A house extension is one of the most common building projects on the Gold Coast. Whether you need more living space, an extra bedroom, or a better connection between indoor and outdoor areas, extending your home can transform how you live without the cost and disruption of moving.
The most popular type on the Gold Coast. Adds living space to the back of your home, typically creating an open-plan kitchen, dining, and living area connecting to the backyard. Works well because it doesn’t affect street presentation and has the simplest approval pathway.
Uses the side yard to add width. Works well on wider blocks for bedroom wings, enlarged garages, or wider living areas. Minimum 1.5 metres side setback required.
Adds floor area by building up. Ideal for smaller blocks where ground-level extension isn’t practical. More complex and expensive due to structural requirements. See our detailed guide on second storey additions for more.
A separate structure connected by a breezeway or covered walkway. Avoids structural challenges of connecting to existing walls. Popular for home offices, studios, and teenage retreats.
| Extension Type | Size Range | Cost Per Sqm | Total Cost Range |
|---|---|---|---|
| Basic rear extension (living area) | 20-40 sqm | $2,200-$3,000 | $44,000-$120,000 |
| Kitchen + living extension | 30-50 sqm | $2,500-$3,500 | $75,000-$175,000 |
| Bedroom + ensuite addition | 20-35 sqm | $2,800-$3,800 | $56,000-$133,000 |
| Large rear extension | 50-80 sqm | $2,400-$3,200 | $120,000-$256,000 |
| Second storey addition | 80-150 sqm | $2,800-$4,500 | $224,000-$675,000 |
Add to construction costs: design ($3,000-$12,000), engineering ($2,000-$5,000), council/certifier ($2,000-$5,000), demolition ($2,000-$10,000), landscaping ($5,000-$20,000).
Extensions cost 10-30% more per sqm than new builds because connecting to existing structure is complex, services need extending, and matching materials adds cost. For broader cost context, see our guide on custom home building costs.
The junction between existing and new is the most critical detail. Poor connections result in cracks, level changes, mismatched rooflines, and materials that don’t match. Good design resolves these so the extension looks original.
Extensions can darken existing rooms. Good design maintains natural light, preserves cross-ventilation, and uses skylights where needed. Learn more about passive design principles for the Gold Coast climate.
On the Gold Coast, indoor-outdoor flow is essential. Design the extension and outdoor area together.
Locating new wet areas close to existing plumbing minimises cost. Moving wet areas to the opposite end can add $10,000-$20,000 in plumbing alone.
New extensions need their own structural system. Movement joints between old and new prevent cracking from differential settlement.
| Stage | Duration |
|---|---|
| Consultation and site assessment | 1-2 weeks |
| Concept design | 3-4 weeks |
| Documentation | 3-5 weeks |
| Approval | 3-6 weeks |
| Builder selection | 2-4 weeks |
| Construction | 8-24 weeks |
For a detailed breakdown of what happens at each stage, see our guide on working with a building designer. For approval details, see our guide to the Gold Coast council approval process.
In most cases, yes — a major advantage over knockdown rebuild. Expect disruption during the connection phase. If your extension involves the kitchen, plan temporary cooking for 4-8 weeks.
Yes. Any extension adding floor area or involving structural work requires Building Approval. See our guide to building approval vs development approval for details.
Standard setbacks: 1.5m from side boundaries (single storey), 2m (two storey). Rear: typically 6m. Check the Gold Coast building codes for specifics.
A well-designed extension typically adds 1.2-1.8x the construction cost in property value.
Compare extension cost with buying larger in the same area (including stamp duty). In established Gold Coast suburbs, extending is often significantly cheaper.
Requires body corporate committee approval in addition to council approval.
Ask your building designer. Designers who produce good documentation have relationships with builders who appreciate that quality.
House extensions on the Gold Coast cost $2,200-$3,500 per sqm. The key is thoughtful design integrating new with existing, thorough documentation, and early identification of structural and services considerations.
Design Science specialises in house extensions on the Gold Coast. David Steadman’s dual qualifications ensure your extension integrates seamlessly while staying within budget. Book a $280 consultation.
David Steadman
Licensed Builder & Building Designer
David Steadman is the founder of Design Science, a Gold Coast building design practice backed by over 30 years of hands-on construction experience. One of few Australians holding both a QBCC Builder's Licence and Building Designer licence, David brings a rare combination of design thinking and practical building knowledge to every project.
