How to Prepare for a Home Extension in Perth – A Planning Blueprint 

Deciding to extend your home is exciting. Maybe the family has grown, the living spaces feel cramped, or you’ve simply realised that the home you love, in the suburb you love, just needs more room to breathe. Whatever’s driving the decision, planning a home extension in Perth is a significant undertaking, and the preparation you do before a builder ever sets foot on site will have a direct impact on how smoothly and successfully your project unfolds. 

At Nexus Homes Group, we’ve been helping Perth homeowners navigate this process for years, specialising in ground floor extensions, second storey additions and home renovations across Perth’s suburbs. One thing we’ve learnt throughout the years is that the homeowners who feel most confident throughout their project are the ones who understood the process before it began until it ends.  

Achieve the confidence by learning the foundation, from site constraints and council approvals to structural considerations and costs so there are no hidden surprises along the way. 

Step 1: What Can Your Block Actually Support?  

The first step in planning any home extension is understanding what your block will and won’t allow.  

Many homeowners in Perth begin designing their plan before this groundwork is conducted and what looks great on paper doesn’t always translate to what’s permissible or practical on site. Therefore, it is best to conduct a site assessment before you begin.

Items that you need to look at during the assessment: 

• Easements and rights-of-way: Drainage, services or access easements can quietly restrict where you’re able to build 
• Slope and soil conditions: Reactive soils are common across Perth’s suburbs and can add to earthworks and footing costs if not identified early 
• Existing structure condition: Particularly important for second storey extensions in Perth, where walls, roof and footings need to carry additional load 
• Orientation: Perth’s overshadowing rules protect solar access for both you and your neighbours, and factoring this in early prevents design rework later 

Older Perth homes, especially those built before 1990, weren’t always designed to accommodate a second storey. Identifying this beforehand will save you time, money, and frustration compared to discovering it midway through designing your plans. 

Step 2: Understand Council Approvals and the Approvals Pathway 

In Perth, the planning system is administered by individual local councils. Each of this councils operates under their own Local Planning Scheme. Therefore, your property’s zoning and council’s specific policies will determine what kind of extension you are able build and which approvals pathway applies. 

Approval Type	When It Applies
Building Permit only	Project fully complies with R Codes (“permitted development”)
Development Application (DA)	Second storey additions, complex sites, setback variations

Knowing which pathway applies to your project early on it important before work begins. A DA approval will save you a lot of time as timeline surprises are one of the most common sources of stress for homeowners mid-project. 

Step 3: Get to Know the R Codes 

If there’s one document that shapes house extensions in Perth more than any other, it’s Western Australia’s Residential Design Codes, also known as the R Codes. They set the rules for what can be built, where and at what scale. 

Key R Code provisions that affect extensions: 

• Setbacks: minimum distances from street, side and rear boundaries (these increase for upper floor walls) 

• Lot coverage: most R20 zones allow around 50–55% of the lot to be covered by buildings 

• Open space: a minimum proportion of your lot must remain as usable private open space 

• Wall height and overshadowing: directly affects what neighbours can raise objections to 

• Privacy screening: required for upper floor windows and balconies that would otherwise overlook adjoining properties 

Your R Code zoning, including R20, R40, R60 and so on, determines which specific rules apply. The R Codes were also updated in 2023 with the introduction of the Medium Density Standards, which affect properties zoned R30 and above. 

Navigating the R Codes without experience can be genuinely confusing. At Nexus, we guide clients through this clearly and without the jargon and we know when it’s worth applying for a design variation to maximise what’s possible on your site. 

Step 4: Understand What a Home Extension Actually Costs and Whether It’s Worth the Money 

By the time homeowners come to us, there are usually a few financial questions sitting in the background – we’ve covered some of these queries below.

Cost benchmarks for home extensions in Perth: 

Extension Type	Typical Cost Range (per m²)	Notes
Ground floor extension	$4,000 – $5000/m² (approx)	Less structural complexity: site conditions vary
Second storey extension	$4,500 – $5,500+/m² (approx)	Includes structural upgrades to existing home

 

Please note: the figures above are provided as a general pricing guide only and may vary depending on your property type, materials used, finishes, construction method and a range of other project-specific factors. We recommend speaking with our team for a more accurate estimate based on your individual circumstances.

