How Much Does a Renovation Cost per Square Metre?
A practical guide to renovation and extension costs in Brisbane
One of the first questions homeowners ask when considering a renovation or extension is how much will it cost per square metre?
A square-metre rate can be useful for establishing an early construction budget, but renovations are more difficult to price this way than new homes. Two projects adding the same amount of floor area can have very different costs depending on the work required to the existing house, the site and the level of finish.
The first step is therefore to understand what the square-metre rate actually applies to.
Indicative renovation and extension costs
The following rates provide a broad starting point for budgeting architect-designed renovation and extension projects in Brisbane.
Type of work | Indicative construction cost |
Light renovation of existing areas | $1,500–$2,500/m² |
Substantial renovation of existing areas | $2,500–$4,000/m² |
Straightforward new extension | $3,500–$4,500/m² |
Typical architect-designed extension | $4,500–$6,000/m² |
Complex / high-specification extension | $6,000–$8,000+/m² |
Decks / covered outdoor areas | $2,000–$3,500/m² |
These rates apply to building work only and exclude GST. They are intended as a preliminary budgeting guide rather than a construction estimate. Actual costs will depend on the project scope, existing building, site conditions, structural requirements, level of finish and market conditions.
Renovating existing areas
Not every square metre of a renovation costs the same.
A light renovation might largely retain the existing structure and room layout while upgrading finishes, joinery and selected fixtures.
A substantial renovation may involve removing walls, altering openings, replacing kitchens and bathrooms, upgrading electrical and plumbing services, replacing floors or ceilings and carrying out structural work.
Once significant parts of the existing house are being reconstructed, the cost per square metre can begin to approach that of completely new construction.
This is one reason simply applying an extension rate to the additional floor area can significantly underestimate the cost of a renovation.
Adding new floor area
New enclosed extensions are generally easier to assess using a square-metre rate.
For a reasonably straightforward extension, an early allowance of around $3,500–$4,500/m² excluding GST may provide a useful starting point.
For the type of architect-designed renovation involving good-quality finishes, substantial glazing, considered detailing and integration with an existing home, $4,500–$6,000/m² excluding GST is likely to be a more useful preliminary range.
Projects involving complex structures, difficult sites, extensive glazing, bespoke joinery or particularly high levels of finish can exceed $6,000/m² and, in some cases, considerably more.
Kitchens and bathrooms cost more
Floor area alone doesn't describe what is being built.
Twenty square metres containing bedrooms and circulation is quite different from twenty square metres containing a new kitchen, bathroom and laundry.
Kitchens and bathrooms typically contain considerably more cabinetry, appliances, plumbing, waterproofing, tiling, fixtures and services than bedrooms or living spaces.
Extensive glazing, custom joinery, fireplaces, feature lighting and higher-specification finishes can have a similar effect.
This is why two extensions of identical size can have quite different construction costs.
Decks and covered outdoor areas
Decks, verandahs and covered outdoor living areas generally cost less per square metre than fully enclosed construction because they don't contain the same level of internal finishes and services.
As a preliminary guide, we suggest allowing approximately $2,000–$3,500/m² excluding GST.
Again, there can be substantial variation. Elevated decks, complex roofs, outdoor kitchens, extensive balustrading, stairs and difficult structural conditions can push costs higher.
Some costs don't relate to floor area at all
This is particularly important with renovations.
A project may require significant expenditure without adding any additional floor area. Typical examples include:
demolition and removal
raising or supporting the existing house
excavation and retaining walls
structural strengthening
asbestos or hazardous-material removal
difficult site access or cranage
stormwater and drainage work
sewer and water alterations
electrical and plumbing upgrades.
These costs are one of the main reasons a simple extension area × $/m² calculation can give a misleading result.
A worked example
Consider a substantial renovation involving an 80m² extension, renovation of 100m² of the existing house and a 25m² covered deck.
Using rates towards the middle of the indicative ranges:
Work | Calculation | Allowance |
New extension | 80m² × $5,000/m² | $400,000 |
Existing house renovation | 100m² × $2,500/m² | $250,000 |
Covered deck | 25m² × $2,500/m² | $62,500 |
Base building work | $712,500 | |
Site, demolition & structural allowance | $60,000 | |
Construction subtotal ex GST | $772,500 | |
GST | $77,250 | |
Indicative construction budget incl GST | $849,750 |
If we had looked only at the new extension and calculated:
80m² × $5,000/m² = $400,000
we would have arrived at a figure less than half the indicative construction budget for the complete project.
That's why the question “What does an extension cost per square metre?” and “What will my renovation cost?” are not quite the same thing.
Construction cost isn't the total project budget
Even the $849,750 in the example above isn't necessarily the amount required to complete the project.
A complete project budget may also need to allow for:
Construction cost+
Construction contingency+
Architect and consultant fees+
Approvals and statutory costs+
Costs outside the building contract
= Total Project Budget
This distinction becomes particularly important when deciding what you can afford to build.
If you have $800,000 available for the entire project, for example, you don't necessarily have an $800,000 construction budget.
Our Renovation Project Budget Calculator is designed to help work backwards from your available funds and understand how much may realistically be available for the building work.
So, what $/m² rate should you use?
For an initial conversation about a substantial architect-designed Brisbane renovation, $4,500–$6,000/m² excluding GST for new enclosed extension areas is a useful starting range.
But it shouldn't be applied indiscriminately to the entire project.
The more useful approach is to separately consider:
new floor area + existing-house renovation + outdoor areas + site and structural work.
As the design develops and more information becomes available, those broad allowances can then be replaced with more project-specific cost information.
Define the project before you design it
Cost is most useful when it's considered alongside the design rather than after it.
Our Project Definition process starts by understanding your property, what you're trying to achieve and the budget available before progressing into detailed design.
The concept design and Opinion of Probable Construction Cost (OPC) provide an early reality check, allowing the proposed scope and available budget to be considered together.
Where a misalignment is identified, we refine the design or project scope while changes are quick and inexpensive to make, before progressing to the next stage.
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