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How Much Does a Home Extension Cost in Mandurah?

Home Extensions Mandurah

How does a new conservatory, garden, storey, patio, or office sound to you? Getting a home extension can be a great way to increase your home value and provide you with some extra functionality in the meantime. 

The best thing is that you have so much flexibility in terms of fixtures, fittings, size, cost, and style. Given the increase in the cost of land in Australia, a home extension is something of a bargain as compared to the purchase of a new plot. And considerably less stressful!

However, there’s quite a bit of variance in terms of home extensions and their associated costs. After all, it’s reasonable that adding on another small living space for family gatherings will be priced much less than adding on an entire storey to your home.

Let’s examine the variance components of home extension cost to give you a more nuanced understanding as you consider options for your house. 

Home extension cost: the overview

The cost of a home extension will be priced on a square metre basis. As a (pretty general) average, you can expect to pay between $1,300-2,100 per square metre. However, there is huge variance from this average. The factors that affect the price are mainly the type of extension and the quality of inclusions. The type of extension will have the largest effect. 

The average price per square metre for a kitchen extension is going to be far more than a bedroom extension. Consider that kitchens require much more plumbing, electrical, and fixtures compared to a bedroom. And a ground-level extension is going to be more affordable than building an extra storey. This is because there is added complexity with the height element involved. You can pay around 50% more for a second storey extension. It can also be a little more difficult to get planning permission to extend vertically as opposed to horizontally. 

Be aware that smaller extensions will be more expensive on a price per square metre basis. Getting a DA from the local council is a fixed cost regardless of extension size. 

Another huge thing to be mindful of is that the initial price is just an estimate. You would be best advised to allow ~15% for the likely event of additional costs for unforeseen expenses. When the council accepts your initial design, it can be quite problematic to get things changed. If so, it will be at increased cost and stress. 

Home extension cost: other considerations

There are many other considerations when it comes to home extensions. If you are extending your home with a bathroom or kitchen, the cost is going to increase drastically. This is because the inclusions such as tiles, granite countertops, and appliances are going to bump up the price. And the price for the home extension won’t include the cost of demolition and disposal. The following list should give you an indication of things that affect the cost of home extensions:

  • Quality of fixtures and fittings
  • Home extension type (kitchen, bathroom, bedroom, second storey)
  • Total surface area
  • Consultancy fees
  • Council approval fees
  • Changes and adjustments
  • Demolition and disposal
  • Heating and air conditioning
  • Excavation and preparation work

Home extension cost per type

The following table gives rough figures for the cost of the various different kinds of home extensions. Converting a cellar or basement is far more expensive due to the complexity involved. Second storey extensions and basement/cellar conversion are far more expensive than some of the other options available. 

Extension Type (80m2)






Basement Conversion



Garage Conversion



Granny Flat



Ground Floor Extension



Second Storey Extension



How can I reduce the cost of a home extension?

It does depend on what your expectations are: if you want a state-of-the-art kitchen or bathroom, you’re going to pay for it. But if you’re a little more flexible, then there are multiple options available. If you reduce space, you can save considerably. Cutting back from 80 square metres to 60 square metres will save you an enormous amount of money. At nearly $1,500 per square metre, that’s a savings of $30,000. 

Another thing you could do is convert a garage, which will work out far more cheaply than an extension. This is not always an option but can be a very direct way to increase your living space while reducing your expenditure. The more simple the home extension, the more affordable it will be. So if you want an extension with lots of angles in a strange shape, the cost will increase as compared to a regular rectangle or square design. 

Will using an architect add to the home extension costs?

Using an architect will add considerably to the costs and is not recommended for home extensions. It’s often better to use a design and build contractor than an architect. This holds true for the construction of homes, but it holds doubly true for an extension. 

Most architectural drafts do not actually go ahead, despite paying quite a fee for them. The architect is less familiar with the building process and what’s practical to complete. Moreover, they get paid regardless of what happens! 

Extensions are far more simplistic than building a new home and going to an architect is often overkill. Even for very elaborate home extensions, the use of an architect might not be the best idea. If the design needs to be changed, for whatever reason, then it can add to the cost considerably. 

