House Extension Cost Adelaide: Indicative Ranges
Every row in the table below comes from a published guide written by a builder or a cost-guide site, and each row links to its source with the date we reviewed it. These are indicative ranges, they are not specific to any suburb, and they are not quotes. Two of the guides are written by builders who want your business, so treat them as one input and not as a price list.
How to read the ranges
The sources do not count the same things. One builder's guide says its per-square-metre ranges include design, engineering, approvals, construction and standard finishes. Another says its ranges cover construction only and include GST, with design, engineering, approvals and a contingency on top. That is why the same kind of extension can appear at different prices, and why you should ask each business to say exactly what its quote covers.
What commonly moves the price
- Soil and footings, because a builder's guide says much of Adelaide sits on reactive clay
- Slope, access and how close the new work is to the boundary
- Joining new work to an old house, including the roof tie-in
- Structural changes such as removing a load-bearing wall or adding a staircase
- Asbestos, heritage requirements and other site matters one guide says can add cost
- Finishes, fittings and the size of the kitchen or bathroom inside the new space
Approvals and insurance
Approval fees, plans and engineering are separate items in some quotes and bundled in others. Building indemnity insurance is also part of the picture. The SA Government says it is required for domestic building work that needs council approval and costs $20,000 or more, and that the builder arranges and pays for it. Ask whether it is included, and ask to see the certificate.
What the table leaves out
The ranges do not include furniture, landscaping, temporary accommodation if you move out, or changes you make once work has started. They also do not include any work to the existing house that the builder finds is needed, such as repairs to an old roof or wiring. Add these to your own budget and ask each builder to price them separately, so you can see where a total comes from before you decide.
Using the table
Take the ranges to a conversation, not to a negotiation. Ask each business what its quote includes and compare scope line by line, not just the total.
Scroll the table sideways to see all columns.
| Single-storey rear extension, all-in | AUD $2800–$4500 per square metre | Templeton Built: extension costs Adelaide (20 March 2026) The builder's guide says its range includes design, engineering, approvals, construction and standard finishes. |
|---|---|---|
| Second-storey addition, all-in | AUD $3500–$5500 per square metre | Templeton Built: extension costs Adelaide (20 March 2026) Same guide and inclusions. Soil, slope, asbestos removal and heritage requirements can add to the cost. |
| High-end extension with premium finishes | AUD $5000–$7000 per square metre | Templeton Built: extension costs Adelaide (20 March 2026) The guide states the range as $5,000 to $7,000 or more per square metre. |
| Ground-floor extension, construction only | AUD $2500–$3700 per square metre | RAW Structures: how much does a home extension cost in Adelaide (25 August 2026) A builder's guide. It includes GST and covers construction only. Design, engineering, approvals and a contingency are extra. |
| Second-storey addition, construction only | AUD $2900–$4500 per square metre | RAW Structures: how much does a home extension cost in Adelaide (25 August 2026) Same guide, construction only and including GST. A different range from the first guide, which is why quotes matter. |
| Single-room addition of about 40 square metres | AUD $100000–$150000 per project | RAW Structures: how much does a home extension cost in Adelaide (25 August 2026) The guide's indicative cost for a project of that size. Construction only. |
| Open-plan living extension of about 60 square metres | AUD $150000–$225000 per project | RAW Structures: how much does a home extension cost in Adelaide (25 August 2026) The guide adds that a structural allowance is on top. |
| Removing a load-bearing wall | AUD $8000–$25000 per wall | RAW Structures: how much does a home extension cost in Adelaide (25 August 2026) The guide says this commonly covers the beam, propping and engineering. |
| Staircase for a second storey | AUD $15000–$30000 per staircase | RAW Structures: how much does a home extension cost in Adelaide (25 August 2026) The guide says it is commonly needed and takes space from the floor plan below. |
| Structural engineering for a second storey | AUD $2000–$10000 per project | RAW Structures: how much does a home extension cost in Adelaide (25 August 2026) The guide's range for confirming that the existing footings and frame can carry a second level. |
| One-bedroom granny flat, 35 to 45 square metres, turnkey | AUD $110000–$160000 per dwelling | What's The Damage: granny flat cost Adelaide (updated October 2026) A cost guide that says approvals and site preparation are often quoted apart from the build. Includes GST. |
| Two-bedroom granny flat, about 60 square metres, turnkey | AUD $140000–$210000 per dwelling | What's The Damage: granny flat cost Adelaide (updated October 2026) Same guide. Includes GST. |
| Development approval and building consent for a granny flat | AUD $3000–$11000 per project | What's The Damage: granny flat cost Adelaide (updated October 2026) Same guide's indicative range. Your council and design decide the real fees. |