How Much Does An Extension Cost In Australia?

melbourne extension kitchen

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.

The cost of building a house extension varies from $965 to $2,710 per square metre. This applies to 50m2 to 150m2 ground and upper floor extensions.

Prices for labour and other inclusions must also be considered.

A clearly defined plan will help you to determine project specifics and the expected cost of each element required for house extensions. Expect to pay more for extension projects requiring foundation works, engineering assessment and major structural alterations.


Find a home extension builder to work in a timely and professional manner to ensure the quality of construction. Before the actual construction commences, make sure to finalise the design specifications. Initial consultations are done to properly layout your costings.

Costs for a ground-level house extension in Australia start from around $70,000. When house prices are high, as they are in many parts of Australia at the moment, adding a room or extending your living area on the ground floor can be a more affordable way to create space than moving. Here are some things to consider when planning your extension. At MJS Construction Group, we have the best home builders selection to make your house a dream come true.

extension kitchen melbourneHow Can You Plan For A Ground-level Extension?

Ground floor extensions are typically more affordable than converting the loft or excavating basement space. A same-level extension typically costs anywhere between $70,000+, depending on where you live, the project specifications, your choice of materials including cladding, labour and project management. Adding more windows and internal walls contribute to cost too.

Be aware that smaller renovations can work out slightly more expensive per square metre than larger renovations as many of the overheads such as getting a DA from the council are a fixed cost. We advise getting a fixed price from your renovation consultant before the project starts to ensure your renovation comes in on a budget. If your budget is tight, focus on the things you need, rather than want, to start with. You can always upgrade finishes, fixtures and fittings in years to come.

Early estimates from your renovation consultant are usually a guide based on a series of assumptions. Even when you get the actual quote, plan in a contingency budget of at least 15% for unforeseen extras or problems. This will help you cover expenses, such as having to repair leaks or taking care of structural problems without jeopardising your project.

Your builders will work from architectural plans. Major building work typically requires a planning permit from your local council as well as a building permit from a registered building surveyor. You can organise these yourself or employ someone else, such as your renovation consultant, to do it on your behalf.

Once the council accepts the drawings for your project, it can be difficult to make changes, and this is one reason why Concept Drawings of a renovation are so useful. They may be more expensive than line drawings. Still, they show you exactly what your finished renovation will look like, which means it’s easier to identify any misunderstandings or problems earlier in the process.

Why Consider A House Extension?

Why consider a house extension when you could sell your house and move to a larger home? Here are four good reasons to consider adding a house extension:

  • If you like the area you’re living in, you don’t have to move
  • Make the changes you want to make and not settle for something that’s just okay
  • A home extension may be more affordable than moving to a larger home
  • You may be attached to your current home and not want to leave

Remember that moving involves expenses and a great deal of effort. First, you have to put your home on the market and look for a suitable new home. If your house is smaller than you would like, a larger home is going to cost more. Think about moving costs, bank charges and other costs and a home extension may be less expensive than moving. Check out our range of dual occupancy builder for your dream house.

How Much Does A Home Extension Cost?

You won’t know the exact cost of a home extension until you’ve made plans and know how large the extension is going to be and what will be included in the extension, as a general rule, an 80 square metre ground floor extension costs between $164,500 and $310,000. That works out to between $2056m2 and $3875m2. The difference is in the type of construction and the quality of the inclusions.

If you’re adding a second storey, the cost will be about 50 per cent more than a ground floor extension. The reason for this is because a second storey doesn’t require foundation work and other major expenses. If you want to add a second storey, the square metre cost will be between $3084 and $5812. If you need a second storey, it will be cheaper than making a larger ground floor extension, and less land will be needed for the extension.

These are the basic costs for a home extension, but depending on what needs to be done, a home extension can be more expensive. For example, you may need to have excavation work done. That will add to the cost. Since a home extension includes knocking out a wall, that may be an extra expense, and the home may also need some minor renovations.

