How to Add a Double Storey Extension to a Single Storey Home

Adding a second storey is one of the most transformative ways to expand your home, but its success hinges on three critical questions: Is it structurally feasible? Can you afford it? And will your local council approve it? This comprehensive guide provides the practical tools you need to assess your project’s viability, create a realistic budget, and navigate the approval process, all before you invest in professional consultations.

While only a qualified structural engineer can provide definitive confirmation, you can conduct a preliminary “Red Flag Assessment” in under an hour. This involves a visual inspection for structural concerns and reviewing your property documentation to identify your foundation type as specified in the original building plans.

Complete this simple assessment to gauge your foundation’s potential:

1. Crack Check: Are there diagonal wall cracks wider than a 20-cent coin? (Y/N)
2. Original Plans: Do your house plans specify “strip footings” or “raft slab” foundations? (These typically offer better load distribution) (Y/N)
3. Soil Classification: Is your property built on reactive clay soil (Class H, E, or P under AS 2870)? (Y/N)
4. Mature Trees: Are there established trees within 5 metres of your proposed extension? (Y/N)
5. Age Factor: Was your home built before 1980 when foundation standards were less stringent? (Y/N)

What Your Results Mean:

Answering “Yes” to questions 1, 3, or 5, or having no documentation for question 2, indicates that a structural engineer’s assessment is essential. Even answering “No” to all questions doesn’t eliminate the need for professional evaluation, it simply suggests fewer obvious obstacles.

Immediate Action Items:

• Walk your home’s perimeter and photograph any visible cracks
• Locate your original building documentation (often filed with your property title or council records)
• Request a soil report from your local council if unavailable

1. Premium Finishes: Kitchen and bathroom fit-outs can add $30,000-$80,000 beyond basic construction
2. Temporary Accommodation: Budget for 3-6 months of alternative housing during structural work
3. Service Upgrades: Electrical boards and plumbing often require expensive updates to meet current Australian Standards (AS/NZS 3000:2018 for electrical installations)

In Australia, you’ll need both planning permission (Development Application) and building approval (Building Permit/Certificate) for virtually all second storey additions. Unlike single-storey extensions that may qualify as Complying Development in some states, second storeys require full council assessment due to their impact on neighbours and streetscape. Navigate your approval requirements:

• Start → Will the extension exceed your area’s height limits? → YES = Full DA Required
• NO → Will it reduce neighbour’s solar access below council minimums? → YES = Full DA Required
• NO → Will it create overlooking into neighbour’s private open space? → YES = Full DA Required
• NO → Does it comply with your area’s Floor Space Ratio? → NO = Full DA Required

Solar Access Requirements: Most Australian councils require that your extension doesn’t reduce your neighbour’s solar access below minimum standards, typically 2-3 hours of direct sunlight to living areas and private open space between 9am and 3pm on June 21 (winter solstice).

Overlooking and Privacy: The Building Code of Australia (under the National Construction Code) and local Development Control Plans typically require:

• 9-metre separation between habitable room windows
• Privacy screens for balconies and windows within 9 metres of boundaries
• Highlight windows or obscure glazing where privacy cannot be achieved

A second storey extension makes financial sense when its total cost is substantially less than the combined expense of selling and buying a larger home in your area. Factor in stamp duty (which can exceed $50,000 on median-priced homes in Sydney or Melbourne), agent fees, and moving costs. This decision-making process shares similarities with choosing between a knock down rebuild vs renovation.

• Choose to Extend if: You’re in a premium location, established school catchment, or have unique site advantages (views, corner block, heritage streetscape)
• Choose to Move if: You need substantial land area changes, require different suburb amenities, or your property has heritage restrictions

Plan for a 10-14 month journey from initial concept to completion. This includes 4-5 months for design and approvals, followed by 6-9 months of construction.

1. Feasibility & Budget Assessment (Month 1): Complete the assessments in this guide
2. Professional Team Assembly (Month 2): Engage architect, structural engineer, and possibly a town planner
3. Design Development (Months 2-3): Iterate designs balancing your needs with planning constraints
4. DA Submission & Assessment (Months 4-6): Council review period (typically 40-60 business days)
5. Construction Certificate/Building Permit (Month 7): Detailed documentation and certification
6. Tender & Builder Selection (Month 8): Obtain minimum three quotes from licensed builders
7. Construction Phase (Months 9-13): Foundation strengthening, frame erection, roofing, fit-out
8. Occupation Certificate & Handover (Month 14): Final inspections and compliance sign-off

Ensure your builder provides:

• A fixed-price contract (HIA or MBA standard contract)
• Home Warranty Insurance (mandatory for work over $20,000 in most states)
• Clear milestone payment schedule tied to completed stages
• Regular private certifier or council inspections at critical stages

The most successful projects are those where homeowners enter with eyes wide open to both the challenges and opportunities. With proper planning and the right professional team, your second storey extension can deliver the space your family needs while adding substantial value to your greatest asset. Would you like a quote on creating your dream second storey? Given Jonathan Homes a call today – we’d be glad to help!