Home Improvement

How Much Does a House Extension Cost in Australia

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So, you’ve been a proud homeowner for some time now but your family living space needs have changed? You’re probably thinking about making some major shifts, regarding your property. Should you move to a much larger house? Or would it be better if you renovated or extended your home?

On that note, many Australians, who are faced with such a dilemma, choose to remodel their houses, in order to accommodate their need for extra space.

If you’re on that path yourself, wondering and researching how much a house extension or conversion costs, keep on reading.

Table of Contents:

How to get a reliable house extension cost estimate

Let’s say, you’re done with the brainstorming of what you want to gain in terms of additional living space, be it a guest room, a granny flat, a conservatory-like living room or another bedroom.

You’ve come up with a rough budget to the extent of ‘I won’t go over such and such amount’. The next logical step is to approach a building or home improvement company in the hope to get a comparative and reliable price on their house extension project.

And this is where all sorts of quote-related pitfalls could gradually spring up. From missing to include any demolition work to forgetting to budget for any building cost overruns, you could easily get an estimate that is only seemingly matching the limit of what you’re prepared to pay.

No house remodelling company can give you a realistic price quote unless you complete a series of steps beforehand. You’ll need to contact all the professionals or private experts who can provide you with the required preliminary surveys and all necessary reports.

Getting an accurate cost estimation you need a detailed land survey by a registered land surveyor, a soil report by a geotechnical engineer, a concept design and a structural survey.

Only then an experienced quantity or building surveyor can offer you a cost estimate, based on the above, as well as on the present floor area rates for the type of extension you intend to have (same-ground, two-storey, etc.).

The building surveyor will include other costs, as well, such as the builder’s markup, GST and more.

After completing the exploratory project works stage, you can get an insight on what to budget for your dream house extension and start looking for a specialist to draw your plans.

You will need the plans to present to a builder, along with every other piece of document, you’ve gathered, and a list of all the materials, fixtures and fittings, in order to get a quote for the actual work.

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Pre-building work expenses

Below, we list various possible fees and costs that you may need to budget for, depending on the specificity of your house extension project.

Not all of them will apply for your situation, especially if the home redesign work is on a small scale or, say, it involves conversion of an existing structure.

We can help you with the extending of your house! For more information see our services on our main site.

Planning, surveys, consultation & design costs for your house extension

  • A land surveyor fee ($850 – $3,550)
    The detailed survey, which will depict the boundaries of the site and all the existing structures and site features, is usually submitted with the local authorities for approval.
  • Planning permit and building regulations fees
    They will vary, depending on the type of work you’ll have done (the permits can be sorted out for you and obtained by a private town planner (another cost) or by the building company.
  • Soil report fees ($300- $560)
    Not always necessary.
  • Structural engineer fees ($2,000 – $3,200)
    The cost is often applicable when structural changes are envisaged in the project.
  • Building surveyor/estimator ($1,800 – $2,300)
    You may approach an independent one before selecting the builders who will realise your dream house extension.
  • Design Fees
    A registered building designer or an architect will be the specialist who will design your project, with fees ranging greatly based on their experience – ($9,000 – $13,000) – payable to a building designer, who will be the common-sense choice for private residential projects and ($25,000 – $46,500) – charged by an architect, usually commissioned by an affluent private client or for designing commercial or public buildings.
  • Draftsman fees ($4,200 – $6,600)
    The professional who will draw the plans, based on the given design (the plans are also submitted for a council approval).
  • Interior design fees
    If applicable – they vary, depending on the expert’s experience ($50 – $90 per hour).

The sq. m. factor vs. the type of extension

Project estimates, based on sq. m. rates alone, are never reliable. Still, they are used when approximate costs need be calculated.

The rates vary by location and are interrelated to the type of work, you intend to have done.

Just as a guide, you can expect to pay anything from $1,300 to $2,200 per sq.m. for a single-storey extension. For a two-storey house extension, the price rises often by 50%. Converting your loft into a usable space will cost you from $1,600 to $2,600 per sq.m., depending on the scope of work and the various fittings you want to be installed.

A garage conversion is probably one of the cheapest ways to create extra space that you can utilise for something more than keeping your clutter or occasionally store your car. You’re equally likely to get a quote of $7,000 or $ 32,000, depending on what you’re going to make out of your garage.