What is the cost for designs and permits?

Again, this can vary considerably depending on your local municipality and the type of extension you are looking to have built. You might encounter costs for any one, or more, of the following:

Home Extension Service

Low Cost

High Cost

Land Surveyor Fee



Soil Report Fee



Structural Engineer Fee



Building Surveyor Fee



Design Fee



Draftsman Fee



Interior Design Fee

$60 (hourly)

$100 (hourly)

If you use a design and build contractor, you can avoid or reduce many of these fees. Because the designer is also the builder, they consolidate many of the activities into one, giving you a better price. It will also save you a lot of work with regard to councils and permits as they will be intimately familiar with the process. 

Why is there so much variance in the cost of home extensions?

Extensions are a very broad area with many moving parts. Especially when you consider the possible inclusions and upgrades, your budget is the only limit. Generally speaking, however, the average home extension cost will be around $1,300-2,100 per square metre for horizontal extensions. 

At least you can work off this metric if you’re on a budget and get reasonably good extensions and inclusions at this price range. It’s the things you forget to account for that can really impact what you end up paying. And there’s a lot of things to account for when it comes to home extensions. 

What are the most overlooked elements in terms of home extension costs?

We have identified the five most prominent items that can increase the cost of a home extension. These are not well reflected in the average price per square metre and can easily bring costs up or down. They include:

  1. Fittings/Inclusions – There can be a major discrepancy between the cost of low-end inclusions and high-end inclusions. The total home extension cost per square metre often does not account for this. 
  2. Extension Type – The home extension cost does not account for the type of home extension. Adding a bedroom extension is a lot cheaper than adding a studio extension with a bathroom and kitchen. 
  3. Demolition – Demolition work is not included in the home extension cost. It is totally separate, and you will need to do it yourself, hire an external team, or talk to the home extension service about it as an extra line item. 
  4. Designs and Permits – Finalizing the scope of your project, consulting with experts, and applying for permissions are all additional costs outside the price per square metre cost metric. 
  5. Quality of Site – If you have a slope on the land or other foundational work that’s required before the build can even start, it can really increase the cost per square metre. The same is true if you have a poor quality site (uneven, soft, rock deposits) or one that is difficult to access. 

Are home extensions worth it?

If you’re thinking about adding on to your home, you probably have a particular space challenge in mind. Any option that will solve those issues for you may be well worth it. Compared to moving home, the extension is most certainly worth the money. When moving, you have to take into account the following:

  • Real estate agent’s commission
  • Marketing the home
  • Conveyancing
  • Cleaning and/or styling your home
  • Possible repairs or renovations
  • Moving costs

This does not account for the stress of finding a suitable new home and setting down roots in a completely new setting. Compared to a horizontal extension, moving home will work out to be far more expensive in multiple ways. 

Still, it does depend on the type of extension. Granny flats and garage conversions are very affordable and efficient extensions in comparison to building a second storey. 

What’s the most cost-effective home extension in Mandurah?

This really depends on your individual circumstance and what you need. However, granny flats can generate an amazing return on investment. You can get high-quality granny flats in the region of $60,000-100,000.

For example, a 40m2 granny flat, including plumbing and electricity, may cost around $80,000. But you can rent it out for $1,000 per week immediately, which could see you break even in a little over 18 months. Granny flats are also easy to get approval for (if they are under a certain height) and can be constructed in less than two months in many instances. 

Next to this would be garage conversions since the structure and foundation are already in place. This can easily be converted into a rentable studio, though you might miss the loss of your garage. Building an additional storey is usually not a cost-effective home extension unless you compare it to the cost of moving to a different location. 

Where can I find a reliable home extension builder in Mandurah?

Compass Homes has 28 years of experience in Western Australia as a registered, licensed, and insured home builder. Our methodology is simple and cost effective, providing clients with an easy approach to home extensions. 

Our design and build process is far more affordable (not to mention efficient) than traditional methods and gives you increased control and more financial freedom. We’ve basically made a complex procedure as streamlined as it can possibly be. 

Call Reece Grantham on 04 0372 4878 for more information regarding affordable home extensions in Mandurah. 

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