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Home Extension Cost Guide · NSW · 2026How Much Does a Home Extension Cost in NSW?
Ground floor and second storey addition costs, approval pathways, and what makes extension costs variable — from a licensed NSW builder.
Direct answer: A ground floor home extension in NSW costs between $2,500 and $4,500/sqm for construction. A 40sqm extension runs $100,000–$180,000. A second storey addition (80–120sqm) costs $220,000–$600,000 due to structural requirements. All home extensions over $5,000 require a licensed NSW builder. DA or CDC approval is required for most extensions.
Cost Comparison: Ground Floor vs. Second Storey
| Extension Type | Size | Estimated Cost 2026 |
|---|---|---|
| Ground floor — standard | 30–40 sqm | $80,000 – $150,000 |
| Ground floor — mid-spec (kitchen/living) | 50–70 sqm | $130,000 – $260,000 |
| Ground floor — premium | 60–80 sqm | $200,000 – $340,000 |
| Second storey — full addition | 80–100 sqm | $220,000 – $420,000 |
| Second storey — premium finishes | 100–130 sqm | $350,000 – $600,000+ |
Why Second Storey Additions Cost More
A second storey addition adds structural complexity that a ground floor extension doesn’t have. The existing ground floor structure needs to be assessed by a structural engineer — roof members, load-bearing walls, and footing capacity must all be verified before the addition can sit on top. The roof comes off. The ceiling of the ground floor becomes the structural platform. A temporary weatherproofing arrangement protects the house during construction.
After construction, the staircase — typically $15,000–$35,000 including structural work — takes floor area from the existing level. And the roofline tie-in must match the existing roof in pitch, tile or metal profile, and material grade to satisfy the building certifier and the council’s development conditions. None of this is unique to individual builders — it’s the nature of the work. But a builder who’s done second storey additions before will have a more accurate price from day one.
Approval Pathway
Most NSW home extensions require DA or CDC approval. The approval pathway depends on the size, height, setbacks, site coverage, and whether your property has heritage overlays or flood/bushfire constraints. A builder who offers to start without appropriate approvals is creating risk for you — unapproved structures are at risk of demolition orders, can’t be sold without resolution, and void your building insurance for the new work.
For an extension quote in Greater Sydney, call Jay on 0451 151 336.
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Ground floor and second storey. Licensed NSW builder. Jay responds within one business day.