By Blue Horizon Projects · · 8 min read
Contents
It's the first question almost every client asks, and the honest answer is that a second storey addition is priced by what sits underneath it as much as what goes on top. Two identical upper floors on two different Central Coast homes can differ by six figures.
Why there is no single square-metre rate
A new build starts from a clean site with known conditions. An addition starts from a house someone else built, often decades ago, to standards that have since changed. Until an engineer has assessed the existing footings, wall structure and roof framing, any rate per square metre is a guess dressed up as a quote.
Indicative cost ranges
As a planning starting point only - not a quotation - these are the bands we see across Central Coast projects.
| Scope | Typical range | Common inclusions |
|---|---|---|
| Partial upper floor (2 bed, 1 bath) | $350k – $480k | New floor structure, stair, basic ground-floor make-good |
| Full upper floor (3–4 bed, 2 bath) | $480k – $700k | Full second storey, retreat, ground-floor reconfiguration |
| Upper floor plus major ground works | $700k+ | Structural upgrades, new kitchen, services replacement |
What moves the number most
- Footing capacity - underpinning or new pad footings can add tens of thousands before a wall goes up.
- Roof structure - a truss roof is usually removed entirely, a conventional roof sometimes partly retained.
- Access - narrow or steep sites raise crane, scaffold and handling costs materially.
- Ground-floor disruption - a stair has to land somewhere, and that often triggers a broader reconfiguration.
- Finish level - the same footprint can vary 30% on selections alone.
Costs people forget
- Design, engineering and certification fees
- Temporary accommodation during roof-off stages
- Electrical switchboard and service upgrades
- Landscaping and make-good after scaffolding comes down
- A genuine contingency - we suggest 8–10%
The cheapest quote on the table is usually the one with the least written in it. Compare inclusions before you compare totals.
How to budget properly
Start with a site visit and a preliminary feasibility figure before you commission full design documentation. Spending a little on assessment early is what stops a project stalling after $30,000 of drawings that the budget was never going to support.
Frequently asked
- Is a second storey cheaper than extending out?
- Rarely per square metre - going up costs more to build. It's chosen because it preserves yard space and can unlock views, not because it's cheaper.
- How long does a second storey addition take?
- Most run six to ten months on site, after a design and approvals period of three to eight months.
- Does a second storey add value?
- In view-capable and family-oriented Central Coast suburbs it typically does, though the uplift varies by street and should never be the sole justification.