Guide
Knockdown rebuild or renovate
This decision is usually made on feel and then justified with numbers. It is worth doing in the other order.
Both paths keep the thing you actually bought, which is the location. What they differ on is how much of the existing building constrains what you end up with, and how predictable the cost is.
Question one: can you demolish?
This is a planning question, not a budget one, and it is the one to answer first. A heritage control, a conservation area, a character overlay or a significant tree can make demolition difficult or impossible. Being inside a conservation area can reach a house that is not itself listed. Our area pages report the heritage and overlay mapping for the suburb so you know whether the question applies before you commission anything.
Question two: what are you actually keeping?
A renovation keeps the structure, and with it the floor level, the footing system, the wall framing and whatever is inside the walls. If the existing house is sound and the layout suits, that is a genuine saving. If the structure is poor or the level is wrong, you can spend rebuild money to get a compromised result.
Question three: how much do you want to change?
Renovations are most efficient when they work with the existing structure and least efficient when they fight it. Moving wet areas, changing the roof line and removing structural walls each erode the saving. Past a certain point a rebuild is both cheaper and better.
Predictability
This is the difference people underestimate. A new build on a cleared site is a known quantity: the design is drawn, the site is classified, the scope is visible. A renovation involves opening up an existing building, and what is behind the wall is not fully known until it is open. Renovation budgets carry more variation risk, and the contingency should reflect that.
Timeline
Demolition adds time at the front — service disconnections, asbestos assessment where the era suggests it, the demolition approval itself. Renovation often adds time in the middle, when something is uncovered. Neither is reliably faster.
Questions people ask before deciding
Is an extension a better option than a knockdown rebuild?
It is the third option this question usually gets framed without, and it changes the answer. An extension keeps the existing house and adds to it, so it inherits the existing floor level, footing system and services — the same constraints a renovation inherits, plus a junction between old and new that has to be detailed and waterproofed. It is the right call when what you have is sound and what you want is more of it. It is the wrong call when the existing layout is the problem, because an extension cannot fix a plan you are keeping.
Is “demolish and rebuild” the same as a knockdown rebuild?
Yes — they are the same path under different names, and builders use both. What matters is not the term but whether demolition is permissible on your block, which is a planning question answered by the controls mapped over it rather than by the builder.
Can I keep the slab and rebuild on it?
Rarely, and it is worth establishing early rather than assuming. An existing slab was designed for the house that sits on it, to the soil classification and the standards of its era. Reusing it constrains the new floor plan to the old footprint and load paths, and it has to be assessed by an engineer before anyone designs to it. Most knockdown rebuilds remove it.
Can I live there while the work happens?
Not during a knockdown rebuild — the house is gone. During a renovation it depends on how much of the house the work touches and whether the wet areas stay usable. Builders price staged work differently from vacant-site work, so if you intend to stay, say so before the quote rather than after.
Which path is more predictable on cost?
A new build on a cleared site, because the scope is drawn before anyone starts. A renovation prices what can be seen and discovers the rest after demolition begins — the variations that follow are not usually anyone behaving badly, they are the building telling you what is behind the walls.
What we would ask a builder
Have you done both on this kind of house, in this council area? What did you find behind the walls last time? And for a renovation specifically: what is your process when the scope changes mid-job? See questions to ask a builder and how a knockdown rebuild runs.
Where heritage mapping is heaviest
Heritage is the control that most often decides a knockdown rebuild against you, and your own house does not have to be listed for a conservation area to reach it. 421 of 1264 suburbs we have mapped carry twenty or more heritage records intersecting them. These are the ones to check the address on before you price a demolition.
New South Wales
- Mosman — 543 records
- Goulburn — 522 records
- Hunters Hill — 505 records
- Grafton — 499 records
- Wahroonga — 439 records
- Ashfield — 360 records
- 244 more in New South Wales →
Victoria
Western Australia
- Fremantle — 1231 records
- East Fremantle — 688 records
- Claremont — 558 records
- North Fremantle — 337 records
- Albany — 195 records
- Subiaco — 193 records
- 18 more in Western Australia →
South Australia
- North Adelaide — 725 records
- Norwood — 296 records
- Strathalbyn — 172 records
- Mount Gambier — 131 records
- Mount Barker — 129 records
- Prospect — 116 records
- 45 more in South Australia →
Read from each state's own published planning data and dated on every suburb page. Suburb-level, not a report on your block.
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