Does your family need extra space because you just welcomed a new bundle of joy? Maybe you require a home office or want to move some relatives in with you. Whatever your reason for needing a bigger home, knowing how much a house extension costs is the first step to achieving it.

When you reach the point that the household feels as though they’re living on top of each other, you’re faced with two options: buy or rent a bigger home, or extend your existing home so that it meets the needs of your growing family.

Given today’s tough housing market, for many Aussies, an extension is the most affordable way to get the extra space they need. And in this article, building designer, Martina Hayes maps out exactly what costs you should expect for various kinds of house extensions.

Advantages Of A House Extension

There are a number of reasons why an extension outweighs moving house, including:

• You remain settled in your community
• Kids don’t need to move schools
• You have the creative control to personalise your home the way you want to
• Extending usually costs less overall than buying a new home
• The family avoids the upheaval of packing and moving
• You increase the value of your property

Types Of House Extensions

Depending on your property, an extension can be undertaken in two ways, either you:

• Add a second storey on top of your existing home (‘going up’), or
• Extend the footprint outwards into the backyard (‘going out’)

But the question is, which option is cheaper? And how much will it actually cost to add an extra storey or to push out into the backyard?

Below, Martina shares her extensive experience and breaks down the cost of a house extension to help you set your budgets and start planning.

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Overview Of House Extension Costs In Australia*

Have a look at the table below. First, you need to distinguish whether you wish to go up or out. Then, measure the area of the extension and multiply it by the price per square metre. If the addition includes a new kitchen or new bathroom, you need to add those costs on top.

	Price per m2	Add for kitchen	Add for each bathroom
Ground floor extension	$2000 – $2700	$50,000 – $70,000	$36,000 – $56,000
First-floor addition	$3400 – $3600	$50,000 – $70,000	$36,000 – $56,000

These prices include:

• Demolition
• Excavation
• Building materials such as timber frames, bricks and roof
• Windows
• Doors internal and exterior
• Flooring
• Insulation
• Plumbing
• Electrical services

Ground Floor Extension (‘going out’)

For a brick-veneer ground floor extension, you should allow for $2,200 to $2,700 per square metre. This includes quality finishes but not high-end. So, how do you determine if you are on the lower or higher end of this range? It depends on the:

• Foundation required
• Building materials used
• Size of extension (the smaller the higher the cost per m2)
• Site access to your block and whether it is sloping or flat

First-Floor Extension (‘going up’)

Not everyone has a big enough backyard to push out horizontally. If this is the case, consider building another storey on top of your existing property. But, be aware that it won’t be just the walls of your house going up, but your expenses too – you need to allow for $3,400 to $3,600 per square metre.

Here are a few reasons why a vertical expansion is usually more expensive:

• You need a staircase
• You lose your roof and need to build a new one
• The existing ground floor walls may need reinforcement to carry the weight of the second storey

Add Costs For A New Kitchen

Whether you are extending up or out, adding a new kitchen to the equation increases the costs of your project considerably.

For a standard, good-quality kitchen you will need to allow $50,000 to $70,000 for cabinetry and stone benchtop alone. Not included in this amount are your kitchen appliances; if you are buying contemporary appliances like an induction cooktop and a steam oven, ensure you allow extra.

But as always, when it comes to renovating or building, the sky is the limit. Nowadays it is easy to spend over $100,000 on a kitchen with luxurious touches like a stone splashback, 2PAC finishes and high-end appliances.

Add Costs For Each New Bathroom

Another space that is tough on the budget is the bathroom for which you need to allow $36,000 to $56,000 each. And the biggest bathroom costs are actually in labour – think tiling, waterproofing, plumbing and electrical work.

Not even one-third of the overall bathroom cost goes to materials used, such as tiles, a new vanity, shower screen, bathtub and more. So, saving on fixtures and finishes doesn’t have a huge impact on the overall bathroom expenses, unfortunately. (That means you should choose what you want!)

Overall House Extension Cost: An Example

Wondering what you need to put aside for a ground floor extension measuring 120m2 that includes a new bathroom and kitchen? Based on the table above, you need to allow between $350,000 to $450,000 to get it all done.

When adding another storey on top with an area of 120m2 including an ensuite for you and a bathroom for the kids, it would come up with $480,000 to $544,000 when it’s all finished and ready for living.

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Other Costs To Consider For A House Extension

Quality Builders

It is assumed that the work will be carried out and managed by a quality builder. They will be a member of either The Housing Industry Association (HIA) or the Master Builders Association (MBA). Both industry bodies require proof of industry skills and knowledge while also offering workshops for continuous professional development. To be a member of one of these associations can be regarded as an endorsement for the builder.

Homeowner’s Insurance

Also included in your costs is the premium for The Home Building Compensation Fund (HBCF), which is often called the homeowner’s warranty. This provides a safety net for you in case your licensed builder or contractor goes into insolvency, disappears or dies. The premium alone can be between $3,000 and $6,000 for a simple ground-floor home extension.

Fees for design, planning and building permits

Also, allow for the following additional costs when preparing your overall budget:

• A building designer or architect for planning your new space
• Surveyor for surveying your block of land and property
• Engineer for structural assessment and compliance
• Council or private certifier for building permit DA or CDC
• Interior designer for impeccable looks, flow and functionality

As a rule of thumb for all of these services combined, you should allow $40,000 to $80,000 towards your home extension project.

To wrap it up and avoid renovation regrets later on, ensure you have a contingency of 10 to 20% of the construction cost as unwanted surprises can pop up when getting into the structure of an existing building. Make sure you are prepared for some unforeseen expenses that may arise during the construction process.

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So, Is The Cost Of A House Extension Worth It?

If nothing else, this article has shown you that house extensions don’t come cheap in Australia.

But with property prices being some of the highest in the world, it is possible for your return on investment to multiply in the years to come. This is particularly true when the extension is exceptionally well-planned and executed with quality craftsmanship. So yes, a house extension can be very worthwhile.

But before going down the path of considering the resale of your property, make the most of your recently extended family haven first. Sit back, relax and enjoy family living with all the space you need. And you can’t put a figure on this, can you?

This article was written by Martina Hayes, a qualified interior designer and building designer located on Sydney’s lower north shore. With 10+ years of experience in the industry, Martina specialises in whole-house renovations and is passionate about transforming houses into functional and fabulous homes.

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Looking for more renovation inspiration? Take a peek at our collection of reno stories and find out how other Australians have transformed their homes for the better.