Key Takeaways
Home extensions can range from $80,000 to $300,000+ depending on size, structure, access, finishes, approvals, and services.
Structural work, engineering, approvals, roofing, foundations, and services are major cost drivers.
Double storey extensions are usually more complex and expensive than single storey additions.
Always check whether design, approvals, engineering, contingency, and site conditions are included.
Overview
Home extension costs depend on the size of the addition, structural complexity, site access, approvals, materials, trade availability, and how the new work connects to the existing building.
1. Typical Home Extension Costs
Use these ranges as a practical planning benchmark before comparing quotes. Final pricing depends on size, access, materials, labour, finish level, and site-specific conditions.
Small Extension
$80,000 – $140,000
Small room addition, simple structure, limited service relocation, and standard finishes.
Medium Extension
$140,000 – $220,000
Larger living area, structural changes, roofing integration, approvals, and moderate finishes.
Large / Complex Extension
$220,000 – $300,000+
Large footprint, double storey work, complex access, premium finishes, or major service changes.
2. What Affects the Cost?
Every project is different. These are the major factors that can move the final price up or down.
Structural Work
Foundations, beams, roof integration, and load-bearing changes can materially affect cost.
Approvals
Council approvals, engineering, certification, and design documentation may add significant fees.
Site Access
Restricted access, sloping blocks, and difficult material movement can increase labour cost.
Services
Electrical, plumbing, drainage, air conditioning, and service upgrades can affect final pricing.
3. Cost Breakdown
Here is a typical cost split for this type of project in Australia.
Total
$165,000
Structure
$65,000
39%
Site Work
$25,000
15%
Services
$22,000
13%
Finishes
$35,000
21%
Approvals & Professional Fees
$18,000
12%
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