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What house extension building cost aspects to consider

Estimating the cost of the building work is hard, as many factors play in the process. For instance, labour for some jobs will be charged per hour (around $70 per hour), whereas with other types of renovation jobs – tradesmen work per sq. m. (plastering, tiling, painting, etc.).

Essential cost variables

There are various project expenses, which may comprise the final cost of your house extension or renovation work. They’re unique for each house renovation, but here are the general ones.

  • The size of the project
    The bigger and more complex, the more expensive it will be.
  • The type of materials, fixtures and fittings
    Naturally, a marble floor is pricier than vinyl flooring or the fancy lighting, you choose, will also come at a cost.
  • Unusual terrain
    Builders will factor any difficult-to-work-with aspects related to the landscape and soil type, in their price.
  • The size of the building company
    Small businesses have fewer overheads and will charge you slightly less than a large and popular building firm.
  • Profit margin
    Builders need to make a profit but what their markup percentage will be, is hard to say (around 20-30%).
  • Builders’ preliminaries
    From setting up a scaffold to other arising mid-project costs, the company will detail out a bill of quantities that comprise the preliminary costs.
  • Construction overruns
    These include time and cost overruns, with the former – related to delays and the latter – related to unexpected project revisions or other unanticipated events;
  • The access to your property
    Builders will charge you more if their work is affected by difficult access to the site and a lack of convenient parking spot.
  • Builders waste removal
    Regardless of whether the builders waste disposal is included in the quote as part of the final preliminary expenses or you need to make additional provisions for the cleanup by hiring another company, this still costs money.

Overlookable expenses

  • Planning delays
    From getting the right approvals and permits in time to various other agencies protracting the start or progress of your project – expect the unexpected at your expense.
  • Weather factors
    Stormy conditions, rain, downpours or bushfires in the area will incur delays and unpredicted costs.
  • Seasonal aspects and holidays
    Builders’ work during busy summer periods is often slightly more expensive than if done during lulls in the industry sector; or if your project extends over the Christmas holidays, this may have an impact on the final cost.

Home redesign and house extension trends

Let’s look into some home extension ideas that can inspire you and even help you save some money in the long run.


A conversion of an existing room, structure or a separate building is often cheaper than building a brand new storey or an additional room on the same floor. So, you can get that needed extra bedroom out of converting your loft.

Passive Design

Incorporate a smart, passive design in your new extension to save on heating and contribute to the environment. You can take advantage of heaps of information on the matter from Australia’s guide to environmentally sustainable homes.

Connect to your outdoors

Be it through an easy-to-install decking, which won’t cost you that much, or by connecting two existing structures and enclosing the space in between entirely with glass – you can enjoy your garden in rain or shine, either way.

Glazed Timber Extension

This is more or less a type of conservatory but done simply out of timber and glass. Whether you’ll turn it into a living room or a kitchen, it’s entirely up to you.

Use a sloped terrain to your advantage

You can embrace a difficult landscape and erect a veranda-like structure that can be turned into an additional room and still continue to garden the area underneath it.

Create space for a home office

Working mostly from home? Then, why not design your office with better productivity and comfort in mind? It doesn’t matter if you’re planning to use your garage for your home office conversion project or you’ll create a quiet, ergonomic workspace under the stairs that lead to the upper floor.

Up your home value with a second bathroom

Adding a second bathroom may prove a relatively costly venture but no doubt that it will be worth it! It’ll not only make life easier if you have a large family but it will also boost the resale value of your house.

Let’s discuss your house extension! We can help create the home you’ve always wanted!

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Travis Walker
Travis Walker
4 years ago

It’s a really helpful post! Thanks for the share.

Victoria Addington
Victoria Addington
3 years ago

I\’m glad that you provided the average cost of the house extension. My husband and I are planning to purchase the vacant lot beside our lot to get additional space for the house. Good thing the single-story extension costs around $1,300 to $2,200 per sq.m., which fits my budget. Hopefully, I can find one here in town.

3 years ago

Wow, I can’t believe how much it is going to cost me to do this project. If I get a builders licence will that bring the cost down, substantially????? Also I didn’t mention that, my youngest Daughter, her Husband and their 3 gorgeous children live with us already. So the house at this stage has 6 bedrooms, 3 bathrooms, 3 living spaces and a rumpus room. So I am trying to see if an outdoor kitchen, can bypass all the existing regulations surrounding fir wall issues????????

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