Granny flats — or ancillary dwellings, as they’re officially known — have never been more popular in Western Australia. Whether you’re housing an ageing parent, generating rental income, or creating a self-contained space for adult kids, a well-built granny flat can add real flexibility to your property.
If you haven’t looked into the rules recently, you may be surprised at how much has changed. Since mid-2024, Western Australia’s planning regulations have been significantly relaxed, making it easier and faster for homeowners in Bunbury and across the South West to add a granny flat to their property.
Here’s a plain-English guide to the current granny flat rules in WA for 2026.
What Changed with WA’s Granny Flat Rules?
The biggest shift came in April 2024, when the WA Government amended the Residential Design Codes (R-Codes) to remove key barriers that previously stopped many homeowners from building ancillary dwellings.
The headline changes were:
No minimum lot size. Previously, your block had to be at least 350 square metres to qualify for a granny flat. That requirement has been scrapped. If your block is zoned residential, you can now build one regardless of size — provided the design meets other relevant standards.
Planning approval often not required. For granny flats up to 70 square metres that meet the deemed-to-comply requirements (setbacks, site cover, parking and so on) under your local planning scheme, a planning application is generally not required. If your design or site falls outside the deemed-to-comply criteria, a development application may still be needed — your builder or council can confirm.
Building permit always required. A building permit is mandatory for safety and structural compliance. Processing times vary by council and the completeness of the application — your builder or certifier can give you a current estimate.
Reduced parking requirements. The previous requirement for an extra car bay has been relaxed in many locations — particularly in areas with reasonable access to public transport or town centres.
How Big Can a Granny Flat Be in WA?
Under current WA regulations, ancillary dwellings must not exceed 70 square metres of floor space to qualify for the simplified approval pathway. That’s enough room for a comfortable one- or two-bedroom dwelling with a kitchen, bathroom, and living area.
If you want something larger, you’ll need to go through a full planning approval process, which involves more time and documentation. For most homeowners, the 70m² limit is more than adequate.
Setbacks and Design Requirements
Even where planning approval isn’t required, your granny flat must still comply with setback requirements — the minimum distances your structure must sit from property boundaries, neighbouring buildings, and the street. These vary depending on your local planning scheme.
In Bunbury and the broader South West, the City of Bunbury and the relevant shires each maintain their own local planning schemes that sit alongside the state R-Codes. The setback rules applicable to your specific block may differ from those applying to a property in Perth.
Other design elements to consider include:
- Building height limits — typically capped at single-storey for rear ancillary dwellings, though this can vary.
- Stormwater and drainage — South West WA’s winter rainfall patterns mean proper drainage management is essential.
It’s always worth checking with your local council or a qualified builder before you begin, as design requirements can vary property to property.
Who Can Live in a Granny Flat in WA?
One of the lesser-known changes in the 2024 reforms is that the occupant restriction has been removed. Previously, ancillary dwellings were intended primarily for family members. Now, anyone can live in them — relatives, friends, or private tenants under a rental arrangement.
This makes a granny flat a more flexible proposition for South West WA homeowners than it used to be. Whether the use case is rental, family accommodation, or somewhere between, the regulatory pathway is the same.
How Much Does a Granny Flat Cost to Build in WA?
Build costs vary considerably depending on size, materials, site conditions, and current market pricing for trades and materials. The fairest answer is: every project is different, and a builder needs to walk the site to give you a meaningful number.
In regional WA, including the South West, labour and material costs can differ from metro Perth, so it’s worth getting local quotes from builders who understand the regional market. Site preparation, connecting services (water, sewer, power), and any landscaping work are all separate costs to factor in. For a realistic budget, get a detailed scope from your builder before committing.
Coastal and Climate Considerations for South West WA
Building in Bunbury and the South West comes with some climate-specific considerations:
Coastal exposure. Properties near the coast — and many in Bunbury and surrounding areas qualify — may be subject to higher wind loads and salt-air corrosion. Building materials, particularly steel fixings, cladding, and window frames, should be rated for coastal conditions where appropriate.
Winter rainfall. The South West has a Mediterranean climate with wet winters. Granny flat designs should account for adequate waterproofing, roof drainage, and underfloor ventilation to manage moisture effectively.
Energy efficiency. Under the National Construction Code, all new WA homes and ancillary dwellings must meet the current minimum energy-efficiency rating (currently a 7-star NatHERS rating for most new residential builds). Good insulation, appropriate glazing, and passive solar design are worth building in from the start — particularly in the South West where both heating and cooling demands apply.
Getting Started: What to Do First
If you’re considering a granny flat in Bunbury or the South West, here’s a practical starting sequence:
- Check your zoning. Confirm your property is residentially zoned and identify any local planning overlays that might affect design.
- Review setback requirements. Contact the City of Bunbury or your local shire to understand the specific setbacks and design standards that apply to your block.
- Engage a builder early. A builder experienced in ancillary dwellings can help you design within the rules from the outset, avoiding costly redesigns down the track.
- Apply for a building permit. Once your plans comply with the R-Codes and local requirements, your builder will lodge the building permit on your behalf.
- Build and connect services. Your builder coordinates structural construction; separate licensed trades manage electrical, plumbing, and other service connections.
Let Element Structures Help
At Element Structures, we work on residential construction and renovation across Bunbury and the South West WA region. We’re across WA’s current building codes and the local council requirements that apply in this area.
Whether you’re considering a modest retreat for a family member or a fully self-contained rental unit, we can help you understand your options.
Contact Element Structures for a free, no-obligation quote. We work across Bunbury, Australind, Busselton, Harvey, and the broader South West WA region.
This article is general information only. Planning and building requirements can vary based on your specific property and local council, and the rules change over time. Always confirm current rules with the City of Bunbury or your relevant local government authority before commencing any works.