Tools
What will your extension really cost?
Tell us how much space you want, what goes in it and how it joins the house. You get an honest range built from the same figures we publish on our home extensions page, with preliminaries shown separately and the choices that move the number spelled out.
- Based on our published pricing
- Live results, no sign-up
- Itemised quote to follow
The calculator
Build your extension estimate
Five quick questions. The range updates as you go, from $70,000 for a modest rear addition to $300,000 for a full-width open plan transformation.
Your extension
Your indicative range
From
To
$126,000 to $141,000
Most extensions we build: $70k–$300k
How it adds up
- Building works30 m² at $3,220–$3,700 per m²
- $97k–$111k
- PreliminariesDesign, engineering and council approvals, plus site set-up: fencing, temporary services, waste, insurances, supervision
- $30,000
What is driving it
- Widening an opening into the house+$5k
- A new kitchen in the extension+$6k
- Mid-range finishes+$9k
Indicative range only. A site visit and an itemised quote confirm the real price. Every Strava Group quote lists inclusions, exclusions and preliminaries separately, with any provisional sums shown openly.
Honest numbers
How this estimate is worked out.
This calculator uses the numbers we publish: a ground floor rate per square metre, set by your finish level and how complex the work is, plus preliminaries.
A modest rear addition sits at one end of the band, a full-width open plan transformation with structural openings back into the house at the other.
| Figure | What it covers | Where it comes from |
|---|---|---|
| $2,500–$4,500 /m²Ground floor extension work. Finish level and complexity decide where in this band your project sits. | Ground floor extension work. Finish level and complexity decide where in this band your project sits. | Home extensions |
| approx. $30,000Preliminaries, on top of build cost: design, engineering and council approvals, plus site set-up such as site fencing, temporary services, waste removal, insurances and supervision. | Preliminaries, on top of build cost: design, engineering and council approvals, plus site set-up such as site fencing, temporary services, waste removal, insurances and supervision. | Home extensions |
| $70,000–$300,000What most extensions run, depending on size and how much of the existing structure has to change. | What most extensions run, depending on size and how much of the existing structure has to change. | Home extensions |
| 16–60 m²The size range those figures imply: the bottom rate on a small addition up to the top rate on a large one. | The size range those figures imply: the bottom rate on a small addition up to the top rate on a large one. | Home extensionsworked out from it |
| 12–20 weeksTime on site for most extensions, with design and approvals before that. | Time on site for most extensions, with design and approvals before that. | Home extensions |
What moves the price
Six things that decide where you land.
The band is wide because extensions are wide. When we walk your home and yard, these six things tell us where in it you are likely to land.
- 01
How much of the house changes
Usually the largest single factor. A new doorway is simple; taking out the back wall for open plan means steel, engineering and temporary propping. - 02
Wet areas and kitchens
A bathroom carries more trades per square metre than any other room: plumbing, waterproofing to AS 3740, tiling. Kitchens add cabinetry and services. - 03
Site access
A side extension on a tight boundary, a battleaxe block or a narrow frontage all slow the work and add cost before a wall goes up. - 04
The join between old and new
We detail every new-to-existing junction properly and re-brace the adjoining structure, because that join is where extensions crack and leak in year seven. - 05
Finish level
Tiles, tapware, joinery, flooring and lighting. The same room can be built to a sensible standard or a premium one; the calculator shows the difference. - 06
Approvals
A CDC takes about 4 to 8 weeks; a DA can take up to 6 months, depending on council. We choose the pathway and manage it. See our process.
Clear scope
What is in the range, and what is not.
Included in the range
- Building works for the new floor area at the rate for your finish level
- A new kitchen and/or bathroom if you ticked them
- The structural connection back into the house you selected
- Preliminaries of about $30,000: design, engineering and council approvals, plus site set-up (fencing, temporary services, waste, insurances, supervision)
Not in the range
- Renovating the existing rooms (it can be staged alongside: you pay preliminaries once and open the walls once)
- Items that genuinely cannot be priced until walls open, like hidden services or structure; we list these as provisional sums, in plain sight
- Difficult ground, rock or unusual site access found on inspection
- Furniture, loose appliances and landscaping beyond the build
Every project is quoted properly after a site inspection. Ready to go further? Read about home extensions in Sydney, or compare going up with the extend or build up tool.
Keep planning
More tools
- 02
Second Storey Cost Calculator
Price a new upper floor against our fixed price packages, bedroom by bedroom.
Floor size · bedrooms · bathrooms · stair · finish
Open the tool - 03
Renovation Cost Calculator
Pick the rooms, tell us the house, see where a renovation budget really goes.
Rooms · house age · structural walls · finish
Open the tool - 04
Extend or Build Up?
Extend at ground level or add a level: cost, time and yard compared for the same space.
Space to add · yard size · finish
Open the tool - 05
Project Timeline Planner
From first call to handover, stage by stage, with the month you could move in.
Project type · approval pathway
Open the tool
Get the real number for your home.
A builder walks your home with you, then prepares a written, itemised estimate: inclusions, exclusions and preliminaries listed separately. We respond within 24 to 48 business hours. No cost, no obligation.