A home extension in Perth starts from $80,000 with House & Co. The cost depends on the type of extension, size, structural complexity, and site conditions. These are indicative guide prices based on typical Perth projects as at April 2026.
Every extension is site-specific. Soil type, existing structure condition, council requirements, and inclusions (bathroom, kitchen, laundry) all affect the final figure. A fixed-scope quote following site assessment and design approval is the only accurate figure for your extension.
Extension Type | Price Range (Guide) | Typical Inclusions | Permit Required? |
Single-storey room addition(1–2 rooms) | $80,000 – $120,000 | Design, building permit, structural engineering, slab, frame, roof, external walls, internal fit-out, electrical, painting | Yes — building permit |
Single-storey rear extension(open plan living) | $100,000 – $160,000 | As above plus larger floor area, potentially new kitchen or living/dining, bifold or stacker doors to alfresco | Yes — building permit |
Granny flat addition(ancillary dwelling) | $120,000 – $180,000 | Self-contained dwelling: living, bedroom, bathroom, kitchenette or kitchen, laundry — all wet areas and trades | Yes — planning approval + building permit |
Second-storey addition(full upper level) | $150,000 – $250,000+ | Structural engineering (full load assessment), staircase, upper level framing, roof, 2–4 bedrooms, 1–2 bathrooms, all trades | Yes — planning approval + building permit |
All prices are guide figures for Perth metro as at April 2026. Site-specific factors — soil type, access, existing structure condition, and council requirements — can materially affect the final cost. House & Co conducts a site assessment before any design or quoting work begins.
Stage | Indicative Cost (Guide) | Notes |
3D architectural design | $3,000 – $8,000 | Included in House & Co fixed-scope agreement. 3D model before any commitment. |
Structural engineering report | $2,000 – $5,000 | Required for all extensions. Assesses load paths, footing design, and beam specifications. |
Energy efficiency assessment | $800 – $1,500 | Required for all new WA residential construction under NCC Section J. |
Building permit (council fees) | $1,500 – $4,000 | Council fee based on value of works. House & Co manages the application. |
Demolition and site preparation | $2,000 – $8,000 | Opening up the existing structure, footing excavation, service relocation. |
Concrete slab or floor system | $8,000 – $20,000 | Slab-on-ground typical in Perth. Suspended floor for sloping sites. Footings vary by soil class. |
Framing and roof structure | $15,000 – $35,000 | Timber or steel frame. Roof to match existing home (tile or Colorbond). |
External cladding and windows | $8,000 – $20,000 | Brick veneer, rendered lightweight frame, or matching existing. Windows and external doors. |
Internal fit-out | $15,000 – $40,000 | Internal walls, insulation, sheeting, cornice, painting, flooring. |
Electrical | $5,000 – $12,000 | Switchboard upgrade if required, all circuits, lighting, air conditioning wiring. |
Plumbing (if wet areas included) | $5,000 – $15,000 | Full bathroom/laundry/kitchen plumbing by licensed Perth plumber. |
Wet area fit-out (if included) | $20,000 – $50,000 | Bathroom, ensuite, laundry, or kitchen — same cost as standalone renovations. |
All home extensions in Perth require a building permit from your local council or a private building surveyor. House & Co manages the permit application as part of every extension project.
Permit Type | When Required | Typical Timeframe |
Building permit | All structural extensions | 6–12 weeks (council)3–6 weeks (private certifier) |
Planning approval | Granny flats, second-storey additions, extensions near boundaries | 8–16 weeks |
Structural engineering report | All extensions | 1–2 weeks |
Energy efficiency assessment | All new WA residential construction | 1 week |
How much does a home extension cost in Perth? A home extension in Perth costs from $80,000 with House & Co. Single-storey room additions start from $80,000. Full single-storey rear extensions with open plan living start from $100,000. Granny flat additions range from $120,000 to $180,000. Second-storey additions start from $150,000 and reach $250,000 and above for full upper levels. These are indicative guide prices only — every extension is site and design specific.
How much does a single-storey home extension cost in Perth? A single-storey room addition in Perth costs $80,000–$120,000 for 1–2 room additions to an existing footprint. A larger single-storey rear extension creating open plan living costs $100,000–$160,000. Prices include design, permits, structural engineering, construction, and fit-out. Site conditions, soil type, and access complexity affect final cost.
How much does a second-storey addition cost in Perth?A second-storey addition in Perth costs $150,000–$250,000 and above, depending on the size of the upper level, structural complexity, and quality of finish. Second-storey additions require planning approval and building permits in WA, plus a structural engineering assessment. House & Co manages the full permit and engineering process.
How much does a granny flat cost to build in Perth?A granny flat addition in Perth costs $120,000–$180,000 depending on size, inclusions (bathroom, kitchen, or laundry), and site conditions. Granny flats require both planning approval and a building permit. R-code zoning on your property determines whether a granny flat (ancillary dwelling) is permitted — House & Co checks zoning before any design work begins.
Do I need a building permit for a home extension in Perth? Yes — all home extensions in Perth require a building permit. Structural extensions also require a structural engineering report and an energy efficiency assessment under the NCC. House & Co manages the full permit application — you do not need to deal with the council directly. Permit approval typically takes 6–12 weeks for residential extensions.
How long does a home extension take in Perth?Design and permit approval: 8–16 weeks. On-site construction: 12–24 weeks depending on size and complexity. Total from first consultation to completion: 6–12 months for most Perth residential extensions. Second-storey additions and granny flats are at the longer end due to planning approval requirements.
Does a home extension add value in Perth?Yes — adding bedrooms, living space, or a self-contained dwelling consistently adds value in Perth. A well-executed single-storey extension adding a bedroom and bathroom to a Subiaco or South Perth home typically adds more to the property value than the extension cost. Extensions are particularly effective in inner Perth suburbs where land cost makes moving expensive and the addition of space is highly valued by buyers.
Can I add a bathroom or kitchen to my home extension?Yes — and this is one of the most common briefs House & Co receives. Adding a bathroom or kitchen to an extension brings the full wet area scope (waterproofing, licensed plumber and tiler, all compliance) into the one project. Trades are already on site for the extension structure — coordinating wet areas simultaneously is more efficient than a separate project later.
Related Cost Guides & Renovation Pages
Every cost guide links back to the relevant spoke page and up to the hub. Use these to plan multi-room projects or compare scopes.
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