Your kids need their own space, or your elderly parents are moving closer. Maybe you’re working from home permanently now, or you just need somewhere quiet that isn’t the dining table. Whatever’s driving your need for more space, you’re weighing up two very different options – and the choice matters.
Both granny flats and extensions add square metres to your property, but they work in completely different ways. One gives you a separate dwelling with its own kitchen and bathroom. The other expands your existing home. One might earn you rental income. The other might give you the open-plan kitchen you’ve wanted for years.
Let’s break down what actually makes sense for your Perth property, your family’s needs, and your budget.
Quick Takeaways
- Granny flats can cost from $130,000–$200,000+ for a self-contained dwelling in your backyard. They provide privacy, potential rental income of $300–$550/week
- Home extensions cost $150,000–$500,000+, depending on size and complexity. They expand your main home’s footprint, maintain a cohesive living space, and suit families who want everyone under one roof.
- Your choice depends on whether you need an independent living space (granny flat) or an integrated home expansion (extension) – and how you value privacy versus togetherness.
Understanding What You’re Choosing Between
A granny flat is a standalone, self-contained dwelling built on your property. It has its own entrance, kitchen, bathroom, and living area. You can use it for ageing parents, adult children, a home office, or rent it out for ongoing income.
A home extension adds space directly onto your existing house. This might be extra bedrooms, a bigger kitchen, a new living area, or a second storey. Everything connects to your main home – same roof, shared systems, one household.
What This Actually Costs in Perth
Let’s talk real numbers for 2025.
Perth granny flats typically cost:
- One-bedroom budget build: From $130,000
- Two-bedroom standard: $150,000–$180,000
- Larger designer builds: $200,000+
These prices include the building, but you’ll need to budget for site preparation, utility connections, and council fees on top.
Home extensions in Perth run:
- Ground floor addition: $2,000–$4,000 per square metre
- Second storey: $350,000–$600,000 total project cost
- Full renovation extension: $150,000–$500,000+, depending on scope
When a Granny Flat Makes More Sense
You’re probably better off with a granny flat if you need:
Rental Income
Granny flats in Perth suburbs generate between $300 and $550 per week, depending on size and location. That’s $15,600 to $28,600 annually – enough to cover your build cost within 5-8 years. Read more about granny flat rental income.
Real Privacy
If your ageing parents are moving in but everyone wants their own space, a granny flat gives them independence while keeping them close. The same applies to adult kids who aren’t quite ready to buy but need autonomy.
A Quiet Workspace
Working from home with kids around? A backyard granny flat gives you a proper office with a door that closes. For those with creative or hands-on jobs or hobbies, a custom shed could also be a great option.
Future Flexibility
A granny flat adapts as your life changes. It can be a parent’s home today, your teenager’s retreat tomorrow, and a rental property when everyone moves out. That’s harder to achieve with an extension that’s permanently attached to your house.
When an Extension Makes More Sense
Extensions work better when you want:
Everyone Under One Roof
Growing families who want shared living areas, easier supervision of young kids, and that sense of togetherness benefit from extensions. You’re expanding your home, not dividing your property.
To Transform Your Home Layout
If your kitchen is too small, your living areas feel cramped, or you need that master bedroom with an ensuite, an extension lets you reconfigure how your whole house works. You can knock through walls, open up sight lines, and create the flow you’ve always wanted.
Maximise Your Home’s Potential
Extensions often add more value per dollar spent compared to granny flats, especially in suburbs where larger family homes command premium prices. You’re improving the main asset rather than adding a secondary one.
Outdoor Space Is Limited
A second-storey extension preserves your backyard. If your kids need room to play, you love entertaining on your Perth patio, or your garden matters to you, building up instead of out makes sense.
Perth-Specific Considerations
Perth’s regulations changed in 2024 to make granny flats easier. Most no longer need planning approval from your local council, though you still need a building permit. Your property generally needs to be at least 450m², and the granny flat can’t exceed 70m² of internal living space.
Home extensions require council approval if they’re substantial. Anything affecting your home’s structure, roof line, or setbacks from boundaries needs to go through the proper channels. The process takes longer but gives you more flexibility in what you build.
Perth’s climate also plays a role. Both options benefit from good insulation, but granny flats are typically smaller and cheaper to cool in summer. Extensions need careful planning around orientation, especially if you’re building west-facing additions that’ll cop the full afternoon sun.
Ready to Add Space to Your Perth Property?
Both options increase your property value. Both give you more space. The right choice depends on how you live, what you need that space to do, and what matters most to your family’s lifestyle. Take your time, get proper quotes for both options, and choose the one that serves you best for the next decade – not just right now.
Phoenix Patios specialises in quality granny flats, patios, and outdoor structures across Perth. We handle everything from design and approvals through to final construction. Call us for an obligation-free consultation to discuss which option works best for your property and budget.