What moves the price
| Factor | Why it matters |
|---|---|
| Out or up | Going up means engineering, new structure, stairs and roof work, roughly 50% more per m². |
| Kitchens and bathrooms | Plumbing, waterproofing, tiling and joinery make wet areas the dearest rooms. |
| Matching the house | Finding bricks, roofing and windows to match can cost more than new materials. |
| Asbestos | Pre-1990 homes may need testing and licensed removal where the work disturbs it. |
| Site access | No side or rear access slows deliveries and machinery. |
| Living in during works | Staging the job around your household can add time and protection costs. |
Costs people forget to budget for
- Structural engineering and the energy assessment
- Building approval and certification
- Asbestos testing and removal where the work disturbs it
- Upgrading the switchboard, hot water or drainage for the new rooms
- Somewhere to stay if you need to move out
- Repainting or reflooring the rooms next to the extension so old and new match
Is it cheaper to build out or up?
| Ground floor | Second storey | |
|---|---|---|
| Cost per m² | Lower | About 50% higher |
| Keeps the backyard | No | Yes |
| Living at home during works | Usually | Often not, for part of it |
| Engineering | Footings and tying into the roof | The existing structure gets checked first |
Canberra specifics that affect your budget
ACT or NSW changes the timeline
In the ACT most extensions need building approval, and bigger ones a DA as well. In NSW a compliant extension can go through a CDC, often within a few weeks. Approval time is money if you are paying rent elsewhere.
Upgrade while the walls are open
An extension is the cheapest time to add insulation, double glazing and a heat pump to the rest of the house. It adds to the quote but pays you back every winter.
How to get more extension for your money
- Keep wet areas together, so the plumbing runs are short.
- Reuse what works: existing walls, windows and services, where they suit the new layout.
- Use standard window and door sizes instead of custom ones.
- Lock in finishes before work starts, so you are not paying for changes.
- Ask about a rebuild if the quote is creeping towards the cost of a new home.
Questions people ask about extension costs
What makes one extension cost more than another?
Wet areas, structure and the site. A simple living room costs less per square metre than one with a bathroom or kitchen, and a second storey costs more than building out. The site and design decide the final price, which is why we quote after seeing the house.
Is a second storey cheaper than building out?
Not per square metre. But it can be better value if building out would cost you most of the yard, or the block has no room to extend.
Do I need an engineer for an extension?
Almost always for structural work, and always for a second storey, to check the footings, beams and existing structure.
Can I save money by doing it in stages?
Sometimes. Planned properly, the first stage does not need undoing, but each stage has its own setup and approval costs.
Should I renovate or knock down and rebuild?
If you would change most of the house, get both priced. We do both, so we can lay them side by side for you.
A guide only. This is general information, not a quote or financial advice. Your price depends on your design, your site and what you choose.