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How to budget when building a home extension

Your guide to home extensions while staying on budget

When you need more room in your home you might be looking at either buying a new property and moving, or investing in a home extension on your existing property. By renovating and extending your home, you are investing in your home and adding real value. This can result in a higher sale price if you do decide to move in the future.

With the average cost of a home in Melbourne of at least a million dollars, there are also significant stamp duty costs that can be avoided by extending your home.

While a home extension adds value, it is still a costly investment. You need to budget carefully and watch your spending to ensure you stay on target.

This article covers some key tips for planning and executing a home extension while keeping as close to your anticipated budget as possible.

Do you need a quote for your home extension? Supa Group’s full-service Design and Build team can help you execute your project from start to finish. 

Make a (realistic) home extension budget

A successful home extension budget requires careful planning right from the start. Before you even get a quote you should sit down and work out exactly what type of home extension you want, and identify your must-haves.

  • • Be generous with what you are expecting; whether you are funding your renovation with cash or through a loan, your overall home extension expenses need to be realistic for what is to come.
  • • It is important to consider your total costs beyond the extension itself, including planning permits and rental costs while construction is taking place.
  • • Add a generous buffer onto your home extension costs for any additional expenses that will likely come up over the course of your renovation.


Once you know what you are after and what you can afford, you will be able to speak to some builders and get quotes on the work you want completed.

Get a detailed quote

getting a home extension quote

The best way to get an idea of your realistic costs is to speak to a builder and get a detailed quote including all possible expenses. Beware of builders who may low-ball you to get your business, only to invoice you for much higher actual costs later on. Compare quotes, and if one builder’s costs are significantly lower than the others it may be that they are underquoting.

  • • Look at previous projects the builder has completed and ask to speak to the customers first hand.
  • • If your builder is reputable they will be happy to show you evidence of their past projects.
  • • Your builder should also fully explain what is not included in their quoted price, as these costs need to be taken into consideration for the the total cost of your extension.


A good builder will provide you with an accurate and detailed cost estimate which will be pretty close to the end result, notwithstanding anything unforeseen.

Permits and rebates

When planning a home extension there are the costs of your extension build, and then there are ‘hidden’ or additional costs which are associated with getting your project approved and protecting yourself with insurance.

  • • Your home extension must take into account any Victorian Government Building Regulations and meet the necessary standards.
  • • Your builder will be able to discuss additional expenses relating to permits and fees and will work with you to ensure your budget anticipates these costs.


There are also a range of government rebates for energy efficient additions to your home which you may be able to leverage.

Unexpected costs and expenses

Even the most organised of projects can still go awry when unexpected expenses come up, which is why your overall budget needs to be generous. It is far better to budget for more than what you expect and have money left over than it is to have to take out a loan because you underestimated the costs.

  • • Consider setting up a spreadsheet which you can use to monitor every single cost once you are underway — no matter how small — so that you know exactly what you are spending and can track your overall costs.
  • • You may find it useful to speak to your builder about the most effective way to track your costs and get them to provide you with an itemised list of each building stage.


Engage in some research about costs for fixtures and fittings ahead of time and you may be able to lock in some savings on your building budget before you have even started with the project.

Why choose Supa Group?

At Supa Group, we are proud to be an industry leader with more than 40 years of experience. When you work with Supa Group, you always get the benefit of a fixed-price contract for the completion of your home extension works. This can help with the estimate of your costs and will avoid any nasty surprises later on down the line.

Whether you are looking to undertake a ground floor extension or a second storey extension we are committed to quoting accurately and giving you a set date for completion.

Our expertise in the home extensions space means that we will provide you with a realistic estimate, and get the work done on budget and on time.

Find out more about how we can help you with your home extension and explore our gallery for inspiration.