House Extension Costs 2025: A Guide for Parents
Witten by Martina Hayes
Is your family outgrowing your current home? Whether you’re welcoming a new baby, need a dedicated study space for school-aged children or want to create a spacious parents’ retreat as your me space, the need for extra space grows as families evolve.
When it comes to increasing your living space, you generally have two options: moving to a bigger home or extending your existing one to better suit your family’s needs.
Why Choose a House Extension?
If your home is in a great location—close to schools, childcare and work—then an extension might be the best choice. Depending on your property, you can:
- Extend outwards into the backyard, or
- Build upwards by adding a second storey.
But how much does it cost to add more space to your home? Let’s break it down so you can budget effectively.
Overview of House Extension Costs
Use the table below as a general guide. Start by deciding whether to expand outwards or upwards, then calculate the area you wish to extend. If you’re adding a kitchen or bathroom, be sure to include those costs as well.
| Price per additional square metre | Add for kitchen | Add for each bathroom | |
| Ground floor extension | $2,400 – $2,900 | $45,000 – $80,000 | $35,000 – $50,000 |
| First floor addition | $3,800 – $4,200 | $45,000 – $80,000 | $35,000 – $50,000 |
This information is a general estimate and can vary based on your city and specific site conditions. All costs include GST.
Ground Floor Extension
For a brick veneer ground floor extension, costs range from $2,400 to $2,900 per m², depending on factors such as:
- Foundation requirements
- Size (smaller extensions have a higher cost per m²)
- Site access and terrain (sloping or flat)
- Building materials
Adding a Second Storey
If extending outward isn’t feasible, you may consider building up. However, adding a second storey typically costs more, ranging from $3,800 to $4,200 per m². This is because it involves:
- Removing and replacing the existing roof
- Strengthening ground floor walls to support extra weight
- Installing a staircase
Additional Costs to Consider
Kitchen Addition
Adding a family-friendly, good-quality kitchen with an island bench will cost between $45,000 and $80,000 for cabinetry and benchtops. If you want premium finishes, costs can exceed $120,000. Appliances such as ovens, cooktops, and dishwashers are additional.
Bathroom Addition
Bathrooms are among the most labour-intensive parts of an extension, with costs ranging from $35,000 to $50,000 each. Plumbing, tiling and waterproofing account for most expenses, while materials such as tapware, vanity and tiles make up the rest.
Cost Examples
Here’s what you might expect to pay for common home extension scenarios:
- Ground Floor Extension (120m², with 1 bathroom and 1 kitchen):
Total Cost: $368,000 to $478,000 - Second Storey Addition (120m², with 2 bathrooms):
Total Cost: $536,000 to $604,000
All estimates assume work is done by a reputable builder, ensuring professional quality and compliance with building codes to keep your family safe.
Other Expenses to Budget For
Design and Approvals
Architectural drawings, engineering, and council approvals can range from $40,000 to $90,000.
Insurance
The Home Building Compensation Fund (HBCF) premium typically costs $3,000 to $6,000 for ground-floor extensions, providing financial protection if the builder becomes insolvent.
Plan for Unforeseen Costs
Unexpected expenses can arise, especially when renovating an older home. It’s wise to set aside a contingency fund of at least 20% of your total budget to cover any surprises.
Will a House Extension Add Value to Your Home?
While extending your home is a significant investment, it can also increase your property’s value—especially in Australia’s competitive real estate market. A well-planned extension provides more space and enhances your family’s comfort and lifestyle.
However, the real value is creating a home that perfectly suits your family’s needs. After all, you can’t put a price on the happiness and convenience of having the right space for your loved ones.
Martina Hayes is a qualified and creative interior designer and building designer with over 10 years of experience and is passionate about bringing out the best in your space. Founding her own business in 2014 and seeing it thriving, she has engaged a small number of team members. Their qualification and dedication are paramount to maintaining the highest standard of professionalism within the team. From the Greenwich studio on the lower north shore, the design firm serves the entire Sydney area.