The Importance Of Passive Design

Using passive design principles when planning your extension means your home will need less heating and cooling to keep it at a comfortable temperature all year round. Design for passive solar protects a house from the summer sun and promotes the escape of heat while letting the sun in during winter and helping ensure that heat is retained. These strategies, combined with effective shading, insulation and sealing (except in tropical regions) can help reduce your reliance on artificial heating and cooling systems. Visit the Australian Government website YourHome for more information.

How Do You Create An Open-plan Home?

Open-plan homes, particularly those with good indoor-outdoor flow, are popular all over Australia. So it’s hardly surprising that one of the most common alterations is the creation of one large kitchen/dining/living space. Opening up walls is usually a straightforward process; however, load-bearing walls may need to be strengthened, which will incur additional costs. Any electrical or plumbing points within the wall would also have an impact on the overall cost. If you are looking to remove a non-load-bearing wall between two rooms, you may be able to get this taken out and tidied on the same day.

kitchen extension melbourne

How Can I Create Indoor-outdoor Flow?

Perennially popular bi-fold doors provide virtually uninterrupted views of outdoor areas and have come a long way over recent years. Look for doors with a smooth sliding function made from timber that will complement your deck if you have one. A corner design opens up space even more to give you that great outdoor feeling.

Sliding doors take up less space than bi-folds and can be a great option, particularly if you’re looking for a door to open on to a more compact area. While they don’t open up completely, they do allow for controlled ventilation, depending on how far they are open. The two standard types of sliding doors are top hung or bottom rolling systems. Top hung doors allow the bottom sill to be completely flush, but they often require increased lintel support and installation generally takes longer, which costs more. Bottom rolling systems suit larger, heavier glass panels.

Factors Impacting the Cost of a House Extension

When it comes to adding additional living space to your home, several factors impact house extension prices. For example, there’s a vast difference between the living room extension cost that’s on the ground level as opposed to the second storey extension cost of building another floor. This generally involves the removal of the existing roof, installing a new sub-floor, building exterior walls, and constructing a new roof.

Debris Removal

Major home renovations for extending living space will also come with a significant mess. You will need to hire a skip bin in order to safely and effectively remove the deconstruction and new construction debris. To see what a skip bin cost in your area, click here (link to skip bin cost guide) for more information.

Siding Replacement

For example, if your home has siding that is no longer available, the cost of home extension will increase because you will need to reside your entire house. Special order siding materials can also come with a premium price tag. This is a conversation that you need to have with your building contractor.

Windows and Doors

There are several brand name windows and doors in today’s marketplace. Some are economical with basic energy-efficiency properties, while others are made of better materials and have superior energy-efficiency ratings. Depending on how many windows and doors you need for your home extension and your budget, you may need to weigh out your options.

Type of Roof

Considering adding a second storey for your home extension project? This is also an excellent time to talk to your builder about energy-efficient roofing materials and the design of the roof itself. Your second storey extension costs will also depend on the type of roof that you install. Did you know? By adding an energy-efficient roof to your home not only decreases your heating and cooling costs, but it also adds property value and curb appeal.

Basement Extension

Adding a basement extension will significantly increase the project’s overall cost. This typically involves the hiring of excavation equipment and labour as well as hiring other tradies like concreters, plumbers, electricians, and HVAC technicians.

Kitchens and Bathrooms

Anytime you add a kitchen or bathroom to your home extension design, you can expect the price to increase by several thousands of dollars. Kitchens and bathrooms are the two most expensive rooms in any structure. This is due to the required fixtures, cabinets, countertops, plumbing, electrical, flooring, appliances, and other components. 

All of these factors also come with other considerations that include:

  • Type of extension
  • Building permits
  • Size of skip bin
  • Extension size
  • Materials used
  • Time is taken to complete the project
  • Planning cost
  • Accessibility to the project
  • Unexpected cost to add a room to the house with hidden problems
  • Post project completion costs (furnishings, lighting, flooring, painting, tiling etc.

Depending on the design features that you want can also impact the cost. Additionally, you may also need to enlist the services of a professional architect or home builder to draw the floor plans to ensure the structural integrity and energy efficiency of the design.