Extending out vs building up.  

Ground floor extensions or modular extensions are generally less structurally complex, but they consume outdoor space and require sufficient land. Second storey additions use vertical space, which is well-suited to Perth’s smaller suburban lots although the cost of upgrading the existing structure needs to be factored in from the start.  

The impact of home extension on property value.  

A well-designed extension almost always adds meaningful value particularly in Perth’s Western Suburbs, where land is constrained and demand for larger family homes is consistently strong. Extensions delivering additional bedrooms, bathrooms and functional living space tend to perform best. We’ve written about which upgrades add the most value if you’d like to explore this further. 

Where costs concentrate.  

For ground floor extensions, the biggest line items are typically structural work, wet areas and glazing. For second storey projects, the second storey addition process involves a structural upgrade of the existing home where it reinforces footings, walls and replacing the roof, combined with staircase construction. Knowing this early will help you prioritise your budget from the very beginning. Getting your budget set up correctly from the start is one of the most valuable things you can do before your project begins. 

Step 5: What’s Really Involved in a Second Storey Extension 

Second storey additions are one of Nexus’s core specialities. They’re transformative for the right home and the right family. It delivers significant additional space without having to sacrifice backyard or garden. But they involve structural complexity that’s important to understand beforehand. 

Key structural considerations for second storey extensions in Perth: 

• Footing and slab capacity: existing footings may need underpinning or extension to carry upper floor loads 

• Wall frame integrity: existing timber or brick veneer walls often require reinforcement before they can support a second storey 

• Roof removal: the existing roof needs to come off entirely, creating a weather-exposure window that requires careful scheduling 

• Upper floor structural system: engineers specify beams, posts, joists and flooring to suit the new load requirements 

• Wind loading compliance: Perth is subject to significant wind events; second storey structures must comply with the relevant wind rating for your area 

A structural engineer is non-negotiable for any second storey project. They will assess the existing home’s capacity, specify the new structural elements, and produce the engineering documentation required for your building permit. 

If you’re considering a second storey addition, we’ve developed a dedicated eBook 5 Critical Considerations Before Investing In A Second Storey Addition which walks through these decisions in detail.

Step 6: Your Neighbours Are Part of the Process 

Something that surprises many homeowners is the role their neighbours can play in the approvals process. In Western Australia, certain development applications, particularly those involving upper floor additions may trigger a formal requirement for neighbour consultation. 

Even where that’s not legally required, speaking with your neighbours early is always good practice. A neighbour who first hears about your plans through a council notification rather than a friendly conversation is far more likely to raise concerns. Most well-designed extensions don’t face serious objection, but delays at the approvals stage push out your construction timeline and add to holding costs. 

A good designer will address overshadowing and privacy provisions at the concept stage, resolving them on paper rather than mid-approval. 

Step 7: When to Bring in a Designer and Engineer 

A common question we always hear: who do I engage first, and when? 

Consultant	When to Engage	What They Do
Building designer / architect	Early, before committing to a builder	Concept drawings, R Code compliance, design options
Structural engineer	Once design is settled	Structural assessment, engineering specifications, permit documentation
Builder	After design is sufficiently developed	Accurate pricing, construction methodology, approvals coordination

The decisions made at the design stage are the cheapest ones to change. Getting the design right upfront saves time and money at every stage that follows. 

At Nexus, we coordinate this entire process on behalf of our clients. We connect them with trusted designers and engineers, managing the documentation, and guiding the approvals pathway through to construction. Our clients tell us that having one point of accountability across all of this makes the experience far less stressful than managing it themselves. 

Confident Planning Makes for Better Outcomes 

A home extension is one of the most meaningful investments a Perth homeowner can make, and not just financially, but in terms of how your family lives day to day. The planning phase is where that investment is either protected or put at risk. 

Understanding your site, the R Codes, the approvals pathway and the structural requirements before you engage a builder means you go in with your eyes open and far fewer surprises along the way. 

If you’re in the early stages of exploring your options, read our complete guide to designing a family home renovation and our article on common mistakes homeowners make with home extensions before your first consultation. You can also browse our past projects for inspiration. 

When you’re ready to have a conversation with a team that will guide you through every step with honesty and care, we’d love to hear from you. Request a design consultation or quote with us here.