The decision frame
The build-under-versus-knockdown question is rarely a pure cost calculation. It turns on structural condition, planning constraints, sentiment value, neighbourhood character and how the project sequences against your life stage.
When build-under tends to win
Build-under is usually the stronger option when the existing house is worth keeping and the site limits what a replacement could deliver.
- The upstairs structure is sound and worth preserving
- The property sits in a character or heritage overlay that restricts replacement
- The first floor has good ceiling heights and original features worth keeping
- You're willing to manage the structural complexity of working over a 100-year-old timber frame
When knockdown rebuild tends to win
A knockdown rebuild usually makes more sense when the upstairs is too far gone to save and the site allows a fresh plan.
- Termite, rot or structural damage means the upstairs needs more than half its frame replaced
- The property is not in a character overlay (rare in inner Brisbane)
- You want a contemporary plan the existing footprint can't accommodate
- You have a builder willing to fixed-price a new build and don't want owner-builder risk
Costs at a high level
A full Brisbane knockdown rebuild typically prices in the same band as a raise and build-under once you include demolition, slab, two-storey build and external works. The cost gap is often smaller than owners expect, but the risk profiles are very different.
Our Coorparoo build-under cost $331,510 (2018-2020). See the full breakdown.
The hidden tax: time
Both options take similar elapsed time on site, but the risk sits in different places. Build-under projects often carry more variation risk because you're working around an existing structure, while knockdowns carry more planning approval risk in heritage-sensitive Brisbane suburbs.
