Where the space can come from
A bedroom addition can be built out into the yard, up as part of a second storey, or sometimes into an existing roof space or garage. Each has different costs. A single-room addition is one of the simplest forms of extension, and a published guide gives about $100,000 to $150,000 for one of around 40 square metres, construction only, as an indicative figure, not a quote.
Adding an ensuite
An ensuite adds a wet area, which means plumbing, drainage, waterproofing, ventilation and electrical work. Ask who will do each part, and ask for the licence numbers of the plumber and electrician. Ask where the waste pipe will run, whether the floor will need to step down and how the waterproofing will be done and documented. A bathroom is a small room with many trades, so ask how the builder coordinates them.
Fitting into the old house
The new room needs to connect to the old one. A builder's guide says the junction between old and new construction is one of the biggest challenges in any extension. Ask how the new room will be accessed, whether a hallway or wardrobe has to change, and how the builder will deal with floor levels and the roofline. If the house is older, ask whether the wiring and switchboard can handle the extra load.
Staging and living there
A bedroom addition at the back of the house often lets the family keep living in it, but dust and noise are certain. Ask each builder how they will protect the existing house, where tradespeople will park and store materials, and how long the existing rooms will be disturbed.
Approvals and insurance
A builder's guide says extensions need approval under the Planning and Design Code. PlanSA points owners to code.plan.sa.gov.au to see the policies that apply at an address. The SA Government says building indemnity insurance is required for domestic work needing council approval and costing $20,000 or more, and the certificate should reach you and the council before work starts. Ask who lodges the application and whether insurance is included.
Checking the contractor
The SA Government says people and businesses who carry out or organise building work for others must hold a building work contractor's licence. Ask for the licence details and check it on the licence register.
Asbestos
If the house is older, tell every builder before they quote and ask how they would handle suspected asbestos. Read the SA Government guidance for homeowners and do not disturb suspected material.
Planning the layout
Decide what you want the room to do. A child's bedroom, a main suite with a walk-in robe and a guest room all need different sizes. Mark where the door, the window and the wardrobe might go, and where you want the ensuite relative to the bed. A builder or designer can improve on a rough sketch, and they quote better when they understand what matters to you.
The wet area in detail
An ensuite has a shower, a toilet and a vanity in a small space, and every pipe has to fall to a drain. Ask each builder how the floor will be graded, where the exhaust fan will vent to, and what is in the quote for tiles, fittings, a mirror and a heated towel rail. Ask them to list the allowance for tapware and tiles in writing, so you can see what happens if you pick something dearer.
Heating, cooling and privacy
New bedrooms are often the hottest or coldest rooms in the house. Ask how the room will be heated and cooled, whether extra insulation is included, and how the window faces the sun and the neighbours. Ask what is in the price for curtains or blinds, and what happens to the cost if the ceiling height or window size changes.
Storage and finishes
New bedrooms need built-in robes, flooring and paint, and these are sometimes left out of the building price. Ask what is included, what is an allowance and what you will arrange yourself, and ask how the builder will match the new floor and paint to the rooms next to it.
Noise and sleep
Ask where the new bedroom sits relative to the street, the kitchen and the neighbours, and what is included to reduce noise from outside or from the rest of the house.
How much does a bedroom addition cost in Adelaide?
A published guide gives about $100,000 to $150,000 for a single-room addition of around 40 square metres, construction only. Ensuite fittings and design are separate. These are not quotes.
Does an ensuite need local trades?
Plumbing and electrical work generally need local trades in South Australia. Ask for licence numbers and check them on the register.
Can I add a bedroom in the roof space?
Sometimes, but it depends on the structure and the rules. Ask each builder and your council.
What should I ask about waterproofing?
Ask who does it, what the system is and what documentation you will receive when the work is finished.
Sources
- RAW Structures: how much does a home extension cost in Adelaide (25 August 2026)
- Templeton Built: extension costs Adelaide (20 March 2026)
- PlanSA: find out if you need approval
- SA.GOV.AU: building work contractor's licence
- SA.GOV.AU: check occupational licence holders
- SA.GOV.AU: building indemnity insurance