How to get a reliable house extension cost estimate

Let’s say, and 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.

kitchen extension

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.

Other House Extension Costs To Consider

The basic cost of a house extension should include all the basics including roofing, cladding, interior cladding, insulation, windows and doors. It may not include other items, though:

  • Heating and air conditioning may be extra expenses
  • A bathroom can add to the cost of a house extension
  • A kitchen adds to the cost
  • Quality inclusions will add to the cost
  • The cost will not include the cost of having plans drawn up or council fees
  • Furnishing the extension will add to the cost

A house extension is a waterproof shell. It will be ready to move in when finished, but will not include furnishings, blinds or curtains, lighting fixtures and other items. If a bathroom or kitchen is needed, the cost of plumbing and bathroom or kitchen fit-outs has to be factored into the cost. How much will a bathroom or kitchen cost?

A typical bathroom renovation costs:

  • $5000 to $15,000 for a budget bathroom
  • $15,000 to $25,000 for an average sized bathroom with mid-range fittings
  • $25,000+ for a high-end bathroom

Bathroom renovations include ripping out the old bathroom. If you’re adding a home extension, bathroom builders won’t have to tear out old fittings, but you will face other expenses. For example, the plumber will have to install pipes and sewerage. An electrician will have to install new wiring, lighting and outlets. Because of these expenses, a new bathroom may cost closer to the higher end of the scale.

A typical kitchen renovation costs:

  • $10,000 to $22,000 for a budget renovation
  • $22,000 to $35,000 for a mid-range kitchen
  • $35,000+ for a high-end kitchen

Like the bathroom, the cost won’t include tearing out an old kitchen but will include new plumbing and electricity. You won’t know how much a new kitchen will cost until you get quotes from kitchen installers, plumbers and electricians, but the cost will probably be higher than a kitchen renovation.

A bathroom or kitchen will be a greater expense than most other extra costs. If you feel your current kitchen is too small, what else would you use the space for? Think about ways to make it feel more spacious. Add larger windows or, if you don’t have an open plan kitchen, knock out a wall to make the kitchen feel larger.

You may need a bathroom in a house extension, but how large does it need to be? If you already have a larger bathroom, an ensuite bathroom may be all you need. It will cost less than a large bathroom and may be perfect for the extension.  Finding the right duplex build  is an important decision. Check out our range of the best home design constructions at MJS Construction Group.

Consider All The House Extension Costs

Remember a house extension costs more than just the cost of the extension. Consider all the costs before you commit to an extension. Do you need 80m2 or will a smaller extension be within your budget? A 60m2 extension can save between $20,000 and $75,000 depending on the quality of inclusions. That amount of money can pay for most if not all of the furnishings, curtains and other inclusions.

Do all your costings first and don’t leave anything out. Remember to include:

  • Furnishings
  • Lighting
  • Curtains or blinds
  • Heating and air conditioning
  • Flooring
  • Painting
  • Exterior painting if needed
  • Excavation work

Check the quotes you receive from builders carefully. Do they include knocking out walls or excavation work? If not, those will be additional expenses. Some home extension builders will include everything in their quotes. If a quote is higher than another, it may include those costs. If in doubt, ask the builders what is included in their quotes and what is not included. A quote should list everything. If it does not, a builder may be trying to get your business by undercutting other builders. They will add other costs on later, though, so make sure you know what is in your quotes.

A house extension is not inexpensive, but moving to a larger house can be even more expensive. The house will cost more, and you will have other expenses to think about. These will include:

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

Add up all the costs and a house extension is usually less expensive than moving. It can also be easier since you don’t have to leave home while the building is going on and can go about your daily business. As a bonus, if you decide to sell, the house extension can add its value or more to the cost of the home. Home extensions make good sense, both economically and for your peace of mind.

Prior to construction, check if the builder’s expertise is focused on residential extensions. Request for sample works to help you choose.

Most importantly, verify their credentials. Ask to see a copy of their updated licence and insurance to help protect your finances. Read online reviews and check customer references. Their experience also determines the quality of home extension works.

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