House Extension Questions and Answers
Plain answers to questions Adelaide homeowners ask before they extend. Each answer points to an official or published source where we can, and none of it is legal or building advice.
How much does a house extension cost in Adelaide?
Published 2026 guides give a wide spread. A builder's guide gives $2,800 to $4,500 per square metre for a single-storey rear extension and $3,500 to $5,500 for a second storey, including design, engineering and approvals. Another builder's guide gives $2,500 to $3,700 and $2,900 to $4,500, but for construction only. They are indicative, not quotes.
Why do two guides give different prices?
They count different things. One includes design, engineering and approvals, and the other covers construction only and includes GST. Neither is a quote, so ask each business what its price includes.
Do I need approval before I extend?
Many extensions need planning and building approval from the council before work starts. PlanSA points owners to the policy tool at code.plan.sa.gov.au to see the rules for an address. A builder's guide says extensions need approval under the Planning and Design Code. Ask your council and ask each builder who lodges the application.
How long does approval take?
It depends on the project and the council, and we cannot say. A builder's guide says a straightforward application can be quick and one that varies from the standard rules takes longer, so ask your council and your builder for a timeline in writing.
Does a builder need a licence in South Australia?
The SA Government says individuals and businesses that carry out or organise building work for others must be local as building contractors. Check the licence details on the public register for occupational licence holders.
Which trades need their own licences?
The SA licence register covers builders, plumbers, gas fitters and electricians, among others. Ask who will do the plumbing and electrical work and ask for their licence numbers.
What is building indemnity insurance?
The SA Government says it protects you and future owners if the builder dies, disappears or becomes insolvent, where work is not finished or defective work needs fixing. It is required for domestic building work that needs council approval and costs $20,000 or more.
When does the insurance have to be in place?
The SA Government says building work cannot start until the builder has taken out the insurance and both you and the council have received a copy of the certificate.
How long can I claim for defective work?
The SA Government says defective works claims can usually be made up to five years from the date the work was completed. Check the policy and ask the insurer if you are unsure.
Do I have to tell a buyer about the insurance if I sell?
The SA Government says that when you sell the property you must disclose whether indemnity insurance is in place. Keep the certificate with your records.
Can I extend over the whole back yard?
That depends on the planning rules for your property and the council, and we cannot say. Use the PlanSA policy tool and ask the council before you spend money on plans.
Do heritage or character areas affect extensions?
A South Australian builder's guide says overlays are common in some inner suburbs. We do not summarise those rules. Ask the council whether any overlay applies to your address.
What if my house may contain asbestos?
Tell every builder before they quote, ask how they would handle suspected material and do not disturb it yourself. Read the SA Government asbestos guidance for homeowners.
Can a granny flat be built in my yard?
Sometimes. A cost guide notes that South Australia sets limits on what counts as a granny flat, and approval and site preparation are often quoted separately. Ask the council what applies to your block.
What does it cost to join a new room to an old house?
There is no single figure, but one builder's guide says the junction between old and new is one of the biggest challenges and that soil, slope, asbestos and heritage can add to the cost. Ask each builder how it would handle your house.
Do you recommend a builder?
Contact House Extensions Adelaide about house extensions in Adelaide.