or back of the house for added convenience.
• Attached garage with room above – Maximise vertical space by adding a room above the garage.
• Outdoor living area – Install a pergola or gazebo to create a relaxing outdoor retreat.
• Small bathroom or kitchen extension – Add extra functionality by expanding these essential rooms.

Two-Storey Extension Ideas

A two-storey extension can provide much-needed space and improve your home’s layout. Consider these ideas:

• Kitchen & Master Suite – A larger kitchen and dining area downstairs, with a master bedroom and ensuite upstairs.
• Open-plan living & more bedrooms – Create a spacious living area on the ground floor, with additional bedrooms and bathrooms on the second floor.
• Home office & guest suite – Have your home office downstairs with a guest suite or extra bedrooms above.
• Family room & master suite – Use the ground floor for a family room or playroom, with a luxurious master suite upstairs.
• Teenager zone & home gym – A separate living area for older children on the second floor, with a home gym or hobby room downstairs.

Keep in mind that second-storey extensions typically require a building permit from your local council. You may also need to consult a structural engineer to ensure your home can support the additional level safely.

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House extension costs Vs value: Is it worth the investment?

A house extension can significantly enhance your home’s space and functionality, but is it a worthwhile investment? The answer depends on factors like location, extension type, and overall market demand.

How Much Value Can an Extension Add?

A well-planned extension can increase property value by 10–30%, especially in high-demand areas. Kitchen and living space extensions often add more value than extra bedrooms, while high-quality finishes can further boost appeal.

When Does an Extension Make Financial Sense?

• The cost per m² is lower than buying a larger home.
• It improves the home’s functionality and livability.
• It aligns with market demand, such as adding bedrooms in family-friendly areas.

Potential Downsides

• Overcapitalisation – Spending more than the home’s resale value increase.
• Hidden Costs – Permits, structural changes, and unforeseen expenses.
• Disruption – Construction can take months and impact daily life.

Final Verdict

A house extension can be a smart investment if it adds value without exceeding market limits. Careful planning and budgeting are key to ensuring a positive return.

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Getting a house extension quote

To get an accurate understanding of extension costs, it’s crucial to obtain multiple quotes from different builders. This allows you to compare prices and services before making a final decision. Additionally, take the time to check references and review previous work to ensure the contractors have a good reputation and experience.

What to Look for in Quotes

When reviewing quotes, be sure to clarify what is and isn’t included in the price. For example:

• Excavation and demolition – Are these tasks included, or will they incur extra charges?
• Materials and finishes – Are high-quality materials or custom finishes part of the quote, or are they extra costs?

While many builders include these expenses in their quotes, lower quotes might indicate that additional work (such as excavation or demolition) hasn’t been accounted for, leading to unexpected costs later on.

Request an Itemised Quote

To avoid confusion, always ask for an itemised quote. This should clearly outline the cost of materials, labour, permits, and any extra work, ensuring that you know exactly what will be covered.

This approach helps ensure transparency and prevents surprises as the project progresses.

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* All costs and prices quoted were sourced at the time this cost guide was written and should only be used as an estimate.