How much does a home extension cost in Sydney?

Quite literally the million-dollar question and the question I get asked more than almost any other — how much is this going to cost? And the honest answer is — it depends. It depends on the scope and the quality, availability of trades, style of construction… so many factors. But there are real numbers worth knowing before you start planning.

Let me give you the framework for understanding renovation and extension costs in Sydney — because the numbers vary enormously depending on who you ask. Your building designer and your builder will give you one figure, and your mates will tell you that they are wrong and they built for a fraction of that cost.

What the per-square-metre figures leave out

You may see costs from an online search as low as $1,500/m² to $7,000/m², but, as a broad guide, construction cost quotes in Sydney for quality residential work never meet those lower costs.

Figures such as $2,700–$5,100/m² for new construction or extensions to an existing building, from sources such as Archicentre Australia’s Cost Guide 2026, come with many exclusions and qualifiers, such as “shell only”, “does not include wet areas”, “does not include services upgrades, or consequential work to existing building” and “indicative square metre rates are for basic shell only and the extended roofline over the shell”. These figures also don’t cover the real project costs, as they don’t include landscaping, designer’s fees, engineering, council or certifier fees, or other consultants. The total can easily add up to $6,000–$12,000/m².

Why the high costs?

Depending on finishes, site conditions, how complex the work is, individual tastes, complex construction… quite literally an almost infinite number of variables, costs can swing wildly. A basic square box, gyprock lined, standard sized windows and doors, minimum ceiling height, level block, easy access, no unknown site conditions, close to the city, minimum lighting, basic kitchen, etc. is the most affordable, but most people want a better outcome.

But it can also swing the other way. Most of us have seen Grand Designs — the homeowner moves forward with the build without a clear budget, they make changes (“must have the Scandinavian tapware… ooh, and the $80,000 oven”), and they haven’t finalised cost decisions and had them costed before they start building. “Scope creep”, or “while we’re doing it” inclusions, can add dramatically to the build costs.

Square-metre rates are only part of the picture. Fixed costs — demolition, site preparation, connection to services, site access, contamination, scaffolding, heritage, proximity to other buildings, geomorphology, professional fees, approvals and certification — don’t scale linearly with size. Renovating an existing space can be costly without adding floor space. A smaller extension can cost proportionally more per square metre than a larger one because those fixed costs are spread across less built area.

Design fees: a percentage or a fixed fee?

Fees can vary dramatically as well. An architect can typically charge 10–18% of the build cost, when a building designer who is a member of the Building Designers Association of Australia (BDAA) may cost you 3–7% for much the same quality of service and design.

Fixed fees, as opposed to a “percentage of construction cost” fee, also mean that there is no advantage for the designer if the costs blow out. I have heard the horror stories of renovators who are given a cost estimate, generally based on the lower square metre rate, with all of the exclusions and qualifications, they have their approvals and have their hearts set on the design… then the quotes come in. And this time they include all of the exclusions. The worst part is that the designer on a percentage fee is now actually entitled to more of your money!

What a realistic budget looks like

For a typical rear ground-floor extension in the Sydney metro area, a realistic all-in budget including professional fees, council fees, and contingency can vary dramatically. As a rule of thumb, an upper-floor addition is 30–50% more expensive per m².

Some of the budgets for recent renovation projects of ours are from $450,000 to $2,500,000 and everything else in between.

The most important number is your total budget — not the per-square-metre rate. Designing to a budget that’s realistic for your scope, site, and finish level is one of the most useful things I work out early in a project — real-world numbers, not wishful thinking. It avoids the expensive problem of falling in love with a design, spending money on that dream and falling short.

If you are wanting to save the hassle and headache of spending thousands just to find out whether you can achieve your dream, our Exploration Package, at $795, is a great way of answering a lot of your concerns at the outset of your journey.